Two steps closer to finding another Earth

This past week, there were two more news items of great interest relating to exoplanets, and the search ultimately for another Earth-like planet.

The first, from the Kepler mission, is that the previously reported possible planet Kepler 9d, only 1.5 times larger than Earth, is likely to soon be announced as confirmed. Other news from the mission will also be announced in November according to the same update.

Artist's conception. Credit: Lynette Cook

Then, another very significant announcement from ground-based observatories at the University of California Santa Cruz, the University of Hawaiʻi at Mānoa and the Carnegie Institution of Washington, that for the first time, a small rocky planet has been confirmed orbiting well within the “habitable zone” of a nearby star, the region where temperatures would allow liquid water to exist on a planet; not too hot and not too cold. One of six known planets orbiting the red dwarf star Gliese 581, about 20 light years away, it is estimated to have a mass about three times that of Earth, and a diameter of only about 1.2 to 1.4 times that of Earth. Additional reports here, here and here. A good quote from the UCSC article indicates how planets like this are probably quite common:

The researchers also explored the implications of this discovery with respect to the number of stars that are likely to have at least one potentially habitable planet. Given the relatively small number of stars that have been carefully monitored by planet hunters, this discovery has come surprisingly soon.

“If these are rare, we shouldn’t have found one so quickly and so nearby,” Vogt said. “The number of systems with potentially habitable planets is probably on the order of 10 or 20 percent, and when you multiply that by the hundreds of billions of stars in the Milky Way, that’s a large number. There could be tens of billions of these systems in our galaxy.”

This also brings the total count of known exoplanets so far to 492 and we’ve still only scratched the surface…