Posted on by Nancy Atkinson

25% of Sun-Like Stars Could Host Earth-Sized Worlds

Artists impression of a distant solar system. Credit: ESO

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A five-year survey of nearby solar-mass stars has provided astronomers with an estimate of how many stars of this type could have Earth-size planets. Andrew Howard and Geoffrey Marcy from the University of California Berkeley studied 166 G and K stars within 80 light-years of Earth, determining the number, mass and orbital distance of any of the stars’ planets. Since Earth-sized worlds have not yet been found, they extrapolated the number of that size of planets, based on the fraction of stars that host Neptune to super-Earth sized planets. Their findings are encouraging, since it means planets the size of Neptune and smaller are probably much more common than gas-giant planets, like Jupiter. But what they found also conflict with current models of planet formation and migration.


“Of about 100 typical sun-like stars, one or two have planets the size of Jupiter, roughly six have a planet the size of Neptune, and about 12 have super-Earths between three and 10 Earth masses,” said Howard. “If we extrapolate down to Earth-size planets – between one-half and two times the mass of Earth – we predict that you’d find about 23 for every 100 stars.”

“This is the first estimate based on actual measurements of the fraction of stars that have Earth-size planets,” said Marcy. Previous studies have estimated the proportion of Jupiter and Saturn-size exoplanets, but never down to as small as this study, and the astronomers say this enabled them to estimate the Earth-size planets.

“What this means,” Howard added, “is that, as NASA develops new techniques over the next decade to find truly Earth-size planets, it won’t have to look too far.”

Using the 10-meter Keck telescopes in Hawaii, the astronomers measured the small wobble of each star from the tug of orbiting planets. For systems with multiple planets, teasing out the radial velocity signature of each planet is very complex, since each signature is extremely small. The more times a star is observed, the better the data. Current techniques allow detection of planets massive enough and near enough to their stars to cause a wobble of about 1 meter per second. That means they saw only massive, Jupiter-like gas giants up to three times the mass of Jupiter (1,000 times Earth’s mass) orbiting as far as one-quarter of an astronomical unit (AU) from the star, or smaller, closer super-Earths and Neptune-like planets (15-30 times the mass of the earth). An AU is 93 million miles, the average distance between the earth and the sun.

Histogram of stellar masses for Eta-Earth stars. Credit: Howard, et al.

Only 22 of the stars had detectable planets – 33 planets in all – within this range of masses and orbital distances. After accounting statistically for the fact that some stars were observed more often than others, the researchers estimated that about 1.6 percent of the sun-like stars in their sample had Jupiter-size planets and 12 percent had super-Earths (3-10 Earth masses). If the trend of increasing numbers of smaller planets continues, they concluded, 23 percent of the stars would have Earth-size planets.

Based on these statistics, Howard and Marcy, — who is also member of NASA’s Kepler mission to survey 156,000 faint stars in search of transiting planets — estimate that the telescope will detect 120-260 “plausibly terrestrial worlds” orbiting some 10,000 nearby G and K dwarf stars with orbital periods less than 50 days.

“One of astronomy’s goals is to find ‘eta-Earth,’ the fraction of sun-like stars that have an earth,” Howard said. “This is a first estimate, and the real number could be one in eight instead of one in four. But it’s not one in 100, which is glorious news.”

They were able to only detect close-in planets, so they say there could be even more Earth-size planets at greater distances, including within the habitable zone — or Goldilocks zone — located at a distance form the star where conditions are not too hot or too cold to allow the presence of liquid water.

But the researchers note that their results conflict with current models of planet formation and migration, where it is thought that nascent planets spiral inward towards the sun because of interactions with the gas in the disk. Such models predict a “planet desert” in the inner region of solar systems. But that’s where all the planets are being found.

“Just where we see the most planets, models predict we would find no cacti at all,” Marcy said. “These results will transform astronomers’ views of how planets form.”

