23Apr2013

Has Kepler Found Ideal SETI-Target Planets?

An artistic view of the system seen from Kepler-62f. The host star is slightly redder than our sun. The smaller exoplanets Kepler-62b (1.3 times Earth’s radius) & Kepler-62c (0.5 times Earth’s radius) are close to the star. Kepler-62d (2 times Earth’s radius) is significantly bigger and closer, Kepler-62e (1.6 times Earth’s radius) & Kepler-62f (1.4 times Earth’s radius) are relatively close to each other and both are sustaining water and rocky surface as suggested by the clouds’ color, water, atmosphere and rocks Credit: Danielle Futselaar/SETI Institute

Searching for some extra-terrestrial intelligence? Then NASA’s Kepler mission may very well have discovered a new planetary system to aim for. They have ideal locations. Orbiting a star slightly smaller than the Sun are five small planets – two of which fall into the “Super Earth” category and may consists of ice and rock. What makes them exciting is that they are located in the habitable zone and if life exists there, may have evolved to the point where civilization and technology may have developed. Could it be detectable? 

Let’s take you back… back when the NASA Kepler mission was launched on March 9, 2007. At the time, the Delta II rocket was carrying the hopes and dreams of a large community of scientists who had devoted themselves to the study of extra-solar planets – planets in orbit around other stars. The Kepler mission’s main scientific objective is exploration of the structure and diversity of planetary systems. How does it work? Kepler focuses itself continually on a field of 150,000 stars to ferret out small dips in brightness due to the transits of a planet. To date, Kepler has already been a successful NASA mission with the discovery of 2,740 planet candidates with estimated sizes from Mercury to larger than Jupiter. A fifth of these planet candidates are also called “super-Earths”, a new class of planets, without analog in our solar system, with a radius between 1.25 to 2 times the radius of our planet.

Kepler-22b -- Comfortably Circling within the ...

Kepler-22b — Comfortably Circling within the Habitable Zone (Photo credit: NASAblueshift)

Just days ago, in a scientific article published in Science magazine and through a NASA press conference, the Kepler team announced the discovery of a multiple planet system, composed of 5 Earth-sized and super-Earth planets orbiting a K-type star. However, bear in mind the discovery of these planets was indirect since Kepler astronomers observed the attenuation of the host star’s brightness due to the passage of a planet in the line of sight, and not the planets themselves. The validation of this planetary system was confirmed by a statistical analysis based on previous detections of multiple planets by Kepler.

“By estimating the rate of false-positives due the remote possibility of additional planet-hosting stars in the photometric aperture we have strong confidence that we have discovered two genuine transiting super-Earth planets in the habitable zone of their host star. Such calculations are only possible because of the thousands of additional transiting extrasolar planets that Kepler has discovered” said Jason Rowe, Research Scientist at the Carl Sagan Center of the SETI Institute and co-author of the work.

According to the research paper, the outermost planet, named Kepler-62f (radius about 1.4 times Earth’s radius and a period of 267 Earth days) is located in the habitable zone of the parent star. As we know, the habitable zone is a region where an “Earth similar” planet might be home to liquid water. The team expanded the definition of the Habitable Zone by taking into account the evolution of the brightness of the host star. Their calculations suggest that Kepler-62e (radius about 1.6 times Earth’s radius and a period of 122 Earth days) was also in the habitable zone so that liquid water could have existed on its surface, too. Just as Venus and Mars may have once hosted water on their surfaces some one to four billion years ago, the Kepler team’s calculations suggest that Kepler-62e (radius about 1.6 times Earth’s radius and a period of 122 Earth days) may fall into the broad zone where water could exist on its surface.

Kepler bkgd.sm

Kepler bkgd.sm (Photo credit: Wikipedia)

“These discoveries move us farther down the road to discovering planets similar to Earth. While we don’t know if Kepler-62e and f are rocky or whether they have liquid water pooling on their surfaces, their existence shows that the incidence of small worlds in the habitable zone of sun-like stars is high. Thus we can look forward to the discovery and detailed characterization of Earth’s cousins in the years and decades to come by future missions and telescopes.“ said Jon Jenkins Senior Scientist at the Carl Sagan Center of the SETI Institute and also co-author of the work.

Right now the “Goldilocks” planets masses aren’t clear because they are simply too small to produce detectable gravitational effects between the parent star and themselves. However, considering a lower upper limit for their mass and the age of the star, estimated to be 7 billion years, the team suggests that both planets are solid and either made of a dry rocky material, like Earth, or a large body of water surrounding a core of iron and rock. Even though the Kepler-62 system is just a bit too distant to fully characterize if they have atmospheres with our current equipment, they still pose great potential.

“Since December of 2011, the SonATA program to search for extraterrestrial intelligence with the Allen Telescope Array has been focusing on the Kepler exoplanet candidates and especially those planets expected to be within the “Habitable Zone” of their stars. Our surveys improve on previous, generally narrowband SETI by covering the radio frequency range where Earth’s atmosphere is most transparent, including many frequencies never before observed. We expect to complete a meaningful survey of these stars in less than 1 year — be sure to check back soon.” says Gerry Harp, Director of the Center for SETI Research.

Original Story Source: SETI Institute News Release. Submitted by Tammy Plotner for “Dave Reneke’s World of Space and Astronomy News”.

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