LHS 1478 b

Lore & Background

LHS 1478 b was discovered as a transiting exoplanet around a fairly inactive red dwarf star. Its orbit is extremely close to the star, at just 0.018 AU, completing one revolution every 1.9 days. The planet's inclination of 87° relative to the plane of the sky allows it to transit its host star as seen from Earth.

The planet has a mass of 2.27 Earths and a radius of 1.17 Earths, yielding a bulk density of 7.7 g/cm³. This density is consistent with a terrestrial composition dominated by iron (roughly 30%) and magnesium silicate (roughly 70%). With an equilibrium temperature of 585 Kelvin, LHS 1478 b receives 21 times more stellar energy than Earth does from the Sun, making liquid water impossible on its surface and suggesting the presence of a Venus-like atmosphere.

The host star's low activity level makes LHS 1478 b a favorable target for spectroscopic studies with the James Webb Space Telescope. It belongs to a family of small rocky planets—including GJ 357 b, GJ 1132 b, and GJ 486 b—where meaningful JWST measurements are feasible. JWST observations disfavor the possibility of a low-albedo bare rock, indicating that the planet either possesses an atmosphere or has a high albedo without one.

Reader's Guide

LHS 1478 b holds significance as a nearby super-Earth that can be studied in detail with the James Webb Space Telescope. Its host star's low activity reduces interference for spectroscopic observations, placing it among a select group of small rocky planets where JWST can obtain meaningful measurements. The planet's high density and composition—roughly 30% iron and 70% magnesium silicate—mark it as a terrestrial world, while its extreme insolation and equilibrium temperature of 585 K rule out liquid surface water. The JWST data disfavor a low-albedo bare rock scenario, leaving two possibilities: the planet has an atmosphere, or it has a high albedo without an atmosphere. This ambiguity underscores the planet's legacy as a test case for distinguishing between bare rocky surfaces and atmospheres on hot super-Earths. Its Venus-like atmospheric potential makes it a comparative analog for understanding how close-in rocky planets evolve under intense stellar irradiation. The planet's inclusion in a family of JWST-accessible rocky worlds highlights its role in advancing the characterization of terrestrial exoplanet atmospheres.

Did You Know?

• LHS 1478 b orbits its star at a distance of only 0.018 AU, completing an orbit every 1.9 days.
• The planet has a bulk density of 7.7 g/cm³, consistent with a composition of roughly 30% iron and 70% magnesium silicate.
• JWST observations disfavor a low-albedo bare rock, suggesting the planet may have an atmosphere or a high albedo without one.