ExoMars

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ExoMars
ЭкзоМарс

Artist's illustration of ExoMars' Trace Gas Orbiter (left), Schiaparelli lander (middle), and rover (right)
Mission type	Mars reconnaissance
Operator	ESA · RFSA
Website	exploration.esa.int/mars (ESA) exomars.cosmos.ru (RFSA)
Mission duration	Elapsed: 2 years, 6 months and 12 days
ExoMars ESA mission insignia

ExoMars (Exobiology on Mars) is a two-part astrobiology project to search for evidence of life on Mars, a joint mission of the European Space Agency (ESA) and the Russian space agency Roscosmos. The first part, launched in 2016, placed a trace gas research and communication satellite into Mars orbit and released a stationary experimental lander (which crashed). The second part is planned to launch in 2020, and to land the ExoMars rover on the surface, supporting a science mission that is expected to last into 2022 or beyond.

ExoMars goals are to search for signs of past life on Mars, investigate how the Martian water and geochemical environment varies, investigate atmospheric trace gases and their sources and by doing so demonstrate the technologies for a future Mars sample return mission. The mission will search for ancient biosignatures of Martian life, employing several spacecraft elements to be sent to Mars on two launches.

The ExoMars Trace Gas Orbiter (TGO) and a test stationary lander called Schiaparelli were launched on 14 March 2016. TGO entered Mars orbit on 19 October 2016 and will proceed to map the sources of methane (CH
4) and other trace gases present in the Martian atmosphere that could be evidence for possible biological or geological activity. The TGO features four instruments and will also act as a communications relay satellite. The Schiaparelli experimental lander separated from TGO on 16 October and was maneuvered to land in Meridiani Planum, but it crashed on the surface of Mars. The landing was designed to test new key technologies to safely deliver the 2020 rover mission.
In 2020, a Roscosmos-built lander (ExoMars 2020 surface platform) is to deliver the ESA-built ExoMars Rover to the Martian surface. The rover will also include some Roscosmos built instruments. The second mission operations and communications will be led by ALTEC's Rover Control Centre in Italy.

History

An ExoMars rover as an exhibit at Gasometer Oberhausen, Germany

Since its inception, ExoMars has gone through several phases of planning with various proposals for landers, orbiters, launch vehicles, and international cooperation planning, such as the defunct 2009 Mars Exploration Joint Initiative (MEJI) with the United States. Originally, the ExoMars concept consisted of a large robotic rover being part of ESA's Aurora Programme as a Flagship mission and was approved by the European Space Agency ministers in December 2005. Originally conceived as a rover with a stationary ground station, ExoMars was planned to launch in 2011 aboard a Russian Soyuz Fregat rocket.

ExoMars begun in 2001 as part of the ESA Aurora program for the human exploration of Mars. That initial vision called for rover in 2009 and later a sample return mission. Another mission intended to support the Aurora program is a Phobos sample return mission. In December 2005, the different nations composing the ESA gave approval to the Aurora program and to ExoMars. Aurora is an optional program and each state is allowed to decide which part of the program they want to be involved in and to what extent (e.g. how much funds they want to put into the program). The Aurora program was initiated in 2002 with support of twelve nations: Austria, Belgium, France, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland, the United Kingdom and Canada.

In 2007, Canadian-based technology firm MacDonald Dettwiler and Associates Ltd. (MDA) was selected for a one-million-euro contract with EADS Astrium of Britain to design and build a prototype Mars rover chassis for the European Space Agency. Astrium was also contracted to design the final rover.

On July 2009 NASA and ESA signed the Mars Exploration Joint Initiative, which proposed to utilise an Atlas rocket launcher instead of a Soyuz, which significantly altered the technical and financial setting of the ExoMars mission. On 19 June, when the rover was still planned to piggyback the Mars Trace Gas Orbiter, it was reported that a prospective agreement would require that ExoMars lose enough weight to fit aboard the Atlas launch vehicle with a NASA orbiter.

Mars Astrobiology Explorer-Cacher (MAX-C) rover

Then the mission was combined with other projects to a multi-spacecraft mission divided over two Atlas V-launches: the ExoMars Trace Gas Orbiter (TGO) was merged into the project, piggybacking a stationary meteorological lander slated for launch in January 2016. It was also proposed to include a second rover, the MAX-C.

In August 2009 it was announced that the Russian Federal Space Agency (now Roscosmos) and ESA had signed a contract that included cooperation on two Mars exploration projects: Russia's Fobos-Grunt project and ESA's ExoMars. Specifically, ESA secured a Russian Proton rocket as a "backup launcher" for the ExoMars rover, which would include Russian-made parts.

On 17 December 2009, the ESA governments gave their final approval to a two-part Mars exploration mission to be conducted with NASA, confirming their commitment to spend €850 million ($1.23 billion) on missions in 2016 and 2018.

In April 2011, because of a budgeting crisis, a proposal was announced to cancel the accompanying MAX-C rover, and fly only one rover in 2018 that would be larger than either of the vehicles in the paired concept. One suggestion was that the new vehicle would be built in Europe and carry a mix of European and U.S. instruments. NASA would provide the rocket to deliver it to Mars and provide the sky crane landing system. Despite the proposed reorganisation, the goals of the 2018 mission opportunity would have stayed broadly the same.

Under the FY2013 Budget President Obama released on 13 February 2012, NASA terminated its participation in ExoMars due to budgetary cuts in order to pay for the cost overruns of the James Webb Space Telescope. With NASA's funding for this project completely cancelled, most of these plans had to be restructured.

On 14 March 2013, representatives of the ESA and the Russian space agency (Roscosmos), signed a deal in which Russia became a full partner. Roscosmos will supply both missions with Proton launch vehicles with Briz-M upper stages and launch services, as well as an additional entry, descent and landing module for the rover mission in 2018. Under the agreement, Roscosmos was granted three asking conditions:

1. Roscosmos will contribute two Proton launch vehicles as payment for the partnership.
2. The Trace Gas Orbiter payload shall include two Russian instruments that were originally developed for Fobos-Grunt.
3. All scientific results must be intellectual property of the European Space Agency and the Russian Academy of Sciences (i.e. Roscosmos will have full access to research data).

ESA had originally cost-capped the ExoMars projects at €1 billion, (USD 1.3 billion) but the withdrawal of the U.S. space agency (NASA) and the consequent reorganisation of the ventures will probably add several hundred million euros to the sum so far raised. So on March 2012, member states instructed the agency's executive to look at how this shortfall could be made up. One possibility is that other science activities within ESA may have to step back to make ExoMars a priority. On September 2012 it was announced that new ESA members, Poland and Romania will be contributing up to €70 million to the ExoMars mission. ESA has not ruled out a possible partial return of NASA to the 2018 portion of ExoMars, albeit in a relatively minor role.

Russia's financing of ExoMars could be partially covered by insurance payments of 1.2 billion rubles ($40.7 million USD) for the loss of Fobos-Grunt, and reassigning funds for a possible coordination between the Mars-NET and ExoMars projects. On 25 January 2013, Roscosmos fully funded the development of the scientific instruments to be flown on the first launch, the Trace Gas Orbiter (TGO).

As of March 2014, the lead builder of the ExoMars rover, the British division of Airbus Defence and Space, had started procuring critical components, but the 2018 rover mission was still short by more than 100 million euros, or $138 million. The wheels and suspension system are paid by the Canadian Space Agency and are being manufactured by MDA Corporation in Canada.

Status

A prototype of the ExoMars Rover at the 2015 Cambridge Science Festival

In January 2016 it was announced that the financial situation of the 2018 mission 'might' require a 2-year delay. Italy is the largest contributor to ExoMars, and the UK is the mission's second-largest financial backer.

The rover was scheduled to launch in 2018 and land on Mars in early 2019, but in May 2016 ESA announced that the launch would occur in 2020 due to delays in European and Russian industrial activities and deliveries of the scientific payload.

