The first step in finding life outside our own planet is to find a planet like our own: small, rocky, and at just the right distance from the star that liquid water could exist on its surface.
That’s why a press conference yesterday from NASA, which was planned and announced on Monday, is so exciting: The space agency, along with partners around the world, has found seven potentially Earth-like planets orbiting a star called “Trappist-1”, about 40 light-years away. The discovery sets a record for both the most Earth-size planets and the most potentially habitable planets ever discovered around a single star.
“It’s the first time that so many planets of this kind are found around a same star,” Michaël Gillon, the lead author of the Nature paper announcing the discovery, said in a press conference. “The seven planets … could have some liquid water and maybe life on the surface.”
— NASA (@NASA) February 22, 2017
Three of the planets – classified as Trappist-1e, f and g – orbit in the star’s “habitable” or so-called “Goldilocks” zone, meaning water can most likely exist on the surface of them due to suitable temperatures. One of them, Gillon said, has a mass “strongly suggest a water-rich composition.” And it’s possible that the other four could have liquid water, too, depending on the composition of their atmospheres, the astronomers said.
Trappist-1 and its orbiting exoplanets are located in the constellation Aquarius. And it’s a solar system very different from our own.
For one, Trappist-1 is a tiny, “ultra-cool” dwarf star. It’s cool because it’s small: just about a tenth of the mass of our sun and about one-thousandth as bright. But its low mass allows its planets to orbit it very closely and remain in the habitable zone.
The strange planetary system is quite compact, with all of the planets orbiting their star closer than Mercury orbits the sun. Specifically, the distance at which the planets orbit their star is comparable to the distance of Jupiter to its moons.
“If you were on the surface of one of these planets, you would see the other ones as we see the moon, or a bit smaller,” says Michaël Gillon, an astronomer at the University of Liège in Belgium. “The view would be very impressive.”
All the planets are believed to be rocky, and are all believed to be around the size of Earth, give or take 10 to 20 percent. Julien de Wit of MIT, one of the astronomers on the research team, says these planets have a “winning combination” of being temperate, Earth-size and ideally suited for follow-up observations with telescopes to analyze their atmospheres.
The star’s dimness is actually what led to the discoveries of these planets. When astronomers search for exoplanets, they typically look for a temporary dimming of a star — an indication that a planet has passed in front of it.
“Maybe the most exciting thing here is that these seven planets are very well suited for detailed atmospheric study,” Gillon said. The James Webb Space Telescope, set to launch in 2018, will have the ability to measure the chemical composition of exoplanet atmospheres. If the atmospheres contain telltale gases like ozone, oxygen, or methane, life could exist there. “We can expect that in a few years, we will know a lot more about these [seven] planets,” Amaury Triaud, another of the paper’s co-authors, said.
If this all sounds a bit familiar, it’s because astronomers announced three potentially habitable planets around Trappist-1 in May. Today’s reveal adds four more to the mix.
Right now, the astronomers are beginning to study the planets’ atmospheres with the telescopes they have. And from these observations, they feel fairly confident that the planets are rocky. “For detailed characterization, we will need James Webb,” Triaud said.
These planets are believed to be tidally locked to the star, with each planet having a permanent day side and a permanent night side. And because the planets are so close together, they’d appear in the sky like moons.
“With this discovery, we’ve made a giant, accelerated leap forward in our search for habitable worlds and life on other worlds potentially,” Sara Seager, a leading exoplanet expert at MIT, said during the announcement. This one star system, she said, gives astronomers many chances to look for life, and refine their understanding of exoplanets in small-star systems.
Another promising fact is that tiny, cool stars like Trappist-1 are some of the most common in the galaxy. Investigating them will likely yield more exoplanet discoveries which will help get us closer to finding places like Earth.
As NASA’s associate administrator Thomas Zurbuchen said, “Finding another Earth-like planet isn’t a matter of ‘if’, but ‘when’.“