TRAPPIST

New solar system found to have 7 Earth-size planets

seven planets
seven planets

Astronomers have just identified a nearby solar system hosting seven Earth-sized planets. Most intriguing: Three planets that orbit its central star — known as TRAPPIST-1 — may even be within a habitable zone. That means they fall within a region that could support life as we know it. As such, these newfound worlds are good sites to focus a search for alien life.

TRAPPIST-1’s big planetary family also hints that many more cousins of Earth may exist than astronomers had thought.

“It’s rather stunning that the system has so many Earth-sized planets,” says Drake Deming. He’s an astronomer at the University of Maryland in College Park. It seems like every stable spot where a planet could be, there is an Earth-sized one. And that, he adds, “bodes well for finding habitable planets.”

Astrophysicist Michaël Gillon works at the University of Liège in Belgium. He was part of a team that last year announced they had found three Earth-sized planets around TRAPPIST-1. This dwarf star is only about the size of Jupiter. It’s also much cooler than the sun. And it’s a relative neighbor to Earth, a mere 39 light-years away in the constellation Aquarius.

Follow-up observations with the Spitzer Space Telescope and additional telescopes on the ground now show that what first had appeared to be a third planet is actually a quartet of Earth-sized ones. Three of these may be habitable.

If those planets have Earthlike atmospheres, their surfaces may even host oceans of liquid water. Or at least that’s what Gillon and his colleagues reported online February 22 in Nature. Their data also offer signs of a seventh, outermost planet.

How they spotted the new worlds

All seven planets were detected by watching how their star dims as each passes — or transits — in front of it. Scientists measured how much of the star’s light each transit blocked from Earth’s view. Knowing how big a planet would have to be to do that, the astronomer calculated that all seven must have roughly the same radius as Earth.

Those dips in starlight also showed how fast the planets orbit their star: The innermost one makes a round trip in 1.5 Earth days. The outermost one takes roughly 20 days.

The planets’ masses range from about half to 1.5 times that of Earth. To figure that out, the researchers looked at the way the six inner planets tug on each other. The mass and size data then allowed the team to calculate the planets’ densities. All of this suggested that the inner six are rocky, as Earth is.

The length of each planet’s day — how quickly it spins on its axis — may sync with its sun’s orbit. That would make the innermost planet’s day 1.5 Earth days long and the outermost one’s 20 Earth days long. That would be like Earth rotating once in 365 days…

Astronomers Find Seven ‘Earth-Like’ Planets Orbiting a Cool Star

Astronomers say they’ve discovered seven Earth-sized planets in tight orbit around a cool, dim star about 39 light-years from us—and all seven are located in the habitable zone that could potentially host life. This is the first time a planetary system oriented to this kind of star has been detected—and its discovery holds the potential to lead us to a lot more exoplanets. An international team of researchers reported their findings in a letter published today in the journal Nature.

“It’s the first time we have seven planets in this temperate zone … that can be called terrestrial,” lead author Michaël Gillon, of Belgium’s Université de Liège, said in a press briefing. “So many is really, really surprising.”

TRAPPIST-1 is an ultracool dwarf star that’s 1/80th the brightness of the Sun and similar in size to Jupiter. All seven planets in its system are within 20 percent of the size and mass of Earth, and their density measurements indicate they’re likely of rocky composition. They’re clutched by TRAPPIST-1 in tight orbits—all would fit well within the orbit of Mercury. But unlike in our solar system, where such closeness to a hot star renders life impossible, the TRAPPIST-1 planetary system, with its cool celestial heart, could potentially host liquid water and organic molecules.

The first three planets were spotted in early 2016 by some of the same researchers involved in the current findings, including Gillon. As the planets cross in front of the star during their orbits, they cause the star, which emits light in the infrared, to briefly dim. Such transits, or eclipses, provide a common way for astronomers to detect exoplanets.

Using telescopes in Chile, South Africa, Spain, the UK, and Morocco, the researchers followed up on these transit signals multiple times in 2016, most notably in late September with a 20-day, nearly continuous monitoring of the star using the Spitzer Space Telescope, currently located about 145 million miles from us in an Earth-trailing orbit around the Sun. By moving our view off the Earth, researchers were able to detect 34 separate transits. This turned out to be the result of seven planets—six in near-resonant orbit—crossing in front of their home star. (The transit of the seventh was detected only once, so the orbit of this planet, known as TRAPPIST-h, hasn’t been determined yet.)

The planets have relatively narrow surface temperature fluctuations—about 100 degrees—despite their proximity to their home star. (Compare that to Mercury, which has temperature variations of nearly 1200F.) The researchers write that three of the planets—E, F, and G—“could harbor water oceans on their surfaces,…