Howard and Marcy report their results in the Oct. 29 issue of the journal Science.

Sources: UC Berkeley, Science

Posted on by Jon Voisey

The Hunt for Young Exoplanets

While there is a great deal of excitement and effort in the hopes of finding small, terrestrial sized exoplanets, another realm of exoplanet discovery that is often overlooked is that of ones of differing ages to explore how planetary systems can evolve. The first discovered exoplanet orbited a pulsar, showing that planets can be hardy enough to survive the potential violent deaths of their parent stars. On the other end, young planets can help astronomers constrain how planets form and a potential new discovery may help in those regards.


Historically, astronomers have often avoided looking at stars younger than about 100 million years. Their young nature tends to make them unruly. They are prone to flares and other eccentric behaviors that often make observations messy. Additionally, many young stars often retain debris disks or are still embedded in the nebula in which they formed which also obscures observations.

Despite this, some astronomers have begun developing targeted searches for young exoplanets. The age of the exoplanet is not independently derived, but instead, taken from the age of the host star. This too can be difficult to determine. For isolated stars, there are precious few methods (such as gyrochronology) and they generally have large errors associated with them. Thus, instead of looking for isolated stars, astronomers searching for young exoplanets have tended to focus on clusters which can be dated more easily using the main sequence turn off method.

Through this methodology, astronomers have searched clusters and other groups, such as Beta Pictoris which turned up a planet earlier this year. The Beta Pic moving group boasts an age of ~12 million years making it one of the youngest associations currently known.

Trumpler 37 (also known as IC 1396 and the Elephant Trunk Nebula) is one of the few clusters with an even younger age of 1-5 million years. This was one of several young clusters observed by a team of German astronomers led by Gracjan Maciejewski of Jena University. The group utilized an array of telescopes across the world to continuously monitor Trumpler 37 for several weeks. During that time, they discovered numerous flares and variable stars, as well as a star with a dip in its brightness that could be a planet.

The team cautions that the detection may not be a planet. Several objects can mimic planetary transit lightcurves such as “the central transit of a low-mass star in front of a large main-sequence star or red giant, grazing eclipses in systems consisting of two main-sequence stars and a contamination of a fainter eclipsing binary along the same line of sight.” Due to the physics of small objects, the size of brown dwarfs and many Jovian type planets are similar leading difficulty in distinguishing from the light curve alone. Spectroscopic results will have to be undertaken to confirm the object truly is a planet.

However, assuming it is, based on the size of the dip in brightness, the team predicts the planet is about twice the radius of Jupiter, and about 15 times the mass. If so, this would be in good agreement with models of planetary formation for the expected age. Ultimately, planets of such age will help test our understanding of how planets form, whether it be from a single gravitational collapse early on, or slow accretion over time.

Posted on by Jon Voisey

The Tug of Exoplanets on Exoplanets

Earlier this year, I wrote about how an apparent change in the orbital characteristics of a planet around TrES-2b may be indicative of a new planet, much in the same way perturbations of Uranus revealed the presence of Neptune. A follow up study was conducted by astronomers at the University of Arizona and another study on planet WASP-3b also enters the fray.

The new study by the University of Arizona team, observed the TrES-2b planet on June 15, 2009, just seven orbits after the observations reported by Mislis et al. that reported the change in orbit. The findings of Mislis et al. were that, not only was the onset of the transit offset, but the angle of inclination was slowly changing. Yet the Arizona team found their results matched the previous data sets and found no indication of either of these effects (within error) when compared to the timing predictions from other, previous studies.

Additionally, an unrelated study led by Ronald Gilliland of the Space Telescope Science Institute discussing various sampling modes of the Kepler telescope used the TrES-2b system as an example and had coincidentally preceded and overlapped on of the observations made by Mislis et al. This study too found no variation in orbital characteristics of the planet.

