BellaOnline Forums Education Astronomy Kepler and the search for another Earth

The first exoplanet orbiting a sunlike star was discovered in 2005, using a method that favors large planets close to their stars. But by 2010 half of the discoveries used a different method and smaller ones were discovered. (Searching for Extrasolar Planets explains how this works.)

But the revolution came when Kepler was launched. Over a thousand Kepler planet discoveries have been confirmed. With the vast amount of data available astronomers now have a better sense of the size range (and other characteristics) of extrasolar planets. And, of course, one thing they're looking for is another Earth. That means a small planet in its star's habitable zone. The habitable zone – also known as the Goldilocks zone – is where basic conditions would permit liquid water to exist on the surface.

A few days ago NASA announced that Kepler has found a dozen new smallish planets in habitable zones to add to its existing list. I should add here that we don't know much about these planets, but know enough to say they aren't really likely to be earthlike.

Here is a graphic showing Small planets in the habitable zone.

Kepler-452b and Earth Kepler-452b is the first known near-Earth-size planet orbiting in the habitable zone of a sun-like star. The artistic concept compares Earth (left) to the new planet, which is about 60% larger. BTW we don't know if the planet has oceans and continents. Both planets orbit a G2-type star, but the Kepler star is 6 billion years old, 1.5 billion years older than our Sun. As stars age, they become larger, hotter and brighter.

I tend to take the hyperbole about new planets with a grain of salt anyway, but have recently read an analysis of the data for "Earth's cousin" by David Wilson a PhD student at the University of Warwick in England.

Kepler 452b takes about one Earth year to orbit its star, which is about the same size as the Sun, though a billion years older. The planet's radius is 1.6 times that of Earth, so it's a super Earth. But its size is right on the boundary between being a rocky world and being a gaseous world similar to Neptune. Planetary scientists don't really understand the factors that decide which it will be, and we don't have any nearby examples of such a planet. The current models make the likelihood of Kepler 452b having a rocky surface between 49% and 62%.

The new planet is in the habitable zone of its star, but that's not a guarantee of anything good. Venus is nearly in the Sun's habitable zone and it's nowhere near being habitable – or even visitable.

But he still thinks it's a fascinating discovery. I agree.