New Rocky "Venus Twin" Exoplanet Discovered

This illustration shows the transiting planet GJ 1132b to scale against its host star GJ 1132. Zach Berta-Thompson

A new exoplanet, dubbed a "Venus twin," has been discovered orbiting a red dwarf star only 39 light-years from us. This is three times closer than any other confirmed Earth-sized exoplanet.

The planet, named GJ1132b, has a radius 16 percent larger and is 60 percent more massive than Earth, but it has an estimated density very similar to Earth and Venus. It orbits its host star very quickly, in just 1.6 days, and has an average distance from it of 2.3 million kilometers (1.4 million miles). 

Although it’s very close to its star and receives 19 times more energy than Earth, the planet is relatively cool. The surface temperature is estimated between 400 and 600 kelvins (120 to 320°C or 260 to 620°F), definitely too hot for life to thrive but cool enough for the planet to hold on to its atmosphere. Scientists suspect it might host an atmosphere similar to Venus based on its temperature, size, and composition.

"GJ1132b is much cooler than most other known rocky planets,"  Dr Zach Berta-Thompson, lead author of the study published in the journal Nature, told IFLScience. "This means the molecules in its atmosphere are moving much slower than they would be in hotter planets. Except for the very lightest molecules (like hydrogen or helium) which move very fast, the gas molecules in GJ1132b's atmosphere move slowly enough that they can't escape the gravity of the planet. The planet's gravity traps them, thereby retaining an atmosphere." 

The researchers are hoping to use Hubble to produce deep observations of the planet and hopefully catch a glimpse of the likely atmosphere. Being so close to Earth, telescopes that are currently being built such as the James Webb Space Telescope (JWST) should also be able to precisely characterize its atmosphere. 

The object orbits an M-star, one of the most common stars in the Milky Way. For each yellow star, like our Sun, there are 12 red dwarfs like GJ 1132. They are smaller and fainter than the Sun, and recent studies have pointed out that most M-dwarfs have Earth-size planets orbiting them, but all of the ones discovered so far were too far away to allow a direct atmospheric observation. 

"GJ1132b provides an exciting opportunity for astronomers to observe the atmosphere of a rocky planet outside the Solar System," added Dr, Berta-Thompson. "For me, the most exciting thing is to think about the many observations that we will make of this planet over the next decade, to learn what processes shape planetary atmospheres throughout the galaxy." 

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