A Medley of Potpourri

Saturday, February 1, 2014

What Actually Happens While You Sleep and How It Affects Your Every Waking Moment

by Maria Popova

“We are living in an age when sleep is more comfortable than ever and yet more elusive.”

The Ancient Greeks believed that one fell asleep when the brain filled with blood and awakened once it drained back out. Nineteenth-century philosophers contended that sleep happened when the brain was emptied of ambitions and stimulating thoughts. “If sleep doesn’t serve an absolutely vital function, it is the greatest mistake evolution ever made,” biologist Allan Rechtschaffen once remarked. Even today, sleep remains one of the most poorly understood human biological functions, despite some recent strides in understanding the “social jetlag” of our internal clocks and the relationship between dreaming and depression. In Dreamland: Adventures in the Strange Science of Sleep (public library), journalist David K. Randall — who stumbled upon the idea after crashing violently into a wall while sleepwalking — explores “the largest overlooked part of your life and how it affects you even if you don’t have a sleep problem.” From gender differences to how come some people snore and others don’t to why we dream, he dives deep into this mysterious third of human existence to illuminate what happens when night falls and how it impacts every aspect of our days.

Most of us will spend a full third of our lives asleep, and yet we don’t have the faintest idea of what it does for our bodies and our brains. Research labs offer surprisingly few answers. Sleep is one of the dirty little secrets of science. My neurologist wasn’t kidding when he said there was a lot that we don’t know about sleep, starting with the most obvious question of all — why we, and every other animal, need to sleep in the first place.

But before we get too anthropocentrically arrogant in our assumptions, it turns out the quantitative requirement of sleep isn’t correlated with how high up the evolutionary chain an organism is:

Lions and gerbils sleep about thirteen hours a day. Tigers and squirrels nod off for about fifteen hours. At the other end of the spectrum, elephants typically sleep three and a half hours at a time, which seems lavish compared to the hour and a half of shut-eye that the average giraffe gets each night.

Humans need roughly one hour of sleep for every two hours they are awake, and the body innately knows when this ratio becomes out of whack. Each hour of missed sleep one night will result in deeper sleep the next, until the body’s sleep debt is wiped clean.

What, then, happens as we doze off, exactly? Like all science, our understanding of sleep seems to be a constant “revision in progress”:

Despite taking up so much of life, sleep is one of the youngest fields of science. Until the middle of the twentieth century, scientists thought that sleep was an unchanging condition during which time the brain was quiet. The discovery of rapid eye movements in the 1950s upended that. Researchers then realized that sleep is made up of five distinct stages that the body cycles through over roughly ninety-minute periods. The first is so light that if you wake up from it, you might not realize that you have been sleeping. The second is marked by the appearance of sleep-specific brain waves that last only a few seconds at a time. If you reach this point in the cycle, you will know you have been sleeping when you wake up. This stage marks the last drop before your brain takes a long ride away from consciousness. Stages three and four are considered deep sleep. In three, the brain sends out long, rhythmic bursts called delta waves. Stage four is known as slow-wave sleep for the speed of its accompanying brain waves. The deepest form of sleep, this is the farthest that your brain travels from conscious thought. If you are woken up while in stage four, you will be disoriented, unable to answer basic questions, and want nothing more than to go back to sleep, a condition that researchers call sleep drunkenness. The final stage is REM sleep, so named because of the rapid movements of your eyes dancing against your eyelids. In this stage of sleep, the brain is as active as it is when it is awake. This is when most dreams occur.

(Recall the role of REM sleep in regulating negative emotions.)

Randall’s most urgent point, however, echoes what we’ve already heard from German chronobiologist Till Roenneberg, who studies internal time — in our blind lust for the “luxuries” of modern life, with all its 24-hour news cycles, artificial lighting on demand, and expectations of round-the-clock telecommunications availability, we’ve thrown ourselves into a kind of circadian schizophrenia:

We are living in an age when sleep is more comfortable than ever and yet more elusive. Even the worst dorm-room mattress in America is luxurious compared to sleeping arrangements that were common not long ago. During the Victorian era, for instance, laborers living in workhouses slept sitting on benches, with their arms dangling over a taut rope in front of them. They paid for this privilege, implying that it was better than the alternatives. Families up to the time of the Industrial Revolution engaged in the nightly ritual of checking for rats and mites burrowing in the one shared bedroom. Modernity brought about a drastic improvement in living standards, but with it came electric lights, television, and other kinds of entertainment that have thrown our sleep patterns into chaos.

