The seven worlds of 75$33,67
All are Earth sized and some might have water
A new planetary system has dominated the field of exoplanetary science this year: TRAPPIST-1. In May, a team of astronomers announced they had found a system of seven Earth-sized planets in orbit around an ultra-cool red dwarf, designated TRAPPIST-1 after the small telescope in Chile that it was discovered with. The planets are all close to the star, with orbits lasting a matter of days, but the star’s cool temperature means that some could still potentially hold liquid water on their surfaces.
The system was found during TRAPPIST’s survey of 50 low-mass stars, a prototype search to test the idea that such stars could be home to observable planets. Smaller, dimmer stars are well suited to studying transiting planets because the signs of a planet aren’t as swamped by the star’s glare.
“We are already doing many follow up observations,” says Michael Gillon from the Université de Liège, who led the TRAPPIST team. “Most notably we are trying to measure the masses of the planets.”
The masses range between 0.2 and 1.6 times the mass of the Earth, and once these are pinned down precisely researchers will be able to measure their density. In turn, this will give them an idea of the planetary composition and what kind of atmosphere they might have.
“We are currently trying to look for atmospheres with Hubble but it can only find low-density atmospheres that are rich in hydrogen. But, if we can detect hydrogen, that’s a strong indication that they have an atmosphere that is rich in water,” says Gillon.
Though astronomers will likely have to wait until the next generation of telescopes are operational to really understand these planets, they are already trying to work out what they might be able to find.
“There was a study of the star itself,” Gillon continues. “Its ultraviolet and X-ray emission isn’t intense enough to have stripped the planets of their atmosphere and water completely, so they remain good habitable planet candidates.” The emissions also show that the star, and so the planets, are between 5 to 10 billion years old, much older than the Earth’s 4.5 billion years. Could life have evolved on these planets?
“The conditions are not Earth-like, it’s not Earth Two. But at least a few of these planets could have liquid water. That, along with the energy from the star and the fact that organic molecules composed of hydrocarbons are quite common, means you could have the emergence of life on one of these planets,” he says.
The seven planets all orbit close to their parent star, an ultra-cool red dwarf
Despite their proximity to their star, several of the TRAPPIST worlds could possess liquid water