Gliese 486 b artist's concept

Other Worlds

Scientists discover a 'Rosetta Stone' planet in the hunt for life in the universe

This hellish world could be key.

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Exoplanets offer a tantalizing possibility: with each new discovery, these at-times strange worlds fuel our search for life in the universe and the quest to find a planet like our own.

Now, in a study published Thursday in the journal Science, a team of astronomers from the Max Planck Institute for Astronomy announced the discovery of a nearby exoplanet that could be an ideal target for the search for habitability. The reason why is to do with the cloud of gas potentially enshrouding the planet — its atmosphere.

Studying the atmospheres of exoplanets in orbit around the smallest and most common kinds of stars in the universe, like this one, could help us find out if any of those planets could sustain life.

What's new — Trifon Trifonov, a planetary scientist the Institute and lead author of the new study, surveyed about 350 red dwarf stars, looking for signs of planets orbiting them. Red dwarfs are stars that can be as much as 0.6 and as little as 0.08 the mass of our Sun. These small stars are the most common stars in the universe. In the process, he and his team stumbled upon a rocky super-Earth that's right in our cosmic neighborhood.

Located just 26 light-years away, the exoplanet orbits the red dwarf star Gliese 486. The planet, Gliese 486 b, has a mass 2.8 times that of Earth and is around 30 percent larger than our planet. It is unlikely that the exoplanet itself could support life, but the proximity to Earth make it an ideal candidate to study the atmosphere of other, potentially habitable planets.

"Gliese 486 b is a remarkable discovery, which will likely become the 'Rosetta Stone' for atmospheric investigations of rocky exoplanets, some of which are likely habitable," Trifonov tells Inverse.

"The greatest story about this planet is that we don't know most of the story."

Unlike other similar exoplanets, Gliese 486 b may have retained some of its atmosphere from the turbulent early years of its home star, having many of the right conditions to maintain an atmosphere.

An illustration of the newly discovered exoplanet as it orbits around its host star at a close proximity that makes it a hot, dry world like Venus.RenderArea

"Discovering an atmosphere in Gliese 486 b will be very important because that would give hope for finding primordial atmosphere on other potentially habitable rocky planets around M dwarf stars," Trifonov says.

How they did it — The explosion in exoplanet discoveries is thanks in part to NASA’s Kepler and the Transiting Exoplanet Survey Satellite (TESS) missions. Both missions cataloged stars looking for signs of exoplanets. While Kepler focused in on an area near the constellation Cygnus, while TESS performs a more general survey of 200,000 of the brightest stars in the sky.

Both Kepler and TESS use the transit method, looking for small dips in the light of a star, indicating a planet is passing in front of it. Gliese 486 b was discovered partially using the transit method, as well as another method called radial velocity that looks for the tug of a planet on its home star. The planet is the third closest known transiting exoplanet, though there are planets closer to us that are not known to transit.

Jon Jenkins, a researcher at the NASA Ames Research Center and one of the investigators on the Kepler and TESS missions, says he's excited to learn more about the newly discovered exoplanet as scientists continue to observe it.

"The greatest story about this planet is that we don't know most of the story. Most of the story is yet to be told," Jenkins tells Inverse. "So that's what makes it so exciting."

Jenkins, who is a co-author on the study, has been involved in the discovery of many small and rocky exoplanets before, but says that Gliese 486 b is special because it's cold enough to be a rocky world instead of a lava world, and yet warm enough to possibly support an atmosphere.

Artistic impression of the surface of the newly discovered hot super-Earth Gliese 486 b. With a temperature of about 700 Kelvin (430 °C), Gliese 486 b possibly has an atmosphere.RenderArea

Super-Earths are, as the name suggests, planets around two and up to 10 times the mass of Earth. Some might be rocky, like Earth, while others might be more of an ocean world, and others still may be gaseous planets.

Why it matters — Currently, we know of 4,300+ exoplanets orbiting around most types of stars — and 3,000 more suspected exoplanets await confirmation.

The hope driving many of these efforts is that we might find worlds similar to our own — and in the process, see if conditions are right on them for life.

Future missions like the James Webb Space Telescope and the Extremely Large Telescope will be large enough to look for one thing that has thus far mostly eluded astronomers: detecting atmospheres around smaller rocky planets. Without our atmosphere, Earth would be barren and quite cold. If it didn’t have its atmosphere the temperature at the surface would reach as low as -20 degrees Celsius, Billy Quarles, a researcher at the Georgia Institute of Technology’s School of Physics, told Inverse in an interview in November, 2019.

Earth’s atmosphere is what makes it habitable compared to its neighboring planet Venus. Venus can’t sustain life because its atmosphere — which is mostly carbon dioxide, nitrogen, and sulfuric acid — traps in heat, making it the hottest planet in the Solar System.

The newly discovered exoplanet has a composition that appears to be similar to that of Earth and Venus with signs of a metallic core. It orbits around its host star on a circular trajectory at a distance of 2.5 million kilometers, taking 1.5 days to complete an orbit.

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The surface temperature of the planet reaches a scorching 700 Kelvin, approximately 430 degrees Celsius. Gliese 486 b may have a hot and dry landscape with glowing lava rivers snaking through a solid rocky surface.

Gliese 486 b may have kept its atmosphere likely because of its high gravity. The exoplanet has a gravitational pull 70 percent stronger than what we would experience on Earth, according to the researchers.

Although Gliese 486 b itself is unlikely habitable, it provides for the perfect conditions to probe at the atmosphere of a rocky exoplanet.

What's next — The team of scientists behind the study plan on conducting future observations of the newly discovered exoplanet to look for signs of an atmosphere with the upcoming James Webb Telescope, which is scheduled to launch in October of this year.

"Gliese 486 b has a shorter orbital period, which allows for a more precise observing schedule to seek signs of an atmosphere," Trifonov says.

The launch of future telescopes that are better suited to probe at these foreign worlds will likely take our search for exoplanets to the next level.

Jenkins recalls that 25 years ago, the field of exoplanets did not exist but today, exoplanets are an exciting part of astronomy.

"It's one of those endeavors (that) really captures the imagination of everyone," he says. "I think what makes them so compelling is that it puts us and our Solar System into perspective with what's going on with planets throughout the galaxy."

Abstract: Spectroscopy of transiting exoplanets can be used to investigate their atmospheric properties and habitability. Combining radial velocity (RV) and transit data provides additional information on exoplanet physical properties. We detect a transiting rocky planet with an orbital period of 1.467 days around the nearby red dwarf star Gliese 486. The planet Gliese 486 b is 2.81 Earth masses and 1.31 Earth radii, with uncertainties of 5%, as determined from RV data and photometric light curves. The host star is at a distance of ~8.1 parsecs, has a J-band magnitude of ~7.2, and is observable from both hemispheres of Earth. On the basis of these properties and the planet’s short orbital period and high equilibrium temperature, we show that this terrestrial planet is suitable for emission and transit spectroscopy.
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