One of the key incentives behind hunting down exoplanets is to find alien worlds with qualities similar to Earth. But in the case of a newly-discovered exoplanet orbiting a star only 16 light-years away, although astronomers may call it ‘habitable’ and a ‘super-Earth,’ it’s likely anything but.
Gliese 832c orbits a red dwarf star and it was discovered by the international Anglo-Australian Planet Search team led by Robert Wittenmyer of the University of New South Wales, Australia. The discovery has been accepted for publication in the Astrophysical Journal.
Red dwarfs are small, dim stars that generate far less energy than our sun. Therefore, for a red dwarf-orbiting planet to maintain water in a liquid state on its surface, it must orbit much closer to the star. In the case of Gliese 832, its ‘habitable zone’ is very compact and Gliese 832c has an orbital period of just under 36 days. The possibly-rocky world, which is around 5 times the mass of Earth, is therefore considered ‘habitable.’ In fact, Gliese 832c is considered to be the third-most habitable world known so far on the Earth Similarity Index (ESI).
But don’t go having dreams of blue skies, opal oceans and lush, alien forests — this world would likely choke any life (well, life as we know it).
“Given the large mass of the planet, it seems likely that it would possess a massive atmosphere, which may well render the planet inhospitable,” said co-investigator Chris Tinney, also of UNSW. “A denser atmosphere would trap heat and could make it more like a super-Venus and too hot for life.”
Like Venus, Gliese 832c is probably enduring intense warming caused by a runaway greenhouse effect. In this case, although the planet’s orbital location should allow liquid water to persist, any water would likely be ripped apart on a molecular level by intense atmospheric heating and ultraviolet light from the star, a process known as dissociation.
Of course, the astronomers have no idea what chemicals are contained within Gliese 832c’s atmosphere. The world was discovered through its gravitational pull on its parent star, so no information about its atmosphere (if it indeed has one) and any water it contains is known. The wobbling effect (which can be detected through precise radial velocity measurements) was detected by combining observations by the Anglo-Australian Telescope (AAT) at Siding Spring Observatory, Australia, the 6.5 meter Magellan Telescope and the European Southern Observatory’s 3.6 meter telescope (both located in Chile).
In 2009, the same team detected another planet around Gliese 832. Thought to be a large gas giant like Jupiter, Gliese 832b has a 9 year orbit around the star. It is for this reason that astronomers believe the system to resemble the multi-planetary structure of our solar system, only more compact. And more planets could be discovered in the future.
“With an outer giant planet and an interior potentially rocky planet, this planetary system can be thought of as a miniature version of our Solar System,” added Tinney.
So beware the headlines that suggest Gliese 832c is ‘Earth-like’ — it is more likely ‘Venus-like’ and very alien to us terrestrial lifeforms.