Work has morphed into a twenty-four-hour fact of life, bringing its own set of standards and expectations when it comes to sleep … Sleep is ingrained in our cultural ethos as something that can be put off, dosed with coffee, or ignored. And yet maintaining a healthy sleep schedule is now thought of as one of the best forms of preventative medicine.

Reflecting on his findings, Randall marvels:

As I spent more time investigating the science of sleep, I began to understand that these strange hours of the night underpin nearly every moment of our lives.

Indeed, Dreamland goes on to explore how sleep — its mechanisms, its absence, its cultural norms — affects everyone from police officers and truck drivers to artists and entrepreneurs, permeating everything from our decision-making to our emotional intelligence.

Friday, January 31, 2014

Final Keystone XL report: No major boost in greenhouse gasses

By Deena Winter / January 31, 2014

AP photo

YOUR TURN: Now it’s up to Secretary of State John Kerry to make a recommendation to President Obama on the fate of the proposed Keystone XL pipeline.

By Deena Winter | Nebraska Watchdog
Updated 4:05 p.m.

LINCOLN, Neb. — The U.S. State Department’s final environmental review of the proposed Keystone XL oil pipeline mirrors earlier conclusions that the pipeline wouldn’t significantly contribute to greenhouse gas emissions.

The report reiterated last year’s draft report conclusion that the pipeline is unlikely to significantly impact the rate of extraction of oil sands or the continued demand for heavy crude oil in the U.S.
Now that the State Department’s environmental review of TransCanada’s application for a federal permit to build the pipeline is complete, a 90-day review by various federal agencies will commence to determine whether the pipeline is in the national interest, since it crosses a national border. The final decision is expected to be made by Secretary of State John Kerry and President Obama.

Canadian pipeline company TransCanada first applied for permission to build the pipeline in late 2008, but it ran into a wall of opposition in Nebraska. Nebraska pipeline fighters have taken part in and helped organize protests from the governor’s mansion to Washington, D.C., even as most of the Republican statewide public officials have pushed for approval.

Courtesy photo

REPORT: The U.S. State Department released its final environmental report Friday on the proposed Keystone XL oil pipeline that would cross America. The report found the pipeline would not significantly affect greenhouse gas emissions.

The Keystone XL pipeline would bisect Nebraska, with nearly 200 miles of pipe buried in a dozen counties. A grassroots group called Bold Nebraska has battled against a foreign company having the power to take land from landowners and possible contamination of the massive Ogallala Aquifer by oil spills.

Pipeline opponents successfully lobbied Obama to reject TransCanada’s initial application in late 2011 and forced the company to reroute the pipeline around the ecologically fragile Sandhills. That’s the route reviewed in the latest State Department reports.

The new report noted that most pipeline spills are small: of the 1,692 incidents between 2002 and 2012, 79 percent were small (up to 2,100 gallons) and just 4 percent were large spills where the oil would migrate away from the release site. It also said modeling indicates “aquifer characteristics would inhibit the spread of released oil, and impacts from a release on water quality would be limited.”

Pipeline opponents in Nebraska have questioned why TransCanada didn’t build the pipeline parallel to its existing Keystone One pipeline that crosses eastern Nebraska, away from the Sandhills and aquifer. The report noted this, but concluded it wasn’t a reasonable alternative because it wouldn’t meet Keystone’s contractual obligations to transport 100,000 barrels per day of crude oil from the Bakken oil play in North Dakota. Also, the corridor would be longer, increasing the risk of spills.

The proposed pipeline has put Obama in a difficult position where he must decide whether to live up to his promises to combat climate change or appease labor unions that generally support the pipeline and jobs it would bring. Obama said last year the pipeline should only be built if it doesn’t increase carbon emissions.

Russ Girling, TransCanada president and chief executive officer, told reporters Friday that while opponents will continue to make noise, “The science continues to show that this pipeline can and will be built safety.”

“This pipeline certainly is in the national interest of the United States,” he said.

Bold Nebraska Executive Director Jane Kleeb saw victories in the fact that the report acknowledged the revised route still crosses the Sandhills, which she called a “big shift” from earlier reports.
Environmental groups vowed to keep the pressure on Obama to reject the project.

“Our side continues to gain ground because landowners and environmentalists are now working together,” Kleeb said Friday.

Regardless of the president’s final verdict, a Nebraska lawsuit could still throw another obstacle in the path of the proposed 1,179-mile pipeline. Landowners who oppose the pipeline sued the state, challenging the constitutionality of a law that changed the pipeline route approval process, giving the governor and state environmental regulators the authority to approve or deny the revised route through Nebraska, rather than the Public Service Commission.

