Search This Blog

Tuesday, September 2, 2014

Kuiper belt

Kuiper belt

From Wikipedia, the free encyclopedia
 
Known objects in the Kuiper belt, derived from data from the Minor Planet Center. Objects in the main belt are colored green, whereas scattered objects are colored orange. The four outer planets are blue. Neptune's few known trojans are yellow, whereas Jupiter's are pink. The scattered objects between Jupiter's orbit and the Kuiper belt are known as centaurs. The scale is in astronomical units. The pronounced gap at the bottom is due to difficulties in detection against the background of the plane of the Milky Way.

The Kuiper belt /ˈkpər/, sometimes called the Edgeworth–Kuiper belt (after the astronomers Kenneth Edgeworth and Gerard Kuiper), is a region of the Solar System beyond the planets, extending from the orbit of Neptune (at 30 AU) to approximately 50 AU from the Sun.[1] It is similar to the asteroid belt, but it is far larger—20 times as wide and 20 to 200 times as massive.[2][3] Like the asteroid belt, it consists mainly of small bodies, or remnants from the Solar System's formation. Although most asteroids are composed primarily of rock and metal, most Kuiper belt objects are composed largely of frozen volatiles (termed "ices"), such as methane, ammonia and water. The Kuiper belt is home to at least three dwarf planets: Pluto, Haumea, and Makemake. Some of the Solar System's moons, such as Neptune's Triton and Saturn's Phoebe, are also believed to have originated in the region.[4][5]

Since the belt was discovered in 1992,[6] the number of known Kuiper belt objects (KBOs) has increased to over a thousand, and more than 100,000 KBOs over 100 km (62 mi) in diameter are believed to exist.[7] The Kuiper belt was initially thought to be the main repository for periodic comets, those with orbits lasting less than 200 years. However, studies since the mid-1990s have shown that the belt is dynamically stable, and that comets' true place of origin is the scattered disc, a dynamically active zone created by the outward motion of Neptune 4.5 billion years ago;[8] scattered disc objects such as Eris have extremely eccentric orbits that take them as far as 100 AU from the Sun.[nb 1]

The Kuiper belt should not be confused with the hypothesized Oort cloud, which is a thousand times more distant. The objects within the Kuiper belt, together with the members of the scattered disc and any potential Hills cloud or Oort cloud objects, are collectively referred to as trans-Neptunian objects (TNOs).[11]

Pluto is the largest member of the Kuiper belt, and the second largest known TNO, the largest being Eris in the scattered disc.[nb 1] Originally considered a planet, Pluto's status as part of the Kuiper belt caused it to be reclassified as a "dwarf planet" in 2006. It is compositionally similar to many other objects of the Kuiper belt, and its orbital period is characteristic of a class of KBOs, known as "plutinos", that share the same 2:3 resonance with Neptune.

History

After the discovery of Pluto, many speculated that it might not be alone. The region now called the Kuiper belt was hypothesized in various forms for decades. It was only in 1992 that the first direct evidence for its existence was found. The number and variety of prior speculations on the nature of the Kuiper belt have led to continued uncertainty as to who deserves credit for first proposing it.

Hypotheses

The first astronomer to suggest the existence of a trans-Neptunian population was Frederick C. Leonard. Soon after Pluto's discovery by Clyde Tombaugh in 1930, Leonard pondered whether it was "not likely that in Pluto there has come to light the first of a series of ultra-Neptunian bodies, the remaining members of which still await discovery but which are destined eventually to be detected".[12] That same year, astronomer Armin O. Leuschner suggested that Pluto "may be one of many long-period planetary objects yet to be discovered."[13]
Astronomer Gerard Kuiper, after whom the Kuiper belt is named

In 1943, in the Journal of the British Astronomical Association, Kenneth Edgeworth hypothesized that, in the region beyond Neptune, the material within the primordial solar nebula was too widely spaced to condense into planets, and so rather condensed into a myriad of smaller bodies. From this he concluded that "the outer region of the solar system, beyond the orbits of the planets, is occupied by a very large number of comparatively small bodies"[14] and that, from time to time, one of their number "wanders from its own sphere and appears as an occasional visitor to the inner solar system",[15] becoming a comet.

In 1951, in an article for the journal Astrophysics, Gerard Kuiper speculated on a similar disc having formed early in the Solar System's evolution; however, he did not believe that such a belt still existed today. Kuiper was operating on the assumption common in his time that Pluto was the size of the Earth and had therefore scattered these bodies out toward the Oort cloud or out of the Solar System. Were Kuiper's hypothesis correct, there would not be a Kuiper belt today.[16]

The hypothesis took many other forms in the following decades. In 1962, physicist Al G.W. Cameron postulated the existence of "a tremendous mass of small material on the outskirts of the solar system".[17] In 1964, Fred Whipple, who popularised the famous "dirty snowball" hypothesis for cometary structure, thought that a "comet belt" might be massive enough to cause the purported discrepancies in the orbit of Uranus that had sparked the search for Planet X, or, at the very least, massive enough to affect the orbits of known comets.[18] Observation, however, ruled out this hypothesis.[17]

In 1977, Charles Kowal discovered 2060 Chiron, an icy planetoid with an orbit between Saturn and Uranus. He used a blink comparator, the same device that had allowed Clyde Tombaugh to discover Pluto nearly 50 years before.[19] In 1992, another object, 5145 Pholus, was discovered in a similar orbit.[20] Today, an entire population of comet-like bodies, called the centaurs, is known to exist in the region between Jupiter and Neptune. The centaurs' orbits are unstable and have dynamical lifetimes of a few million years.[21] From the time of Chiron's discovery in 1977, astronomers have speculated that the centaurs therefore must be frequently replenished by some outer reservoir.[22]

Further evidence for the existence of the Kuiper belt later emerged from the study of comets. That comets have finite lifespans has been known for some time. As they approach the Sun, its heat causes their volatile surfaces to sublimate into space, gradually evaporating them. In order for comets to continue to be visible over the age of the Solar System, they must be replenished frequently.[23] One such area of replenishment is the Oort cloud, a spherical swarm of comets extending beyond 50,000 AU from the Sun first hypothesised by astronomer Jan Oort in 1950.[24] The Oort cloud is believed to be the point of origin of long-period comets, which are those, like Hale–Bopp, with orbits lasting thousands of years.

There is, however, another comet population, known as short-period or periodic comets, consisting of those comets that, like Halley's Comet, have orbital periods of less than 200 years. By the 1970s, the rate at which short-period comets were being discovered was becoming increasingly inconsistent with their having emerged solely from the Oort cloud.[25] For an Oort cloud object to become a short-period comet, it would first have to be captured by the giant planets. In 1980, in the Monthly Notices of the Royal Astronomical Society, Uruguayan astronomer Julio Fernández stated that for every short-period comet to be sent into the inner Solar System from the Oort cloud, 600 would have to be ejected into interstellar space. He speculated that a comet belt from between 35 and 50 AU would be required to account for the observed number of comets.[26] Following up on Fernández's work, in 1988 the Canadian team of Martin Duncan, Tom Quinn and Scott Tremaine ran a number of computer simulations to determine if all observed comets could have arrived from the Oort cloud. They found that the Oort cloud could not account for all short-period comets, particularly as short-period comets are clustered near the plane of the Solar System, whereas Oort-cloud comets tend to arrive from any point in the sky. With a “belt”, as Fernández described it, added to the formulations, the simulations matched observations.[27] Reportedly because the words "Kuiper" and "comet belt" appeared in the opening sentence of Fernández's paper, Tremaine named this hypothetical region the "Kuiper belt".[28]

Discovery

The array of telescopes atop Mauna Kea, with which the Kuiper belt was discovered

