K2-291 b
confirmed planet • updated: 2019-01-22
K2-291 b circles the star K2-291, which is slightly smaller and cooler than our Sun. Scientists found it using the transit method — watching for tiny dips in starlight as the planet crosses the face of its star.
This page summarizes a catalog entry. If a measurement is missing, it is not shown or guessed. Some values can differ slightly between studies; when that happens, we describe the range rather than picking a favorite without evidence.
Scientific context
Scientific context: This profile layers interpretation on top of archival measurements. Modeled bands appear where direct detections (like spectra or transits) are not listed.
What we can’t claim: surface conditions, biology, or breathable atmosphere without direct spectra.
K2-291 b is a rocky or rocky-core planet with a mass and size suggesting it may have a thick atmosphere. It orbits extremely close to its star — about 3% of Earth’s distance from the Sun — so it’s very hot. The orbit appears nearly circular, and the planet likely always shows the same face to its star, like our Moon does to Earth.
Glossary (plain English)
- AU: the average Earth–Sun distance.
- Semi-major axis: the planet’s average distance from its star.
- Eccentricity: how oval the orbit is (0 = circle).
- Radial velocity: finding a planet by measuring a star’s tiny “wobble.”
- m·sin i: a minimum mass estimate; the true mass can be higher if the orbit is tilted.
- Equilibrium temperature: a rough estimate from starlight alone, not a surface reading.
K2-291 b was first reported in 2019 using the Transit method. The discovery is linked to observations from K2.
In transit work, astronomers watch for tiny, repeating dips in a star’s light as the planet passes in front of it. Follow-up observations help rule out false positives and refine the orbit.
The catalog lists an orbital period of about 2.23 days, a semi-major axis near 0.033 AU.
The orbit’s eccentricity is 0.00, which describes how stretched the orbit is.
The archive reports a mass scale of 0.0 MJ.
A catalog radius is also listed, which (together with mass) helps constrain density and interior structure.
Why “m·sin i” shows up on RV planets
K2-291 b orbits K2-291.
A temperature near 5520 K places it on the sun-like side of the main sequence. The system is about 293.7 light‑years away.
Several key parameters are not present in this single catalog row. Missing fields don’t mean the science is unknown—only that this particular snapshot doesn’t carry the values.
In this case the most noticeable gaps are: catalog equilibrium temperature. As new observations arrive, archives often refresh these entries (and sometimes revise earlier numbers).
Scientists keep revisiting systems like this because each new instrument pass can tighten uncertainties: better timing improves the orbit, better spectra improves the star, and better follow‑up can confirm or refute competing solutions. Even when a planet is well‑established, refined stellar properties can shift the inferred planet size, temperature, and habitability context. Transit systems are especially valuable because they can be re‑observed for decades to detect subtle changes in timing or additional planets.