Seven planets orbiting one star. All of them roughly the size of Earth. A record three in what is considered the habitable zone, the distance from the host star where liquid water could exist on the surface. The system a mere 40 light-years away.
The latest impressive additions to the world of exoplanets orbit the dwarf star known as TRAPPIST-1, named after a European Southern Observatory telescope in Chile.
Previously a team of astronomers based in Belgium discovered three planets around this dim star, but now that number has increased to include the largest number of Earth-sized planets found to date, as well as the largest number in one solar system in the habitable zone.
This is a very different kind of sun-and-exoplanet system than has generally been studied. The broad quest for an Earth-sized planet in a habitable zone has focused on stars of the size and power of our sun. But this one is 8 percent the mass of our sun — not that much larger than Jupiter — and with a luminosity (or energy) but 0.05 percent of that put out by our sun.
The TRAPPIST-1 findings underscore one of the recurring and intriguing aspects of the exoplanet discoveries of the past two decades — the solar systems out there are a menagerie of very different shapes and sizes, with exoplanets of a wild range of sizes orbiting an equally wide range of types and sizes of stars.
Michaël Gillon of the STAR Institute at the University of Liège in Belgium, and lead author of the discovery reported in the journal Nature, put it this way: “This is an amazing planetary system — not only because we have found so many planets, but because they are all surprisingly similar in size to the Earth.”
At a NASA press conference, he also said that “small stars like this are much more frequent than stars like ours. Now we have seven Earth-sized planets to study, three in the habitable or ‘Goldilocks’ zone, and that’s quite promising for search for life beyond Earth.”
He said that the planets are so close to each other than if a person was on the surface of one, the others would provide a wonderful close-up view, rather like our view of the moon.… Read more