If the route review process is deemed unconstitutional, TransCanada would have to go back to square one with siting. A district judge hasn’t yet made a ruling after a one-day trial in September.
Contact Deena Winter at deena@nebraskawatchdog.org.

Researchers report on new catalyst to convert greenhouse gases into chemicals

By Karen B. Roberts

(Phys.org) —A team of researchers at the University of Delaware has developed a highly selective catalyst capable of electrochemically converting carbon dioxide—a greenhouse gas—to carbon monoxide with 92 percent efficiency. The carbon monoxide then can be used to develop useful chemicals.
The researchers recently reported their findings in Nature Communications.

"Converting carbon dioxide to useful chemicals in a selective and efficient way remains a major challenge in renewable and sustainable energy research," according to Feng Jiao, assistant professor of chemical and biomolecular engineering and the project's lead researcher.

Co-authors on the paper include Qi Lu, a postdoctoral fellow, and Jonathan Rosen, a graduate student, working with Jiao.

The researchers found that when they used a nano-porous silver electrocatalyst, it was 3,000 times more active than polycrystalline silver, a catalyst commonly used in converting carbon dioxide to useful chemicals.

Silver is considered a promising material for a carbon dioxide reduction catalyst because of it offers high selectivity—approximately 81 percent—and because it costs much less than other precious metal catalysts. Additionally, because it is inorganic, silver remains more stable under harsh catalytic environments.

The exceptionally high activity, Jiao said, is likely due to the UD-developed electrocatalyst's extremely large and highly curved internal surface, which is approximately 150 times larger and 20 times intrinsically more active than polycrystalline silver.

A UD engineering research team led by Feng Jiao has developed a highly selective catalyst capable of electrochemically converting carbon dioxide to carbon monoxide with 92 percent efficiency.
Credit: Evan Krape

Jiao explained that the active sites on the curved internal surface required a much smaller than expected voltage to overcome the activation energy barrier needed drive the reaction.
The resulting carbon monoxide, he continued, can be used as an industry feedstock for producing synthetic fuels, while reducing industrial carbon dioxide emissions by as much as 40 percent.
To validate whether their findings were unique, the researchers compared the UD-developed nano-porous silver catalyst with other potential carbon dioxide electrocatalysts including polycrystalline silver and other silver nanostructures such as nanoparticles and nanowires.

Testing under identical conditions confirmed the non-porous silver catalyst's significant advantages over other silver catalysts in water environments.

Reducing greenhouse carbon dioxide emissions from fossil fuel use is considered critical for human society. Over the last 20 years, electrocatalytic carbon dioxide reduction has attracted attention because of the ability to use electricity from renewable energy sources such as wind, solar and wave.

Ideally, Jiao said, one would like to convert carbon dioxide produced in power plants, refineries and petrochemical plants to fuels or other chemicals through renewable energy use.
A 2007 Intergovernmental Panel on Climate Change report stated that 19 percent of greenhouse gas emissions resulted from industry in 2004, according to the Environmental Protection Agency's website.

"Selective conversion of carbon dioxide to carbon monoxide is a promising route for clean energy but it is a technically difficult process to accomplish," said Jiao. "We're hopeful that the catalyst we've developed can pave the way toward future advances in this area."

Explore further: Process holds promise for production of synthetic gasoline

More information: A selective and efficient electrocatalyst for carbon dioxide reduction." Qi Lu, Jonathan Rosen, Yang Zhou, Gregory S. Hutchings, Yannick C. Kimmel, Jingguang G. Chen, Feng Jiao. Nature Communications 5, Article number: 3242 DOI: 10.1038/ncomms4242 . Received 10 September 2013 Accepted 10 January 2014 Published 30 January 2014

Journal reference: Nature Communications

Glass that bends but doesn’t break

Natural forms inspire McGill researchers to develop a technique to make glass less brittle

Published: 29 Jan 2014

Normally when you drop a drinking glass on the floor it shatters. But, in future, thanks to a technique developed in McGill’s Department of Mechanical Engineering, when the same thing happens the glass is likely to simply bend and become slightly deformed. That’s because Prof. François Barthelat and his team have successfully taken inspiration from the mechanics of natural structures like seashells in order to significantly increase the toughness of glass.

