feb 292012

Above: The focal plane of the Kepler space telescope

Nasa has announced that 1,091 new transiting extrasolar planet candidates have emerged in data received from planet-hunting space telescope, Kepler. It brings the total count up to 2,321 exoplanet candidates
That number comes from data spanning May 2009 to September 2010, where nearly 5,000 periodic planetary transit-like signals (where a planet passes in front of a star, revealing its presence) were received, and subsequently vetted against known phenomena that could be masquerade as a transit.

An example: eclipsing binary stars. When two stars orbit each other and block each others’ light, it can look like a planetary transition.

The data shows a clear trend towards finding smaller planets at longer orbital periods — meaning planets more like Earth than like Jupiter. This latest data dump contains over 200 Earth-size candidates and more than 900 that are smaller than super-Earths (double our planet’s 12,756km diameter).

That’s a 197 percent increase in small planets from Kepler’s catalogue before this data was added. In comparison, there has only been a 52 percent bump in planets that are heftier than super-Earths.

There has also been a 123 percent increase in candidates that take more than 50 days to orbit their star, and only 85 percent more planets that zip around in less than 50 days. So what’s causing this trend towards smaller, slower stars?

For a telescope in our solar system to see an exoplanet in transit, the planet’s orbit must be lined up edgewise to us. “The probability for an orbit to be properly aligned is equal to the diameter of the star divided by the diameter of the orbit,” a spokesperson for Nasa, explains.

So for giant planets in four-day orbits, the alignment probability is about ten percent. As for an Earth-like planet in an Earth-like orbit, the probability of Kepler catching it in the act is just 0.5 percent.

Kepler’s looking at thousands of stars, but because big planets are more likely to be found, they’re going to come up early in the data. The more interesting, Earth-like and potential habitable planets are going to take a little longer to find.

That’s a worry when Kepler is coming to the end of its three-year mission. This month, several co-investigators of the mission will propose to Congress to extend the telescope’s funding at the Nasa Astrophysics Senior Review,explains Lauren Weiss of the Astro-PH journal’s Astrobites blog.

In Barack Obama’s proposed 2013 budget for Nasa, the president would cut Kepler’s funding from $19.6 million to $13.6 million next year, then cut cash to the space telescope entirely from 2014.

So far, Kepler has confirmed the existence of 61 planets outside our solar system. That includes Kepler 22b — an Earth-like planet orbiting a Sun-like star, and Kepler 16b — the Tatooine-like planet that orbits two stars.


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