The Search for Extraterrestrial Intelligence, or SETI, is a speculative venture. There is currently zero evidence for the existence of extraterrestrial life, let alone intelligent extraterrestrial life - why the heck are we bothering to search for life forms advanced enough to blast radio waves into space? As speculative as this hunt may be, it is based on sound science methodology and, should the slightest hint of alien intelligence be detected, it would transform our understanding about our place in this grand cosmic sandbox.
Listening to random stars in the hope that one may play host to a transmitting alien civilization is beyond speculative, however - given enough time and computational power, yes, it only ever has a low probability of success. But say if we know that a given star plays host to a planet, not too dissimilar to Earth, orbiting within a magical distance from its host star that is just the right temperature for liquid water to exist on its rocky surface? Wouldn't it make sense to aim our radio telescopes at those star systems?
Wouldn't it make even more sense to aim our radio antennae at star systems containing several exoplanets, two of which have Earth-like qualities and orbit within the star's "habitable zone"?
NEWS: Kepler-62: A Star System With Two Earths?
Well, with the help of NASA's premier exoplanet hunter Kepler, SETI has found a natural partner in the hunt for transmitting extraterrestrials, and on Thursday (April 18) Kepler mission scientists announced the discovery of a tantalizing star system named Kepler-62.
Kepler-62 is known to have at least five worlds orbiting it. Two of the exoplanets, Kepler-62e and Kepler-62f, are located within the star's habitable zone with orbital periods of 122 and 267 days, respectively. But the groundbreaking thing about this pair is the fact they are very small and may even possess rocky surfaces. "e" is 1.6 times the size of Earth and "f" is 1.4 times the size of Earth. Sadly, at 1,200 light-years distant, that's all we know about the alien worlds. They are too far away for followup observations by ground-based observatories to determine their masses and any hope of detecting their atmospheric chemistry will be unlikely for some time.
Still, this is exciting as Kepler-62e and f are the smallest worlds detected by Kepler to date that orbit within the habitable zone of their star, allowing liquid water to exist (if it is indeed present), thereby potentially supporting the evolution of life as we know it on their hypothetical rocky surfaces.
PHOTOS: Top Exoplanets for Alien Life
In an effort to refine the search for extraterrestrial intelligence(s), data from the Kepler exoplanet hunter has been used to perform directed SETI searches. This is a paradigm-shift from the days of guessing which stars might host exoplanets. Kepler is reducing the uncertainty of hunting for ETIs. So far, astronomers carrying out directed SETI searches have turned up empty handed, but these are very early days. And as Kepler-62 demonstrates, there are a lot more promising worlds out there to study.
"These discoveries move us farther down the road to discovering planets similar to Earth," said Jon Jenkins Senior Scientist at the Carl Sagan Center of the SETI Institute and co-author of the Kepler-62 study. "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."
"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," added Gerry Harp, Director of the Center for SETI Research. "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."
PHOTOS: Exquisite Exoplanetary Art
The discovery of one "habitable" exoplanet is exciting. An approximately Earth-sized exoplanet inside a star's habitable zone is very exciting. But finding two? That's the equivalent of striking exoplanetary gold. Lacking any further clues, it doubles the life-giving qualities of that star system. It also spawns some interesting ideas that would, until now, have remained purely in the realms of science fiction.
What if an advanced civilization evolved on the outer planet Kepler-62f when the host star was younger (and therefore hotter)? As the K-type dwarf (slightly smaller and dimmer than the sun) cooled, its habitable zone would have shrunk. Although the world technically remains inside the habitable zone today, would the reduction in stellar energy have forced a hypothetical alien race into extinction? Or did it motivate a planetary exodus to the warmer Kepler-62e? Might the inhabitants be gazing at the neighboring world as we are currently looking at Mars for colonization?
Perhaps, as Discovery News' Ray Villard describes, we live in a compulsive universe. In a compulsive universe, if the ingredients for life are there, anything is possible. Therefore, life may have evolved on both worlds independently! This is purely a sci-fi notion, but it does pose an interesting thought experiment: What if both Kepler-62 alien civilizations have discovered each other and, assuming they come from the "life as we know it" mold, an interplanetary (or is that interexoplanetary?) conflict spawned rapid advances in space technology?
Perhaps, in the spirit of whittling down the best "directed SETI" targets, Kepler-62 may be an even riper target to listen out for extraterrestrial signals - the rapid advancement of technology through conflict could have accelerated space travel and interstellar communications in such star systems.
Alternatively, nothing of the sort happened in Kepler-62 - "e" and "f" could be barren, radiation-soaked worlds. They could bear little resemblance to the rich bounty of organics found in the solar system.
But then again, they might, a fact that will - rightfully - drive SETI studies for many years to come.
Read more about SETI's intentions for follow-up studies of this exciting star system.
Image: Artist's impression of Kepler-62f. Credit: NASA Ames/JPL-Caltech