Three newly-discovered planets orbiting 'ultra cool' dwarf star could host life, astronomers say

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Three newly-discovered Earth-sized planets orbiting a nearby dwarf star could host life, astronomers have said.

The planets, discovered by an international team of scientists using the TRAPPIST space telescope in Chile, orbit around a dim, cool dwarf star which has been named TRAPPIST-1.

At least one of the planets lies in the star's habitable zone, and scientists believe the conditions could be right on all three to support life. It's an important discovery in the search for extraterrestrial life, and future research could reveal interesting new details about the mysterious system.

TRAPPIST-1 is an 'ultracool' dwarf star, around the size of Jupiter and far less bright and warm than the Sun. Even if it can't support life, the discovery is still significant, since these kinds of stars have never been observed to have orbiting planets before.

Emmanuel Jehin, a European Southern Observatory (ESO) researcher and co-author of a study on the discovery, said in a statement: "So far, the existence of such 'red worlds' orbiting ultra-cool dwarf stars was purely theoretical, but now we have not just one lonely planet around such a faint red star but a complete system of three planets!"

After observing TRAPPIST-1 with telescopes, the scientists noticed that it appeared to dim slightly, at regular intervals. By studying further, they determined that this dimming was due to the planets passing in front of the star, proving the existence of the system.

According to the ESO astronomers, the furthest-out planet lies in the star's 'habitable zone'. This is an area of space where the temperature is mild enough for liquid water to exist, an essential building block of life as we know it.

The team believes the planets are 'tidally locked', with one side facing the planet at all times, and the other shrouded in permanent darkness. Even on the other two planets, however, the temperate boundary between the light and dark side could be the perfect place for life.

It might not be possible to scour the planets for alien creatures, but by observing them from Earth, we can get a good idea of their habitability.

By looking at the star and observing the light that passes around the planets, the scientists can deduce the rough composition of their atmospheres. The presence of certain chemicals, such as oxygen or carbon dioxide, could point to the presence of life. Earth-based observations can also reveal whether its surface is rocky, icy or metallic.

If the planets orbited a normal star, the bright light would obscure them. But since TRAPPIST-1 is so dim, it's possible to get a clear image of them from Earth.

Michael Gillon, an ESO astronomer and lead author of a study on the discovery, said: "Systems around these tiny stars are the only place where we can detect life on an Earth-sized exoplanet with our current technology."

"If we want to find life elsewhere in the universe, this is where we should start to look."

Relatively close, in cosmic terms. The star lies around 39 light years from Earth, or around 299 trillion miles. That's a long way, but it's much closer than Kepler 452B, a distant exoplanet known as 'Earth 2.0', which is around 1,400 light years away. Closer stars are obviously easier to study than distant ones, so TRAPPIST-1 could provide fertile ground for further research.

Finding life on an alien planet would obviously be the most significant scientific discovery in history. But even if the planets are dead, the team's findings would still have major implications for astronomy.

Now that scientists know ultracool dwarfs can have orbiting planets, they can start studying others for similar satellites. Around 15 per cent of all the stars in the galaxy are ultracool dwarfs, so there's potentially millions of exoplanets out there which could be able to host life.

Scientists will be able to probe further into the nature of the planets using existing technology. However, with the James Webb Space Telescope, set for launch in 2018, and the forthcoming ESO 'Extremely Large Telescope', astronomers will be able to look for signs of life in greater detail than ever before.

According to MIT's Julien de Wit, a co-author of the study, the discovery represents a "giant step" in the search for life in the universe.