Another day, another exoplanet hailed as a good place to look for signs of life. In fact, the ESO press release suggests LHS 1140b “may be the new holder of the title ‘best place to look for signs of life beyond the Solar System.’”
Let’s take a look.
First, the basics. This exoplanet sits 40 light-years away from Earth as it orbits a faint red dwarf star named LHS 1140 once every 25 days. The new planet, designated LHS 1140b, has a diameter of around 11,000 miles. 1.4 times that of Earth. But it’s much more massive at nearly seven times the mass of Earth. That suggests it’s most likely made of rock with a dense iron core.
Astronomers estimate the planet’s age to be at least five billion years old.
The MEarth facility first noticed the telltale sign of a dip in light as the exoplanet passed in front of its star. ESO’s HARPS instrument followed up and confirmed a super-Earth was responsible. This same instrument also helped figure out the planet’s orbital period and mass.
But what about the star? Red dwarfs are tricky. The amount of sunlight this super-Earth receives is about half as much as Earth. That also means the habitable zone is much closer to the star. A closer orbit mean the likelihood of a planet being tidally locked increases. Meaning, one side of the planet always faces the star while the other faces away. One side is warm; the other is cold.
Plus, red dwarfs spew a lot of high-energy radiation during their younger years. The team of astronomers responsible for this discovery believes LHS 1140b entered the habitable zone around 40 million years after the star formed. That would have put the exoplanet right in the thick of the star’s volatile energy blasts.
A young red dwarf would have no problem stripping away water from a planet’s atmosphere. If that did happen, it would have caused a runaway greenhouse effect like we see on Venus. But if LHS 1140b was able to withstand the brunt of its star’s radiation, it’s possible signs of life are lurking there.
“The present conditions of the red dwarf are particularly favorable — LHS 1140 spins more slowly and emits less high-energy radiation than other similar low-mass stars,” explains Nicola Astudillo-Defru, one of the astronomers behind the discovery.
Here’s one theory on how this super-Earth could have water on it today:
The planet’s large size means that a magma ocean could have existed on its surface for millions of years. This seething ocean of lava could feed steam into the atmosphere long after the star has calmed to its current, steady glow, replenishing the planet with water.
Right now, LHS 1140b looks like an attractive target for further observation. NASA’s Hubble Space Telescope will take a look soon to see how much high-energy radiation is pouring onto the exoplanet. If that data comes back and looks good, the next generation of telescopes will conduct observations of the planet’s potential atmosphere.
Xavier Delfosse and Xavier Bonfils, both members of the team, talked more about the discovery. “The LHS 1140 system might prove to be an even more important target for the future characterization of planets in the habitable zone than Proxima b or TRAPPIST-1. This has been a remarkable year for exoplanet discoveries!”
We have the plenty of planets to look at. Now, we just have to wait for the telescopes to catch up and tell us more. Much more.