Another test they applied to determine if the orbit was changing was the depth of the eclipse. Mislis’ team predicted that the trend would slowly cause the plane of the orbit to change such that, eventually, the planet would no longer eclipse the star. But before that happened, there should be a period of time where the area blocked by the planet was covering less and less of the star. If that were to happen, the amount of light blocked would decrease as well until it vanished all together. The Arizona team compared the depth of the eclipses they observed with the earlier observations and found that they observed no change here either.

So what went wrong with the data from Mislis et al.? One possibility is that they did not properly account for differences in their filter when compared with that of the original observations by which the transit timing was determined. Stars have a feature known as limb darkening in which the edges appear darker due to the angle at which light is being released. Some light is scattered in the atmosphere of the star and since the scattering is wavelength dependent, so too is the effects of the limb darkening. If a photometric filter is observing in a slightly different part of the spectrum, it would read the effects differently.

While these findings have discredited the notion that there are perturbations in the TrES-2b system, the notion that we can find exoplanets by their effects on known ones is still an attractive one that other astronomers are considering. One team, lead by G. Maciejewski has launched an international observing campaign to discover new planets by just this method. The campaign uses a series of telescopes ranging from 0.6 – 2.2 meters located around the world to frequently monitor stars with known transiting planets. And this study may have just had its first success.

In a paper recently uploaded to arXiv, the team announced that variations in the timing of transits for planet WASP-3b indicate the presence of a 15 Earth mass planet in a 2:1 orbital resonance with the known one. Currently, the team is working to make followup observations of their own including radial velocity measurements with the Hobby-Eberly Telescope owned by the University of Texas, Austin. With any luck, this new method will begin to discover new planets.

UPDATE: It looks like Maciejewski’s team has announced another potential planet through timing variations. This time around WASP-10.

Posted on by Jon Voisey

The Habitability of Gliese 581d

The Gliese 581 system has been making headlines recently for the most newly announced planet that may lie in the habitable zone. Hopes were somewhat dashed when we were reminded that the certainty level of its discovery was only 3 sigma (95%, whereas most astronomical discoveries are at or above the 99% confidence level before major announcements), but the Gliese 581 system may yet have more surprises. When the second planet, Gliese 581d, was first discovered, it was placed outside of the expected habitable zone. But in 2009, reanalysis of the data refined the orbital parameters and moved the planet in, just to the edge of the habitable zone. Several authors have suggested that, with sufficient greenhouse gasses, this may push Gliese 581d into the habitable zone. A new paper to be published in an upcoming issue of Astronomy & Astrophysics simulates a wide range of conditions to explore just what characteristics would be required.

The team, led by Robin Wordsworth at the University of Paris, varied properties of the planet including surface gravity, albedo, and the composition of potential atmospheres. Additionally, the simulations were also run for a planet in a similar orbit around the sun (Gliese 581 is an M dwarf) to understand how the different distribution of energy could effect the atmosphere. The team discovered that, for atmospheres comprised primarily of CO2, the redder stars would warm the planet more than a solar type star due to the CO2 not being able to scatter the redder light as well, thus allowing more to reach the ground.

One of the potential roadblocks to warming the team considered was the formation of clouds. The team first considered CO2 clouds which would be likely towards the outer edges of the habitable zone and form on Mars. Since clouds tend to be reflective, they would counteract warming effects from incoming starlight and cool the planet. Again, due to the nature of the star, the redder light would mitigate this somewhat allowing more to penetrate a potential cloud deck.

Should some H2O be present its effects are mixed. While clouds and ice are both very reflective, which would decrease the amount of energy captured by a planet, water also absorbs well in the infrared region. As such, clouds of water vapor can trap heat radiating from the surface back into space, trapping it and resulting in an overall increase. The problem is getting clouds to form in the first place.