2016 first spacecraft launch

The spacecraft containing ExoMars Trace Gas Orbiter (TGO) and Schiaparelli launched on 14 March 2016 (Livestream began at 08:30 GMT [03:30 AM EDT]). Four rocket burns occurred in the following 10 hours before the descent module and orbiter were released. Signal from the Orbiter was successfully received at 21:29 GMT of the same day, which confirmed that the launch was fully successful and the spacecraft is on its way to Mars. Shortly after separation from the probes, the Briz-M upper booster stage possibly exploded a few kilometers away, however apparently without damaging the orbiter or lander. The spacecraft, which housed the Trace Gas Orbiter and the Schiaparelli lander, took its nominal orbit towards Mars and was seemingly in working order. Over the next two weeks, controllers continued to check and commission its systems, including the power, communications, startrackers, and guidance and navigation system.

Mission objectives

The scientific objectives, in order of priority, are:

• to search for possible biosignatures of past Martian life.
• to characterise the water and geochemical distribution as a function of depth in the shallow subsurface.
• to study the surface environment and identify hazards to future manned missions to Mars.
• to investigate the planet's subsurface and deep interior to better understand the evolution and habitability of Mars.
• achieve incremental steps ultimately culminating in a sample return flight.

The technological objectives to develop are:

• landing of large payloads on Mars.
• to exploit solar electric power on the surface of Mars.
• to access the subsurface with a drill able to collect samples down to a depth of 2 metres (6.6 ft)
• to develop surface exploration capability using a rover.

Mission profile

ExoMars is a joint programme of the European Space Agency (ESA) and the Russian space agency Roscosmos. According to current plans, the ExoMars project will comprise four spacecraft: two stationary landers, one orbiter and one rover. All mission elements will be sent in two launches using two heavy-lift Proton rockets.

Contributing agency	First launch in 2016	Second launch in 2020
	Proton rocket	Proton rocket
	Two instrument packages for the TGO	Russian-built landing system and surface science platform will deliver the rover to the surface. Russia will provide various scientific instruments for the lander and rover.
ESA	ExoMars Trace Gas Orbiter	ExoMars rover, and various scientific instruments on the rover
	Schiaparelli EDM lander

The two landing modules and the rover will be sterilised in order not to contaminate the planet with Earth life forms. Cleaning will require a combination of sterilising methods, including ionising radiation, UV radiation, and chemicals such as ethyl and isopropyl alcohol.

First launch (2016)

Trace Gas Orbiter

The Trace Gas Orbiter (TGO) is a Mars telecommunications orbiter and atmospheric gas analyzer mission that was launched on 14 March 2016. The spacecraft arrived in the Martian orbit in October 2016. It delivered the ExoMars Schiaparelli EDM lander and then proceed to map the sources of methane on Mars and other gases, and in doing so, help select the landing site for the ExoMars rover to be launched in 2020. The presence of methane in Mars' atmosphere is intriguing because its likely origin is either present-day life or geological activity. Upon the arrival of the rover in 2021, the orbiter would be transferred into a lower orbit where it would be able to perform analytical science activities as well as provide the Schiaparelli EDM lander and ExoMars rover with telecommunication relay. NASA provided an Electra telecommunications relay and navigation instrument to ensure communications between probes and rovers on the surface of Mars and controllers on Earth. The TGO would continue serving as a telecommunication relay satellite for future landed missions until 2022.

Schiaparelli EDM lander

Model of the ExoMars Schiaparelli EDL Demonstrator Module (EDM). During its descent it returned 600 MB of data, but it did not achieve a soft landing.

The Entry, Descent and Landing Demonstrator Module (EDM) called Schiaparelli, was intended to provide the European Space Agency (ESA) and Russia's Roscosmos with the technology for landing on the surface of Mars. It was launched together with the ExoMars Trace Gas Orbiter (TGO) on 14 March 2016 and was scheduled to land softly on 19 October 2016. No signal indicating a successful landing was received, and on 21 October 2016 NASA released a Mars Reconnaissance Orbiter image showing what appears to be the lander crash site. The lander was equipped with a non-rechargeable electric battery with enough power for four sols. The soft landing should have taken place on Meridiani Planum during the dust storm season, which would have provided a unique chance to characterise a dust-loaded atmosphere during entry and descent, and to conduct surface measurements associated with a dust-rich environment.

Once on the surface, it was to measure the wind speed and direction, humidity, pressure and surface temperature, and determine the transparency of the atmosphere. It carried a surface payload, based on the proposed meteorological DREAMS (Dust Characterisation, Risk Assessment, and Environment Analyser on the Martian Surface) package, consists of a suite of sensors to measure the wind speed and direction (MetWind), humidity (MetHumi), pressure (MetBaro), surface temperature (MarsTem), the transparency of the atmosphere (Optical Depth Sensor; ODS), and atmospheric electrification (Atmospheric Radiation and Electricity Sensor; MicroARES). The DREAMS payload was to function for 2 or 3 days as an environmental station for the duration of the EDM surface mission after landing.

Second launch (2020)

Russian landing system

The second mission, scheduled for launch in July 2020, will have an 1800 kg Russian-built landing platform system derived from the 2016 Schiaparelli EDM lander, to place the ExoMars rover on the surface of Mars. This lander platform will be built 80% by the Russian company Lavochkin, and 20% by ESA. Lavochkin will produce most of the landing system's hardware, while ESA will handle elements such as the guidance, radar and navigation systems. Lavochkin's current landing strategy is to use two parachutes; one will open while the module is still moving at supersonic speed, and another will deploy once the probe has been slowed down to subsonic velocity. The heat shield will eventually fall away from the entry capsule to allow the ExoMars rover, riding its retro-rocket-equipped lander, to come for a soft landing on legs or struts. The surface platform lander will then deploy ramps for the rover to drive down.

Critics have stated that while Russian expertise may be sufficient to provide a launch vehicle, it does not currently extend to the critical requirement of a landing system for Mars.

Surface platform

After landing on Mars in 2021, the rover will descend from the platform via a ramp. The platform is expected to image the landing site, monitor the climate, investigate the atmosphere, analyse the radiation environment, study the distribution of any subsurface water at the landing site, and perform geophysical investigations of the internal structure of Mars. Following a March 2015 request for the contribution of scientific instruments for the landing system, there will be four instruments; the two European-led instruments selected are:

• the Lander Radioscience experiment (LaRa) will study the internal structure of Mars, and will make precise measurements of the rotation and orientation of the planet by monitoring two-way Doppler frequency shifts between the surface platform and Earth. It will also detect variations in angular momentum due to the redistribution of masses, such as the migration of ice from the polar caps to the atmosphere.
• the HABIT (HabitAbility: Brine, Irradiation and Temperature) package will investigate the amount of water vapour in the atmosphere, daily and seasonal variations in ground and air temperatures, and the UV radiation environment.
• two Russian-led instruments will monitor pressure and humidity, UV radiation and dust, the local magnetic field and plasma environment.

The platform is expected to operate for at least one Earth year, and its instruments might be powered by a radioisotope thermoelectric generator to provide long-term power.

Rover

An early design ExoMars rover test model at the

ILA 2006 in Berlin

 

The ExoMars rover will land in 2021 and is designed to navigate autonomously across the Martian surface.

Instrumentation will consist of the exobiology laboratory suite, known as "Pasteur analytical laboratory" to look for signs of biomolecules and biosignatures from past life. Among other instruments, the rover will also carry a 2-metre (6.6 ft) sub-surface core drill to pull up samples for its on-board laboratory. The rover will have a mass of about 207 kg (456 lb).

The ExoMar's rover includes the Pasteur instrument suite, including the Mars Organic Molecule Analyzer (MOMA), MicrOmega-IR, and the Raman Laser Spectrometer (RLS). Examples of external instruments on the rover include:

• Mars Multispectral Imager for Subsurface Studies
• Infrared Spectrometer for ExoMars
• ADRON-RM

Landing site selection

Oxia Planum, near the equator, is the selected landing site for its potential to preserve biosignatures and smooth surface

A primary goal when selecting the rover's landing site is to identify a particular geologic environment, or set of environments, that would support —now or in the past— microbial life. The scientists prefer a landing site with both morphologic and mineralogical evidence for past water. Furthermore, a site with spectra indicating multiple hydrated minerals such as clay minerals is preferred, but it will come down to a balance between engineering constraints and scientific goals.
Engineering constraints call for a flat landing site in a latitude band straddling the equator that is only 30° latitude from top to bottom because the rover is solar-powered and will need best sunlight exposure. The landing module carrying the rover will have a landing ellipse that measures about 105 km by 15 km. Scientific requirements include landing in an area with 3.6 billion years old sedimentary rocks that are a record of the past wet habitable environment. The year before launch, the European Space Agency will make the final decision. By March 2014, the long list was:

• Aram Dorsum
• Coogoon Valles
• Hypanis Vallis
• Mawrth Vallis
• Oxia Planum
• Simud Valles
• Southern Isidis

Following additional review by an ESA-appointed panel, four sites, all of which are located relatively near the equator, were formally recommended in October 2014 for further detailed analysis:

• Aram Dorsum
• Hypanis Vallis
• Mawrth Vallis
• Oxia Planum

On 21 October 2015, Oxia Planum was reported to be the preferred landing site for the ExoMars rover.