In 1987, astronomer David Jewitt, then at MIT, became increasingly puzzled by "the apparent emptiness of the outer Solar System".[6] He encouraged then-graduate student Jane Luu to aid him in his endeavour to locate another object beyond Pluto's orbit, because, as he told her, "If we don't, nobody will."[29] Using telescopes at the Kitt Peak National Observatory in Arizona and the Cerro Tololo Inter-American Observatory in Chile, Jewitt and Luu conducted their search in much the same way as Clyde Tombaugh and Charles Kowal had, with a blink comparator.[29] Initially, examination of each pair of plates took about eight hours,[30] but the process was sped up with the arrival of electronic charge-coupled devices or CCDs, which, though their field of view was narrower, were not only more efficient at collecting light (they retained 90% of the light that hit them, rather than the 10% achieved by photographs) but allowed the blinking process to be done virtually, on a computer screen. Today, CCDs form the basis for most astronomical detectors.[31] In 1988, Jewitt moved to the Institute of Astronomy at the University of Hawaii. Luu later joined him to work at the University of Hawaii's 2.24 m telescope at Mauna Kea.[32] Eventually, the field of view for CCDs had increased to 1024 by 1024 pixels, which allowed searches to be conducted far more rapidly.[33] Finally, after five years of searching, on August 30, 1992, Jewitt and Luu announced the "Discovery of the candidate Kuiper belt object" (15760) 1992 QB1.[6] Six months later, they discovered a second object in the region, (181708) 1993 FW.[34]

Studies conducted since the trans-Neptunian region was first charted have shown that the region now called the Kuiper belt is not the point of origin of short-period comets, but that they instead derive from a linked population called the scattered disc. The scattered disc was created when Neptune migrated outward into the proto-Kuiper belt, which at the time was much closer to the Sun, and left in its wake a population of dynamically stable objects that could never be affected by its orbit (the Kuiper belt proper), and a population whose perihelia are close enough that Neptune can still disturb them as it travels around the Sun (the scattered disc). Because the scattered disc is dynamically active and the Kuiper belt relatively dynamically stable, the scattered disc is now seen as the most likely point of origin for periodic comets.[8]

Name

Astronomers sometimes use the alternative name Edgeworth–Kuiper belt to credit Edgeworth, and KBOs are occasionally referred to as EKOs. However, Brian G. Marsden claims that neither deserves true credit: "Neither Edgeworth nor Kuiper wrote about anything remotely like what we are now seeing, but Fred Whipple did".[35] David Jewitt comments: "If anything ... Fernández most nearly deserves the credit for predicting the Kuiper Belt."[16]

KBOs are sometimes called kuiperoids, a name suggested by Clyde Tombaugh.[36] The term trans-Neptunian object (TNO) is recommended for objects in the belt by several scientific groups because the term is less controversial than all others—it is not an exact synonym though, as TNOs include all objects orbiting the Sun past the orbit of Neptune, not just those in the Kuiper belt.

Origins

Simulation showing outer planets and Kuiper belt: a) before Jupiter/Saturn 2:1 resonance, b) scattering of Kuiper belt objects into the Solar System after the orbital shift of Neptune, c) after ejection of Kuiper belt bodies by Jupiter

The precise origins of the Kuiper belt and its complex structure are still unclear, and astronomers are awaiting the completion of several wide-field survey telescopes such as Pan-STARRS and the future LSST, which should reveal many currently unknown KBOs. These surveys will provide data that will help determine answers to these questions.[2]

The Kuiper belt is believed to consist of planetesimals, fragments from the original protoplanetary disc around the Sun that failed to fully coalesce into planets and instead formed into smaller bodies, the largest less than 3,000 kilometres (1,900 mi) in diameter.

Modern computer simulations show the Kuiper belt to have been strongly influenced by Jupiter and Neptune, and also suggest that neither Uranus nor Neptune could have formed in their present positions, as too little primordial matter existed at that range to produce objects of such high mass. Instead, these planets are believed to have formed closer to Jupiter. Scattering of planetesimals early in the Solar System's history would have led to migration of the orbits of the giant planets: Saturn, Uranus and Neptune drifted outwards while Jupiter drifted inwards. Eventually, the orbits shifted to the point where Jupiter and Saturn reached an exact 2:1 resonance; Jupiter orbited the Sun twice for every one Saturn orbit. The gravitational repercussions of such a resonance ultimately disrupted the orbits of Uranus and Neptune, causing Neptune's orbit to become more eccentric and move outward into the primordial planetesimal disc, which sent the disc into temporary chaos.[37][38][39] As Neptune's orbit expanded, it excited and scattered many TNO planetesimals into higher and more eccentric orbits.[40] Many more were scattered inward, often to be scattered again and in some cases ejected by Jupiter. The process is thought to have reduced the primordial Kuiper belt population by 99% or more, and to have shifted the distribution of the surviving members outward.[39]

However, this currently most popular model, the "Nice model", still fails to account for some of the characteristics of the distribution and, quoting one of the scientific articles,[41] the problems "continue to challenge analytical techniques and the fastest numerical modeling hardware and software". The model predicts a higher average eccentricity in classical KBO orbits than is observed (0.10–0.13 versus 0.07).[39] The frequency of paired objects, many of which are far apart and loosely bound, also poses a problem for the model.[42]

Structure

File:Dust Models Paint Alien's View of Solar System.ogv
Dust in the Kuiper belt creates a faint infrared disc.

At its fullest extent, including its outlying regions, the Kuiper belt stretches from roughly 30 to 55 AU. However, the main body of the belt is generally accepted to extend from the 2:3 resonance (see below) at 39.5 AU to the 1:2 resonance at roughly 48 AU.[43] The Kuiper belt is quite thick, with the main concentration extending as much as ten degrees outside the ecliptic plane and a more diffuse distribution of objects extending several times farther. Overall it more resembles a torus or doughnut than a belt.[44] Its mean position is inclined to the ecliptic by 1.86 degrees.[45]

The presence of Neptune has a profound effect on the Kuiper belt's structure due to orbital resonances. Over a timescale comparable to the age of the Solar System, Neptune's gravity destabilises the orbits of any objects that happen to lie in certain regions, and either sends them into the inner Solar System or out into the scattered disc or interstellar space. This causes the Kuiper belt to possess pronounced gaps in its current layout, similar to the Kirkwood gaps in the asteroid belt. In the region between 40 and 42 AU, for instance, no objects can retain a stable orbit over such times, and any observed in that region must have migrated there relatively recently.[46]

Classical belt

Between the 2:3 and 1:2 resonances with Neptune, at approximately 42–48 AU, the gravitational influence of Neptune is negligible, and objects can exist with their orbits essentially unmolested. This region is known as the classical Kuiper belt, and its members comprise roughly two thirds of KBOs observed to date.[47][48] Because the first modern KBO discovered, (15760) 1992 QB1, is considered the prototype of this group, classical KBOs are often referred to as cubewanos ("Q-B-1-os").[49][50] The guidelines established by the IAU demand that classical KBOs be given names of mythological beings associated with creation.[51]
The classical Kuiper belt appears to be a composite of two separate populations. The first, known as the "dynamically cold" population, has orbits much like the planets; nearly circular, with an orbital eccentricity of less than 0.1, and with relatively low inclinations up to about 10° (they lie close to the plane of the Solar System rather than at an angle). The second, the "dynamically hot" population, has orbits much more inclined to the ecliptic, by up to 30°. The two populations have been named this way not because of any major difference in temperature, but from analogy to particles in a gas, which increase their relative velocity as they become heated up.[52] The two populations not only possess different orbits, but different colors; the cold population is markedly redder than the hot. If this is a reflection of different compositions, it suggests they formed in different regions. The hot population is believed to have formed near Jupiter, and to have been ejected out by movements among the gas giants. The cold population, on the other hand, has been proposed to have formed more or less in its current position, although it might also have been later swept outwards by Neptune during its migration,[2][53] particularly if Neptune's eccentricity was transiently increased.[39] Although the Nice model appears to be able to at least partially explain a compositional difference, it has also been suggested the color difference may reflect differences in surface evolution.[39]