“Mollusk shells are made up of about 95 per cent chalk, which is very brittle in its pure form,” says Barthelat. “But nacre, or mother-of-pearl, which coats the inner shells, is made up of microscopic tablets that are a bit like miniature Lego building blocks, is known to be extremely strong and tough, which is why people have been studying its structure for the past twenty years.”

Previous attempts to recreate the structures of nacre have proved to be challenging, according to Barthelat. “Imagine trying to build a Lego wall with microscopic building blocks. It’s not the easiest thing in the world.” Instead, what he and his team chose to do was to study the internal ‘weak’ boundaries or edges to be found in natural materials like nacre and then use lasers to engrave networks of 3D micro-cracks in glass slides in order to create similar weak boundaries. The results were dramatic.

The researchers were able to increase the toughness of glass slides (the kind of glass rectangles that get put under microscopes) 200 times compared to non-engraved slides. By engraving networks of micro-cracks in configurations of wavy lines in shapes similar to the wavy edges of pieces in a jigsaw puzzle in the surface of borosilicate glass, they were able to stop the cracks from propagating and becoming larger. They then filled these micro-cracks with polyurethane, although according to Barthelat, this second process is not essential since the patterns of micro-cracks in themselves are sufficient to stop the glass from shattering.

The researchers worked with glass slides simply because they were accessible, but Barthelat believes that the process will be very easy to scale up to any size of glass sheet, since people are already engraving logos and patterns on glass panels. He and his team are excited about the work that lies ahead for them.

“What we know now is that we can toughen glass, or other materials, by using patterns of micro-cracks to guide larger cracks, and in the process absorb the energy from an impact,” says Barthelat. “We chose to work with glass because we wanted to work with the archetypal brittle material. But we plan to go on to work with ceramics and polymers in future. Observing the natural world can clearly lead to improved man-made designs.”

To read the full paper: ‘Overcoming the brittleness of glass through bio-inspiration and micro-architecture’ by F. Barthelat et al in Nature Communications: http://www.nature.com/ncomms/2014/140128/ncomms4166/full/ncomms4166.html
The research was funded by the Natural Sciences and Engineering Research Council of Canada (NSERC) and the Canada Foundation for Innovation (CFI), with partial support for one of the authors from a McGill Engineering Doctoral Award. The authors acknowledge useful technical advice by the company Vitro.
To contact the researcher directly: François Barthelat | Dept. Of Mechanical Engineering | McGill University | 514-398-6318

Contact Information

Contact: Katherine Gombay

Organization: Media Relations Office

Email: katherine.gombay@mcgill.ca

Office Phone: 514-398-2189

Who's the most significant historical figure?

From Leonardo da Vinci to Einstein, and Shakespeare to Stephen King, two data analysts have ranked the most significant people in history – do the results seem right?

Portrait of man in black with shoulder-length, wavy brown hair, a large sharp nose, and a distracted gaze

Steven Skiena and Charles B Ward

Shakespeare, Austen, Homer, King, Dickinson and Shelley

The Literary Top 50 … top row from left: Shakespeare, Austen and Homer;

bottom row: King, Dickinson and Shelley

People love lists, and are perhaps even more fascinated by rankings – lists organised according to some measure of value or merit. Who were the most important women in history? The best writers or most influential artists? Our least illustrious political leaders? Who's bigger: Hitler or Napoleon? Picasso or Michelangelo? Charles Dickens or Jane Austen? John, Paul, George or Ringo?

We work in the fields of data and computer science and do not answer these questions as historians might, through a principled assessment of a person's achievements. Instead, we aggregate millions of opinions. We rank historical figures just as Google ranks web pages, by integrating a diverse set of measurements of reputation into a single consensus value.

Significance is related to fame but measures something different. According to our system, forgotten US President Chester A Arthur (who we rank at 499) is more historically significant than pop star Justin Bieber (ranked 8,633), even though Arthur may have a less devoted following and certainly has lower contemporary name recognition. We believe our computational, data-centric analysis provides new ways to understand and interpret the past.

Historically significant figures leave statistical evidence of their presence behind, if one knows where to look for it. We use several data sources to fuel our ranking algorithms. Most important is Wikipedia, the web-based, collaborative, multi-lingual encyclopedia. Wikipedia is enormous, featuring well over 3m articles in its English edition alone. But we use it in a manner quite different from the typical reader, by analysing the Wiki pages of more than 800,000 people to measure quantities that should correspond to historical significance. We would expect that more significant people should have longer Wikipedia pages than those less notable because they have greater accomplishments to report. The Wiki pages of people of higher significance should attract greater readership than those of lower significance. The elite should have pages linked to by other highly significant figures, meaning they should have a high PageRank, the measure of importance used by Google to identify important web pages. We combine these other variables into a single number using a statistical method called factor analysis. But we need one final correction: to fairly compare contemporary figures such as Britney Spears against, say, Aristotle, we must adjust for the fact that today's stars will fade from living memory over the next several generations. By analysing traces left in millions of scanned books, we hope to measure just how fast this decay occurs, and correct for it.

