Astronomers have found a rocky planet orbiting a small star that is within easy telescope views from Earth.
The planet circles too close to its parent star, a red dwarf known as Gliese 1132, for any water to remain liquid, a condition believed to be necessary for life. But astronomers suspect it has other attributes that are directly related to the search for life beyond Earth, namely an atmosphere.
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"We have long imagined how rocky planets around other stars -- particularly small stars -- maybe be similar or distinct from the planets in the solar system," Massachusetts Institute of Technology astronomer Zachory Berta-Thompson wrote in an email to Discovery News. "With this planet, we will finally be able to observe one! "
Viewing conditions should be ideal. The planet, known as GJ 1132b, is slightly bigger than Earth and is in an orbit that is nearly edge-on to an Earth-based observer's line of sight.
The trump card is that the system is only 39 light-years away, a stone's throw by cosmic yardsticks and three times closer than any previously discovered Earth-sized planet.
It was discovered in May with an eight-telescope array located at the Cerro Tololo Inter-American Observatory in Chile.
As GJ 1132b passes in front of its star, telescopes will be able to measure the small fraction of starlight that passes through the planet's atmosphere. Scientists can then analyze the light for telltale chemical fingerprints of atmospheric gases and conditions. Ultimately, scientists want to be able to scan distant planets' atmospheres for chemical signatures of life.
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GJ 1132b should prove an excellent starting point. Its parent star is about one-fifth the size of the sun, so the planet blocks a higher percentage of starlight during transits than similarly sized planets orbiting sun-like stars. GJ 1132b also transits every 1.6 days, presenting lots of viewing opportunities.
"Astronomers love transiting planets because the transit geometry allows them to unambiguously measure a planet's mass and radius (and thus to determine its bulk density), thereby providing basic information about its chemistry," University of Maryland astronomer Drake Deming wrote in a commentary in this week's Nature.
Orbiting just 1.4 million miles from its parent star, GJ 1132b is likely tidally locked (like the moon is to Earth) with a hot side of the planet facing the star, and a cool one facing away.
"An atmosphere could redistribute the heat," Deming wrote in an email to Discovery News. "The equilibrium temperature we calculate for this planet is above the habitable range, but with tidal locking and modest heat redistribution there could be habitable regions on the planet."
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Water, however, is another matter.
"The planet is very hot, hotter than Venus," said Berta-Thompson. "Any water there would vaporize instantly, and could be lost quickly from the top of the atmosphere, as starlight breaks up water molecules into oxygen and hydrogen, and the hydrogen gets lost to space.
"Our expectation going in is that the atmosphere might look something like Venus', with lots of carbon dioxide and nitrogen gas. Depending on how much water was there in the first place, it might even be possible for the atmosphere to have a substantial molecular oxygen content. This obviously wouldn't be from photosynthetic life (like Earth's O2), but rather from the dissociation of water followed by hydrogen-escape," he wrote in an email.
Scientists won't have to wait long to find out. Scanning exoplanets' atmospheres is one of the primary goals for NASA's upcoming James Webb Space Telescope, slated for launch in 2018.
Meanwhile, astronomers plan to use the existing Hubble space observatory to see if GJ 1132b has any sibling planets.
The research is published in this week's Nature.