Seven Earth-like planets found orbiting star could hold life
THE SOLAR SYSTEM AN IDEAL LABORATORY FOR STUDYING ALIEN WORLDS, RESEARCHERS SAY
Anewfound solar system just 39 light years away contains seven warm, rocky, Earth-like planets, scientists say. The discovery, reported yesterday in the journal Nature, represents the first time astronomers have detected so many terrestrial planets orbiting a single star. Researchers say the system is an ideal laboratory for studying alien worlds and could be the best place in the galaxy to search for life beyond Earth.
“Before this, if you wanted to study terrestrial planets, we had only four of them and they were all in our solar system,” said lead author Michal Gillon, an exoplanet researcher at the University of Liege in Belgium. “Now we have seven Earthsized planets to expand our understanding. Yes, we have the possibility to find water and life. But even if we don’t, whatever we find will be super interesting.”
The newly discovered solar system resembles a scaleddown version of our own. The star at its centre, an ultracool dwarf called TRAPPIST-1, is less than a tenth the size of the sun and about a quarter as warm. Its planets circle tightly around it; the closest takes just a day and a half to complete an orbit, the most distant takes about 20 days. If these planets orbited a larger, brighter star they’d be fried to a crisp. But TRAPPIST-1 is so cool that all seven of the bodies are bathed in just the right amount of warmth to hold liquid water. And three of them receive the same amount of heat as Venus, Earth and Mars, putting them in “the habitable zone,” that Goldilocks region where it’s thought life can thrive.
Still, “Earth-like” is a generous term to describe these worlds. Though the planets of the TRAPPIST-1 system resemble Earth in terms of size, mass, and the energy they receive from their star, there’s a lot that makes our planet liveable beside being a warm rock.
Further observation is required to figure out what the TRAPPIST-1 planets are made of, if they have atmospheres, and whether they hold water, methane, oxygen and carbon dioxide — the molecules that scientists consider “biosignatures,” or signs of life.
The closest star to our solar system is Proxima Centauri, some 4.3 light years away. Using our current technology, travel there would take thousands of years — a short journey relative to size of the universe.
No, last night’s news conference by Nasa did not announce that it had found intelligent life forms in the White House.
But National Aeronautics and Space Administration (Nasa) officials were expected to give details of a major discovery beyond our solar system.
While Nasa was keeping tight-lipped before last night’s news conference, it had said the conference was about “exoplanets”. So what is an exoplanet? According to Elizabeth Howell at space.com, an exoplanet is the name given to a world that orbits any star other than our own Sun.
The closest star to our solar system is Proxima Centauri, some 4.3 light years away. Using our current technology, travel there would take thousands of years — and that’s a short journey in travel times relative to the rest of the size of the universe.
Last August, scientists revealed Proxima Centauri has an Earth-sized planet in orbit around it, that they have called Proxima B. Additionally, the rocky globe circling moves in the so-called “Goldilocks zone” that would make liquid water on its surface a possibility.
Why Goldilocks? Just like the children’s fairy tale; not too close to the sun so that it’s so hot that any water would be immediately vaporised once the surface temperature reaches 100 degrees Celsius — the boiling point of water, when it turns to steam; and not too cold, so far away from the sun that the water is deeply frozen, below 0 degrees Celsius.
The hunt for exoplanets is a relatively new phenomenon in space exploration.
The first to be discovered was 51 Pegasi b — also called Dimidium — in 1995 by two European astronomers.
Telescopes
Michel Mayor and Didier Queloz were peering through their terrestrial-based telescopes looking for “wobbling suns”.
Basically, a planet is big — and has mass, even if it’s made up of huge volumes of mostly gas. The bigger the planet, the more mass — and more mass means more gravity, or pull. We know gravity as the force that makes things fall, or keeps us stuck to the Earth.
But a planet’s gravity when it circles close to a sun will cause the light from that sun to wobble as it transits — hence “wobbling suns”. Mayor and Queloz realised that if they looked for suns that were wobbling, that effect was caused by an orbiting planet.
That eureka moment led to the discovery of 51 Pegasi b — confirming that Earthlike planets could exist elsewhere beyond our solar system. The more planets that circle suns, the more chances of finding planets within the Goldilocks zones that could support life.