The inclusion of nitrogen gas (common in the atmospheres of planets in the solar system) had little effect on the simulations. The primary reason was the lack of absorption of redder light. In general, the inclusion only slightly changed the specific heat of the atmosphere and a broadening of the absorption lines of other gasses, allowing for a very minor ability to trap more heat. Given the team was looking for conservative estimates, they ultimately discounted nitrogen from their final considerations.

With the combination of all these considerations, the team found that even given the most unfavorable conditions of most variables, should the atmospheric pressure be sufficiently high, this would allow for the presence of liquid water on the surface of the planet, a key requirement for what scientists maintain is critical for abiogenesis. The favorable merging of characteristics other than pressure were also able to produce liquid water with pressures as low as 5 bars. The team also notes that other greenhouse gasses, such as methane, were excluded due to their rarity, but should the exist, the ability for liquid water would be improved further.

Ultimately, the simulation was only done as a one dimensional model which essentially considered a thin column of the atmosphere on the day side of the planet. The team suggests that, for a better understanding, three dimensional models would need to be created. In the future, they plan to use just such modeling which would allow for a better understanding of what was happening elsewhere on the planet. For example, should temperatures fall too quickly on the night side, this could lead to the condensation of the gasses necessary and put the atmosphere in an unstable state. Additionally, as we discover more transiting exoplanets and determine their atmospheric properties from transmission spectra, astronomers will better be able to constrain what typical atmospheres really look like.

Posted on by Nancy Atkinson

Could Chance for Life on Gliese 581g Actually Be “100%”?

Orbital Period
The orbits of planets in the Gliese 581 system are compared to those of our own solar system. The Gliese 581 star has about 30 percent the mass of our Sun, and the outermost planet is closer to its star than the Earth is to the Sun. The 4th planet, G, is a planet that could sustain life. Credit: Zina Deretsky, National Science Foundation

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The announcement yesterday of the discovery of the closest Earth-sized planet found so far that also exists in the habitable zone around its star is certainly exciting (read our previous article for all the details). Gliese 581g is surely a potential habitable planet where liquid water could exist on the planet‘s surface, and many are touting the old adage of where there’s water, there’s life. However, some quotes from one of the scientists involved in the discovery might be feeding some wild speculation about the potential for life on this extrasolar planet and elsewhere. “Personally, given the ubiquity and propensity of life to flourish wherever it can, I would say, my own personal feeling is that the chances of life on this planet are 100 percent,” said discoverer and astronomer Steven Vogt during a press briefing yesterday. “I have almost no doubt about it.”

Yes, that is an exact quote. He really used those words. He also said that it would be pretty hard to imagine that water wouldn’t exist on the planet, given the ubiquity of water in our solar system and beyond, and the habitable region in which this planet orbits.

Also participating in the briefing was Paul Butler of the Carnegie Institution of Washington, which provided funds for the observations at the Keck I telescope, and his comments were more tempered.

“Any discussion of life on at this point is purely speculative,” Butler said. “What we know is that this planet exists at the right distance for liquid water it has the right amount of mass to hold on to its atmosphere and any liquid water on the surface. So any subsequent discussion of life there is purely speculative. That being said, on the Earth anywhere you find liquid water you find life in overwhelming abundance. The question should be, if this planet has liquid water, how can you rule out life doesn’t exist? It is pretty probable that anywhere you find liquid water pooling, that you would find life existing.”

Are Vogt’s claims too extreme, or were they made in exhilaration during an exciting announcement? This has been a topic of debate on Twitter this morning. Some wondered if Vogt had been misquoted, and many expressed that Vogt’s words may fuel off-the-deep-end speculation about the certainty of life on another world.

“Until we know more about this planet and the origin of life itself, any claim of certain habitation is idiotic and does not serve science,” said Dr. Stuart Clark (@DrStuClark), author and astronomy journalist. To clarify, he wanted others to know that he thinks just the claim is idiotic, not the discovery or the people involved.