The delay of the rover mission to 2020 from 2018 meant that Oxia Planum was no longer the only favourable landing site due to changes in the possible landing ellipse. Both Mawrth Vallis and Aram Dorsum, surviving candidates from the previous selection, could be reconsidered. ESA convened further workshops to re-evaluate the three remaining options and in March 2017 selected two sites to study in detail;

• Mawrth Vallis
• Oxia Planum

The final selection is scheduled to occur approximately a year before launch.

Planetary protection

From Wikipedia, the free encyclopedia

 

A Viking lander being prepared for dry heat sterilization – this remains the "Gold standard" of present-day planetary protection.

Planetary protection is a guiding principle in the design of an interplanetary mission, aiming to prevent biological contamination of both the target celestial body and the Earth in the case of sample-return missions. Planetary protection reflects both the unknown nature of the space environment and the desire of the scientific community to preserve the pristine nature of celestial bodies until they can be studied in detail.

There are two types of interplanetary contamination. Forward contamination is the transfer of viable organisms from Earth to another celestial body. Back contamination is the transfer of extraterrestrial organisms, if such exist, back to the Earth's biosphere.

History

The potential problem of lunar and planetary contamination was first raised at the International Astronautical Federation VIIth Congress in Rome in 1956.

In 1958 the U.S. National Academy of Sciences (NAS) passed a resolution stating, “The National Academy of Sciences of the United States of America urges that scientists plan lunar and planetary studies with great care and deep concern so that initial operations do not compromise and make impossible forever after critical scientific experiments.” This led to creation of the ad hoc Committee on Contamination by Extraterrestrial Exploration (CETEX), which met for a year and recommended that interplanetary spacecraft be sterilized, and stated, “The need for sterilization is only temporary. Mars and possibly Venus need to remain uncontaminated only until study by manned ships becomes possible”.

In 1959, planetary protection was transferred to the newly formed Committee on Space Research (COSPAR). COSPAR in 1964 issued Resolution 26 affirming that:

the search for extraterrestrial life is an important objective of space research, that the planet of Mars may offer the only feasible opportunity to conduct this search during the foreseeable future, that contamination of this planet would make such a search far more difficult and possibly even prevent for all time an unequivocal result, that all practical steps should be taken to ensure that Mars be not biologically contaminated until such time as this search has been satisfactorily carried out, and that cooperation in proper scheduling of experiments and use of adequate spacecraft sterilization techniques is required on the part of all deep space probe launching authorities to avoid such contamination.

Signatories of the Outer Space Treaty - includes all current and aspiring space faring nation states. By signing the treaty, these nation states have all committed themselves to planetary protection.

  Signed and ratified

  Signed only

  Not signed

In 1967, the US, USSR, and UK ratified the United Nations Outer Space Treaty. The legal basis for planetary protection lies in Article IX of this treaty:

"Article IX: ... States Parties to the Treaty shall pursue studies of outer space, including the Moon and other celestial bodies, and conduct exploration of them so as to avoid their harmful contamination and also adverse changes in the environment of the Earth resulting from the introduction of extraterrestrial matter and, where necessary, shall adopt appropriate measures for this purpose...

This treaty has since been signed and ratified by 104 nation states. Another 24 have signed but not ratified. All the current space-faring nation states have both signed and ratified it. Amongst nations with space faring aspirations, some have not yet ratified: the United Arab Emirates, Syria and North Korea have signed but not yet ratified.

The Outer Space Treaty has consistent and widespread international support, and as a result of this, together with the fact that it is based on the 1963 declaration which was adopted by consensus in the UN National Assembly, it has taken on the status of customary international law. The provisions of the Outer Space Treaty are therefore binding on all states, even those who have neither signed nor ratified it.

For forward contamination, the phrase to be interpreted is "harmful contamination". Two legal reviews came to differing interpretations of this clause (both reviews were unofficial). However the currently accepted interpretation is that “any contamination which would result in harm to a state’s experiments or programs is to be avoided”. NASA policy states explicitly that “the conduct of scientific investigations of possible extraterrestrial life forms, precursors, and remnants must not be jeopardized”.

COSPAR recommendations and categories

The Committee on Space Research (COSPAR) meets every two years, in a gathering of 2000 to 3000 scientists, and one of its tasks is to develop recommendations for avoiding interplanetary contamination. Its legal basis is Article IX of the Outer Space Treaty.

Its recommendations depend on the type of space mission and the celestial body explored. COSPAR categorizes the missions into 5 groups:

• Category I: Any mission to locations not of direct interest for chemical evolution or the origin of life, such as the Sun or Mercury. No planetary protection requirements.
• Category II: Any mission to locations of significant interest for chemical evolution and the origin of life, but only a remote chance that spacecraft-borne contamination could compromise investigations. Examples include the Moon, Venus, and comets. Requires simple documentation only, primarily to outline intended or potential impact targets, and an end of mission report of any inadvertent impact site if such occurred.
• Category III: Flyby and orbiter missions to locations of significant interest for chemical evolution or the origin of life, and with a significant chance that contamination could compromise investigations e.g., Mars, Europa, Enceladus. Requires more involved documentation than Category II. Other requirements, depending on the mission, may include trajectory biasing, clean room assembly, bioburden reduction, and if impact is a possibility, inventory of organics.
• Category IV: Lander or probe missions to the same locations as Category III. Measures to be applied depend on the target body and the planned operations. "Sterilization of the entire spacecraft may be required for landers and rovers with life-detection experiments, and for those landing in or moving to a region where terrestrial microorganisms may survive and grow, or where indigenous life may be present. For other landers and rovers, the requirements would be for decontamination and partial sterilization of the landed hardware."

Missions to Mars in category IV are subclassified further:

• Category IVa. Landers that do not search for Martian life - uses the Viking lander pre-sterilization requirements, a maximum of 300,000 spores per spacecraft and 300 spores per square meter.
• Category IVb. Landers that search for Martian life. Adds stringent extra requirements to prevent contamination of samples.
• Category IVc. Any component that accesses a Martian special region (see below) must be sterilized to at least to the Viking post-sterilization biological burden levels of 30 spores total per spacecraft.

• Category V: This is further divided into unrestricted and restricted sample return.

• Unrestricted Category V: samples from locations judged by scientific opinion to have no indigenous lifeforms. No special requirements.
• Restricted Category V: (where scientific opinion is unsure) the requirements include: absolute prohibition of destructive impact upon return, containment of all returned hardware which directly contacted the target body, and containment of any unsterilized sample returned to Earth.

For Category IV missions, a certain level of biological burden is allowed for the mission. In general this is expressed as a 'probability of contamination', required to be less than one chance in 10,000 of forward contamination per mission, but in the case of Mars Category IV missions (above) the requirement has been translated into a count of Bacillus spores per surface area, as an easy to use assay method.

More extensive documentation is also required for Category IV. Other procedures required, depending on the mission, may include trajectory biasing, the use of clean rooms during spacecraft assembly and testing, bioload reduction, partial sterilization of the hardware having direct contact with the target body, a bioshield for that hardware, and, in rare cases, complete sterilization of the entire spacecraft.

For restricted Category V missions, the current recommendation is that no uncontained samples should be returned unless sterilized. Since sterilization of the returned samples would destroy much of their science value, current proposals involve containment and quarantine procedures. For details, see Containment and quarantine below. Category V missions also have to fulfill the requirements of Category IV to protect the target body from forward contamination.

