Ignored Exoplanet May Be a Watery World

Mark Brown, Wired UK May 18, 2011
http://www.wired.com/wiredscience/2011/05/gliese-581d-exoplanet

Gliese 581g, a habitable Earth-like exoplanet orbiting the red dwarf, thrilled astronomers when it was discovered in September 2010 as it was the most feasibly habitable exoplanet yet observed. But a few months later its entire existence was brought into question — no one has seen any significant signal from 581g since. It could have just been noise in the stellar wobbles of the faraway red dwarf.

The mysterious 581g sat in the so-called Goldilocks zone, where it orbited at just the right distance from its roasting parent star that water, if it existed on the planet, would neither boil nor freeze.

But now a group of French researchers, led by British scientist Robin Wordsworth, have taken another look at the data for 581d — another of the red dwarf’s planets — performing a comprehensive 3-D climate simulation on the planet. The simulation uses fundamental physical principles to look at a wide range of conditions, and account for any atmospheric cocktail of gases, clouds and aerosols.

To the team’s surprise, it believes that 581d would have a dense carbon dioxide atmosphere, which would give the planet a stable and warm climate. In a press release, France’s National Centre for Scientific Research (CNRS) concluded that 581d is likely warm enough to hold liquid water, in “oceans, clouds and rainfall”.

Anyone who stood on the planet would probably see clear blue skies, like on Earth, also. Most planets’ thick atmospheres bounce the majority of sunlight back into space. On Earth, and potentially 581d, the Rayleigh scattering phenomenon lets more sunlight in, leading to blue skies and a warmer climate.

But if humans ever did walk on 581d they’d still find a pretty bizarre planet with very un-Earthlike conditions. The dense air and thick clouds would drape the surface in a perpetually murky red twilight, and its hulking mass (at least 5.6 times that of Earth) means surface gravity would be double that of Earth’s.

“The most important implication of these results,” a spokesperson for the Scientific Research center said in a press release, “may be the idea that life-supporting planets do not in fact need to be particularly like the Earth at all.”

Exoplanet List to Smash Over 1000?

From Scientific American:

Thirty million kilometers away, trailing the pale blue dot that is Earth as it orbits the sun, is a spacecraft designed to find some of the countless other pale blue dots that may speckle the galaxy. NASA launched this spacecraft, known as Kepler, in 2009 to take a census of Earth-like planets in the hopes of figuring out how common—or how rare—are the conditions under which life has thrived here.

Just over halfway into that 3.5-year campaign, Kepler has not been on the job long enough to conclusively identify any habitable worlds, but its discoveries are growing ever more tantalizing. In a field where small is good—small meaning less like Jupiter and more like Earth—the latest batch of planets netted by the space observatory includes five of the eight smallest worlds now known outside the solar system. All five of the new extrasolar planets, or exoplanets, as well as one more world whose properties are not yet fully understood, orbit a sunlike star called Kepler 11, some 2,000 light-years away. A group of researchers announced the discovery of the six-planet Kepler 11 system in the February 3 issue of Nature. (Scientific American is part of Nature Publishing Group.)

Almost simultaneously, the Kepler team was preparing a list of more than 1,200 additional objects the spacecraft has located that may also be planets. "We have a huge number of candidates," says Kepler's principal investigator, Bill Borucki of NASA Ames Research Center, Moffett Field, Calif. "It's very exhilarating," says Borucki, who first put forth the idea for Kepler in 1984 and proposed the concept several times before getting NASA's approval and funding. The data on the numerous candidates are somewhat preliminary and require validation, but a new analysis by a pair of astrophysicists at the California Institute of Technology suggests that the percentage of false positives among Kepler's candidate planets may be less than 10 percent.

