Updated 12:14 pm ET Wednesday, December 7
The quest to find life beyond planet Earth took a huge leap forward on Monday when NASA scientists announced that their Kepler spacecraft had discovered a planet located in the habitable zone around its star: Kepler-22b, which is estimated to have a pleasant surface temperature of 70 degrees and the capability to support liquid water.
But as with most great discoveries, the finding of Kepler-22b raised more questions than it answered: Specifically, what is the composition of the planet’s surface? Is it rocky, primarily liquid, or gaseous — the latter of which would make life more improbable, though only slightly.
We don’t know the answer to that question yet, as the planet’s mass has yet to be estimated. But scientists will have a better idea come summer 2012, when the Kepler field is once again visible to ground-based observatories.
“We will continue to work hard to get the required measurements starting next summer (2012) when the Kepler field again becomes visible at night,” wrote Nick Gautier, Kepler project scientist at NASA’s Jet Propulsion Laboratory in Pasadena, in an email to TPM.
“However, there is no guarantee that we will, in fact, be able to make a good measurement,” he added. “If we get a mass, we can combine it with the measured diameter of Kepler-22b to get a density from which we can guess at the planet’s composition.”
The reason behind the six or more month wait has to do with both the location of the planet Kepler-22b in the sky and the way the Kepler mission works.
Kepler’s field of view encompasses an area between the constellations Vega and Cygnus. The spacecraft, locked in an Earth-chasing heliocentric orbit (around the Sun), is constantly watching this region to detect minute changes in light from stars, some of which signify the shadow of an eclipsing planet. This is the same process that lead to the discovery of Kepler-22b.
But even when a planetary candidate is detected, scientists then attempt to double-check and verify the data obtained by the Kepler-22b spacecraft with ground-based telescopes.
Unfortunately, the Cygnus region is only visible from the ground in the Northern Hemisphere during the summer months, hence the need to wait until summer 2012 to get a better view of Kepler-22b and the other 2,326 potential planetary candidates identified by the mission so far.
Even when Kepler-22b’s mass is estimated, there’s a chance that the planet could be ruled an unlikely candidate for life. As Gautier explained: “If a density determination shows that Kepler-22b very likely has a deep atmosphere we would be hard pressed to imagine habitability like the Earth since Kepler-22b would then have no rocky surface like Earth.”
That’s because a deep atmosphere would likely mean that Kepler-22b was a gaseous planet. The planet’s radius has already been estimated at 2.4-times the size of Earth’s, which means that it has a much stronger gravity, enough to trap hydrogen and helium gasses.
However, even in that case, Gautier said that it was impossible to decidedly rule out life on the planet.
“‘Decidedly’ is a pretty strong word considering we know so little about life off the Earth,” Gautier told TPM.
Until then, the scientists from Kepler will be busy analyzing their most recent crop of findings. We’ll update when we hear more from the Kepler team.
First update: Corrected second sentence of third paragraph to clarify that the planet (and the Kepler field) will become visible to ground-based observatories again in summer 2012.