Mars special regions

A special region is a region classified by COSPAR where terrestrial organisms could readily propagate, or thought to have a high potential for existence of Martian life forms. This is understood to apply to any region on Mars where liquid water occurs, or can occasionally occur, based on the current understanding of requirements for life.

If a hard landing risks biological contamination of a special region, then the whole lander system must be sterilized to COSPAR category IVc.

Target categories

Some targets are easily categorized. Others are assigned provisional categories by COSPAR, pending future discoveries and research.

The 2009 COSPAR Workshop on Planetary Protection for Outer Planet Satellites and Small Solar System Bodies covered this in some detail. Most of these assessments are from that report, with some future refinements. This workshop also gave more precise definitions for some of the categories:

Category I

“not of direct interest for understanding the process of chemical evolution or the origin of life.” 

• Io, Sun, Mercury, undifferentiated metamorphosed asteroids

Category II

… where there is only a remote chance that contamination carried by a spacecraft could jeopardize future exploration”. In this case we define “remote chance” as “the absence of niches (places where terrestrial microorganisms could proliferate) and/or a very low likelihood of transfer to those places.” 

• Callisto, comets, asteroids of category P, D, and C, Venus, Kuiper belt objects (KBO) < 1/2 size of Pluto.

Provisional Category II

• Ganymede, Titan, Triton, the Pluto-Charon system, and other large KBOs (> 1/2 size of Pluto), Ceres,

Provisionally, they assigned these objects to Category II. However, they state that more research is needed, because there is a remote possibility that the tidal interactions of Pluto and Charon could maintain some water reservoir below the surface. Similar considerations apply to the other larger KBOs.

Triton is insufficiently well understood at present to say it is definitely devoid of liquid water. The only close up observations to date are those of Voyager 2.

In a detailed discussion of Titan, scientists concluded that there was no danger of contamination of its surface, except short term adding of negligible amounts of organics, but Titan could have a below surface water reservoir that communicates with the surface, and if so, this could be contaminated.
In the case of Ganymede, the question is, given that its surface shows pervasive signs of resurfacing, is there any communication with its subsurface ocean? They found no known mechanism by which this could happen, and the Galileo spacecraft found no evidence of cryovolcanism. Initially, they assigned it as Priority B minus, meaning that precursor missions are needed to assess its category before any surface missions. However, after further discussion they provisionally assigned it to Category II, so no precursor missions are required, depending on future research.

If there is cryovolcanism on Ganymede or Titan, the undersurface reservoir is thought to be 50 – 150 km below the surface. They were unable to find a process that could transfer the surface melted water back down through 50 km of ice to the under surface sea. This is why both Ganymede and Titan were assigned a reasonably firm provisional Category II, but pending results of future research.
Icy bodies that show signs of recent resurfacing need further discussion and might need to be assigned to a new category depending on future research. This approach has been applied, for instance, to missions to Ceres. The planetary protection Category is subject for review during the mission of the Ceres orbiter (Dawn) depending on the results found.

Category III / IV

“…where there is a significant chance that contamination carried by a spacecraft could jeopardize future exploration.” We define “significant chance” as “the presence of niches (places where terrestrial microorganisms could proliferate) and the likelihood of transfer to those places.” 

• Mars because of possible surface habitats.
• Europa because of its subsurface ocean.
• Enceladus because of evidence of water plumes.

Category V

Unrestricted Category V: “Earth-return missions from bodies deemed by scientific opinion to have no indigenous life forms.”

Restricted Category V: "Earth-return missions from bodies deemed by scientific opinion to be of significant interest to the process of chemical evolution or the origin of life."

In the category V for sample return the conclusions so far are:

• Restricted Category V: Mars, Europa, Enceladus.
• Unrestricted Category V: Venus, the Moon.

with others to be decided.

Other objects

If there has been no activity for 3 billion years, it will not be possible to destroy the surface by terrestrial contamination, so can be treated as Category I. Otherwise, the category may need to be reassessed.

The Coleman-Sagan equation

The aim of the current regulations is to keep the number of microorganisms low enough so that the probability of contamination of Mars (and other targets) is acceptable. It is not an objective to make the probability of contamination zero.

The aim is to keep the probability of contamination of 1 chance in 10,000 of contamination per mission flown. This figure is obtained typically by multiplying together the number of microorganisms on the spacecraft, the probability of growth on the target body, and a series of bioload reduction factors.

In detail the method used is the Coleman-Sagan equation.

${\displaystyle P_{c}=N_{0}RP_{S}P_{t}P_{R}P_{g}}$.

where

${\displaystyle N_{0}}$ = the number of microorganisms on the spacecraft initially

${\displaystyle R}$ = Reduction due to conditions on spacecraft before and after launch

${\displaystyle P_{S}}$ = Probability that microorganisms on the spacecraft reach the surface of the planet

${\displaystyle P_{t}}$ = Probability that spacecraft will hit the planet - this is 1 for a lander

${\displaystyle P_{R}}$ = Probability of microorganism to be released in the environment when on the ground, usually set to 1 for crashlanding.

${\displaystyle P_{g}}$ = Probability of growth. For targets with liquid water this is set to 1 for sake of the calculation.

Then the requirement is ${\displaystyle P_{c}<10 annotation="">$

The ${\displaystyle 10^{-4}}$ is a number chosen by Sagan et al., somewhat arbitrarily. Sagan and Coleman assumed that about 60 missions to the Mars surface would occur before the exobiology of Mars is thoroughly understood, 54 of those successful, and 30 flybys or orbiters, and the number was chosen to endure a probability to keep the planet free from contamination of at least 99.9% over the duration of the exploration period.

Critiques

The Coleman Sagan equation has been criticised because the individual parameters are often not known to better than a magnitude or so. For example, the thickness of the surface ice of Europa is unknown, and may be thin in places, which can give rise to a high level of uncertainty in the equation. It has also been criticised because of the inherent assumption made of an end to the protection period and future human exploration. In the case of Europa, this would only protect it with reasonable probability for the duration of the period of exploration.

Greenberg has suggested an alternative, to use the natural contamination standard - that our missions to Europa should not have a higher chance of contaminating it than the chance of contamination by meteorites from Earth.

As long as the probability of people infecting other planets with terrestrial microbes is substantially smaller than the probability that such contamination happens naturally, exploration activities would, in our view, be doing no harm. We call this concept the natural contamination standard.

Another approach for Europa is the use of binary decision trees which is favoured by the Committee on Planetary Protection Standards for Icy Bodies in the Outer Solar System under the auspices of the Space Studies Board. This goes through a series of seven steps, leading to a final decision on whether to go ahead with the mission or not.

Recommendation: Approaches to achieving planetary protection should not rely on the multiplication of bioload estimates and probabilities to calculate the likelihood of contaminating Solar System bodies with terrestrial organisms unless scientific data unequivocally define the values, statistical variation, and mutual independence of every factor used in the equation.

Recommendation: Approaches to achieving planetary protection for missions to icy Solar System bodies should employ a series of binary decisions that consider one factor at a time to determine the appropriate level of planetary protection procedures to use.

Containment and quarantine for restricted Category V sample return

In the case of restricted Category V missions, Earth would be protected through quarantine of sample and astronauts in a yet to be built Biosafety level 4 facility. In the case of a Mars sample return, missions would be designed so that no part of the capsule that encounters the Mars surface is exposed to the Earth environment. One way to do that is to enclose the sample container within a larger outer container from Earth, in the vacuum of space. The integrity of any seals is essential and the system must also be monitored to check for the possibility of micro-meteorite damage during return to Earth.

The recommendation of the ESF report is that 

“No uncontained Mars materials, including space craft surfaces that have been exposed to the Mars environment should be returned to Earth unless sterilised"

..."For unsterilised samples returned to Earth, a programme of life detection and biohazard testing, or a proven sterilisation process, shall be undertaken as an absolute precondition for the controlled distribution of any portion of the sample.”

No restricted category V returns have been carried out. During the Apollo program, the sample-returns were regulated through the Extra-Terrestrial Exposure Law. This was rescinded in 1991, so new legislation would need to be enacted. The Apollo era quarantine procedures are of interest as the only attempt to date of a return to Earth of a sample that, at the time, was thought to have a remote possibility of including extraterrestrial life.

