Scienceline’s Guide to the Exoplanets: Transmission Target

Transmission Target
Luyten b
Discovered by: High Accuracy Radial-velocity Planet Searcher
Discovered: 2017
Distance from Earth: ~12 light-years
Mass: ~3 Earth masses
Radius: ~1.35 Earth radii
Surface climate: Promising.
Habitability for humans: Promising…

Let’s talk about another nearby Earth-like planet.

Luyten b, also known as GJ273b, is again one of the closest known exoplanets to Earth. And just like so many other planets we’ve talked about, Luyten b orbits a red dwarf quite closely. In its case, Luyten b moves about eight million miles, or 13 million kilometers, from Luyten’s Star, a relatively cool star around a quarter the mass of the Sun.

But unlike many of the other planets we’ve talked about — and unlike the other three known planets in its star system — Luyten b is actually cool enough to host liquid water.

The similarities to Earth don’t end there. Astronomers believe the planet only receives, on average, 6% more sunlight than Earth. As far as astronomers can tell, Luyten b lives, by Earth standards, comfortably in Luyten’s Star’s habitable zone. So comfortably, in fact, that its average surface temperature is just around 19 degrees Celsius, or 66 degrees Fahrenheit — nearly like Earth’s.

The planet isn’t entirely a second Earth. For a start, you may have noticed one critical difference: it’s around three Earth masses, placing it well into the realm of the super-Earths — but not even close to the point around six Earth masses where terrestrial planets start to blur into gas giants.

Additionally, Luyten b actually has a rather elliptical orbit, slightly more elongated than Earth’s near-circular orbit. But instead of causing wild seasons, that orbit likely saved the planet from being tidally locked and enduring extreme temperature variations. Without a runaway greenhouse effect like Venus, it’s likely the planet’s climate is, on the whole, relatively stable.

That’s good for life.

Astronomers don’t know what Luyten b’s surface would actually look like. And if there was life on its surface, what form that would take is a vastly open question. But all the factors seem to point in the direction of the exciting possibility that this planet just a handful of light-years away is, by Earth standards, quite habitable.

If you’re hopeful that there may indeed be Earth-like life on Luyten b, then you are not alone. Soon after Luyten b’s discovery, in October 2017 and again in May 2018, a group associated with Active SETI broadcast music in the direction of Luyten’s Star.

Regardless of the ethical implications of doing such things without the consent of the world, it’s a clear signal that the planet’s existence has gathered the attention of more than just a few exoplanet hunters.