‘Earths Are Common,’ NASA Scientist Says

source: Toronto Star
by: Cathal Kelly

We are surrounded by dozens of habitable planets. We just can’t see them yet, according to a researcher.

In his new book, How to Find a Habitable Planet, geoscientist Jim Kasting suggests that the chances that each of the stars you see in the sky is being rotated by a planet capable of sustaining life are surprisingly high.

Kasting is the chair of NASA’s Exoplanet Exploration Program Analysis Group.

“I’m very optimistic. I think Earths are common,” Kasting said. “If you take any given type of solar star, the chances of finding an Earth-like planet are reasonably good … the odds (of any star being orbited by a habitable planet) might be somewhere between a tenth and a half.”

Let’s put that into perspective. The closest star to our solar system is Alpha Centauri. It’s more than four light years away. That’s about 40 trillion kilometres.

We don’t as yet know if an Earth-like planet orbits Alpha Centauri because we can’t see clearly enough. Stars are very bright. Planets are very dim. One washes out the other.

So this search starts out very basically. Kasting’s initial checklist for habitable planets contains only two boxes.

First, there is its composition – it must be a rock, like Earth, as opposed to gaseous, like Jupiter. Second, it must occupy the proper distance from its sun, so that any incipient life is neither baked nor frozen.

“We think it also needs liquid water … we don’t know for sure that life requires liquid water. We just know that all terrestrial life does,” Kasting said.

The chances increase if scientists are able to detect carbon dioxide, oxygen, ozone and gases like methane or nitrous oxide which are produced by organisms – at least as we currently define them. It stands to reason that the planet should be about the same size as our own.

The current methods of discovering planets cue on the stars they orbit around. The most common is Doppler spectroscopy – observing small shifts in the star’s own orbit and speed relative to Earth caused by the gravitational force exerted by the unseen planet.

Using this blunt instrument, scientists have thus far discovered about 400 planets outside our own solar system. Most of those are gigantic – the size of Jupiter or so – and unlikely for a variety of reasons to fit the habitation bill.

However, we’ve made some recent strides in detection methods. The advent of powerful space-based telescopes increases the sharpness of our view, and expands the astronomer’s tool box.

“What we really need … are telescopes called Terrestrial Planet Finders,” said Kasting. TPF’s can work in the visible or infrared spectrum. A visible spectrum TPF probably requires an aperture of 8 m, which is more than three times bigger than the Hubble telescope.

“The difficult thing is to look at an area very close to a bright star, and block out the light so that you just see the light from the planet,” Kasting said.

The best method, according to Kasting, is to build two craft – one housing the telescope, and the other comprised of a shield to block out light that floats at an angle above the first craft.

The technology to build such devices exists. But the money does not.

There is currently a telescope in space doing the number crunching that might precede TPFs. The Kepler telescope has been in space for about a year searching for, amongst other things, statistical evidence of Earth-like planets.

Kepler is staring at one small patch of the vast Milky Way, monitoring the brightness of 150,000 stars. If an Earth-sized planet passes in front of any of those stars, the nearly imperceptible dimming will be captured by Kepler. There’s an element of luck involved, but once that data is interpreted, Kasting’s 10-50 per cent educated guess will have an empirical benchmark.

“There’s lots of activity. Kepler’s up there now. (Another, better space telescope) SIM Lite could be up there, if the astronomers choose to fund it in the next few years. And TPF - we actually got started building one of those three or four years ago. Until the money ran out.”

Where are we now?

“SIM is sitting in (NASA’s California-based) Jet Propulsion Laboratory, half-finished … They’ve designed the hardware. It could be built very quickly … If they got funding this year, they could launch it in about four years from now.”

SIM is specifically designed to search for Earth-sized planets.

If Kasting’s theories bear fruit, this might provide an entirely new rationale for deep-space exploration. But if TPFs are a ways off, that’s a task of an entirely different order of difficulty.

“I’m a science fiction fan, too. Maybe we’ll get there someday. But that’s well off into the future,” Kasting said. “I’m most interested in what we can do now – which is look at these planets, and try to figure out if they’re habitable, and then, if they’re inhabited.”