Resonances

Distribution of cubewanos (blue), Resonant trans-Neptunian objects (red) and near scattered objects (grey).
Orbit classification (schematic of semi-major axes)

When an object's orbital period is an exact ratio of Neptune's (a situation called a mean motion resonance), then it can become locked in a synchronised motion with Neptune and avoid being perturbed away if their relative alignments are appropriate. If, for instance, an object is in just the right kind of orbit so that it orbits the Sun twice for every three Neptune orbits, and if it reaches perihelion with Neptune a quarter of an orbit away from it, then whenever it returns to perihelion, Neptune will always be in about the same relative position as it began, because it will have completed 1½ orbits in the same time. This is known as the 2:3 (or 3:2) resonance, and it corresponds to a characteristic semi-major axis of about 39.4 AU. This 2:3 resonance is populated by about 200 known objects,[54] including Pluto together with its moons. In recognition of this, the members of this family are known as plutinos. Many plutinos, including Pluto, have orbits that cross that of Neptune, though their resonance means they can never collide. Plutinos have high orbital eccentricities, suggesting that they are not native to their current positions but were instead thrown haphazardly into their orbits by the migrating Neptune.[55] IAU guidelines dictate that all plutinos must, like Pluto, be named for underworld deities.[51] The 1:2 resonance (whose objects complete half an orbit for each of Neptune's) corresponds to semi-major axes of ~47.7AU, and is sparsely populated.[56] Its residents are sometimes referred to as twotinos. Other resonances also exist at 3:4, 3:5, 4:7 and 2:5.[57] Neptune possesses a number of trojan objects, which occupy its L4 and L5 points; gravitationally stable regions leading and trailing it in its orbit. Neptune trojans are often described as being in a 1:1 resonance with Neptune. Neptune trojans typically have very stable orbits.

Additionally, there is a relative absence of objects with semi-major axes below 39 AU that cannot apparently be explained by the present resonances. The currently accepted hypothesis for the cause of this is that as Neptune migrated outward, unstable orbital resonances moved gradually through this region, and thus any objects within it were swept up, or gravitationally ejected from it.[58]

"Kuiper cliff"

Graph showing the numbers of KBOs for a given distance from the Sun. The plutinos are the "spike" at 39 AU, whereas the classicals are between 42 and 47 AU, the twotinos are at 48 AU, and the 5:2 resonance is at 55 AU.

The 1:2 resonance appears to be an edge beyond which few objects are known. It is not clear whether it is actually the outer edge of the classical belt or just the beginning of a broad gap. Objects have been detected at the 2:5 resonance at roughly 55 AU, well outside the classical belt; however, predictions of a large number of bodies in classical orbits between these resonances have not been verified through observation.[55]

Based on estimations of the primordial mass required to form Uranus and Neptune, as well as bodies as large as Pluto (see below), earlier models of the Kuiper belt had suggested that the number of large objects would increase by a factor of two beyond 50 AU,[59] so this sudden drastic falloff, known as the "Kuiper cliff", was completely unexpected, and its cause, to date, is unknown. In 2003, Bernstein and Trilling et al. found evidence that the rapid decline in objects of 100 km or more in radius beyond 50 AU is real, and not due to observational bias. Possible explanations include that material at that distance was too scarce or too scattered to accrete into large objects, or that subsequent processes removed or destroyed those that did.[60] Patryk Lykawka of Kobe University has claimed that the gravitational attraction of an unseen large planetary object, perhaps the size of Earth or Mars, might be responsible.[61][62]

Composition

The infrared spectra of both Eris and Pluto, highlighting their common methane absorption lines

Studies of the Kuiper belt since its discovery have generally indicated that its members are primarily composed of ices: a mixture of light hydrocarbons (such as methane), ammonia, and water ice,[63] a composition they share with comets.[64] The low densities observed in those KBOs whose diameter is known, (less than 1 g cm−3) is consistent with an icy makeup.[63] The temperature of the belt is only about 50 K,[65] so many compounds that would be gaseous closer to the Sun remain solid.

Due to their small size and extreme distance from Earth, the chemical makeup of KBOs is very difficult to determine. The principal method by which astronomers determine the composition of a celestial object is spectroscopy. When an object's light is broken into its component colors, an image akin to a rainbow is formed. This image is called a spectrum. Different substances absorb light at different wavelengths, and when the spectrum for a specific object is unravelled, dark lines (called absorption lines) appear where the substances within it have absorbed that particular wavelength of light. Every element or compound has its own unique spectroscopic signature, and by reading an object's full spectral "fingerprint", astronomers can determine what it is made of.

Initially, such detailed analysis of KBOs was impossible, and so astronomers were only able to determine the most basic facts about their makeup, primarily their color.[66] These first data showed a broad range of colors among KBOs, ranging from neutral grey to deep red.[67] This suggested that their surfaces were composed of a wide range of compounds, from dirty ices to hydrocarbons.[67] This diversity was startling, as astronomers had expected KBOs to be uniformly dark, having lost most of their volatile ices to the effects of cosmic rays.[68] Various solutions were suggested for this discrepancy, including resurfacing by impacts or outgassing.[66] However, Jewitt and Luu's spectral analysis of the known Kuiper belt objects in 2001 found that the variation in color was too extreme to be easily explained by random impacts.[69]

Although to date most KBOs still appear spectrally featureless due to their faintness, there have been a number of successes in determining their composition.[65] In 1996, Robert H. Brown et al. obtained spectroscopic data on the KBO 1993 SC, revealing its surface composition to be markedly similar to that of Pluto, as well as Neptune's moon Triton, possessing large amounts of methane ice.[70]

Water ice has been detected in several KBOs, including 1996 TO66,[71] 38628 Huya and 20000 Varuna.[72] In 2004, Mike Brown et al. determined the existence of crystalline water ice and ammonia hydrate on one of the largest known KBOs, 50000 Quaoar. Both of these substances would have been destroyed over the age of the Solar System, suggesting that Quaoar had been recently resurfaced, either by internal tectonic activity or by meteorite impacts.[65]

Mass and size distribution

Illustration of the power law.

Despite its vast extent, the collective mass of the Kuiper belt is relatively low. The total mass is estimated to range between a 25th and 10th the mass of the Earth[73] with some estimates placing it at one thirtieth of an Earth mass.[74] Conversely, models of the Solar System's formation predict a collective mass for the Kuiper belt of 30 Earth masses.[2] This missing >99% of the mass can hardly be dismissed, as it is required for the accretion of any KBOs larger than 100 km (62 mi) in diameter. If the Kuiper belt had always had its current low density these large objects simply could not have formed.[2] Moreover, the eccentricity and inclination of current orbits makes the encounters quite "violent" resulting in destruction rather than accretion. It appears that either the current residents of the Kuiper belt have been created closer to the Sun or some mechanism dispersed the original mass. Neptune's current influence is too weak to explain such a massive "vacuuming", though the Nice model proposes that it could have been the cause of mass removal in the past. Although the question remains open, the conjectures vary from a passing star scenario to grinding of smaller objects, via collisions, into dust small enough to be affected by solar radiation.[53]

Bright objects are rare compared with the dominant dim population, as expected from accretion models of origin, given that only some objects of a given size would have grown further. This relationship between N(D) (the number of objects of diameter greater than D) and D, referred to as brightness slope, has been confirmed by observations. The slope is inversely proportional to some power of the diameter D:
 \frac{d N}{d D} \propto D^{-q} where the current measures[75] give q = 4 ±0.5.
This implies that
N\propto D^{1-q}+\text{a constant}.
Less formally, there are for instance 8 (=23) times more objects in 100–200 km range than objects in 200–400 km range. In other words, for every object with the diameter of 1,000 km (621 mi) there should be around 1000 (=103) objects with diameter of 100 km (62 mi).

