About 40 light-years from Earth, a small but massive rocky world orbits a cool, red star. It's here, researchers say, where we might find the best chance in our search for life.
The planet is LHS 1140b — a "super-Earth" only about 1.4 times the size of our planet, but with about 6.6 times its mass — that circles its star in what astronomers call the habitable zone, a region around a star where water is able to exist on a planet's surface. In this case, the planet orbits about 10 times closer to its star than Earth does around our sun.
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While astronomers are continually finding planets that are potentially habitable, such as those in the TRAPPIST-1 system which was announced in February, the scientists say this one is even more promising than any to date.
"This is the one we've been searching for," said David Charbonneau, a Canadian at the Harvard-Smithsonian Center for Astrophysics and co-author of the research published in Nature.
What makes this planet so promising is its star, LHS 1140, a red dwarf. These types of stars — believed to be the most abundant in our galaxy — are much smaller and cooler than our own star. And like our star, they emit flares, releasing massive amounts of radiation into space which, in turn, can damage the atmospheres of nearby planets (Earth is protected by its magnetic field). If a star emits this radiation often enough, the atmosphere has no time to repair itself.
Young stars, which are spinning rapidly, emit flares fairly often. And just like humans, once they age, they slow down.
LHS 1140 is an elderly red dwarf, about five billion years old, and after more than two years of observations, not one flare was detected.
The scientists also believe LHS 1140b's size could indicate that some time ago, a magma ocean could have existed for millions of years. The resulting lava could have released steam into the atmosphere at a time when the star was more active.
Searching for oxygen
The scientists aren't wasting any time following up with observations: the next transit (where the planet crosses in front of the star) will occur on Oct. 26 and they've booked several telescopes in Chile to search for signatures of oxygen molecules in the planet's atmosphere. Other signs it could be habitable would be nitrogen molecules. Still, even then, astronomers will have to rule out any other potential sources of the gases.
The lead author of the paper, Jason Dittmann, said that this could take time: the researchers are also hoping to use the James Webb Space Telescope, which won't launch until next year. As well, Dittmann said that larger, ground-based telescopes, such as the 30-metre Giant Magellan Telescope, won't be ready until 2023.
Still, he said he's confident that astronomers will find a habitable planet soon, be it LHS 1140b or another.
"With this planet and TRAPPIST-1, our list is growing larger and larger, and when the next telescopes are built it's just going to completely change everything," he said.
Charbonneau said it may take decades to confirm a world is habitable.
"But the key part is for the first time in human history, we're going to have the ability to probe the atmospheres to see molecules in the atmospheres of temperate, rocky worlds orbiting nearby stars," he said.
A helping hand from Down Under
The planet initially discovered by the MEarth Project, which searches for exoplanets, planets orbiting other stars. This is done by measuring the slight dip in the star's light curve as a planet passes in front of it. Followup observations were made by the European Southern Observatory's High Accuracy Radial Velocity Planet Searcher (HARPS).
In order to confirm the orbital period of an exoplanet, several observations need to be made. But after the discovery of LHS 1140b, astronomers were clouded out from locations where it should be visible.
But in stepped an amateur astronomer.
Using just a 12-inch telescope — a high-end one you can purchase at astronomy stores or online — Thiam-Guan Tan from Perth, Australia, managed to provide the final confirmation that the researchers had correctly calculated the orbital period of the planet.
"It's just incredible what these amateurs are capable of," said Dittmann.
He is excited about eventually answering the question of whether or not we're alone in the universe.
"It's a very human thing to do, to wonder, and people really want to know the answer. And it's just now becoming possible," he said.