We have naturally received strong reactions from readers of our book Who's Bigger? complaining about our computational methodology. Certain historians have complained that Wiki cannot be trusted as a source for anything. This is pretty silly. People find Wikipedia articles to be generally accurate and informative, or else they wouldn't read them. Where do you head to read up on a new topic you are interested in? We think it is clear that anyone (or anything, like our algorithms) that has read all of Wikipedia would be in an excellent position to discourse about the most important people in recorded history.

More cogent is the complaint that our results are culturally biased because we analyse only the English edition of Wikipedia. How can we fairly assess the significance of Chinese poets against US presidents? We agree that any ranking of historical significance is indeed culturally dependent and so, yes, our rankings have an Anglocentric bias. But the depth of Wikipedia is so great that there are hundreds of articles about Chinese poets in the English edition.

Others highlight a few contemporary figures that they deem us to have overrated, such as Britney Spears (689) or Barack Obama (111), and use this anecdotal evidence to sneer. But we also conduct validation procedures, and compare our rankings to public opinion polls, Hall of Fame voting records, sports statistics, and even the prices of paintings and autographs.

Anecdotal evidence is not as compelling as it might seem. British readers have complained that our algorithms don't rank British figures high enough just as strongly as Spanish readers think we are unfair to their compatriots. But our book is designed in part to generate debate.

Our overall top 30

At No 13 … Elizabeth I. Photograph: Getty Images

1 Jesus
2 Napoleon
3 Muhammad
4 William Shakespeare
5 Abraham Lincoln
6 George Washington
7 Adolf Hitler
8 Aristotle
9 Alexander the Great
10 Thomas Jefferson
11 Henry VIII
12 Charles Darwin
13 Elizabeth I
14 Karl Marx
15 Julius Caesar
16 Queen Victoria
17 Martin Luther
18 Joseph Stalin
19 Albert Einstein
20 Christopher Columbus
21 Isaac Newton
22 Charlemagne
23 Theodore Roosevelt
24 Wolfgang Amadeus Mozart
25 Plato
26 Louis XIV
27 Ludwig van Beethoven
28 Ulysses S Grant
29 Leonardo da Vinci
30 Augustus

Top pre-20th-century artists

At No 1 … Leonardo da Vinci Photograph: Bettmann/CORBIS

Art has been a uniquely human activity for more than 40,000 years. But the names of artists went unrecorded for most of this period. The identities of several prominent Greek artists, most notably Phidias, survive through contemporary written accounts and Roman copies of their work. But the notion of artists with distinct identities then faded, not to be revived until the late middle ages. The great painters of the Renaissance dominate our rankings of the most significant pre-20th century artists.

1 Leonardo da Vinci (overall ranking 29)
2 Michelangelo (86)
3 Raphael (140)
4 Rembrandt (189)
5 Titian (319)
6 Francisco Goya (366)
7 El Greco (465)
8 Albrecht Dürer (503)
9 Hans Holbein the Younger (555)
10 Johannes Vermeer (567)
11 Jacques-Louis David (607)
12 Giotto (610)
13 Diego Velázquez (693)
14 Gustave Courbet (965)
15 Hieronymus Bosch (983)

Top modern-era artists

Top of the list … Vincent Van Gogh. Photograph: Rex Features

The Impressionist painters and their successors are at the top of our table of the most significant modern artists. Later movements such as surrealism (Salvador Dalí, 1,021) and abstract expressionism (Jackson Pollock, 1,013) are represented, but by relatively few artists.