And just as on Earth, finding water, preferably in its liquid form, is the key step to finding life.
Once Mayor and Queloz knew what to look for, the search for exoplanets took off. The trouble, though, was that the planets that made suns wobble were big, and gaseous — when you’re close to a sun it’s hot, and most elements on a planet are in their gas state.
The first batch of exoplanets discovered were all large and hot — “hot Jupiters” — all close to the sun in a very quick transit. The transit had to be close for the earth-based telescopes to pick up the wobble over a period of days of observation.
By 2005, teams of astronomers discovered several hundred exoplanets. But the real breakthrough came when Nasa put the Kepler space telescope into orbit.
It began operations in March 2009 and gave the first real glimpse of nearly 150,000 stars within its fixed field of view. Kepler measures the brightness of those stars and can detect when planets move across the suns — not just the big gaseous “hot Jupiters”.
So far, 3,449 exoplanets have been confirmed.
Scientists say that 1,264 of these are ice giants — planets orbiting so far from their suns that everything is in deep freeze — far too cold for liquid water, and hence far too cold to sustain life.
Another 1,043 of these exoplanets are gassy giants — orbiting too close to their suns to make life sustainable.
Disagreement
Then there are 781 exoplanets that fall into the “superEarth” category. Astronomers can’t agree on an exact scientific definition of a “superEarth”, but agree generally that it’s a planet larger that this blue Earth we all travel around our Sun on, but is smaller than the really big planets in our solar system — Uranus and Neptune. These planets could have atmospheres and might be rock, ice, gas, or metal.
One of the “super-Earths” — 55 Cancri e — was believed to be the first known planet to consist largely of diamond, due in part to the high carbon-to-oxygen ratio of its host star.
What’s important is that these “super-Earths” have mass — and most have a mass 10 times greater than Earth’s.
These “super-Earth” planets fall outside the Goldilocks zone but may or may not be able to sustain liquid water on or under their surfaces.
Another 13 exoplanets are classified as “unknown”. We simply don’t know now what they are, what their composition is, but know that they exist.
And then there are the 348 exoplanets that are our best hope of finding the conditions for life to exist — the terrestrials.
These fall into the sweet spot — not too hot, not too cold — and likely with liquid water.
On Nasa’s radar
It’s these that Nasa have been taking a really close look at.
No one believes for a minute that Nasa has found life. Last night’s news conference, however, was expected to detail what Nasa’s best minds believe as be-
Nasa was expected to detail what its best minds believe as being the optimal place where life might exist — the most Earthlike planet found yet, possibly with an atmosphere of oxygen.
ing the optimal place where life might exist — the most Earthlike planet found yet, possibly with an atmosphere of oxygen.
Then there’s the question of what do we mean by life? Just days ago, scientists discovered life trapped in crystals that could be 50,000 years old.
The bizarre and ancient microbes were found dormant in caves in Naica, in Mexico’s northern Chihuahua state, and were able to exist by living on minerals such as iron and manganese, said Penelope Boston, head of Nasa’s Astrobiology Institute.
“It’s super life,” said Boston, who presented the discovery last Friday at the American Association for the Advancement of Science conference in Boston. She said the creatures were like time machines.
If confirmed, the find is yet another example of how microbes can survive in extremely punishing conditions on Earth.
The life forms — 40 different strains of microbes and even some viruses — are so weird that their nearest relatives are still 10 per cent different genetically. That made their closest relative pretty far away, about as far away as humans are from mushrooms, Boston said.
Nasa wouldn’t allow Boston to share her work for outside review before Friday’s announcement so scientists couldn’t say much. But a University of South Florida biologist, Norine Noonan, who wasn’t part of the study but was on a panel where Boston presented her work, said it made sense.
Versatile
“Why are we surprised?” Noonan said. “As a biologist I would say life on Earth is extremely tough and extremely versatile.”
This isn’t the oldest extreme life. Several years ago, a different group of scientists published studies about microbes that may be half a million years old and still alive. Those were trapped in ice and salt, which isn’t quite the same as rock or crystal, Boston said.
The age of the microbes was determined by outside experts who looked at where the microbes were located in the crystals and how fast those crystals grow.