Planet search more than a numbers game

The odds of finding life forms on other planets are shortening, but it is more than just a numbers game.

NASA scientists have doubled the number of confirmed planets that we know about after identifying a further 1,284 in the masses of data being beamed back by the orbiting Kepler telescope. But while the probability that there’s extra-terrestrial life out there would almost appear to be a certainty, finding it and knowing we have found is a completely different and more difficult challenge, says University of Melbourne astrophysicist Dr Katie Mack.

The new analysis has identified a further nine earth-like rocky exoplanets orbiting their suns in the so-called “goldilocks” zone, where liquid water could exist on the surface and potentially support life, increasing the total of known such targets to 21.

Exoplanets are planets outside our solar system. The problem is that the new planets are “transiting” planets that can only be “seen” when they move in front of their suns. That makes it difficult to image them directly to assess their chemical properties. Such information is crucial to even guessing life might exist on a planet, and that information depends not so much on increasing the inventory of planets, but on constantly boosting the strength of high resolution telescopes.

“The new planets confirmed from Kepler are not so much immediate targets to follow up right now, but they are telling us about how common these planets are in the galaxy – this is the big thing out of this announcement,” says Dr Mack, from the School of Physics.

“Transiting planets are not the easiest things to study in terms of looking at them directly, though it isn’t impossible. But if you want to look at a direct image of a planet it is easier if you are seeing it face on around a sun, not transitioning in front of it,” she says.

The new discoveries have all come from applying a new statistical technique to analysing the Kepler data to infer the existence of the new planets from the dimming they cause when they pass in front of their stars.

“Ideally we need to look at the planet itself, which is something Kepler can’t do,” she said. “Ideally we need to be able to look at the planet from a direct image and learn something about its atmosphere and what it is made of,” Dr Mack says.

“We don’t know a lot about these new ones other than their size and the distance from their suns. Kepler is much better at finding planets than telling us a lot about them.”

The key, she says, will be the ongoing effort to increase the power of our telescopes. “It is probably simply a matter of time before we have sufficient resolution to study the atmospheres of more and more exoplanets.’’

The ability of scientists to directly image exoplanets will be enhanced in October 2018 when the new infrared James Webb Space Telescope is launched from French Guiana. The project is an international collaboration between NASA, the European Space Agency and the Canadian Space Agency.

But confirming life on a planet is difficult.

“Life is hard to confirm. If we look at a planetary atmosphere and we are able to figure out what chemicals are in the atmosphere, which we have been able to do a for a couple of exoplanets, we might be able to find a chemical signature that could suggest that life were possible.

“But to confirm life we would need to see a chemical signature that can’t happen without life, and that is always going to be challenging,” Dr Mack says.

According to NASA, almost 5,000 potential exoplanet targets have been identified of which 3,200 have now been verified. Of these 2,325 were discovered by Kepler, which was launched in 2009.

Meantime the hunt for more exoplanets will speed up in August 2017 when NASA is due to launch the new Transiting Exoplanet Survey Satellite. It is expected to catalogue over 3,000 exoplanet candidates over its two-year mission.

Banner Image: An artist’s impression of planets passing in front of their stars. Artwork. W Stenzel/NASA