Scientists have already identified 262 “potentially habitable” planets. If even half of them are confirmed to host life, then life on Earth won't seem as lonely.
On December, NASA Kepler released a list of some 18,400 planet-like detection events, taken from 2010 to 2012. Kepler is a NASA-owned space telescope with mission to search for exoplanets--planets outside the solar system--by finding a planet transiting in front of its parent star.
"When a planet passes in front of its parent star, as seen from our solar system, it blocks a small fraction of the light from that star; this is known as a transit," according to the Kepler Mission information site.
"Measuring repeated transits, all with a regular period, duration and change in brightness, provides a method for discovering and confirming planets and their orbits—planets the size of Earth and smaller in the habitable zone around other stars similar to our Sun," it added.
"There are at least 100 billion planets in the galaxy, just our galaxy," California Institute of Technology in Pasadena assistant professor of planetary astronomy John Johnson said in Caltech statement.
Johnson is also one of the authors of a recent study at Caltech that hints planetary systems within the cosmic norm. The study has recently been accepted for publication in the Astrophysical Journal.
Preliminary analysis of the University of Puerto Rico (UPR) in Arecibo Planetary Habitability Laboratory (PHL) shows 262 exoplanets passing the criteria of habitability--with enough distance from its host star to receive just enough sunlight, and with possibility of containing water to support life.
"These candidates become top priority for further analysis, additional observation and confirmation," according to UPR press release.
Because even the Milky Way contains billions of planets in itself, studying all of them would take generations. From the 18,406 transit-like features among the Kepler Threshold Crossing Event (TCE) dataset, they sifted the list of stellar transits, and other instrumental conditions, that do not match with that of planets.
After additional tests and analysis, astronomers were able to narrow it down to 2,320 candidates called Kepler Object of Interest, subject for further validation.
But "[o]nly the best TCE objects, those with more than three transit events, were selected for the analysis in accordance with the PHL’s Habitable Exoplanet Catalog (HEC) criteria," according to the UPR press statement.
Using "Earth Similarity Index," scientists were able to sort their list and came out with four Mars-size (subterrans), 23 Earth-size (terrans), and 235 superterrans (super Earth-size) planets--262 in all.
This preliminary analysis of PHL at UPR is essential in determining which planets needed further studies.