The reason is that Kepler is not designed to detect extraterrestrial life. The space telescope’s mission is to detect extrasolar planets, something that it has accomplished brilliantly.
Kepler detects exoplanets by observing how the light of target stars dims and then increases. By calculating the length of the dimming and evaluating other data, scientists have been able to determine the size of the planets and the distances they orbit around their home stars.
When Kepler detects a possible extrasolar world, ground-based telescopes follow up with observations to confirm the existence of these extrasolar planets.
Kepler has detected thousands of candidate planets, of which many hundreds have been confirmed by subsequent observations (3). Many of these planets are Jupiter or greater-sized gas giants. A few are rocky worlds, much like Earth or Mars, while some are designated as “super-Earths” meaning that they are much larger and likely have more mass than Earth.
Characteristics to Sustain Life
For a planet to be capable of sustaining life, at least as we know it, it has to have two characteristics. First, it has to be approximately Earth-sized and be a rocky world. Second, it has to lie in the “habitable zone” in orbit around its home star. The habitable zone is far enough from the star that the ambient temperature can sustain liquid water.
Kepler has detected a number of Earth-like worlds and a number of worlds that orbit in the habitable zone of their home stars. But the space telescope has detected only one planet that is both Earth-sized and in the habitable zone (4).
The planet in question is called Kepler 186f. The planet, slightly larger than Earth, orbits a red dwarf star called Kepler 186 that resides 500 light years from Earth in the constellation Cygnus.
Of course, by no means are scientists certain that Kepler 186f is habitable, not to mention contains alien life. NASA does not know what the planet’s mass is, whether it has liquid water, and what its atmosphere consists of.
These questions have to be answered by more powerful telescopes sometime in the future. Right now, though, the planet is the closest we have to a place where aliens might reside.
But, aliens do not have to live on planets. Recently, an anomaly was detected at another star, the afore-mentioned KIC 463852. Kepler detected a number of dips in the light coming from KIC 463852 that did not suggest a small number of larger planets, but rather a host of smaller objects of an unknown nature.
Are Signals Extra Terrestrial?
By process of elimination, scientists narrowed down the possible natural cause of the discovery to a swarm of comets orbiting close to KIC 463852. The theory is that sometime in the distant past, another star passed close by to KIC 463852 and pulled a swarm of comets into orbit around it.
However, some have theorized that the discovery could be explained by the presence of alien megastructures, a swarm of huge solar collectors, artificial habitats, or even a Dyson sphere. The theory has gotten a great deal of play in the media, for obvious reasons. The confirmation of alien artifacts orbiting a star 1,500 light years from Earth would be confirmation that intelligent life did not just arise on Earth.
Scientists are naturally cautious about glomming onto the alien megastructure theory. Many remember how signals detected in the 1960s, once thought to be alien in origin, turned out to be from a natural phenomenon called pulsars (5).
Nevertheless, the SETI organization is directing radio telescopes toward KIC 463852(6) in an attempt to determine whether ET is sending signals. Kepler has not discovered aliens, but it has given us tantalizing hints, which in and of themselves are exciting.