Samples and astronauts were quarantined in the Lunar Receiving Laboratory. The methods used would be considered inadequate for containment by modern standards. Also the lunar receiving laboratory would be judged a failure by its own design criteria as the sample return didn't contain the lunar material, with two failure points during the Apollo 11 return mission, at the splashdown and at the facility itself.

However the Lunar Receiving Laboratory was built quickly with only two years from start to finish, a time period now considered inadequate. Lessons learned from it can help with design of any Mars sample return receiving facility.

Design criteria for a proposed Mars Sample Return Facility, and for the return mission, have been developed by the American National Research Council, and the European Space Foundation. They concluded that it could be based on biohazard 4 containment but with more stringent requirements to contain unknown microorganisms possibly as small as or smaller than the smallest Earth microorganisms known, the ultramicrobacteria. The ESF study also recommended that it should be designed to contain the smaller gene transfer agents if possible, as these could potentially transfer DNA from martian microorganisms to terrestrial microorganisms if they have a shared evolutionary ancestry. It also needs to double as a clean room facility to protect the samples from terrestrial contamination that could confuse the sensitive life detection tests that would be used on the samples.
Before a sample return, new quarantine laws would be required. Environmental assessment would also be required, and various other domestic and international laws not present during the Apollo era would need to be negotiated.

Decontamination procedures

For all spacecraft missions requiring decontamination, the starting point is clean room assembly in US federal standard class 100 cleanrooms. These are rooms with fewer than 100 particles of size 0.5 µm or larger per cubic foot. Engineers wear cleanroom suits with only their eyes exposed. Components are sterilized individually before assembly, as far as possible, and they clean surfaces frequently with alcohol wipes during assembly. Spores of Bacillus subtilis was chosen for not only its ability to readily generate spores, but its well-established use as a model species. It is a useful tracker of UV irradiation effects because of its high resilience to a variety of extreme conditions. As such it is an important indicator species for forward contamination in the context of planetary protection.

For Category IVa missions (Mars landers that do not search for Martian life), the aim is to reduce the bioburden to 300,000 bacterial spores on any surface from which the spores could get into the Martian environment. Any heat tolerant components are heat sterilized to 114 °C. Sensitive electronics such as the core box of the rover including the computer, are sealed and vented through high-efficiency filters to keep any microbes inside.

For more sensitive missions such as Category IVc (to Mars special regions), a far higher level of sterilization is required. These need to be similar to levels implemented on the Viking landers, which were sterilized for a surface which, at the time, was thought to be potentially hospitable to life similar to special regions on Mars today.

In microbiology, it is usually impossible to prove that there are no microorganisms left viable, since many microorganisms are either not yet studied, or not cultivable. Instead, sterilization is done using a series of tenfold reductions of the numbers of microorganisms present. After a sufficient number of tenfold reductions, the chance that there any microorganisms left will be extremely low.

The two Viking Mars landers were sterilized using dry heat sterilization. After preliminary cleaning to reduce the bioburden to levels similar to present day Category IVa spacecraft, the Viking spacecraft were heat-treated for 30 hours at 112 °C, nominal 125 °C (five hours at 112 °C was considered enough to reduce the population tenfold even for enclosed parts of the spacecraft, so this was enough for a million-fold reduction of the originally low population).

Modern materials however are often not designed to handle such temperatures, especially since modern spacecraft often use "commercial off the shelf" components. Problems encountered include nanoscale features only a few atoms thick, plastic packaging, and conductive epoxy attachment methods. Also many instrument sensors cannot be exposed to high temperature, and high temperature can interfere with critical alignments of instruments.

As a result, new methods are needed to sterilize a modern spacecraft to the higher categories such as Category IVc for Mars, similar to Viking. Methods under evaluation, or already approved, include:

• Vapour phase hydrogen peroxide - effective, but can affect finishes, lubricants and materials that use aromatic rings and sulfur bonds. This has been established, reviewed, and a NASA/ESA specification for use of VHP has been approved by the Planetary Protection Officer, but it has not yet been formally published.
• Ethylene oxide - this is widely used in the medical industry, and can be used for materials not compatible with hydrogen peroxide. It is under consideration for missions such as ExoMars.
• Gamma radiation and electron beams have been suggested as a method of sterilization, as they are used extensively in the medical industry. They need to be tested for compatibility with spacecraft materials and hardware geometries, and are not yet ready for review.

Some other methods are of interest as they can sterilize the spacecraft after arrival on the planet.

• Supercritical carbon dioxide snow (Mars) - is most effective against traces of organic compounds rather than whole microorganisms. Has the advantage though that it eliminates the organic traces - while other methods kill the microorganisms, they leave organic traces that can confuse life detection instruments. Is under study by JPL and ESA.
• Passive sterilization through UV radiation (Mars). Highly effective against many microorganisms, but not all, as a Bacillus strain found in spacecraft assembly facilities is particularly resistant to UV radiation. Is also complicated by possible shadowing by dust and spacecraft hardware.
• Passive sterilization through particle fluxes (Europa). Plans for missions to Europa take credit for reductions due to this.

Bioburden detection and assessment

The spore count is used as an indirect measure of the number of microorganisms present. Typically 99% of microorganisms by species will be non-spore forming and able to survive in dormant states, and so the actual number of viable dormant microorganisms remaining on the sterilized spacecraft is expected to be many times the number of spore-forming microorganisms.

One new spore method approved is the "Rapid Spore Assay". This is based on commercial rapid assay systems, detects spores directly and not just viable microorganisms and gives results in 5 hours instead of 72 hours.

Challenges

It is also long been recognized that spacecraft cleaning rooms harbour polyextremophiles as the only microbes able to survive in them. For example, in a recent study, microbes from swabs of the Curiosity rover were subjected to desiccation, UV exposure, cold and pH extremes. Nearly 11% of the 377 strains survived more than one of these severe conditions.

This does not mean that these microbes have contaminated Mars. This is just the first stage of the process of bioburden reduction. To contaminate Mars they also have to survive the low temperature, vacuum, UV and ionizing radiation during the months long journey to Mars, and then have to encounter a habitat on Mars and start reproducing there. Whether this has happened or not is a matter of probability. The aim of planetary protection is to make this probability as low as possible. The currently accepted target probability of contamination per mission is to reduce it to less than 0.01%, though in the special case of Mars, scientists also rely on the hostile conditions on Mars to take the place of the final stage of heat treatment decimal reduction used for Viking. But with current technology scientists cannot reduce probabilities to zero.

New methods

Two recent molecular methods have been approved for assessment of microbial contamination on spacecraft surfaces.

• Adenosine triphosphate (ATP) detection - this is a key element in cellular metabolism. This method is able to detect non cultivable organisms. It can also be triggered by non viable biological material so can give a "false positive".
• Limulus Amebocyte Lysate assay - detects lipopolysaccharides (LPS). This compound is only present in Gram-negative bacteria. The standard assay analyses spores from microbes that are primarily Gram-positive, making it difficult to relate the two methods.

Impact prevention

This particularly applies to orbital missions, Category III, as they are sterilized to a lower standard than missions to the surface. It is also relevant to landers, as an impact gives more opportunity for forward contamination, and impact could be on an unplanned target, such as a special region on Mars.

The requirement for an orbital mission is that it needs to remain in orbit for at least 20 years after arrival at Mars with probability of at least 99% and for 50 years with probability at least 95%. This requirement can be dropped if the mission is sterilized to Viking sterilization standard.

In the Viking era (1970s), the requirement was given as a single figure, that any orbital mission should have a probability of less than 0.003% probability of impact during the current exploratory phase of exploration of Mars.

For both landers and orbiters, the technique of trajectory biasing is used during approach to the target. The spacecraft trajectory is designed so that if communications are lost, it will miss the target.

Issues with impact prevention

Despite these measures there has been one notable failure of impact prevention. The Mars Climate Orbiter which was sterilized only to Category III, crashed on Mars in 1999 due to a mix-up of imperial and metric units. The office of planetary protection stated that it is likely that it burnt up in the atmosphere, but if it survived to the ground, then it could cause forward contamination.