If q is 4 or less, the law would imply an infinite mass in the Kuiper belt. The true function N(D) obviously assumes only integer values, so the fractional values it gives for N at large D cannot be accurate. More accurate models find that the "slope" parameter q is in effect greater at large diameters and lesser at small diameters.[75] It seems that Pluto is somewhat unexpectedly large, having several percent of the total mass of the Kuiper belt. It is not expected that anything larger than Pluto exists in the Kuiper belt, and in fact most of the brightest (largest) objects at inclinations less than 5° have probably been found.[75]

Of course, only the magnitude is actually known, the size is inferred assuming albedo (not a safe assumption for larger objects).

Since January 2010, the smallest Kuiper belt object discovered to date spans 980 m across.[76]

Scattered objects

Comparison of the orbits of scattered disc objects (black), classical KBOs (blue), and 2:5 resonant objects (green). Orbits of other KBOs are gray.

The scattered disc is a sparsely populated region, overlapping with the Kuiper belt but extending as far as 100 AU and farther. Scattered disc objects (SDOs) travel in highly elliptical orbits, usually also highly inclined to the ecliptic. Most models of Solar System formation show both KBOs and SDOs first forming in a primordial comet belt, whereas later gravitational interactions, particularly with Neptune, sent the objects spiraling outward, some into stable orbits (the KBOs) and some into unstable orbits, becoming the scattered disc.[8] Due to its unstable nature, the scattered disc is believed to be the point of origin for many of the Solar System's short-period comets. Their dynamic orbits occasionally force them into the inner Solar System, becoming first centaurs, and then short-period comets.[8]

According to the Minor Planet Center, which officially catalogues all trans-Neptunian objects, a KBO, strictly speaking, is any object that orbits exclusively within the defined Kuiper belt region regardless of origin or composition. Objects found outside the belt are classed as scattered objects.[77] However, in some scientific circles the term "Kuiper belt object" has become synonymous with any icy minor planet native to the outer Solar System believed to have been part of that initial class, even if its orbit during the bulk of Solar System history has been beyond the Kuiper belt (e.g. in the scattered-disc region). They often describe scattered disc objects as "scattered Kuiper belt objects".[78] Eris, which is known to be more massive than Pluto, is often referred to as a KBO, but is technically an SDO.[77] A consensus among astronomers as to the precise definition of the Kuiper belt has yet to be reached, and this issue remains unresolved.

The centaurs, which are not normally considered part of the Kuiper belt, are also believed to be scattered objects, the only difference being that they were scattered inward, rather than outward. The Minor Planet Center groups the centaurs and the SDOs together as scattered objects.[77]

Triton

Neptune's moon Triton
 During its period of migration, Neptune is thought to have captured one of the larger KBOs and set it in orbit around itself. This is its moon Triton, which is the only large moon in the Solar System to have a retrograde orbit; it orbits in the opposite direction to Neptune's rotation. This suggests that, unlike the large moons of Jupiter, Saturn, and Uranus, which are thought to have coalesced from spinning discs of material encircling their young parent planets, Triton was a fully formed body that was captured from surrounding space. Gravitational capture of an object is not easy; it requires some mechanism to slow the object down enough to be snared by the larger object's gravity. Triton may have encountered Neptune as part of a binary (many KBOs are members of binaries; see below); ejection of the other member of the binary by Neptune could then explain Triton's capture.[79] Triton is only slightly larger than Pluto, and spectral analysis of both worlds shows that they are largely composed of similar materials, such as methane and carbon monoxide. All this points to the conclusion that Triton was once a KBO that was captured by Neptune during its outward migration.[80]

Largest KBOs


Artistic comparison of Eris, Pluto, Makemake, Haumea, Sedna, 2007 OR10, Quaoar, Orcus, and Earth. Since the year 2000, a number of KBOs with diameters of between 500 and 1,500 km (932 mi), more than half that of Pluto, have been discovered. 50000 Quaoar, a classical KBO discovered in 2002, is over 1,200 km across. Makemake and Haumea, both announced on July 29, 2005, are larger still. Other objects, such as 28978 Ixion (discovered in 2001) and 20000 Varuna (discovered in 2000) measure roughly 500 km (311 mi) across.[2]

Pluto

The discovery of these large KBOs in similar orbits to Pluto led many to conclude that, bar its relative size, Pluto was not particularly different from other members of the Kuiper belt. Not only did these objects approach Pluto in size, but many also possessed satellites, and were of similar composition (methane and carbon monoxide have been found both on Pluto and on the largest KBOs).[2] Thus, just as Ceres was considered a planet before the discovery of its fellow asteroids, some began to suggest that Pluto might also be reclassified.
The issue was brought to a head by the discovery of Eris, an object in the scattered disc far beyond the Kuiper belt, that is now known to be 27% more massive than Pluto.[81] In response, the International Astronomical Union (IAU), was forced to define what a planet is for the first time, and in so doing included in their definition that a planet must have "cleared the neighbourhood around its orbit".[82] As Pluto shared its orbit with so many KBOs, it was deemed not to have cleared its orbit, and was thus reclassified from a planet to a member of the Kuiper belt.

Although Pluto is currently the largest KBO, there are two known larger objects currently outside the Kuiper belt that probably originated in it. These are Eris and Neptune's moon Triton (which, as explained above, is probably a captured KBO).

As of 2008, only five objects in the Solar System (Ceres, Eris, and the KBOs Pluto, Makemake and Haumea) are listed as dwarf planets by the IAU. However, 90482 Orcus, 28978 Ixion and many other Kuiper-belt objects are large enough to be in hydrostatic equilibrium; most of them will probably qualify when more is known about them.[83][84][85]

Satellites

Of the four largest TNOs, three (Eris, Pluto, and Haumea) possess satellites, and two have more than one. A higher percentage of the larger KBOs possess satellites than the smaller objects in the Kuiper belt, suggesting that a different formation mechanism was responsible.[86] There are also a high number of binaries (two objects close enough in mass to be orbiting "each other") in the Kuiper belt. The most notable example is the Pluto–Charon binary, but it is estimated that around 11% of KBOs exist in binaries.[87]

Exploration

Artist's conception of New Horizons at Pluto

On January 19, 2006, the first spacecraft mission to explore the Kuiper belt, New Horizons, was launched. The mission, headed by Alan Stern of the Southwest Research Institute, will arrive at Pluto on July 14, 2015, and, circumstances permitting, will continue on to study another as-yet-undetermined KBO. Any KBO chosen will be between 40 and 90 km (25 to 55 miles) in diameter and, ideally, white or grey, to contrast with Pluto's reddish color.[88] John Spencer, an astronomer on the New Horizons mission team, says that no target for a post-Pluto Kuiper belt encounter has yet been selected, as they are awaiting data from the Pan-STARRS survey project to ensure as wide a field of options as possible.[89] The Pan-STARRS project, partially operational since May 2010,[90] will, when fully online, survey the entire sky with four 1.4 gigapixel digital cameras to detect any moving objects, from near-Earth objects to KBOs.[91] To speed up the detection process, the New Horizons team established Ice Hunters, a citizen science project that allowed members of the public to participate in the search for suitable KBO targets;[92][93][94] the project has subsequently been transferred to another site, Ice Investigators,[95] produced by CosmoQuest.[96]
The debris discs around the stars HD 139664 and HD 53143. The black central circle is produced by the camera's coronagraph, which hides the central star to allow the much fainter discs to be seen.

