Astronomers just found a super-Earth in the habitable zone of a nearby star — and if it's home to alien life, we have a very reasonable chance of finding it.
An exoplanet survey recently discovered two exoplanets, each slightly larger than Earth, orbiting a red dwarf star about 100 light years away — and one of them is in the star’s habitable zone, where conditions might be right for alien life. Its discoverers are hoping to take a closer look with the James Webb Space Telescope next year.
What’s New — The red dwarf star LP 890-9, also known as SPECULOOS-2, is the second-coolest star astronomers have ever found planets around — in terms of temperature, but also figuratively. (The coolest, in either sense, is still TRAPPIST-1.)
SPECULOOS-2 is about 20% hotter than TRAPPIST-1, with a surface temperature of about 2900 Kelvin — just slightly cooler than Proxima Centauri. To put all of that in perspective, our Sun’s surface temperature is about twice that of SPECULOOS-2 or Proxima Centauri B.
“We observed the star for about five months and detected the first transit of planet c only after two months,” University of Liège astronomer Laetitia Delrez, lead author of the recent study, tells Inverse.
Planet c, formally known as either LP-890-9c or SPECULOOS-2c, orbits its dim red star once every 8.5 days. At that distance, it’s firmly in the system’s habitable zone: the region where temperatures are just right for liquid water and, potentially, for life.
“Based on its size, about 40 percent larger than Earth, we expect the planet to be rocky — we have not yet found exoplanets as small as 1.4 Earth radii that are not rocky,” Delrez says, adding that it’s also probably tidally locked to its star, so one side of the planet is in constant daylight while the other is in endless night.
Delrez and her colleagues at Search for habitable Planets EClipsing ULtra cOOL Stars (SPECULOOS, a Frankenstein’s monster of an alleged acronym, but a genuinely awesome exoplanet survey) had originally trained their telescopes on LP 890-9 to confirm that NASA’s Transiting Exoplanet Survey Satellite, TESS, had actually spotted a planet there. The object TESS had discovered turned out to be a planet about 30 percent larger than our own, whizzing around the star once every 2.7 days — too close to even the relatively cool red dwarf to support life.
The astronomers decided to keep watching LP-890-9 to look for more planets in its orbit, and the decision paid off.
Here’s The Background — The SPECULOOS project is the successor to the TRAPPIST telescopes, the first of which discovered the now-famous TRAPPIST-1 system: a red dwarf star with at least seven rocky planets orbiting it. Three of those planets are in the habitable zone, making the cool star TRAPPIST-1 a hot spot in the search for alien life (or at least livable worlds).
The European Southern Observatory — which hosts four of the SPECULOOS telescopes at its Paranal Observatory in Chile — claims that SPECULOOS “is expected to discover at least a dozen systems similar to TRAPPIST-1.”
SPECULOOS-2 (or LP-890-9, if you prefer), could be the first of those.
Like the James Webb Space Telescope, SPECULOOS sees the universe in infrared light. That’s the best way to see star systems like TRAPPIST-1 and SPECULOOS-2, because most of the light red dwarf stars emit is infrared. It’s also the spectrum that the Webb telescope observes in.
Digging Into The Details – Telescopes and surveys like TESS, SPECULOOS, and Webb all work together to find and study worlds like “planet c.” From its vantage point in orbit, TESS surveys wide swaths of the sky, looking for stars whose brightness changes at regular intervals — a sign that a planet could be passing between Earth and the star.
When the telescope spots something promising, it’s declared an “exoplanet candidate.” Then it’s up to other telescopes, which are better at honing in on specific objects, to take a second look and decide whether the candidate is really an exoplanet.
That’s especially important in the case of red dwarfs like SPECULOOS-2, because TESS was designed to look at the brightest nearby stars.
“For cool red stars such as LP 890-9, our SPECULOOS telescopes also allow us to gather higher-precision data than TESS, because they are optimized to observe this type of stars which emit most of their light in the near-infrared,” explains Delrez. That’s exactly what happened with LP-890-9b.
And once an exoplanet has officially been discovered, Webb could use its even more powerful instruments to study its atmosphere and maybe even look for signs of life.
Why It Matters — SPECULOOS-2c could be a perfect job for Webb. The fact that it’s a roughly Earth-sized world in the habitable zone makes it interesting — but it’s also a relatively easy target.
“What makes this planet such a good target is that it is orbiting a very small star (15 percent the size of our Sun),” says Delrez. SPECULOOS-2 is about 25 percent larger than TRAPPIST-1 (with a radius of roughly 105,000 kilometers to TRAPPIST-1's 84,000 kilometers), and about the same size as Proxima Centauri, the nearest star to the Sun that also has a potentially habitable planet. Our Sun's 697,000 kilometer radius could swallow all three stars with room to spare.
Telescopes like Webb measure the light filtering through an exoplanet’s atmosphere as it passes in front of its star. The smaller the star, the more of its light passes through the exoplanet’s atmosphere on the way to Webb. That gives astronomers more and better data to work with.
“This gives us a license to observe more and find out whether the planet has an atmosphere, and if so, to study its content and assess its habitability,” says University of Birmingham planetary scientist Amaury Triaud, leader of the SPECULOOS working group that scheduled the LP 890-9 observations, in a statement.
What’s next — Delrez and her colleagues plan to submit a proposal to observe SPECULOOS-2c with Webb next year; its schedule for its first year of science is already packed.
And in the meantime, she says they’ll keep looking for new planets — and studying the ones they’ve already found.
“Our team is working on searching for more planets like this with SPECULOOS,” she says, “but we are also involved in the follow-up of the planets we detect, like the TRAPPIST-1 planets, for which atmospheric observations with the JWST already started!”