The red dwarf star TRAPPIST-1, which sits in the constellation of Aquarius and barely the size of Jupiter, 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 study published in the science journal Nature has exposed a wealth of worlds which are generally thought of as being rare.
NASA has just made the incredible announcement: Seven Earth-sized exoplanets around the one star. All are thought to be mostly made up of rock and could potentially support liquid water on their surfaces.
Three are close to the star, and may be a little too hot to hold much liquid water.
One – the seventh – may be an ice world.
But three of them fall comfortably in the “habitable zone” – orbits neither too hot nor too cold.
That means they may have strong potential to sustain life as we know it.
New record! We’ve found 7 Earth-sized planets around a single star outside our solar system; 3 in habitable zone: https://t.co/GgBy5QOTpK pic.twitter.com/NEavRSXDU2
— NASA (@NASA) February 22, 2017
Around a nearby, cold, small star we found 7 rocky Earth-size planets, all of which could have liquid water – key to life as we know it. pic.twitter.com/C2JWjDfBdK
— NASA (@NASA) February 22, 2017 A size comparison of the planets of the TRAPPIST-1 system, lined up in order of increasing distance from their host star. The planetary surfaces are portrayed with an artist’s impression of their potential surface features, including water, ice, and atmospheres. Picture: NASA
CROWDED WITH HOPE
“This is really the first time we have seven planets that we can say are in the terrestrial zone, and it’s really, really surprising,” said study co-author and astronomer at the Université de Liège in Belgium, Michaël Gillon.
Thomas Zurbuchen, associate administrator of the Science Mission Directorate at NASA Headquarters in Washington, said: “The discovery gives us a hint that finding a second Earth is not just a matter of if, but when. Are we alone out there, we are making a leap forward to answering this question.”
"Finding a second Earth is not just a matter of IF but WHEN" – @NASA on 7 Earth-sized planets orbiting single star https://t.co/1gzCf0x21u pic.twitter.com/fWRsY1HCto
— BBC Breaking News (@BBCBreaking) February 22, 2017
The takeaway from all this is, “we’ve made a crucial step toward finding if there is life out there,” said the University of Cambridge’s Amaury Triaud, one of the researchers.
The potential for more Earth-size planets in our Milky Way galaxy is mind-boggling. Scientists made the discovery using the Spitzer space telescope.
Following the announcement, NASA tweeted: “Finding life elsewhere is one of three overarching goals for @NASA science. We are in the middle of a ‘gold-rush’ of this research right now.”
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: NASA
REACTIONS TO INCREDIBLE DISCOVERY
Today’s announcement by @NASA of a "discovery beyond our solar system" is simply breathtaking: https://t.co/zQ2kyfSz83
— Eric Holthaus (@EricHolthaus) February 22, 2017
TRAPPIST-1 "provides humanity w/ its first opportunities at discovering evidence of biology beyond the Solar system"https://t.co/iav8Z6jMUY pic.twitter.com/IiDr777SmJ
— Eric Holthaus (@EricHolthaus) February 22, 2017 — Jason Taub (@POTUS131) February 22, 2017 This NASA supplied artists’ representation of the TRAPPIST-1 solar system shows the possible relative features of its seven Earth-sized planets. Source: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.
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.
Given TRAPPIST-1 is just 39 light years away, this opens up the opportunity for much more detailed observation of the planets as a new generation of telescopes come online, including the Hubble-replacement space-based telescope, the James Webb Telescope next year.
Another specialist planet-hunter will also be launched in 2018, the Transiting Exoplanet Survey Satellite.
An extrapolation of the TRAPPIST-1 red dwarf planets compared to the rocky worlds in our own Solar System. Picture: NASA
THE GRAVITY OF THE SITUATION
With seven worlds all orbiting so close to one another, they may be ‘pulling’ on each other in unusual ways.
“It’s a very small, very compact system,” says ays Emmanual Jehin, a co-author on the study. “The seven planets are all included well inside the orbit of Mercury.”
Such gravitaitonal ‘squeezing’ could heat up the planets’ cores.
This is significant.
It could do to the seventh ice world what is happening with moons like Europa and Enceladus: melt water under its ice surface. Again, this brings with it the potential for life.
It could also contribute towards giving the worlds a magnetic field – a protective shield against the red dwarf’s solar flares.
“This star is extremely quiet compared to other very small stars. It’s very calm compared to Proxima Centauri, for example,” Jehin says. “If we’re optimistic, at least five of the planets—maybe not the first and maybe not the last—but at least five could have some liquid water on the surface, if they have atmospheres and the right pressures.”
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.
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: NASA
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.
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.