Other Kuiper belts

By 2006, astronomers had resolved dust discs believed to be Kuiper belt-like structures around nine stars other than the Sun. They appear to fall into two categories: wide belts, with radii of over 50 AU, and narrow belts (like our own Kuiper belt) with radii of between 20 and 30 AU and relatively sharp boundaries.[97] Beyond this, 15–20% of solar-type stars have an observed infrared excess that is believed to indicate massive Kuiper-belt-like structures.[98] Most known debris discs around other stars are fairly young, but the two images on the right, taken by the Hubble Space Telescope in January 2006, are old enough (roughly 300 million years) to have settled into stable configurations.
The left image is a "top view" of a wide belt, and the right image is an "edge view" of a narrow belt.[97][99] Supercomputer simulations of dust in the Kuiper belt suggest that when it was younger, it may have resembled the narrow rings seen around younger stars.[100]

Are lower pesticide residues a good reason to buy organic? Probably not.

Are lower pesticide residues a good reason to buy organic? Probably not.

The views expressed are those of the author and are not necessarily those of Scientific American.



A lot of organic supporters are up in arms about the recent Stanford study that found no nutritional benefit to organic foods. Stanford missed the point, they say—it’s not about what organic foods have in them, it’s what they don’t. After all, avoidance of pesticide residues is the #1 reason why people buy organic foods.

Yes, conventional foods have more synthetic pesticide residues than organic ones, on average. And yes, pesticides are dangerous chemicals. But does the science support paying significantly more for organic foods just to avoid synthetic pesticides? No.

A Pesticide Is A Pesticide

I’m not saying that pesticides, herbicides, and insect repellants aren’t toxic. I certainly wouldn’t recommend drinking cocktails laced with insect-repelling chemicals, for without a doubt, they can be bad for you. Pesticide exposure has been linked to all kinds of diseases and conditions, from neurodegenerative diseases like Parkinson’s to cancer. What we do know, though, is that natural isn’t synonymous with harmless. As a 2003 review of food safety concluded, “what should be made clear to consumers is that ‘organic’ does not equal ‘safe’.”

I’ve said it before and I’ll say it again: there is nothing safe about the chemicals used in organic agriculture. Period. This shouldn’t be that shocking – after all, a pesticide is a pesticide. “Virtually all chemicals can be shown to be dangerous at high doses,” explain scientists, “and this includes the thousands of natural chemicals that are consumed every day in food but most particularly in fruit and vegetables.”

There’s a reason we have an abundance of natural pesticides: plants and animals produce tens of thousands of chemicals to try and deter insects and herbivores from eating them. Most of these haven’t been tested for their toxic potential, as the Reduced Risk Program of the US Environmental Protection Agency (EPA) applies to synthetic pesticides only. As more research is done into their toxicity, however, we find they are just as bad as synthetic pesticides, sometimes worse. Many natural pesticides have been found to be potential – or serious – health risks, including those used commonly in organic farming.

In head-to-head comparisons, natural pesticides don’t fare any better than synthetic ones. When I compared the organic chemicals copper sulfate and pyrethrum to the top synthetics, chlorpyrifos and chlorothalonil, I found that not only were the organic ones more acutely toxic, studies have found that they are more chronically toxic as well, and have higher negative impacts on non-target species.


My results match with other scientific comparisons. In their recommendations to Parliament in 1999, the Committee on European Communities noted that copper sulfate, in particular, was far more dangerous than the synthetic alternative. A review of their findings can be seen in the table on the right (from a recent review paper). Similarly, head to head comparisons have found that organic pesticides aren’t better for the environment, either.

Organic pesticides pose the same health risks as non-organic ones. No matter what anyone tells you, organic pesticides don’t just disappear. Rotenone is notorious for its lack of degradation, and copper sticks around for a long, long time. Studies have shown that copper sulfate, pyrethrins, and rotenone all can be detected on plants after harvest—for copper sulfate and rotenone, those levels exceeded safe limits. One study found such significant rotenone residues in olives and olive oil to warrant “serious doubts…about the safety and healthiness of oils extracted from drupes treated with rotenone.” Just like with certain synthetic pesticides, organic pesticide exposure has health implications—a study in Texas found that rotenone exposure correlated to a significantly higher risk of Parkinson’s disease. The increased risk due to Rotenone was five times higher than the risk posed by the synthetic alternative, chlorpyrifos. Similarly, the FDA has known for a while that chronic exposure to copper sulfate can lead to anemia and liver disease.

So why do we keep hearing that organic foods have fewer pesticide residues? Well, because they have lower levels of synthetic pesticide residues. Most of our data on pesticide residues in food comes from surveys like the USDA’s Pesticide Data Program (PDP). But the while the PDP has been looking at the residues of over 300 pesticides in foods for decades, rotenone and copper sulfate aren’t among the usual pesticides tested for—maybe, because for several organic pesticides, fast, reliable methods for detecting them were only developed recently. And, since there isn’t any public data on the use of organic pesticides in organic farming (like there is for conventional farms), we’re left guessing what levels of organic pesticides are on and in organic foods.

So, if you’re going to worry about pesticides, worry about all of them, organic and synthetic. But, really, should you worry at all?

You Are What You Eat? Maybe Not.

We know, quite assuredly, that conventionally produced foods do contain higher levels of synthetic chemicals. But do these residues matter?

While study after study can find pesticide residues on foods, they are almost always well below safety standards. Almost all pesticides detected on foods by the USDA and independent scientific studies are at levels below 1% of the Acceptable Daily Intake (ADI) set by government regulators. This level isn’t random – the ADI is based on animal exposure studies in a wide variety of species. First, scientists give animals different amounts of pesticides on a daily basis throughout their lifetimes and monitor those animals for toxic effects. Through this, they determine the highest dose at which no effects can be found. The ADI is then typically set 100 times lower than that level. So a typical human exposure that is 1% of the ADI is equivalent to an exposure 10,000 times lower than levels that are safe in animal models.

Systematic reviews of dietary pesticide exposure all come to the same conclusion: that typical dietary exposure to pesticide residues in foods poses minimal risks to humans. As the book Health Benefits of Organic Food explains, “while there is some evidence that consuming organic produce will lead to lower exposure of pesticides compared to the consumption of conventional produce, there is no evidence of effect at contemporary concentrations.” Or, as a recent review states, “from a practical standpoint, the marginal benefits of reducing human exposure to pesticides in the diet through increased consumption of organic produce appear to be insignificant.”

Reviews of the negative health effects of pesticides find that dangerous exposure levels don’t come from food. Instead, non-dietary routes make for the vast majority of toxin exposures, in particular the use of pesticides around the home and workplace. A review of the worldwide disease burden caused by chemicals found that 70% can be attributed to air pollution, with acute poisonings and occupational exposures coming in second and third. Similarly, studies have found that indoor air concentrations of pesticides, not the amount on foodstuffs, correlate strongly to the amount of residues found in pregnant women (and even still, there was no strong correlation between exposure and health effects). Similarly, other studies have found that exposures to toxic pyrethroids come primarily from the environment. Children on organic diets routeinely had pyrethroids in their systems, and the organic group actually had higher levels of several pyrethroid metabolites than the conventional one. In other words, you have more to fear from your home than from your food.

