by Irene Klotz
April 18, 2013

from Reuters Website





Relative sizes of Kepler habitable zone planets discovered

as of April 18, 2013 in this artist's rendition provided by NASA.
Credit: Reuters/NASA Amers/JPL-Caltech/Handout



Scientists using NASA's Kepler space telescope have found the best candidates yet for habitable worlds beyond the solar system, including a pair of potentially life-friendly planets orbiting the same star, officials said on Thursday.

The planets join a list of about 700 confirmed extra-solar planets discovered since 1995.

The new additions include a pair of planets orbiting a star called Kepler-62, located about 1,200 light years away in the constellation Lyra (see also 'The Prism of Lyra').

Kepler-62's two outermost planets, both about 1.5 times the size of Earth, are located the right distance from their parent star for water - if 'any' exists - to be liquid on the surface.





Water is believed to be necessary for life.

"These two planets are our best candidates for planets that might be habitable, not just in the habitable zone," Kepler lead scientist William Borucki, with NASA's Ames Research Center in Moffett Field, California, told reporters on a conference call.

Computer models indicate the two planets, designated Kepler-62e and 62f, likely are solid bodies comprised of rock, ice or a mix of rock and ice.

The pair have three sister planets that also circle Kepler-62, but those are too close their parent star and likely too hot for surface water.

The Kepler telescope measures slight dips in the amount of light coming from target stars that may be caused by planets passing by, or transiting, relative to the telescope's line of sight.

So far, the Kepler science team has more than 2,700 candidate planets.

Scientists also found two planets circling another Kepler target star, Kepler-69, located about 2,700 light years from Earth in the constellation Cygnus (se also 'The Cygnus Mystery').

Light travels at about 186,000 miles per second, or about 6 trillion miles (10 trillion km) in a year.

The innermost planet is about twice the size of Earth and orbits its parent star in just 13 days, too close for liquid surface water. The second planet, however, which is about 70 percent bigger than Earth, orbits about where Venus is located in the solar system, putting it on the edge of the star's so-called "habitable zone."

More powerful telescopes than Kepler will be needed to fish out more detail about whether the extrasolar planets do indeed 'have water.'

"We're still progressing to find the first truly Earth-like worlds," said astronomer Thomas Barclay, with the Bay Area Environmental Research Institute in Sonoma, California.

The research (Kepler-62 - A Five-Planet System with Planets of 1.4 and 1.6 Earth Radii in the Habitable Zone) is being published in Science and the Astrophysical Journal this week.



This artist's concept provided depicts

NASA's Kepler mission's smallest habitable zone planet.

Photo: AP












Kepler Spies Water Worlds

-   Pair of Exoplanets Sit in Habitable Zone of Star Far Beyond The Solar System   -
by Ron Cowen
18 April 2013

from Nature Website




This illustration shows Kepler-62f,

a newly discovered extrasolar planet (top)

and a similar body, Kepler-62e (bottom left).
David A. Aguilar/CFA


NASA's Kepler spacecraft has discovered two planets that are the most similar in size to Earth ever found in a star's habitable zone - the temperate region where water could exist as a liquid.

The finding, reported online today in Science1, demonstrates that Kepler is closing in on its goal of finding a true twin of Earth beyond the Solar System, says theorist Dimitar Sasselov of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, who is a member of the Kepler discovery team.

Both planets orbit the star Kepler-62, which is about two-thirds the size of the Sun and lies about 1,200 light years (368 parsecs) from the Solar System. The outermost planet from the star, Kepler-62f, has a diameter that is 41% larger than Earth's and takes 267 days to circle its star.


The inner planet, Kepler-62e, has a diameter 61% larger than Earth's and a shorter orbit of 122 days.

Kepler detected the planets by recording the tiny decrease in starlight that occurs when either of them passes in front of their parent star. Astronomers used those measurements to calculate the planets' relative size compared to that star.




Worlds apart

In the Science paper (Kepler-62 - A Five-Planet System with Planets of 1.4 and 1.6 Earth Radii in the Habitable Zone), the Kepler team - led by principal investigator William Borucki of NASA - suggests that the planets are solid, but may be rocky or icy.


But Sasselov believes that the two orbs are likely to be covered entirely by oceans, based on his own unpublished analysis co-authored with colleagues at Harvard-Smithsonian and the Max Planck Institute for Astronomy in Heidelberg, Germany. They theorize that the two water worlds are either liquid all the way down to their core or have a solid surface just beneath a shallower ocean.


The latter model would be more conducive to life as we know it on Earth, where a recycling of material and energy from hydrothermal vents can sustain organisms, Sasselov says.

But some recycling could also occur in a much deeper ocean, owing to deposits of methane and other volatiles trapped in a layer of high-pressure, underground ice that could later be released by convection into the liquid, he notes. Sasselov and two other collaborators describe that model in a preprint on the arXiv server2, which is due to be published in the Astrophysical Journal.

The planets' properties "are all consistent with being habitable", says Lindy Elkins-Tanton, who directs the department of terrestrial magnetism at the Carnegie Institution for Science in Washington DC.


However, it is not guaranteed that the two planets have enough carbon dioxide, a greenhouse gas, to keep the planet warm enough so surface water can exist as a liquid as the researchers have assumed, she cautions.

Jonathan Lunine, a planetary scientist at Cornell University in Ithaca, New York, says that it is impossible to know the composition of the two exoplanets because scientists have not been able to calculate their masses.


That is because Kepler-62e and Kepler-62f exert too feeble a gravitational tug on their parent star to be detected by any existing telescope.





The planets also lie too far away from Kepler-62 for astronomers to use its light to hunt for chemical elements in the planets' atmospheres.



"these are the closest yet to the Earth twin everyone wants to see," Lunine says.