TRAPPIST-1 is a small red dwarf star some 39 light years away which has been found to have seven Earth-like planets in orbit around it. Six could potentially support life. Picture: NASA

The red dwarf star TRAPPIST-1, which sits in the constellation of Aquarius, was thought a year ago to have three planets in orbit around it.

This initial discovery caused scientists to keep a close eye on the star. But now a review of data published in the science journal Nature has exposed a wealth of worlds which are generally thought of as being rare.

Seven Earth-sized exoplanets. All are thought to be mostly made up of rock. And six are judged to be just far enough away from their star to keep water in its liquid state.

That means they may have the potential to sustain life as we know it.

“This is really the first time we have seven planets that we can say are in terrestrial zone, and it’s really, really surprising,” said study co-author and astronomer at the Université de Liège in Belgium, Michaël Gillon.

Out of this world ... The TRAPPIST-1 red dwarf star solar system and its seven ‘Earth-like’ planets compared to Jupiter and its moons, and our own Solar System. Source: NASASource:Supplied

RED DWARF WORLDS

TRAPPIST-1 is a small red dwarf star — barely bigger than the planet Jupiter — on the cooler end of the spectrum. But red dwarfs are the most common type of star in our galaxy.

Up to 50 per cent of the Milky Way is made up of red dwarfs.

That there are seven potentially habitable worlds in orbit around just one of these has enormous implications for the odds of there being alien life.

And any such life is likely to be very odd, given the alien environment.

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But co-author Amaury Triaud from the Institute of Astronomy in Cambridge, UK, says it is very hard to know if such an abundance of Earth-like planets is common.

As for hosting life, there are complications.

Professor Gillon and colleagues emphasise that further observations are required to thoroughly detail the nature of these planets — especially the seventh. This outermost planet has not yet had its orbital period defined.

An extrapolation of the TRAPPIST-1 red dwarf planets compared to the rocky worlds in our own Solar System. Picture: NASASource:Supplied

GETTING A LIFE

Debate continues raging among astrobiologists and astrophysicists as to whether or not planets around small — but active — red dwarf stars can hold an atmosphere long enough for microbial life to take hold.

This is because such worlds need to orbit close to the star for the required warmth, which in turn brings them within the reach of solar flares. Such flares could strip away atmospheres over time, as well as regularly irradiate the planet’s surface.

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These planets are also likely to be ‘tidal locked’ — orbiting with one face permanently turned towards the star, and the other in perpetual darkness. The result would be an environment utterly unlike our own.

“It’s possible their atmospheres are very similar to the Earth, or Venus, or something completely different,” Professor Gillon says.

Earth and the Sun, left, compared to Kepler 452b and its star. Picture: NASASource:Supplied

ALIEN COMPANION

The discovery of potentially habitable exoplanets around TRAPPIST-1 follows a similar announcement by NASA in July 2015: The discovery of ‘Earth’s cousin’, or Kepler 452b.

This world is exciting as it is just 1.6 times larger than Earth, and in orbit around a yellow star similar to our own Sun.

While very little can be discerned from the ‘blip’ the planet makes when it passes between us and its star, it is believed it is both rocky and capable of supporting an atmosphere.

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Once again, exactly what form the planet takes is almost entirely speculation.

Chances are, Kepler 452b is another Venus.

At six billion years, it’s an old world. It is likely to have double our gravity.

But its star is both 20 per cent larger than our own and puts out about 10 per cent more energy.

This means Kepler 452b, which sits on the inner edge of the ‘goldilocks zone’, is likely to be a bit steamy.

That means a climate cascade towards a greenhouse effect — like Venus — is likely.

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