Two international teams of astronomers, including one co-led by a PhD student based at UCL and the University of Edinburgh, have discovered a planet only 40 light years away whose size is between that of Earth and Venus.
The researchers used observations by NASA's TESS (Transiting Exoplanet Survey Satellite). Multiple factors make it a candidate for further study using NASA's James Webb Space Telescope.
TESS stares at a large swath of the sky for about a month at a time, tracking the brightness changes of tens of thousands of stars at intervals ranging from 20 seconds to 30 minutes. Capturing transits - brief, regular dimmings of stars caused by planets passing in front of the stars - is one of the mission's primary goals.
The host star, called Gliese 12, is a cool red dwarf located almost 40 light-years away in the constellation Pisces. The star is only about 27% of the Sun's size, with about 60% of the Sun's surface temperature.
The newly discovered world, named Gliese 12 b, orbits every 12.8 days and is Earth's size or slightly smaller - comparable to Venus. Assuming it has no atmosphere, the planet has a surface temperature estimated at around 107 degrees Fahrenheit (42 degrees Celsius).
Both research teams suggest that studying Gliese 12 b may help unlock some aspects of our own solar system's evolution.
Larissa Palethorpe, a doctoral student at UCL's Mullard Space Science Laboratory and the University of Edinburgh and co-lead of one of the teams, said: "It is thought that Earth's and Venus's first atmospheres were stripped away and then replenished by volcanic outgassing and bombardments from residual material in the solar system.
"Whilst the Earth remained habitable, Venus did not as the runaway greenhouse effect led to a complete loss of water. Because Gliese 12 b is between Earth and Venus in temperature, its atmosphere could teach us a lot about the habitability pathways planets take as they develop."
Co-author Dr Vincent Van Eylen (Mullard Space Science Laboratory at UCL) said: "Gliese 12 b is an incredibly exciting planet because its size is identical to that of Earth. Even though Gliese 12 b is about 15 times closer to its star than Earth is to our Sun, because it orbits such a small star the temperature on the planet may be quite similar to that on Earth.
"That doesn't necessarily guarantee that the planet is habitable, but it does make it a great place to start looking.
"Fortunately it's also a very nearby star, so we will learn much more about the planet and its atmosphere with telescopes like JWST in the next years."
