Gliese 12b: Scientists discover theoretically habitable Earth-size planet

Gliese 12b orbits a cool red dwarf star located just 40 light-years away.
Gliese 12b orbits a cool red dwarf star located just 40 light-years away. Photo credit: R. Hurt/JPL-Caltech/NASA via CNN

Two teams of scientists have discovered a theoretically habitable planet, smaller than Earth but bigger than Venus, orbiting a small star about 40 light-years away.

The exoplanet, named Gliese 12b, orbits a cool red dwarf star situated in the constellation Pisces and is about 27 percent the size of our sun and 60 percent of its temperature, according to the two studies published on Thursday in The Astrophysical Journal Letters and Monthly Notices of the Royal Astronomical Society.

Since its star is so much smaller than the sun, Gliese 12b still falls within the habitable zone - the ideal distance away from a star where liquid water can exist - even though it completes its orbit every 12.8 days.

Working on the assumption that the exoplanet doesn't have an atmosphere, scientists calculated its surface temperature to be around 42 degrees Celsius.

"We've found the nearest, transiting, temperate, Earth-size world located to date," said Masayuki Kuzuhara, a project assistant professor at the Astrobiology Center in Tokyo and co-leader of one of the research teams with Akihiko Fukui, a project assistant professor at the University of Tokyo, in a statement.

Once temperate Earth-size planets have been identified, scientists can then analyze them to determine which elements are contained in their atmospheres and, crucially, whether water is present to sustain life.

"There's only a handful (of exoplanets) we've found that are good candidates for that. And this is our nearest and so that's quite a major discovery," Larissa Palethorpe, a doctoral student at the University of Edinburgh and University College London who co-led the other study, told CNN on Friday.

Understanding Gliese 12b

To spot Gliese 12b, scientists used the publicly available data collected by NASA's Transiting Exoplanet Survey Satellite (TESS) - a telescope that stares at tens of thousands of stars every month, tracking their changes in brightness, which can be evidence of orbiting exoplanets.

It is easier for astronomers to find exoplanets orbiting red dwarf stars since their relatively small size results in a greater dimming effect during each transit.

At the moment, scientists are unsure exactly what constitutes this planet's atmosphere, whether it even has one and if water is present, though Palethorpe said they aren't expecting to find water there.

"There could be no water, and then we know a runaway greenhouse effect has already happened on this planet and it's more like Venus," she said. "There could be water, in which case it's more like us... or there are signatures that can be detectable that would be able to show you that the runaway greenhouse effect is in progress so it could be losing water."

For the next stage of analyzing the exoplanet's atmosphere, scientists are hoping to use the James Webb Space Telescope and conduct spectroscopy analysis. This method involves capturing starlight that shines through an exoplanet's atmosphere and seeing which wavelengths are absorbed by certain molecules, revealing their presence in the atmosphere.

As well as shedding light on the exoplanet itself, Palethorpe said scientists are hoping that this work can help us understand our own planet better.

"What this planet will teach us in particular is what happened for Earth to stay habitable but for Venus to not... It can tell us the habitability patheways that planets take as they develop," she said.

But though the exoplanet could potentially be habitable for humans and is relatively "near" our solar system in astronomical terms, it is unlikely that anyone will visit there soon.

"It's not reachable, it's 12 parsecs away," said Palethorpe, adding that it would take about 225,000 years to reach Gliese 12b with the fastest spacecraft that currently exist.