If that is the case, then Kepler is well on its way to vastly augmenting the roster of known exoplanets, of which there are now 500 or so, and may have already gotten a whiff of several potentially habitable worlds. "We have 54 planets in the habitable zone of their stars," Borucki says, referring to the temperate orbital zone around a star that would allow for the existence of liquid water on a planet. "One of them is 0.9 times the radius of the Earth, and four of them are less than two Earth radii." Any of those would be the most Earth-like world ever detected outside the solar system. What is more, some of the larger, more Jupiter-like planets Kepler is sniffing at in the habitable zone might have moons, and some of those satellites would themselves be potentially habitable. "It's sort of awesome," Borucki says of Kepler's haul. "The implications are that there are an awful lot of planets out there."

A Wealth of Worlds: Kepler Spacecraft Finds 6 New Exoplanets and Hints at 1,200 More
John Matson
February 2, 2011
http://www.scientificamerican.com/article.cfm?id=kepler-11-thousands-extrasolar-planets

Exoplanet Atmospheres Detected from Earth

http://www.space.com/scienceastronomy/090114-exoplanet-atmospheres.html

Exoplanet Atmospheres Detected from Earth
By Andrea Thompson
Senior Writer
14 January 2009

Two independent groups of astronomers have detected the atmospheres of planets around other stars from ground-based telescopes.

Previous observations of the atmospheres of extrasolar planets had been made almost entirely by space-based instruments, such as the Hubble and Spitzer space telescopes, although another team last year detected the signature of sodium in an exoplanet atmosphere.

To date, astronomers have detected several key gases in planets' atmospheres, including:

Carbon dioxide – a potential sign of life, though the planet where the gas was observed was too hot to be habitable.

Water vapor – a key molecule required to support life as we know it.

Silicates (combinations of silicon and oxygen) – components of most rocks on Earth, likely in the form of clouds of dust grains on massive exoplanets.

Sodium – detected in 2001, it marked the first space-based observation of an exoplanet atmosphere.

Ground-based detection is becoming a priority as Hubble ages and Spitzer is set to run out of cryogens, which keep its instruments cool enough to detect infrared radiation (heat), limiting its abilities.

"Others have tried to detect planetary atmospheres from Earth, but to no avail," said the co-author of one of the new studies, Mercedes López-Morales of the Carnegie Institution in Washington, D.C. "We hit it right two nights last summer."

López-Morales and her team observed the planet OGLE-TR056b, a so-called "hot Jupiter."

Hot Jupiters

Hot Jupiters are massive gaseous planets that orbit very close to their stars, whipping around them in two to three days. Their proximity to their parent stars indicates the planets are hot enough to emit radiation in the optical and near-infrared wavelengths and that their radiation is detectable from Earth.

But OGLE-TR056b is faint, sitting about 5,000 light-years away and in a crowded part of the night sky, located in the direction of the center of our galaxy from the Earth's perspective. So López-Morales and her colleagues used the European Southern Observatory's Very Large Telescope (on July 2) and Carnegie's Magellan-Baade telescope (on Aug. 3). Both telescopes are located in Chile.

Only about one out of every 3,000 photons from the star comes from the planet itself. The rest is from the overwhelming light of the star. So astronomers wait until the planet is eclipsed as it orbits behind the star (from the Earth's perspective), which allows for separation of the emissions of the planet from those of the star.

"The planet is glowing red-hot like a kitchen stove burner, but we had to know precisely when the eclipse was going to happen and measure the stellar flux very accurately so it could be removed to reveal the planet's thermal emissions," said lead author of the study David Sing of Institut d'Astrophysique de Paris.

Real hot

The team took more than 600 images of OGLE-TR056b with both telescopes. The planet is hotter than any detected by Spitzer so far — its atmosphere is more than 4,400 degrees Fahrenheit (2,400 degrees Celsius).

The observations also indicated that the planet has little to no cloud cover and a static atmosphere with little circulation, López-Morales told SPACE.com in an email.

Their work will be detailed in an upcoming issue of the journal Astronomy & Astrophysics.

In the same issue of the journal, a Dutch team will explain their detection of the thermal emission in the near-infrared of another exoplanet dubbed TrES-3b. Its atmosphere registered at about 3,000 F (1,700 C).