We just found the first exoplanet close enough to study in depth with todayâs technology â signalling that exoplanet studies are about to become more than mere stamp collecting.
First spotted with the ground-based this May, the new planet, called GJ 1132b orbits a cool red dwarf star just 40 light years away and is slightly larger than Earth, with about 60 per cent more mass. That suggests itâs a rocky world like ours, possibly with an iron core and a mantle made of magnesium silicate.
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But GJ 1132b hugs its star closely, orbiting once every 38 hours, giving it a temperature somewhere between a few dozen and a few hundred degrees too hot to have liquid water.
That heat makes it more like a super-Venus than a super-Earth. But GJ 1132b is exciting because the Hubble Space Telescope should be able to analyse the chemicals in its atmosphere with relative ease, says MEarth team member at the Massachusetts Institute of Technology.
Either Hubble or its successor, the James Webb Space Telescope set for launch in 2018, will hopefully show us which chemical compounds are in the planetâs atmosphere â a major step towards understanding whether the atmospheres of similar worlds just a little further from their stars could be hospitable to life.
âThis is maybe the first rocky exoplanet we can really characterise in the next decade,â says of the University of Washington in Seattle, who was not involved in the discovery.
Setting star
But the planet almost slipped away unnoticed. At the time of year when the MEarth team found the planet, the star that it orbits barely spent any time above the horizon after sunset.
âWe observed it literally as much as we possibly could,â Berta-Thompson says. âEvery clear night there was this hour before the star set where we could get our data.â After a month, the star stopped rising high enough in the sky to be measured at all. The team had to wait many more months for it to return to a visible height.
Now that itâs visible again, the team is using the HARPS instrument in Chile to make a more precise measurement of its mass. The space-based Spitzer telescope is looking for other planets in the same system.
The MEarth team has proposed to make a quick attempt at probing the planetâs atmosphere with the Hubble telescope this year. If the planet has a puffy atmosphere made of hydrogen or helium, those elements should show up. If not, the team will have to choose between doubling down with Hubble or waiting for James Webb.
This world itself is too hot for life, but that doesnât mean the results wonât be interesting, Barnes says. âYouâre not going to be finding things like biosignatures, but you might find definitive proof of volcanoes on a planet around another starâ, in the form of sulphur compounds. That find would be a helpful step toward understanding how the exoplanetâs interior interacts with its atmosphere. âI really hope thatâs going to pan out, because itâs really going to be the biggest challenge in finding habitable planets,â Barnes says.
Hubble also has a good chance of spotting oxygen gas, the same form of oxygen that plants exhale and we breathe â although on GJ 1132b the oxygen is likely to come from .
Canary in a coal mine
Even if we donât spot specific molecules, GJ 1132bâs atmosphere should help us learn whether small stars are safe hosts for planets in the first place. Since dwarf stars are dim, their planets need to orbit close by to stay warm enough for life. But these stars are also prone to solar flares and ultraviolet radiation, which could strip a vulnerable planetâs atmosphere away.
That makes GJ 1132b a canary in a coal mine. âIf those processes are going to obliterate the atmosphere of a habitable planet, theyâll be much stronger on a planet like 1132b,â Berta-Thompson says. If it has an atmosphere at all, that may mean habitable planetsâ atmospheres can survive the slings and arrows of life close to a red dwarf.
In the bigger picture, GJ 1132b represents a step from knowing the statistics of rocky planets in our galaxy to being able to study them as individuals â making it the planetary equivalent of Darwinâs first finch.
âThereâs this huge forest out there of worlds like this one,â Berta-Thompson says. âBut weâve never had the opportunity to look at any one of those trees.â
Journal reference: , DOI: 10.1038/nature15762
Image credits (top to bottom): Jonathan Irwin; Detlev Van Ravenswaay/Science Photo Library