Mars Observer is another Category III mission with potential planetary contamination. Communications were lost three days before its orbital insertion maneuver in 1993. It seems most likely it did not succeed in entering into orbit around Mars and simply continued past on a heliocentric orbit. If it did succeed in following its automatic programming, and attempted the manoeuvre, however, there is a chance it crashed on Mars.

Three landers have had hard landings on Mars. These are Schiaparelli EDM lander, the Mars Polar Lander, and Deep Space 2. These were all sterilized for surface missions but not for special regions (Viking pre-sterilization only). Mars Polar Lander, and Deep Space 2 crashed into the polar regions which are now treated as special regions because of the possibility of forming liquid brines.

Controversies

Meteorite argument

Alberto G. Fairén and Dirk Schulze-Makuch published an article in Nature recommending that planetary protection measures need to be scaled down. They gave as their main reason for this, that exchange of meteorites between Earth and Mars means that any life on Earth that could survive on Mars has already got there and vice versa.

Robert Zubrin used similar arguments in favour of his view that the back contamination risk has no scientific validity.

Rebuttal by NRC

The meteorite argument was examined by the NRC in the context of back contamination. It is thought that all the Martian meteorites originate in relatively few impacts every few million years on Mars. The impactors would be kilometers in diameter and the craters they form on Mars tens of kilometers in diameter. Models of impacts on Mars are consistent with these findings.

Earth receives a steady stream of meteorites from Mars, but they come from relatively few original impactors, and transfer was more likely in the early Solar System. Also some life forms viable on both Mars and on Earth might be unable to survive transfer on a meteorite, and there is so far no direct evidence of any transfer of life from Mars to Earth in this way.

The NRC concluded that though transfer is possible, the evidence from meteorite exchange does not eliminate the need for back contamination protection methods.

Impacts on Earth able to send microorganisms to Mars are also infrequent. Impactors of 10 km across or larger can send debris to Mars through the Earth's atmosphere but these occur rarely, and were more common in the early Solar System.

Proposal to end planetary protection for Mars

In their 2013 paper "The Over Protection of Mars", Alberto Fairén and Dirk Schulze-Makuch suggested that we no longer need to protect Mars, essentially using Zubrin's meteorite transfer argument. This was rebutted in a follow up article "Appropriate Protection of Mars", in Nature by the current and previous planetary protection officers Catherine Conley and John Rummel.

Critique of Category V containment measures

The scientific consensus is that the potential for large-scale effects, either through pathogenesis or ecological disruption, is extremely small. Nevertheless, returned samples from Mars will be treated as potentially biohazardous until scientists can determine that the returned samples are safe. The goal is to reduce the probability of release of a Mars particle to less than one in a million.

Proposal for extension of protection to non-biological considerations

A COSPAR workshop in 2010, looked at issues to do with protecting areas from non biological contamination. They recommended that COSPAR expand its remit to include such issues.
Recommendations of the workshop include:

Recommendation 3 COSPAR should add a separate and parallel policy to
provide guidance on requirements/best practices for protection of non-living/nonlife-related aspects of Outer Space and celestial bodies

Ideas for doing this suggested since the workshop include protected special regions, or "Planetary Parks" to keep regions of the Solar System pristine for future scientific investigation, and also for ethical reasons.

Proposal to extend planetary protection

Astrobiologist Christopher McKay has argued that until we have better understanding of Mars, our explorations should be biologically reversible. For instance if all the microorganisms introduced to Mars so far remain dormant within the spacecraft, they could in principle be removed in the future, leaving Mars completely free of contamination from modern Earth lifeforms.

In the 2010 workshop one of the recommendations for future consideration was to extend the period for contamination prevention to the maximum viable lifetime of dormant microorganisms introduced to the planet.

"'Recommendation 4.' COSPAR should consider that the appropriate protection of potential indigenous extraterrestrial life shall include avoiding the harmful contamination of any habitable environment —whether extant or foreseeable— within the maximum potential time of viability of any terrestrial organisms (including microbial spores) that may be introduced into that environment by human or robotic activity."

In the case of Europa, a similar idea has been suggested, that it is not enough to keep it free from contamination during our current exploration period. It might be that Europa is of sufficient scientific interest that the human race has a duty to keep it pristine for future generations to study as well. This was the majority view of the 2000 task force examining Europa, though there was a minority view of the same task force that such strong protection measures are not required.

"One consequence of this view is that Europa must be protected from contamination for an open-ended period, until it can be demonstrated that no ocean exists or that no organisms are present. Thus, we need to be concerned that over a time scale on the order of 10 million to 100 million years (an approximate age for the surface of Europa), any contaminating material is likely to be carried into the deep ice crust or into the underlying ocean."

Exoplanets

The proposal by the German physicist Claudius Gros, that the technology of the Breakthrough Starshot project may be utilized to establish a biosphere of unicellular organisms on otherwise only transiently habitable exoplanets, has sparked a discussion, to what extent planetary protection should be extended to exoplanets. The discussion involves in particular the long-term perspective of complex vs. bacterial life and the diversity of life in the cosmos.

Directed panspermia

From Wikipedia, the free encyclopedia

 

Directed panspermia is the deliberate transport of microorganisms in space to be used as introduced species on lifeless but habitable astronomical objects.

 

Historically, Shklovskii and Sagan (1966) and Crick and Orgel (1973) hypothesized that life on the Earth may have been seeded deliberately by other civilizations. Conversely, Mautner and Matloff (1979) and Mautner (1995, 1997) proposed that humanity should seed other planetary systems, protoplanetary discs or star-forming clouds with microorganisms, to secure and expand our organic gene/protein lifeform. To avoid interference with local life, the targets may be young planetary systems where local life is unlikely. Directed panspermia can be motivated by biotic ethics that value the basic patterns of organic gene/protein life with its unique complexity and unity, and its drive for self-propagation.

Directed panspermia is becoming possible due to developments in solar sails, precise astrometry, the discovery of extrasolar planets, extremophiles and microbial genetic engineering. Cosmological projections suggest that life in space can then have a future.

History and motivation

An early example of the idea of directed panspermia dates to the early science fiction work Last and First Men by Olaf Stapledon, first published in 1930. It details the manner in which the last humans, upon discovering that the Solar System will soon be destroyed, send microscopic "seeds of a new humanity" towards potentially habitable areas of the universe.

In 1966 Shklovskii and Sagan speculated that life on Earth may have been seeded through directed panspermia by other civilisations. and in 1973 Crick and Orgel also discussed the concept. Conversely, Mautner and Matloff proposed in 1979, and Mautner examined in detail in 1995 and 1997 the technology and motivation to secure and expand our organic gene/protein life-form by directed panspermia missions to other planetary systems, protoplanetary discs and star-forming clouds. Technological aspects include propulsion by solar sails, deceleration by radiation pressure or viscous drag at the target, and capture of the colonizing micro-organisms by planets. A possible objection is potential interference with local life at the targets, but targeting young planetary systems where local life, especially advanced life, could not have started yet, avoids this problem.

Directed panspermia may be motivated by the desire to perpetuate the common genetic heritage of all terrestrial life. This motivation was formulated as biotic ethics that value the common gene/protein patterns of self propagation, and as panbiotic ethics that aim to secure and expand life in the universe.

Strategies and targets

Directed panspermia may be aimed at nearby young planetary systems such as Alpha PsA (25 ly (light-years) away) and Beta Pictoris (63.4 ly), both of which show accretion discs and signs of comets and planets. More suitable targets may be identified by space telescopes such as the Kepler mission that will identify nearby star systems with habitable astronomical objects. Alternatively, directed panspermia may aim at star-forming interstellar clouds such as Rho Ophiuchi cloud complex (427 ly), that contains clusters of new stars too young to originate local life (425 infrared-emitting young stars aged 100,000 to a million years). Such clouds contain zones with various densities (diffuse cloud < dark fragment < dense core < protostellar condensation < accretion disc) that could selectively capture panspermia capsules of various sizes.

Habitable astronomical objects or habitable zones about nearby stars may be targeted by large (10 kg) missions where microbial capsules are bundled and shielded. Upon arrival, microbial capsules in the payload may be dispersed in orbit for capture by planets. Alternatively, small microbial capsules may be sent in large swarms to habitable planets, protoplanetary discs, or zones of various density in interstellar clouds. The microbial swarm provides minimal shielding but does not require high precision targeting, especially when aiming at large interstellar clouds.