“As cool as it is, please realize that right now all we really know about it is its orbit and estimated mass. That’s it.” said Lee Billings (@leebillings), editor at Seed Magazine. “In other words, barring observational evidence that may still be a generation away, Gliese 581g is ‘Earth-like’ only in terms of mass/orbit.”

From our pal Phil Plait, the Bad Astronomer (@badastronomer): “I understand what he meant – he thinks it could have life – but it was phrased unfortunately, and the media have jumped on it, of course.”

From David Masten (@dmasten), CEO of the commercial space company Masten Space Systems: “I have an opinion or 3 about life on anything in Gliese 581! And I’d dare say much closer to zero chance. But I’m not an astrobiologist.”

“Claiming a 100% chance of life on Gliese 581g is definitely an overreach,” said astrophysicist Juan Cabanela (@Juan_Kinda_Guy) at Minnesota State University Moorhead, “given we currently have a sample of 1 planet with life.”

“Vogt’s extrapolation was certainly quite a leap. On the other hand, the media might finally get it that some scientists really do think life everywhere is possible – but not bug-eyed aliens” said Robert Cumming, (@maltesk), journalist at the Swedish magazine “Populär Astronomi.“. “Then we can also discuss why there might not be life everywhere after all.”

Mark Thompson (@PeoplesAstro), Astronomy presenter on BBC’s the One Show said the Vogt’s quote was “absolutely and totally inappropriate. We can’t even be 100% sure it’s made of rock!!!”

From astronomer, educator and journalist Nicole Gugliucci (@noisyastronomer): “The public seems to have enough trouble trusting science these days without scientists making bold statements like that.”

“100% is ridiculous,” Tweeted frequent image contributor to Universe Today, Stu Atkinson (@mars_stu). “No possible way anyone could know that, surely?”

Many expressed excitement over the discovery, and Stu articulated perhaps the most colorful, which was re-tweeted several times yesterday: “Ah, a PROPER planet!” Not a great fat bloated sweaty “Who ate all the pies” ‘hot Jupiter’ tearing insanely around its star.”

What are your views?

*all Tweets used by permission.

Here’s an article about abiogenesis, theories about how life got started here on Earth.

Posted on by Nancy Atkinson

New Earth-sized Exoplanet is in Star’s Habitable Zone

Goldilocks Zone
Artists impression of Gliese 581g. Credit: Lynette Cook/NSF

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An enticing new extrasolar planet found using the Keck Observatory in Hawaii is just three times the mass of Earth and it orbits the parent star squarely in the middle of the star’s “Goldilocks zone,” a potential habitable region where liquid water could exist on the planet’s surface. If confirmed, this would be the most Earth-like exoplanet yet discovered and the first strong case for a potentially habitable one. The discoverers also say this finding could mean our galaxy may be teeming with prospective habitable planets.

“Our findings offer a very compelling case for a potentially habitable planet,” said Steven Vogt from UC Santa Cruz. “The fact that we were able to detect this planet so quickly and so nearby tells us that planets like this must be really common.”

Vogt and his team from the Lick-Carnegie Exoplanet Survey actually found two new planets around the heavily studied red dwarf star Gliese 581, where planets have been found previously. Now with six known planets, Gliese 581 hosts a planetary system most similar to our own. It is located 20 light years away from Earth in the constellation Libra.

The most interesting of the two new planets is Gliese 581g, with a mass three to four times that of the Earth and an orbital period of just under 37 days. Its mass indicates that it is probably a rocky planet with likely enough gravity to hold on to an atmosphere.

The planet is also tidally locked to the star, meaning that one side is always facing the star in sunlight, while the side facing away from the star is in perpetual darkness. One effect of this is to stabilize the planet’s surface climates, according to Vogt. The most habitable zone on the planet’s surface would be on the terminator, the line between shadow and light, with surface temperatures decreasing toward the dark side and increasing toward the light side.

“Any emerging life forms would have a wide range of stable climates to choose from and to evolve around, depending on their longitude,” Vogt said.

