Scientists Expect To Find Life In Space's 'Goldilocks' Zones

The search for planets outside our solar system is often stranger than fiction.

There are more planets than stars in our galaxy.

Unlike scientists of previous generations, this is something researchers can today say with a confidence that has had a profound impact on our understanding of the potential for finding life on worlds other than our own.

To put it into perspective, the Milky Way contains an estimated 400 billion stars. If each of those stars, like our own Sun, has not just one orbiting planet but potentially several, the numbers become almost painfully hard to comprehend.

And that's just within the realms of one galaxy.

That's at least one planet for every star you see when you look up at night. Image: Joshua Moll

But the planet hunting telescope responsible for the catalog of discoveries that lead to this understanding -- NASA's Kepler space telescope -- is reaching the end of its life.

After a spectacularly successful nine years in space, NASA announced in March Kepler was beginning to run out of fuel and is expected to cease operations in the coming months.

"Kepler really has revolutionized how we look at the night sky," Dr. Andrew Rushby, a scientist at NASA's Ames Research Centre told ten daily.

"Around every star in the galaxy, we’re confident now that there’s probably at least one planet -- so more planets than stars without a doubt and that’s something that Kepler has shown us."

Originally launched in 2009 on an intended three-and-a-half year mission to determine if earth-like planets are common or rare outside our own solar system, the telescope has so far discovered 2,680 confirmed exoplanets over two missions. A further 2,723 candidate exoplanets stand the chance to join that list, following further study.

What Are Exoplanets?

Worlds orbiting stars other than our own Sun are known as 'exoplanets' and, while humanity can't physically visit them right now -- the closest one discovered sits comfortably out of reach at 4.5 light-years away from earth (40 trillion kilometres) -- scientists can still study them in the hope of identifying signs of life.

Rushby, a NASA Postdoctoral Fellow and exoplanet expert currently touring Australia for National Science Week, is one such scientist using the Kepler telescope to do just that.

"Exoplanets are incredibly diverse," Rushby said.

"They don’t really follow a single kind of pattern or a single kind of form, and we have to look at each one individually to get a handle on what they are, what they’re made of and how they’ve changed over time.”

This diversity encompasses every aspect of a planet, including their size, which can range from a gas giant larger than Jupiter to near the size of Earth, to their orbit, which can be so close to their respective sun a 'year' lasts only a few days.

Rushby's favourite exoplanet, GJ667Cc, orbits a single small star which itself orbits a double star system.

"So sunsets and sunrise there would be spectacular," he said.

On Thursday, European astronomers reiterated just how extreme exoplanets can be after detecting what appears to be iron and titanium vapour in the atmosphere of the hottest exoplanet scientists are aware of. Kelt-9b is three times the size of Jupiter, and reaching temperatures of up to 4,327 degrees celsius, is hotter than some stars.

KELT-9b is so close to its hot blue host star that the stellar disc covers a sky area seventy times larger than the Sun in Earth sky, heating the atmosphere so much that it contains vapours of atomic metals. Image: Denis Bajram

But a number of these exoplanets -- at least 30 of those confirmed discoveries by Kepler -- are less than twice the size of Earth and exist within their star's habitable zone.

"This is a region around a star where liquid water may be present on the surface of an earth-like planet," Rushby explained.

These 'Goldilocks' zones are where scientists expect to find life.

What's Next In The Search For Habitable Worlds?

The Kepler telescope changed how we saw the universe in less than a decade, so it's unsurprising its upcoming decommission has even got its own Twitter hashtag.

“But that doesn’t mean the science is finished,” Rushby assures.

“There's thousands, probably, of PHD thesis' worth of data still to be analysed. There’s, as it stands right now, over 2000 planet candidates which will have to be confirmed."

There is also more than one NASA telescope waiting to take up Kepler's mantel, including the Transiting Exoplanet Survey Satellite (TESS) which launched in April to survey a sky area 400 times larger than that observed by Kepler, and the James Webb Space Telescope, which with an expected launch date in 2020, represents the future in astronomical observation.

But Rushby says if we are to find life on another planet, it's more likely to be found first in our own solar system first, due to the greater accessibility to its planets and the number of missions focusing on them.