Your home probably contains more pesticides than you ever imagined. Plastics and paints often contain fungicides to prevent mold—fungi that, by the way, can kill you. Your walls, carpets and floors also contain pesticides. Cleaning products and disenfectants contains pesticides and fungicides so they can do their job. Ever used an exterminator to get rid of mice, termites, fleas or cockroaches? That stuff can linger for months. Step outside your house, and just about everything you touch has come in contact with a pesticide. Insecticides are used in processing, manufacturing, and packaging, not to mention that even grocery stores use pesticides to keep insects and rodents at bay. These chemicals are all around you, every day, fighting off the pests that destroy our buildings and our food. It’s not surprising that most pesticide exposures doesn’t come from your food.

That said, there are some studies that have found a link between diet and exposure to specific pesticides, particularly synthetic organophosphorus pesticides. Lu et al. found that switching children from a conventional food diet to an entirely organic one dropped the urinary levels of specific metabolites for malathion and chlorpyrifos to nondetectable levels in a matter of days. But, it’s important to note that even the levels they detected during the conventional diet are three orders of magnitude lower than the levels needed in animal experiments to cause neurodevelopmental or other adverse health effects.

While it might seem that decreasing exposure to pesticides in any way could only be good for you, toxicologists would differ. Contrary to what you might think, lower exposure isn’t necessarily better. It’s what’s known as hormesis, or a hormetic dose response curve. There is evidence that exposure to most chemicals at doses significantly below danger thresholds, even pesticides, is beneficial when compared to no exposure at all. Why? Perhaps because it kick starts our immune system. Or, perhaps, because pesticides activate beneficial biological pathways. For most chemicals, we simply don’t know. What we do know is that data collected from 5000 dose response measurements (abstracted from over 20,000 studies) found that low doses of many supposedly toxic chemicals, metals, pesticides and fungicides either reduced cancer rates below controls or increased longevity or growth in a variety of animals. So while high acute and chronic exposures are bad, the levels we see in food that are well below danger thresholds may even be good for us. This isn’t as surprising as you might think—just look at most pharmaceuticals. People take low doses of aspirin daily to improve their heart health, but at high chronic doses, it can cause anything from vomiting to seizures and even death. Similarly, a glass of red wine every day might be good for you. But ten glasses a day? Definitely not.

No Need To Fear

To date, there is no scientific evidence that eating an organic diet leads to better health.

What of all those studies I just mentioned linking pesticides to disorders? Well, exactly none of them looked at pesticides from dietary intake and health in people. Instead, they involve people with high occupational exposure (like farmers who spray pesticides) or household exposure (from gardening, etc). Judging the safety of dietary pesticide intake by high exposures is like judging the health impacts of red wine based on alcoholics. A systematic review of the literature found only three studies to date have looked at clinical outcomes of eating organic – and none found any difference between an organic and conventional diet. My question is: if organic foods are so much healthier, why aren’t there any studies that show people on an organic diet are healthier than people eating conventionally grown produce instead?

More to the point, if conventional pesticide residues on food (and not other, high exposure routes) are leading to rampant disease, we should be able to find evidence of the connection in longitudinal epidemiological studies—but we don’t. The epidemiological evidence for the danger of pesticide residues simply isn’t there.

If dietary exposure to pesticides was a significant factor in cancer rates, we would expect to see that people who eat more conventionally grown fruits and vegetable have higher rates of cancer. But instead, we see the opposite. People who eat more fruits and vegetables have significantly lower incidences of cancers, and those who eat the most are two times less likely to develop cancer than those who eat the least. While high doses of pesticides over time have been linked to cancer in lab animals and in vitro studies, “epidemiological studies do not support the idea that synthetic pesticide residues are important for human cancer.” Even the exposure to the persistent and villainized pesticide DDT has not been consistently linked to cancer. As a recent review of the literature summarized, “no hard evidence currently exists that toxic hazards such as pesticides have had a major impact on total cancer incidence and mortality, and this is especially true for diet-related exposures.”

The closest we have to studying the effects of diet on health are studies looking at farmers. However, farmers in general have high occupational pesticide exposures, and thus it’s impossible to tease out occupational versus dietary exposure. Even still, in this high-risk group, studies simply don’t find health differences between organic and conventional farmers. A UK study found that conventional farmers were just as healthy as organic ones, though the organic ones were happier. Similarly, while test-tube studies of high levels of pesticides are known to cause reproductive disorders, a comparison of sperm quality from organic and conventional farmers was unable to connect dietary intake of over 40 different pesticides to any kind of reproductive impairment. Instead, the two groups showed no statistical difference in their sperm quality.

In a review of the evidence for choosing organic food, Christine Williams said it simply: “There are virtually no studies of any size that have evaluated the effects of organic v. conventionally-grown foods.” Thus, she explains, “conclusions cannot be drawn regarding potentially beneficial or adverse nutritional consequences, to the consumer, of increased consumption of organic food.”

“There is currently no evidence to support or refute claims that organic food is safer and thus, healthier, than conventional food, or vice versa. Assertions of such kind are inappropriate and not justified,” explain scientists. Neither organic nor conventional food is dangerous to eat, they say, and the constant attention to safety is unwarranted. Worse, it does more harm than good. The scientists chastise the media and industry alike for scaremongering tactics, saying that “the selective and partial presentation of evidence serves no useful purpose and does not promote public health. Rather, it raises fears about unsafe food.”

Furthermore, the focus on pesticides is misleading, as pesticide residues are the lowest food hazard when it comes to human health (as the figure from the paper on the right shows). They conclude that as far as the scientific evidence is concerned, “it seems that other factors, if any, rather than safety aspects speak in favor of organic food.”

If you don’t want to listen to those people or me, listen to the toxicologists, who study this stuff for a living. When probed about the risk that different toxins pose, over 85% rejected the notion that organic or “natural” products are safer than others. They felt that smoking, sun exposure and mercury were of much higher concern than pesticides. Over 90% agreed that the media does a terrible job of reporting the about toxic substances, mostly by overstating the risks. They slammed down hard on non-governmental organizations, too, for overstating risk.

What’s in a Name?

There’s good reason we can’t detect differences between organic and conventional diets: the labels don’t mean that much. Sure, organic farms have to follow a certain set of USDA guidelines, but farm to farm variability is huge for both conventional and organic practices. As a review of organic practices concluded: “variation within organic and conventional farming systems is likely as large as differences between the two systems.”

The false dichotomy between conventional and organic isn’t just misleading, it’s dangerous. Our constant attention to natural versus synthetic only causes fear and distrust, when in actuality, our food has never been safer. Eating less fruits and vegetables due to fear of pesticides or the high price of organics does far more harm to our health than any of the pesticide residues on our food.

Let me be clear about one thing: I’m all for reducing pesticide use. But we can’t forget that pesticides are used for a reason, too. We have been reaping the rewards of pesticide use for decades. Higher yields due to less crop destruction. Safer food because of reduced fungal and bacterial contamination. Lower prices as a result of increased supply and longer shelf life. Protection from pests that carry deadly diseases. Invasive species control, saving billions of dollars in damages—and the list goes on. Yes, we need to manage the way we use pesticides, scrutinize the chemicals involved and monitor their effects to ensure safety, and Big Ag (conventional and organic) needs to be kept in check. But without a doubt, our lives have been vastly improved by the chemicals we so quickly villainize.

If we want to achieve the balance between sustainability, production outputs, and health benefits, we have to stop focusing on brand names. Instead of emphasizing labels, we need to look at different farming practices and the chemicals involved and judge them independently of whether they fall under organic standards.

In the meantime, buy fresh, locally farmed produce, whether it’s organic or not; if you can talk to the farmers, you’ll know exactly what is and isn’t on your food. Wash it well, and you’ll get rid of most of whatever pesticides are on there, organic or synthetic. And eat lots and lots of fruits and vegetables—if there is anything that will improve your health, it’s that.

