LP 890-9 c: Habitable Zone, 8-Day Year
Super-earth around LP 890-9
It is 1.37 times Earth's radius, closest in size to Earth, and 25.3 times Earth's mass. A year there lasts 8.46 days, on an orbit 10 times closer to its star than Mercury is to the Sun. Its equilibrium temperature is 272 K, in the range where liquid water is possible. The host star LP 890-9 runs at 2850 K with 0.12 times the Sun's mass.
What is established here and what is missing
Inside the habitable zone, computed from the star's luminosity. Yes.
A measured mass, not just a radius. Yes.
A measured temperature rather than one derived from the star. Yes.
Any detection of an atmosphere. Not recorded in the archive.
Radius
1.37 Earth radii
Mass
25.3 Earth masses
Equilibrium temperature
272 K (measured)
One year
8.46 days
Orbit radius
0.0398 AU
Host star
LP 890-9 at 2850 K
Distance
106 light-years
Starlight blocked
0.647% at each transit
What the transit gives
The depth of the dip is the ratio of the two discs, so the radius follows.
LP 890-9 has 2 known planets. Systems like this are the ones where architecture can be studied instead of guessed at.
Found by SPECULOOS Southern Observatory in 2022.
Size from the shadow, mass from elsewhere. Most transiting planets never get the second half, and without it composition stays a guess.
LP 890-9 c sits in the habitable zone on the arithmetic alone. That says where \
it orbits, not what it is like. What would you want measured next before calling it promising?