1 Vincent van Gogh (73)
2 Pablo Picasso (171)
3 Claude Monet (178)
4 Henri Matisse (376)
5 Paul Cézanne (389)
6 Edgar Degas (422)
7 Andy Warhol (485)
8 Paul Gauguin (540)
9 Pierre-Auguste Renoir (549)
10 Auguste Rodin (574)
11 Wassily Kandinsky (618)
12 Edouard Manet (640)
13 Camille Pissarro (815)
14 Diego Rivera (915)
15 Edvard Munch (944)
16 James McNeill Whistler (1,002)
17 Jackson Pollock (1,013)
18 Salvador Dalí (1,021)
19 Piet Mondrian (1,051)
20 Georgia O'Keeffe (1,178)

Top 50 literary figures

At No 2 … Charles Dickens. Photograph: Getty Images

Ranking the world's greatest literary figures is a parlour game – just like the ranking of presidents or prime ministers. It exposes the biases inherent in everyone's world-view. But our ranking, it turns out, agrees with others: our top 50 contains 39 members of Daniel Burt's The Literary 100, including his 11 highest-ranked figures. With our Anglocentric source bias, we feature a larger number of British and US writers (but Jane Austen and Emily Dickinson are the only women to make it into the top 50).

1 William Shakespeare (4)
2 Charles Dickens (33)
3 Mark Twain (53)
4 Edgar Allan Poe (54)
5 Voltaire (64)
6 Oscar Wilde (77)
7 Johann Wolfgang von Goethe (88)
8 Dante Alighieri (96)
9 Lewis Carroll (118)
10 Henry David Thoreau (131)
11 Jane Austen (139)
12 Samuel Johnson (141)
13 Homer (152)
14 Lord Byron (158)
15 Walt Whitman (160)
16 John Milton (165)
17 Geoffrey Chaucer (173)
18 Virgil (177)
19 William Wordsworth (182)
20 Stephen King (191)
21 Emily Dickinson (194)
22 Leo Tolstoy (196)
23 Victor Hugo (208)
24 George Bernard Shaw (213)
25 Nathaniel Hawthorne (227)
26 Fyodor Dostoyevsky (244)
27 Miguel de Cervantes (246)
28 Ernest Hemingway (248)
29 HG Wells (249)
30 Herman Melville (251)
31 Rudyard Kipling (259)
32 Sophocles (274)
33 Samuel Taylor Coleridge (280)
34 John Keats (305)
35 Robert Burns (317)
36 Petrarch (326)
37 Percy Bysshe Shelley (329)
38 George Orwell (342)
39 Christopher Marlowe (374)
40 Thomas Hardy (378)
41 Aeschylus (386)
42 Jonathan Swift (391)
43 Rabindranath Tagore (397)
44 Henrik Ibsen (403)
45 James Joyce (406)
46 Henry James (408)
47 Aristophanes (418)
48 Alexander Pushkin (420)
49 Ben Jonson (421)
50 TS Eliot (436)

We generally score popular writers such as Oscar Wilde, Lewis Carroll and Mark Twain higher than we think the literary establishment would. We expect them to be surprised by our rank for horror novelist Stephen King. No other contemporary writer came close to a spot in our Literary 50. But we consider King to be the Dickens [33] of our time, characterised by immense popularity, mind-boggling productivity, and even the serial novel genre.

• Who's Bigger: Where Historical Figures Really Rank by Steven Skiena and Charles B Ward is published by Cambridge.

Kepler Object of Interest From Wikipedia, the free encyclopedia

The Daily Galaxy @dailygalaxy 15m
"Kepler Object of Interest" --A Major Step in the Search for a Twin Solar System http://dailygalay.com pic.twitter.com/xdAjFep76a

A Kepler Object of Interest (KOI) is a star observed by the Kepler spacecraft that is suspected of hosting one or more transiting planets. KOIs come from a master list of 150,000 stars, which itself is generated from the Kepler Input Catalog (KIC). A KOI shows a periodic dimming, indicative of an unseen planet passing between the star and Earth, eclipsing part of the star. However, such an observed dimming is not a guarantee of a transiting planet, because other astronomical objects—such as an eclipsing binary in the background—can mimic a transit signal. For this reason, the majority of KOIs are as yet not confirmed transiting planet systems.

History

The first public release of a list of KOIs was on 15 June 2010 and contained 306 stars suspected of hosting exoplanets, based on observations taken between 2 May 2009 and 16 September 2009. It was also announced that an additional 400 KOIs had been discovered, but would not be immediately released to the public. This was done in order for follow-up observations to be performed by Kepler team members.^[1]

On February 1, 2011, a second release of observations made during the same time frame contained improved date reduction and listed 1235 transit signals around 997 stars.^[2]

Naming convention

Stars observed by Kepler that are considered candidates for transit events are given the designation "KOI" followed by an integer number. For each set of periodic transit events associated with a particular KOI, a two-digit decimal is added to the KOI number for that star. For example, the first transit event candidate identified around the star KOI 718 is designated KOI 718.01, while the second candidate is KOI 718.02 and the third is KOI 718.03.^[2] Once a transit candidate is verified to be a planet (see below), the star is designated "Kepler" followed by a hyphen and an integer number. The associated planet(s) have the same designation, followed by a letter in the order each was discovered.