There has been debate about the other planets found previously around Gliese 581, whether they could be habitable or not. Two of them lie at the edges of the habitable zone, one on the hot side (planet c) and one on the cold side (planet d). While some astronomers still think planet d may be habitable if it has a thick atmosphere with a strong greenhouse effect to warm it up, others are skeptical. The newly discovered planet g, however, lies right in the middle of the habitable zone.

“We had planets on both sides of the habitable zone–one too hot and one too cold–and now we have one in the middle that’s just right,” Vogt said.

The researchers estimate that the average surface temperature of the planet is between -24 and 10 degrees Fahrenheit (-31 to -12 degrees Celsius). Actual temperatures would range from blazing hot on the side facing the star to freezing cold on the dark side.

If Gliese 581g has a rocky composition similar to the Earth’s, its diameter would be about 1.2 to 1.4 times that of the Earth. The surface gravity would be about the same or slightly higher than Earth’s, so that a person could easily walk upright on the planet, Vogt said.

The planet was found using the HIRES spectrometer (designed by Vogt) on the Keck I Telescope, measuring the star’s radial velocity. The gravitational tug of an orbiting planet causes periodic changes in the radial velocity of the host star. Multiple planets induce complex wobbles in the star’s motion, and astronomers use sophisticated analyses to detect planets and determine their orbits and masses.

“It’s really hard to detect a planet like this,” Vogt said. “Every time we measure the radial velocity, that’s an evening on the telescope, and it took more than 200 observations with a precision of about 1.6 meters per second to detect this planet.”

In addition to the radial velocity observations, coauthors Henry and Williamson made precise night-to-night brightness measurements of the star with one of Tennessee State University’s robotic telescopes. “Our brightness measurements verify that the radial velocity variations are caused by the new orbiting planet and not by any process within the star itself,” Henry said.

The researchers also explored the implications of this discovery with respect to the number of stars that are likely to have at least one potentially habitable planet. Given the relatively small number of stars that have been carefully monitored by planet hunters, this discovery has come surprisingly soon.

“If these are rare, we shouldn’t have found one so quickly and so nearby,” Vogt said. “The number of systems with potentially habitable planets is probably on the order of 10 or 20 percent, and when you multiply that by the hundreds of billions of stars in the Milky Way, that’s a large number. There could be tens of billions of these systems in our galaxy.”

Source: University of California – Santa Cruz

Here’s an article about abiogenesis, or the beginning of life on Earth.

Posted on by Nancy Atkinson

An Alien’s View of Our Solar System

We have just begun to try and image distant solar systems around other stars, and hopefully our techniques and technology will improve in the near future so that we can one day find — and take pictures of — planets as small as Earth. But what if another civilization from a distant star was looking at us? What would they see? A new supercomputer simulation tracking the interactions of thousands of dust grains show what our solar system might look like to alien astronomers searching for planets. It also provides a look back to how our planetary system may have changed and matured over time.

Continue reading “An Alien’s View of Our Solar System”

Posted on by Jon Voisey

Electric Resistance May Make Hot Jupiters Puffy

The Sun’s magnetic field

One of the surprises coming from the discoveries of the class of exoplanets known as “Hot Jupiters” is that they are puffed up beyond what would be expected from their temperature alone. The interpretation of these inflated radii is that extra energy must be being deposited in the regions of the atmosphere with large amounts of circulation. This extra energy would be deposited as heat, causing the atmosphere to expand. But from where was this extra energy coming? New research is suggesting that ionized winds passing through magnetic fields may create this process. Continue reading “Electric Resistance May Make Hot Jupiters Puffy”

Posted on by Nancy Atkinson

Scientists Predict Earth-Like Habitable Exoplanet Will Be Found in 2011

An artist’s impression of Gliese 581d, an exoplanet about 20.3 light-years away from Earth, in the constellation Libra. Credit: NASA

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Two astronomers have written a paper and say that the first Earth-like, habitable exoplanet will be announced in May of 2011. Do they have inside information, a crystal ball, or amazing powers of prediction? No, they base their projection on math and trends from the past 15 years of exoplanet discoveries. And if the discoveries continue at their present rate, the researchers say next year is the year of the long awaited holy grail of finding another Earth-like planet out in the cosmos.

