[1] Luyten b is a super-Earth, meaning that it has a mass and/or radius greater than that of Earth, but less than that of Uranus or Neptune.
Radial velocity measurements shows that the planet has a minimum mass of 2.89 M🜨, placing it at the lower end of the super-Earth range.
However, because the host star is so dim, Luyten b falls right within the system's habitable zone and only receives 6% more starlight than Earth.
It has 29.3% the radius, 29% the mass, 0.88% the luminosity of the Sun, and has an effective temperature of 3,382 K. Unlike many nearby red dwarfs, like Proxima Centauri, Luyten's Star is very inactive with a long rotation period of over 118 days.
[1] In October 2017 and 2018, the nonprofit organization METI (Messaging Extraterrestrial Intelligence) sent a message, "Sónar Calling GJ273b", containing dozens of short musical compositions and a scientific "tutorial" towards the planet in hopes of contacting any potential extraterrestrial civilizations.