Kepler data on KOIs

For all 150,000 stars being watched for transits by Kepler, there are estimates of each star's surface temperature, radius, surface gravity and mass. These quantities are derived from photometric observations taken prior to Kepler's launch at the 1.2 m reflector at Fred Lawrence Whipple Observatory.^[3] For KOIs, there is, additionally, data on each transit signal: the depth of the signal, the duration of the signal and the periodicity of the signal (although some signals lack this last piece of information). Assuming the signal is due to a planet, these data can be used to obtain the size of the planet relative to its host star, the planet's distance from the host star relative to the host star's size (assuming zero eccentricity), and the orbital period of the planet. Combined with the estimated properties of the star described previously, estimates on the absolute size of the planet, its distance from the host star and its equilibrium temperature can be made.^[1]^[4]

Sources of confusion

False positives

While it has been estimated that 90% of the KOI transit candidates are true planets,^[5] it is expected that some of the KOIs will be false positives, i.e., not actual transiting planets. The majority of these false positives are anticipated to be eclipsing binaries which, while spatially much more distant and thus dimmer than the foreground KOI, are too close to the KOI on the sky for the Kepler telescope to differentiate. On the other hand, statistical fluctuations in the data are expected to contribute less than one false positive event in the entire set of 150,000 stars being observed by Kepler.^[2]

Misidentification

In addition to false positives, a transit signal can be due to a planet that is substantially larger than what is estimated by Kepler. This occurs when there are sources of light other than simply the star being transited, such as in a binary system. In cases such as these, there is more surface area producing light than is assumed, so a given transit signal is larger than assumed. Since roughly 34% of stellar systems are binaries, up to 34% of KOI signals could be from planets within binary systems and, consequently, be larger than estimated (assuming planets are as likely to form in binary systems as they are in single star systems). However, additional observations can rule out these possibilities and are essential to confirming the nature of any given planet candidate.^[2]

Verifying candidates

Additional observations are necessary in order to confirm that a KOI actually has the planet that has been predicted, instead of being a false positive or misidentification. The most well-established confirmation method is to obtain radial velocity measurements of the planet acting on the KOI.
However, for many KOIs this is not feasible. In these cases, speckle imaging or adaptive optics imaging using ground based telescopes can be used to greatly reduce the likelihood of background eclipsing binaries. Such follow-up observations are estimated to reduce the chance of such background objects to less than 0.01%. Additionally, spectra of the KOIs can be taken to see if the star is part of a binary system.^[2]

Notable KOIs

KOIs with confirmed planets

As of December 5, 2011, Kepler had found 2326 planet candidates and 33 confirmed planets orbiting 19 stars.^[6]

Previously detected planets

Three stars within the Kepler spacecraft's field of view have been identified by the mission as Kepler-1, Kepler-2, and Kepler-3 and have planets which were previously known from ground based observations and which were re-observed by Kepler. These stars are cataloged as GSC 03549-02811, HAT-P-7, and HAT-P-11.^[7]

Planets confirmed by the Kepler team

Eight stars were first observed by Kepler to have signals indicative of transiting planets and have since had their nature confirmed. These stars are: KOI 7, KOI 18, KOI 17, KOI 97, KOI 10, KOI 377, KOI 72, and KOI 157. Of these, KOI 377 and KOI 157 have multiple planets (3 and 6, respectively) confirmed to be orbiting them.^[7]

Planets confirmed by other collaborations

From the Kepler data released to the public, one system has been confirmed to have a planet, KOI 428b.^[8]

KOIs with unconfirmed planets

Kepler-20 (KOI 70) has transit signals indicating the existence of at least four planets. If confirmed, KOI 70.04 would be the smallest extrasolar planet discovered around a main-sequence star (at 0.6 Earth radii) to date, and the second smallest known extrasolar planet after PSR 1257 12 b. The likelihood of KOI 70.04 being of the nature deduced by Kepler (and not a false positive or misidentification) has been estimated at >80%.