Samuel Arbesman from Harvard Medical School in Boston and Gregory Laughlin at the University of California, Santa Cruz take a scientometric approach to their prediction. Scientometrics is the science of measuring and analyzing science, and is often done using bibliometrics which is a measurement of the impact of scientific publications. Arbesman and Laughlin said this type of work highlights the usefulness of predictive scientometric techniques to understand the pace of scientific discovery in many fields.

They use the properties of previously discovered exoplanets along with external estimates for the discovery of the first potentially habitable extrasolar planet.

In their paper they indicate that since astronomers have been discovering extrasolar planets at an increasing rate since 1995 and the discoveries follow a well understood pattern, it should be easy to predict when planet searchers will hit the jackpot.

The first exoplanets found were the massive Jupiter or larger-sized planets which were the easiest to find, and then as techniques improved over the past 15 years, astronomers have found smaller planets, some just a few times more massive than Earth.

A single realization of the habitability of extrasolar planets over time. H values for the extrasolar planets are plotted, with those of the upper envelope (maximum H for a given year of discovery) indicated in black. The black curve is the logistic best- t curve of the upper envelope, using a nonlinear model, where R = 28:78 and y = 2011:10. The horizontal grey line indicates the maximum value of H = 1, the presence of an Earth-like habitable planet. Credit: Arbesman and Laughlin

Arbesman and Laughlin took that rate of discovery, and they also needed to factor in all the variables for what we think will make a planet habitable: the surface temperature must allow liquid water to exist, so that life as we know it can appear, and that depends on the size of the star, how far the planet orbits from its star, and what type of surface the exoplanet has.

They conclude there is a 66 per cent probability of finding another Earth by 2013, a 75 per cent probability by 2020, and a 95 per cent probability by 2264, but the median date of discovery is in May 2011. And not just sometime in May, but “early May.”

In June 2010, the Kepler Telescope team revealed they had found 750 exoplanet candidates, and a fair number of those confirmed might be Earth-sized. They expect they can confirm and announce some of these candidates in February 2011. But Arbesman and Laughlin predict it might take longer. “Because of the limited time base line of the mission to date, the Kepler planet candidates to published in February 2011 may be too hot to support significant values for H (which is their habitability metric),” they wrote in their paper.

So, if their prediction comes true, that might mean another team, such as the HARPS, or Keck, or CoRoT, or other exoplanet-finding wizards might make the discovery.

“It must be noted that by publicizing our prediction, there is a concern that it will become accurate,” Arbesman and Laughlin write in their paper, “simply due to the well-studied Hawthorne Effect. However, due to the large number of observations and long periods of time required to confirm an extrasolar planet discovery, it is unlikely that our prediction at this time will appreciably affect the announcement of the discovery of an Earth-like planet. Therefore, it is reasonable to use the habitability metric curve as a rough prediction for when the first potentially habitable planet will be discovered, in this case, as early as May 2011, and likely by the end of 2013.”

It will be interesting to see how accurate their prediction turns out to be!

Read the paper: “A Scientometric Prediction of the Discovery of the First Potentially Habitable Planet with a Mass Similar to Earth.”