Propulsion and launch

Panspermia missions should deliver microorganisms that can grow in the new habitats. They may be sent in 10⁻¹⁰ kg, 60 μm diameter capsules that allow intact atmospheric entry at the target planets, each containing 100,000 diverse microorganisms suited to various environments. Both for bundled large mass missions and microbial capsule swarms, solar sails may provide the most simple propulsion for interstellar transit. Spherical sails will avoid orientation control both at launch and at deceleration at the targets.

For bundled shielded missions to nearby star systems, solar sails with thicknesses of 10⁻⁷ m and areal densities of 0.0001 kg/m² seem feasible, and sail/payload mass ratios of 10:1 will allow exit velocities near the maximum possible for such sails. Sails with about 540 m radius and area of 10⁶ m² can impart 10 kg payloads with interstellar cruise velocities of 0.0005 c (1.5x10⁵ m/s) when launched from 1 au (astronomical unit). At this speed, voyage to the Alpha PsA star will last 50,000 y, and to the Rho Opiuchus cloud, 824,000 years.

At the targets, the microbial payload would decompose into 10¹¹ (100 billion) 30 µm capsules to increase the probability of capture. In the swarm strategy to protoplanetary discs and interstellar clouds, 1 mm radius, 4.2x10⁻⁶ kg microbial capsules are launched from 1 au using sails of 4.2x10⁻⁵ kg with radius of 0.37 m and area of 0.42 m² to achieve cruising speeds of 0.0005 c. At the target, each capsule decomposes into 4,000 delivery microcapsules of 10⁻¹⁰ kg and of 30 micrometer radius that allow intact entry to planetary atmospheres.

For missions that do not encounter dense gas zones, such as interstellar transit to mature planets or to habitable zones about stars, the microcapsules can be launched directly from 1 au using 10⁻⁹ kg sails of 1.8 mm radius to achieve velocities of 0.0005 c to be decelerated by radiation pressure for capture at the targets. The 1 mm and 30 micrometer radius vehicles and payloads are needed in large numbers for both the bundled and swarm missions. These capsules and the miniature sails for swarm missions can be mass manufactured readily.

Astrometry and targeting

The panspermia vehicles would be aimed at moving targets whose locations at the time of arrival must be predicted. This can be calculated using their measured proper motions, their distances, and the cruising speeds of the vehicles. The positional uncertainty and size of the target object then allow estimating the probability that the panspermia vehicles will arrive at their targets. The positional uncertainty δy (m) of the target at arrival time is given by equation (1), where α_(p) is the resolution of proper motion of the target object (arcsec/year), d is the distance from the Earth(m) and v is the velocity of the vehicle (m/s)

δy = 1.5×10⁻¹³ α_p(d²/v)

Given the positional uncertainty, the vehicles may be launched with a scatter in a circle about the predicted position of the target. The probability P_target for a capsule to hit the target area with radius r_target (m) is the given by the ratio of the targeting scatter and the target area.

P_target = A_target/π(δy)² = 4.4×10²⁵ r_target²v²/(α_p²d⁴)

To apply these equations, the precision of astrometry of star proper motion of 0.00001 arcsec/year, and the solar sail vehicle velocity of 0.0005 c (1.5 × 10⁵ m/s) may be expected within a few decades. For a chosen planetary system, the area A_target may be the width of the habitable zone, while for interstellar clouds, it may be the sizes of the various density zones of the cloud.

Deceleration and capture

Solar sail missions to Sun-like stars can decelerate by radiation pressure in reverse dynamics of the launch. The sails must be properly oriented at arrival, but orientation control may be avoided using spherical sails. The vehicles must approach the target Sun-like stars at radial distances similar to the launch, about 1 au. After the vehicles are captured in orbit, the microbial capsules may be dispersed in a ring orbiting the star, some within the gravitational capture zone of planets. Missions to accretion discs of planets and to star-forming clouds will decelerate by viscous drag at the rate dv/dt as determined by equation (3), where v is the velocity, rc the radius of the spherical capsule, ρc is density of the capsule and ρm is the density of the medium.

dv/dt = -(3v²/2ρ_c) ρ _m/r_c

A vehicle entering the cloud with a velocity of 0.0005 c (1.5 × 10⁵ m/s) will be captured when decelerated to 2,000 m/s, the typical speed of grains in the cloud. The size of the capsules can be designed to stop at zones with various densities in the interstellar cloud. Simulations show that a 35 micron radius capsule will be captured in a dense core, and a 1 mm radius capsule in a protostellar condensation in the cloud. As for approach to accretion discs about stars, a millimetre size capsule entering the 1000 km thick disc face at 0.0005 c will be captured at 100 km into the disc. Therefore, 1 mm sized objects may be the best for seeding protoplanetary discs about new stars and protostellar condensations in interstellar clouds.

The captured panspermia capsules will mix with dust. A fraction of the dust and a proportional fraction of the captured capsules will be delivered to astronomical objects. Dispersing the payload into delivery microcapsules will increase the chance that some will be delivered to habitable objects. Particles of 0.6 - 60 micron radius can remain cold enough to preserve organic matter during atmospheric entry to planets or moons. Accordingly, each 1 mm, 4.2 ×10⁻⁶ kg capsule captured in the viscous medium can be dispersed into 42,000 delivery microcapsules of 30 micron radius, each weighing 10⁻¹⁰ kg and containing 100,000 microbes. These objects will not be ejected from the dust cloud by radiation pressure from the star, and will remain mixed with the dust. A fraction of the dust, containing the captured microbial capsules, will be captured by planets or moons, or captured in comets and delivered by them later to planets. The probability of capture, P_capture, can be estimated from similar processes, such as the capture of interplanetary dust particles by planets and moons in our Solar System, where 10⁻⁵ of the Zodiacal cloud maintained by comet ablation, and also a similar fraction of asteroid fragments, is collected by the Earth. The probability of capture of an initially launched capsule by a planet (or astronomical object) P_planet is given by the equation below, where P_target is the probability that the capsule reaches the target accretion disc or cloud zone, and P_capture is the probability of capture from this zone by a planet.

P_planet = P_target × P_capture

The probability P_planet depends on the mixing ratio of the capsules with the dust and on the fraction of the dust delivered to planets. These variables can be estimated for capture in planetary accretion discs or in various zones in the interstellar cloud.

Biomass requirements

After determining the composition of chosen meteorites, astroecologists performed laboratory experiments that suggest that many colonizing microorganisms and some plants could obtain most of their chemical nutrients from asteroid and cometary materials. However, the scientists noted that phosphate (PO₄) and nitrate (NO₃–N) critically limit nutrition to many terrestrial lifeforms. For successful missions, enough biomass must be launched and captured for a reasonable chance to initiate life at the target astronomical object. An optimistic requirement is the capture by the planet of 100 capsules with 100,000 microorganisms each, for a total of 10 million organisms with a total biomass of 10⁻⁸ kg.

The required biomass to launch for a successful mission is given by following equation. m_biomass (kg) = 10⁻⁸ / P_planet Using the above equations for P_target with transit velocities of 0.0005 c, the known distances to the targets, and the masses of the dust in the target regions then allows calculating the biomass that needs to be launched for probable success. With these parameters, as little as 1 gram of biomass (10¹² microorganisms) could seed Alpha PsA and 4.5 gram could seed Beta Pictoris. More biomass needs to be launched to the Rho Ophiuchi cloud complex, mainly because its larger distance. A biomass on the order of 300 tons would need to be launched to seed a protostellar condensation or an accretion disc, but two hundred kilograms would be sufficient to seed a young stellar object in the Rho Ophiuchi cloud complex.

Consequently, as long as the required physical range of tolerance are met (e.g.: growth temperature, cosmic radiation shielding, atmosphere and gravity), lifeforms viable on Earth may be chemically nourished by watery asteroid and planetary materials in this and other planetary systems.

