200 billion reasons why we’re not alone and one is coming tonight

NASA has made a major announcement about conditions for life existing on one of Saturn’s 62 moons. That, it turns out, is just the beginning.

IT’S the question at the heart of humanity itself, the key to everything we know of ourselves, of our world and even of our gods: Are we alone in the universe?

And now the answer is closer than ever: There are up to 200 billion habitable planets in our galaxy and we may not even be alone in our solar system.

In a few hours NASA is expected to announce that it has found a possible indicator of life on one of Saturn’s 62 moons.

The Cassini spacecraft orbiting Saturn has already detected underground saltwater oceans on the moon Enceladus and Australian National University astrophysicist Brad Tucker says he is “95 per cent” sure that NASA will announce it has discovered changing levels of methane in the atmosphere – a phenomenon driven by organic life, at least here on Earth.

A handy map of the Milky Way, which could contain up to 200 billion habitable planets.

But if that wasn’t staggering enough, consider this. Dr Tucker, a research fellow at the Research School of Astronomy and Astrophysics at Mt. Stromlo Observatory, says it is now estimated that one in five stars have planets similar to earth, that there is an average of 100 billion stars in a galaxy and that there are about two trillion galaxies in the universe.

“Based on what we see of other galaxies 100 billion makes sense and one in five stars has earth-like planets around it,” he told news.com.au.

“So we’re talking about 20 billion earth-like planets in one galaxy alone.”

Extrapolating that out to the whole universe, this means that there are up to 40 billion trillion potentially habitable planets out there.

A diagram of the final orbits of the spacecraft Cassini around Saturn. It will first pass several times just outside the rings, then between the rings and the planet. Credit: NASA/JPL-Caltech

Even just in our own galaxy, the Milky Way, there are believed to be between 300 billion and a trillion stars, meaning 60 billion to 200 billion ones with potential earths holding the right conditions for microorganisms.

“How likely would bacteria and simple organisms be to form intelligent life, we don’t know. But even if it’s 0.001 per cent you still get tens of millions of planets,” Dr Tucker says.

“I just go by the numbers.”

Even assuming that one in 100,000 probability, that would mean 600,000 to 2,000,000 alien inhabited planets in the Milky Way alone.

“And that’s just our galaxy. And maybe that percentage is low!”

What alien life might look like, although probably not.

But the real kicker? “That’s not including the moons.”

This brings us back to our own solar system, where Cassini has been cruising around the moons of the gas giants Jupiter and Saturn.

“There are four or five moons of Jupiter or Saturn that look like they’re very good places to host life and that’s amazing,” says Dr Tucker.

Unfortunately there’s often a catch: “Titan has rivers and lakes but they’re ammonia.”

Bummer.

This is what makes the potential of Enceladus, whose underground oceans are saltwater, extraordinary.

“There will be an announcement tomorrow by NASA and we know they have found oceans under the crust,” Dr Tucker says.

In a tantalising teaser, NASA posted on its website this week:

“NASA will discuss new results about ocean worlds in our solar system from the agency’s Cassini spacecraft and the Hubble Space Telescope during a news briefing 11am PDT (Pacific Daylight Time) on Thursday, April 13 (4am Friday AEST).

“These new discoveries will help inform future ocean world exploration -- including NASA’s upcoming Europa Clipper mission planned for launch in the 2020s -- and the broader search for life beyond Earth.”

Even on our closest neighbour Mars changing levels of methane have been detected, again a possible indication of microbial life. And now?

“It’s not even just planets we’re finding these things on, we’re finding them on moons,” Dr Tucker says.

“That’s why people are excited.”