Nine months ago astronomers announced the discovery of a planet labeled a twin to Venus. A new paper raises the possibility of oxygen in its atmosphere, though its hellish temperatures rule out prospects for life.
By size and mass GJ 1132b is somewhat larger than Earth, rather than smaller like Venus, but its temperature has been estimated as somewhere between 120°C and 320°C (260°F to 620°F). Hot by our standards, but quite a bit cooler than most of the rocky planets we have detected so far, since our methods for finding planets outside the Solar System favor worlds lying close to their parental star.
GJ 1132b orbits just 2.2 million kilometers (1.4 million miles) from its star, 1.5 percent of the Earth-Sun distance. Even though its parental star, GJ 1132, is a red dwarf with a fifth of the Sun's mass, the planet is exposed to far more light than Earth receives.
Unquestionably it is very hot, but the wide estimates of its temperature reflect the possibility of a Venus-style runaway greenhouse effect.
GJ 1132b passes in front of its star often from our point of view, owing to its short orbit. At a distance of 39 light-years, tiny by astronomical standards, GJ 1132b is close enough that we have a chance of detecting the composition of its atmosphere during future transits.
Graduate student Laura Schaefer of the Harvard-Smithsonian Center for Astrophysics has already created a model to examine the chances of finding oxygen, though, and what it would mean if we do. In the Astrophysical Journal (preprint on arXiv), Schaefer has explored how the existence of an ocean of magma during GJ 1132b’s development might affect its atmosphere.
Some of the planet’s initial oxygen would be absorbed by this magma ocean, but Schaefer concluded only a tenth would be captured this way. Far more would escape into space, despite GJ 1132b having stronger gravity than Earth. Nevertheless, Schaefer’s modeling raises several scenarios where some might survive, although it found surviving water vapor is much less likely.
"On cooler planets, oxygen could be a sign of alien life and habitability. But on a hot planet like GJ 1132b, it's a sign of the exact opposite – a planet that's being baked and sterilized," Schaefer said in a statement.
"This planet might be the first time we detect oxygen on a rocky planet outside the solar system," said co-author Dr Robin Wordsworth. The possibility increases the incentive to devote scarce time on the next generation of telescopes to observing this world.
The three known planets in the TRAPPIST-1 system, at a similar distance, may be even better prospects for oxygen, since the less energetic molecules in their cooler atmospheres would be less likely to escape.
Studying planets like GJ 1132b may help us understand Venus’ evolution. Astronomers are puzzled as to why Venus has almost no molecular oxygen, despite being thought to have had water that split, with the hydrogen escaping into space. Speculation Venus once supported a liquid ocean has put renewed interest into the topic.