Before you say otherwise and get mad at me for mentioning it, rotenone is currently a USDA approved organic pesticide. It was temporarily banned, but reapproved in 2010. Before it was banned, it was the most commonly used organic pesticide, and now—well, without public data on pesticide use on organic farms, we have no idea how much it is being used today.
Food picture from FreeFoto.Com

Christie Wilcox  
About the Author: Christie Wilcox is a science writer and blogger who moonlights as a PhD student in Cell and Molecular Biology at the University of Hawaii. Follow on Google+. Follow on Twitter @NerdyChristie.

The Hypercar Lives: Meet VW’s XL1

The Hypercar Lives: Meet VW’s XL1

RMI followers and auto buffs often ask, ‘What happened to the hypercar?’ With the release of VW’s impressively fuel-efficient and strikingly similiar XL1, the world now has an answer.

Original link:  https://medium.com/solutions-journal-summer-2014/the-hypercar-lives-meet-vws-xl1-97603e97612f

Image copyright Volkswagen of America
When VW released the European fuel economy ratings for its new, limited-production XL1 passenger car last summer, you could almost hear the automotive world’s collective jaw drop. The XL1 came in at a staggering 313 miles per Imperial gallon of diesel. That’s the efficiency equivalent of more than 230 miles per U.S. gallon of gasoline. At a time when the 2014 model of the best-selling vehicle in the United States for more than three decades — Ford’s F-150 pickup truck — gets an EPA-rated 23 mpg highway, and the average for all model year 2013 light-duty vehicles sold in the U.S. was just 24.6 mpg, VW had moved the decimal point an entire place to the right.

Engineering leadership and platform fitness

The XL1 is named for its engineering goal: develop a production car that can drive 100 kilometers on 1 liter of fuel (235 miles per U.S. gallon). That was the charge in 1999 to VW engineers by the company’s visionary then-chairman, Ferdinand Piëch, who is Ferdinand Porsche’s grandson and chair of VW’s supervisory board today. “We built the Bugatti and now the XL1,” says Mark Gillies, manager of product and technology communications for VW of America. “Both use extreme technology to achieve almost opposite ends of the [performance] spectrum.”

The XL1’s tiny 2.6-gallon diesel-fuel tank can fuel average driving for more than 310 miles, thanks to a combination of strategies that RMI collectively calls platform fitness. That’s the key to the Hypercar concept developed by RMI chief scientist Amory Lovins in 1991 and evolved by RMI’s Hypercar Center through the 1990s. Hypercars integrate ultralight weight, superior aerodynamics, low-rolling-resistance tires, and a downsized and superefficient electrified powertrain. For example, VW’s XL1 weighs just 1,753 pounds. How? “We used mixed lightweight materials to bring out their best performance in their respective places in the vehicle,” explains Dr. Volker Kaese, VW’s project manager for the XL1. High-temperature-tolerant steel is used in the powertrain. Lighter, more flexible aluminum forms the chassis and crush zones. Polycarbonate side panels save weight and allow sleeker shapes. And the passenger cell is a carbon-fiber monocoque.

Then there’s the XL1’s astonishing aerodynamic drag coefficient. Lower is better, and the XL1’s 0.189 is the best ever in a production car. By comparison, a sleek and streamlined 2014 Corvette Stingray has a drag coefficient of 0.29 and Ford’s popular F-150 is around 0.40. The XL1 shaves drag everywhere it can, covering the rear wheels and replacing protruding side-view mirrors with low-profile, rear-facing cameras displayed on a dashboard screen.

Even before the first XL1 rolled off the production line, some were quick to point out the striking parallels between the Hypercar concept specs of the early 1990s and the real-world specs of today’s production XL1. “The XL1 is a hypercar in the way that might make Amory Lovins smile,” wrote High Gear Media’s Bengt Halvorson, in a piece that ran in the Washington Post. “That’s a nod to one of the creators of the original 1990s Hypercar project from Rocky Mountain Institute.” Similarly, automotive writer David Herron in Torque News noted, “the VW XL1 is the embodiment of the hypercar concept developed by Amory Lovins years ago.”

Besides Lovins himself, no one knows this better than Michael Brylawski. Currently the founder and CEO of Vision Fleet Capital, which works on clean vehicle adoption, he cofounded RMI’s sustainable transportation practice and later led strategy for RMI spinoffs Hypercar, Inc., its successor Fiberforge Corporation, and Bright Automotive. “When I saw the XL1 from VW, the specs looked quite similar to where Amory was predicting well over 20 years ago that vehicle design could go,” he explains. “The XL1 is the purest form of the Hypercar [on the market today]. The similarities are exceptional.”

From Hypercar concept to VW reality

RMI’s Hypercar started in 1990 with a $50,000 seed grant from the Nathan Cummings Foundation to “get Amory to think about cars.” The resulting paper, “Advanced Light Vehicle Concepts,” shocked the National Research Council’s auto-efficiency symposium, says Lovins. Don Runkle, then GM’s head of advanced engineering, took Lovins to lunch, and on a handshake, launched a fruitful two-year process of mutual education.

To say that Lovins, RMI, and Hypercar made a splash in the auto world would be an understatement. The British magazine Car named Lovins the 22nd most powerful person in the global automotive industry (and the only outsider). The Hypercar concept won the ISATA Nissan Prize and a World Technology Award — followed by another to Hypercar, Inc. In 1993, after two years’ validation with the industry, RMI put the Hypercar concept into the public domain so nobody could patent it and to encourage competition leveraging its ideas, while RMI’s for-profit spinoffs sought to commercialize technologies outside automakers’ comfort zone and raise the competitive pressure.

By the first half of the 2000s, you could read about the Hypercar everywhere from Automobile magazine to the Wall Street Journal to Environmental Health Perspectives. But a true Hypercar had yet to leap from the drawing board to the streets. “The roadmap was right, but the distance underestimated,” Brylawski says today.

Covering the rear wheels and eliminating protruding side-view mirors contributed to the XL1's astonishing aerodynamics. Image copyright Volkswagen of America

Indeed, many of Lovins’s predictions have come to pass. Two decades ago he claimed regenerative braking could yield 70 percent efficiency when automakers balked at the idea of exceeding 30. 

Today’s electric vehicles, including the Chevy Volt and Tesla Model S, respectively get 70+ and 80 percent. Meanwhile, the XL1’s specs are an eerily close match with Lovins’s early Hypercar predictions for achievable rolling resistance, aerodynamic drag, and more. (Unfortunately, estimates of fuel economy can’t be directly compared between the Hypercar and XL1 due to differences in their number of seats, U.S. vs. European test cycles, and changes in modeling and test cycle protocols, but both are far into triple digits.)

So if the Hypercar concept is now emergent reality, why aren’t more Hypercars on the road? “There’s a lot of hard work that goes between the idea and the execution,” says Brylawski. And that’s where VW’s XL1 is really notable. It combines an electrified hybrid powertrain, lightweight carbon fiber and other materials, and low aerodynamic drag and rolling resistance, bringing the Hypercar and other 1990s concepts like it — such as GM’s 1991 Ultralite — from drawing board to driver’s seat. Lovins, for his part, is thrilled — he would love to be VW’s first U.S. XL1 customer, he says.

The fuel-efficient road ahead

For all the similarities between Hypercar and XL1, there is at least one major point of departure: cost. The Hypercar was always meant to be competitively priced, but with a sticker price of $150,000, VW’s XL1 certainly is not. Its production run is just 250 copies — a niche, novelty vehicle for aficionados. “It’s something of a one-off,” says VW’s Gillies. “The market is effectively limited for [such an expensive] small economy car.”