Six transit signals released in the February 1, 2011 data are indicative of planets that are both "Earth-like" (less than 2 Earth radii in size) and located within the habitable zone of the host star. They are: KOI 1026.01, KOI 854.01, KOI 701.03, KOI 268.01, KOI 326.01, and KOI 70.03.^[2] A more recent study found that one of these candidates (KOI 326.01) is in fact much larger and hotter than first reported.^[9]

A September 2011 study by Muirhead et al. reports that a re-calibration of estimated radii and effective temperatures of several dwarf stars in the Kepler sample yields six new terrestrial-sized candidates within the habitable zones of their stars: KOI 463.01, KOI 1422.02, KOI 947.01, KOI 812.03, KOI 448.02, KOI 1361.01.[1]

Non-planet discoveries

Several KOIs contain transiting objects which are hotter than the stars they transit, indicating that the smaller objects are white dwarfs formed through mass transfer. These objects include KOI 74, KOI 81 and KOI 959.^[2]^[10]

KOI 54 is believed to be a binary system containing two Class-A stars in highly eccentric orbits with a semi-major axis of 0.4 AU. During periastron, tidal distortions cause a periodic brightening of the system. In addition, these tidal forces induce resonant pulsations in one (or both) of the stars, making it only the 4th known stellar system to exhibit such behavior.^[11]

KOI 126 is a triple star system comprising two low mass (0.24 and 0.21 solar masses) stars orbiting each other with a period of 1.8 days and a semi-major axis of 0.02 AU. Together, they orbit a 1.3 solar mass star with a period of 34 days and a semi-major axis of 0.25 AU. All three stars eclipse one another which allows for precise measurements of their masses and radii. This makes the low mass stars 2 of only 4 known fully convective stars to have accurate determinations of their parameters (i.e. to better than several percent). The other 2 stars constitute the eclipsing binary system CM Draconis.^[12]

References

^ Jump up to: ^a ^b Borucki, William J; et al. (2010). "Characteristics of Kepler planetary candidates based on the first data set: the majority are found to be Neptune-size and smaller". arXiv:1006.2799 [astro-ph.EP].
^ Jump up to: ^a ^b ^c ^d ^e ^f ^g Borucki, William J; et al. (2011-02-01). "Characteristics of planetary candidates observed by Kepler, II: Analysis of the first four months of data". http://kepler.nasa.gov. Retrieved 2011-02-10.
Jump up ^ Brown, Timothy M; et al. (2011). "Kepler Input Catalog: Photometric Calibration and Stellar Classification". arXiv:1102.0342 [astro-ph.SR].
Jump up ^ Seager, Sara (2010). "Exoplanet Transits and Occultations by Joshua N. Winn". Exoplanets. University of Arizona Press. pp. 55–78. ISBN 978-0-8165-2945-2.
Jump up ^ Morton, Timothy D.; Johnson, John Asher (2011). "On the Low False Positive Probabilities of Kepler Planet Candidates". arXiv:1101.5630 [astro-ph.EP].
Jump up ^ Kepler Discoveries NASA Accessed 3 January 2012
^ Jump up to: ^a ^b "Kepler Discoveries". NASA. 2011-02-08. Retrieved 2011-02-12.
Jump up ^ Santerne; Diaz; Bouchy; Deleuil; Moutou; Hebrard; Eggenberger; Ehrenreich et al. (2010). "SOPHIE velocimetry of Kepler transit candidates II. KOI-428b: a hot Jupiter transiting a subgiant F-star". arXiv:1101.0196 [astro-ph.EP].
Jump up ^ Grant, Andrew (8 March 2011). "Exclusive: "Most Earth-Like" Exoplanet Gets Major Demotion—It Isn’t Habitable". 80beats. Discover Magazine. Retrieved 2011-03-09.
Jump up ^ Rowe, Jason F.; et al. (2010). "Kepler Observations of Transiting Hot Compact Objects". The Astrophysical Journal Letters 713 (2): L150–L154. arXiv:1001.3420. Bibcode:2010ApJ...713L.150R. doi:10.1088/2041-8205/713/2/L150.
Jump up ^ Welsh, William F; et al. (2011). "KOI-54: The Kepler Discovery of Tidally-Excited Pulsations and Brightenings in a Highly Eccentric Binary". arXiv:1102.1730 [astro-ph.SR].
Jump up ^ Carter, Joshua A; et al. (2011). "KOI-126: A Triply-Eclipsing Hierarchical Triple with Two Low-Mass Stars". Science 331 (6017): 562–565. arXiv:1102.0562. Bibcode:2011Sci...331..562C. doi:10.1126/science.1201274. PMID 21224439.