Biological payload

The seeding organisms need to survive and multiply in the target environments and establish a viable biosphere. Some of the new branches of life may develop intelligent beings who will further expand life in the galaxy. The messenger microorganisms may find diverse environments, requiring extremophile microorganisms with a range of tolerances, including thermophile (high temperature), psychrophile (low temperature), acidophile (high acidity), halophile (high salinity), oligotroph (low nutrient concentration), xerophile (dry environments) and radioresistant (high radiation tolerance) microorganisms. Genetic engineering may produce polyextremophile microorganisms with several tolerances. The target atmospheres will probably lack oxygen, so the colonizers should include anaerobic microorganisms. Colonizing anaerobic cyanobacteria may later establish atmospheric oxygen that is needed for higher evolution, as it happened on Earth. Aerobic organisms in the biological payload may be delivered to the astronomical objects later when the conditions are right, by comets that captured and preserved the capsules.

The development of eukaryote microorganisms was a major bottleneck to higher evolution on Earth. Including eukaryote microorganisms in the payload can bypass this barrier. Multicellular organisms are even more desirable, but being much heavier than bacteria, fewer can be sent. Hardy tardigrades (water-bears) may be suitable but they are similar to arthropods and would lead to insects. The body-plan of rotifers could lead to higher animals, if the rotifers can be hardened to survive interstellar transit.

Microorganisms or capsules captured in the accretion disc can be captured along with the dust into asteroids. During aqueous alteration the asteroids contain water, inorganic salts and organics, and astroecology experiments with meteorites showed that algae, bacteria, fungi and plant cultures can grow in the asteroids in these media. Microorganisms can then spread in the accreting solar nebula, and will be delivered to planets in comets and in asteroids. The microorganisms can grow on nutrients in the carrier comets and asteroids in the aqueous planetary environments, until they adapt to the local environments and nutrients on the planets.

Signal in the genome

A number of publications since 1979 have proposed the idea that directed panspermia could be demonstrated to be the origin of all life on Earth if a distinctive 'signature' message were found, deliberately implanted into either the genome or the genetic code of the first microorganisms by our hypothetical progenitor. In 2013 a team of physicists claimed that they had found mathematical and semiotic patterns in the genetic code which, they believe, is evidence for such a signature. This claim has not been substantiated by further study, or accepted by the wider scientific community. One outspoken critic is biologist PZ Myers who said, writing in Pharyngula:

Unfortunately, what they’ve so honestly described is good old honest garbage ... Their methods failed to recognize a well-known functional association in the genetic code; they did not rule out the operation of natural law before rushing to falsely infer design ... We certainly don’t need to invoke panspermia. Nothing in the genetic code requires design, and the authors haven’t demonstrated otherwise.

In a later peer-reviewed article, the authors address the operation of natural law in an extensive statistical test, and draw the same conclusion as in the previous article. In special sections they also discuss methodological concerns raised by PZ Myers and some others.

Concept missions

Significantly, panspermia missions can be launched by present or near-future technologies. However, more advanced technologies may be also used when these become available. The biological aspects of directed panspermia may be improved by genetic engineering to produce hardy polyextremophile microorganisms and multicellular organisms, suitable to diverse astronomical objects environments. Hardy polyextremophile anaerobic multicellular eukaryots with high radiation resistance, that can form a self-sustaining ecosystem with cyanobacteria, would combine ideally the features needed for survival and higher evolution.

For advanced missions, ion thrusters or solar sails using beam-powered propulsion accelerated by Earth-based lasers can achieve speeds up to 0.01 c (3 x 10⁶ m/s). Robots may provide in-course navigation, may control the reviving of the frozen microbes periodically during transit to repair radiation damage, and may also choose suitable targets. These propulsion methods and robotics are under development.

Microbial payloads may be also planted on hyperbolic comets bound for interstellar space. This strategy follows the mechanisms of natural panspermia by comets, as suggested by Hoyle and Wikramasinghe. The microorganisms would be frozen in the comets at interstellar temperatures of a few kelvins and protected from radiation for eons. It is unlikely that an ejected comet will be captured in another planetary system, but the probability can be increased by allowing the microbes to multiply during warm perihelion approach to the Sun, then fragmenting the comet. A 1 km radius comet would yield 4.2 x 10¹² one-kg seeded fragments, and rotating the comet would eject these shielded icy objects in random directions into the galaxy. This increases a trillion-fold the probability of capture in another planetary system, compared with transport by a single comet. Such manipulation of comets is a speculative long-term prospect.

Motivation and ethics

Directed panspermia aims to secure and expand our family of organic gene/protein life. It may be motivated by the desire to perpetuate the common genetic heritage of all terrestrial life. This motivation was formulated as biotic ethics, that value the common gene/protein patterns of organic life, and as panbiotic ethics that aim to secure and expand life in the universe.

Molecular biology shows complex patterns common to all cellular life, a common genetic code and a common mechanism to translate it into proteins, which in turn help to reproduce the DNA code. Also, shared are the basic mechanisms of energy use and material transport. These self-propagating patterns and processes are the core of organic gene/protein life. Life is unique because of this complexity, and because of the exact coincidence of the laws of physics that allow life to exist. Also unique to life is the pursuit of self-propagation, which implies a human purpose to secure and expand life. These objectives are best secured in space, suggesting a panbiotic ethics aimed to secure this future.

The longevity of human space-faring technological society is uncertain, and it would be prudent to start a directed panspermia program promptly. This program could secure life and allow it to expand in space and in biodiversity with an immense future for trillions of eons.

Objections and counterarguments

The main objection to directed panspermia is that it may interfere with local life at the targets. The colonizing microorganisms may out-compete local life for resources, or infect and harm local organisms. However, this probability can be minimized by targeting newly forming planetary systems, accretion discs and star-forming clouds, where local life, and especially advanced life, could not have emerged yet. If there is local life that is fundamentally different, the colonizing microorganisms may not harm it. If there is local organic gene/protein life, it may exchange genes with the colonizing microorganisms, increasing galactic biodiversity.

Another objection is that space should be left pristine for scientific studies, a reason for planetary quarantine. However, directed panspermia may reach only a few, at most a few hundred new stars, still leaving a hundred billion pristine for local life and for research. A technical objection is the uncertain survival of the messenger organisms during long interstellar transit. Research by simulations, and the development on hardy colonizers is needed to address this questions.

A third argument against engaging in directed panspermia derives from the view that wild animals do not —on the average— have lives worth living, and thus spreading life would be morally wrong. Ng supports this view, focusing mainly on the fact that almost all animal species have many more offspring than are needed to replace them. The large number of offspring implies that most of them will die before reaching reproductive age, providing only a short window of life before an often unpleasant death. Tomasik agrees, but places significant weight on the extreme suffering many animals experience, especially at death. Plant responds in detail to Tomasik, arguing that because of the vast number of diverse species and the difficulty of rating animal pain and pleasure, we cannot determine if animals have lives worth living. If wild animal lives are overall negative in quality (with more suffering than pleasure), then spreading life through panspermia would be spreading needless pain. From this perspective, directed panspermia is to be strictly avoided, unless and until we can determine that the lives of the animals generated by it would average positive.

In popular culture

The discovery of an ancient directed panspermia effort is the central theme of "The Chase," an episode of Star Trek: The Next Generation. In the story, Captain Picard must work to complete the penultimate research of his late archaeology professor's career. That professor, Galen, had discovered that DNA fragments seeded into the primordial genetic material of 19 worlds could be rearranged to assemble a computer algorithm. Amid competition (and, later, with begrudging cooperation) from Cardassian, Klingon and Romulan expeditions also exploring Galen's research clues, the Enterprise crew discovers that an alien progenitor race had indeed, 4 billion years prior, seeded genetic material across many star systems, thus directing the evolution of many humanoid species.

Genesis project

The German physicist Claudius Gros has proposed that the technology developed by the Breakthrough Starshot initiative may be utilized in a second step to establish a biosphere of unicellular microbes on otherwise only transiently habitable astronomical objects. The aim of this initiative, the Genesis project, would be to fast forward evolution to a stage equivalent of the precambrian period on Earth. Gros argues that the Genesis project would be realizable within 50-100 years, using low-weight probes equipped with a miniaturized gene laboratory for the in situ cell synthesis of the microbes. The Genesis project extends directed panspermia to eukaryotic life, arguing that it is more likely that complex life is rare,  and not bacterial life.