But a high-volume car was never VW’s goal. The XL1 was a proof of concept, says Gillies, to “show the production feasibility; that VW has the vision and drive to get it through to production. It’s one thing to do a concept, but another to show you could actually build the thing.” Its innovations will doubtless inform other models.

A diesel-electric hybrid powertrain, combined with a mixed-material approach that shaves weight without sacrificing performance, enables XL1's impressive fuel economy. Image copyright Volkswagen of America

Despite XL1’s eye-popping mpg rating, VW might have left some efficiency on the table. Lovins notes that Toyota’s 2007 1/X concept car, also a plug-in hybrid, had four seats and the interior volume of a Prius, but weighed only 926 pounds, so even a production-ready version would probably weigh less than the two-seat XL1. “We’re seeing a lot of partially executed solutions,” says Jerry Weiland, the GM veteran who leads RMI’s transportation practice. “Different automakers have done bits and pieces [of the Hypercar concept], but no one has put the whole thing together.”

Equally surprisingly, the XL1 may actually take efficiency further than needed. RMI senior associate Jonathan Walker explains: “VW had a different goal than we do. Their goal was to make a 235-mpg car. In my opinion, you don’t need that,” he says. “RMI’s goal is get off carbon and oil. A 100 mpg car gets you there.” RMI’s Reinventing Fire analysis, he notes, can fuel its efficient vehicles, some at just half XL1’s efficiency, with any mixture of electricity, hydrogen, and advanced biofuels but no oil. “The added capital and cost of going for XL1 levels of efficiency is not worth it,” Walker says. “You start getting diminishing returns.” In other words, more modest but still radically improved fuel efficiency can yield an affordable Hypercar that doesn’t carry an XL1 price tag.

Runkle’s theory of economic gravity

“Amory gets full credit for putting these concepts on the table more than 20 years ago,” says Weiland. “But by now, the automakers have developed and productionized what they saw fit. If they’re not doing something, there’s probably a somewhat rational reason.” One of those reasons is federal fuel economy standards. Until recently, U.S. consumers haven’t been especially concerned about mpg in their car-buying decisions, so automakers have mostly done just enough to meet corporate average fuel economy (CAFE) requirements.

As Walker notes, those requirements, recently stiffened to 54.5 mpg for an automaker’s fleet by 2025, still might not move the needle. Many automakers can make more money paying modest penalties and selling gas-guzzlers than they can complying. Also, more-efficient hybrids and electric vehicles help automakers’ fleets meet the CAFE average standard while still including inefficient SUVs and pickup trucks.

But if CAFE standards are insufficient, that puts the ball squarely back in the court of economics. And Don Runkle has something to say about that.

Runkle is now executive chairman of EcoMotors, a firm pioneering superefficient internal combustion engines (which Lovins thinks could weigh far less than the XL1’s plug-in diesel-electric hybrid). Before EcoMotors, Runkle spent 30 years with GM, leading the Ultralite and other early-1990s Hypercar-esque concepts. “I was always involved in some attempt at extraordinary performance levels,” he says. “Sometimes it was outright speed or acceleration or fuel efficiency. You’re pushing the envelope. In terms of high performance — whether it’s acceleration or top speed — you’re always trying to make sure you had the structural integrity you needed at the lowest mass you could handle” — simultaneously boosting efficiency.

Like the Hypercar, his Ultralite team similarly pursued lightweighting, rolling resistance, aerodynamics, and a downsized powertrain to develop a sporty, 100-mpg, four-seat concept car. At some point, though, Runkle argues that eking out more mpg comes at a cost. If cost is no object, almost any level of performance — fuel economy or otherwise — is possible. But cost is an object. He calls it his theory of economic gravity.

“In a nutshell, it’s not hard to get high fuel economy. That’s a matter of physics,” he explains. “What’s hard is to get a technology that saves more than it costs. That’s economic gravity, where there’s a natural incentive.” Automakers more or less all have a spreadsheet, Runkle says, showing incremental efficiency gain vs. cost for a big portfolio of technology options — electric steering, lightweighting with carbon fiber, LED lights, lower-friction tires. Engineers start with the cheapest options and work their way down the list until they’ve met legal mpg requirements, he says.

“It’s always good to do the Hypercars, the Ultralites,” says Runkle. “They push the envelope. They help clarify the problem and show the promise. Then you can focus more on trying to solve the cost issues.”

A Hypercar for the masses

There is, of course, a very RMI way around the a la carte approach of Runkle’s spreadsheet: whole-systems thinking. “That’s the challenge if you’re only looking at single components versus a systems approach,” says Brylawski. “It’s challenging running a multi-billion-dollar, multi-million-unit auto company without some specializing,” Brylawski continues. “That’s a barrier to more holistic approaches” like VW’s XL1 and BMW’s i3, not to mention RMI’s Revolution concept, an early 2000s SUV designed by Hypercar, Inc. and two Tier Ones.

“What Amory and RMI showed [with Hypercar] is that change is hard but you can end up in a better place. But why change unless you have to?” That’s the rub. Inertia is strong. “The extreme retooling required, metaphorical and literal, hasn’t been compelling enough for automakers,” argues Brylawski. “Not until recently have you had a global regulatory and fuel price environment that makes it worthwhile” — and the threat, proven by Tesla, of outcompeting incumbents by making better autos that people will buy because they’re superior, not just because they’re more efficient.

Now, with automakers like VW leading the charge, and with manufacturing methods like RMI’s Fiberforge spinoff (whose technology was sold last year to German Tier One pressmaker Dieffenbacher), that could be changing. “Fast forward to today,” Brylawski points out. “BMW has a car made largely from carbon fiber. Toyota has a fuel cell car coming out. VW’s XL1 gets hundreds of miles per gallon. We’re seeing a whole host of interesting solutions that read pretty closely out of Amory and RMI’s playbook from the early 1990s.”

Moreover, from VW’s Jetta to Toyota’s Prius, automakers are offering multiple efficient and electrified powertrain options: TDI clean diesel, hybrid, plug-in hybrid electric, all-electric, and extended-range electrics like the Chevy Volt. “It comes back to platform physics. That makes sense to do first,” continues Brylawski. “The combination of platform fitness and electrification is like peanut butter and chocolate creating a Reese’s cup. It’s Amory’s holistic view, and that’s where VW and BMW are ahead of the curve.”

“I think XL1 will stimulate both VW and its competitors — as will BMW’s i3 and i8 — to develop families of diverse vehicles that increasingly converge with our original Hypercar goals,” says Lovins, reflecting on the Hypercar’s influence. “Our early-1990s expectations are now matched by reality in such key areas as mass, drag, tire rolling resistance, braking energy regeneration, and — even exceeding my early hopes — the weight, cost, and performance of electric powertrains. Such advanced vehicles are not only for the select, higher-price markets in which they’re initially being introduced in Germany, but also ultimately for mass markets.”

“It takes a long time, but once you get these things into the market, things start to accrete,” concludes Brylawski. “The Prius outsells every SUV in America. Back in 2000 that was unimaginable.” We’re already, in fact, seeing signs of further traction. Earlier this year BMW increased production on its i3 by 43 percent to meet higher-than-expected consumer demand, and is on track for total annual sales, at U.S. prices starting around $40,000, to be nearly double initial forecasts.

From VW’s pioneering XL1 to BMW’s i3 to even the aluminum-infused, lighter-weight-but-still-built-Ford-tough F-150, Hypercar’s innovative concepts live on.

Written by Peter Bronski, editorial director of RMI. Follow Peter on Twitter.

This article is from the Summer 2014 issue of Rocky Mountain Institute’s Solution Journal. To read more from back issues of Solutions Journal, please visit the RMI website.

Archetype

From Wikipedia, the free encyclopedia https://en.wikipedia.org/wiki/Archetype The concept of an archetyp...