Additional Source: Technology Review Blog

Posted on by Nancy Atkinson

Kepler Discovers Multi-Planet System

Relative sizes and orbital periods of the newly discovered planets and the super-Earth candidate as they cross their host star, Kepler-9. Image courtesy of NASA/Kepler/Darin Ragozzine

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The Kepler mission has discovered a system of two Saturn size planets with perhaps a third planet that is only 1.5 times the radius of Earth. While the news of this discovery is tempered somewhat with the announcement by a team from the European Southern Observatory of a system with five confirmed Neptune-sized planets and perhaps two additional smaller planets, both discoveries highlight that the spacecraft and techniques astronomers are using to find exoplanets are getting the desired results, and excitingly exoplanet reseach now includes the study of multiplanet systems. This discovery is the first time multiple planets were found by looking at transit time variations, which can provide more information about planets, such as their masses.

“What is particularly special about this system, is that the variations in transit times are large enough, that we can use these transit timing to detect the masses of these bodies” said Matthew Holman, Kepler team lead for the study of star Kepler-9, speaking on the AAAS Science podcast. Additionally, these findings should provide the tools astronomers need to determine even more physical conditions of these planets — and others — in the future.

The inner world weighs in at 0.25 Jupiter mass (80 Earths) while the outer world is a slimmer 0.17 Jupiter mass (54 Earths).

The team analyzed seven months of data from the orbiting Kepler telescope, and the two large confirmed planets—Kepler-9b and Kepler-9c— are transiting the parent star at unstable rates. The planets’ 19.2- and 38.9-day transition periods are increasing and decreasing at average, respective rates of four and 39 minutes per orbit.

“One thing that caught our attention right off, is when we do preliminary estimates at the time of the transit, we saw large variations in this particular system. Not only did we see more than one planet transiting, but one planet seemed to be speeding up and one slowing down,” Holman said.

Because period one is roughly twice the other, they have a signature of what is called a 2:1 orbital resonance, where astronomers expect to see large timing variation, due to the orbital gravitational push and pull the systems has on all the objects.

“The variation in transit times depend upon the masses of the planets,” Holman told reporters in a news conference announcing the findings. “The larger the mass the larger the variations. These variations allows us to determine the mass of the objects and we can confirm that they are planets.”

The team also confirmed the objects were planets with radial velocity observations with the Keck I telescope.

The third planet, with a mass several times that of the Earth, is transiting the star in a more interior orbit, but further analysis will be necessary to confirm that this signature is actually a planet.

“We are being very careful at this point to only call it a planet candidate, rather than a confirmed planet,” Holman said. “If it is confirmed it would only have a radius of about 1.5 that of Earth’s. It has a much shorter orbital period of 1.6 days, so it is very close to its host star, so we should be able to see evidence of many transits.”

Holman added that this discovery — regardless of whether they are able to confirm that this is a planet or not — highlights the sensitivity of Kepler to very small signatures.

Holman said the planets have probably migrated to be closer to the star from where they started out when they formed. “Likely they formed with the star, but likely they formed farther out at the “snow line” several times farther away from the star than the Earth is, and by a dynamical process move in closer,” he said in the Science podcast.

The resonance is a signature that some kind of migration had occurred, called convergent migration, where planets are moving towards the star and also coming closer to each other.

From all the transit timing information that has been gathered so far, astronomers are piecing together the migration history of this planetary system. “The whole history of that system may be encoded in the information we have,” said Alycia Weinberger, from the Department of Terrestrial Magnetism at the Carnegie Institution. “Isn’t it cool that what the planetary system looks like today has much to tell us about its history?”.

Kepler looks for the signatures of planets by measuring tiny decreases in the brightness of stars when planets cross in front of, or transit them. The size of the planet can be derived from the change in the star’s brightness. In June, mission scientists announced the mission has identified more than 700 planet candidates, including five systems with more than one planet candidate. This is the first of those systems to be confirmed.

Kepler principal investigator William Borucki said the team is working hard to get these candidates “turned into confirmed planets.”

Asked about why the public seems to be so interested in the Kepler mission, Borucki said, “We addressing a very important question, which is, are there other earths out there and are they frequent? Any answer is important. If we get zero that might mean there is very little life out there in the universe.”

Sources: Science, AAAS Science podcast, NASA,