GJ 3378, also known as LHS 1805, is a red dwarf star located around 25.2 light years (7.73 parsecs) away from Earth in the northern constellation of Camelopardalis. It is a small star with a mass of 0.3 solar masses and a radius of 0.3 solar radii. It is also a cool and quiet star with an effective temperature of and a luminosity of 0.9% solar luminosity.
As of 2026, only one exoplanet, a super-Earth known as GJ 3378b, has been discovered orbiting within the conservative habitable zone. While it is likely that this planet has a terrestrial composition, it is placed near the cosmic shoreline meaning that it is potentially subjected to its parent star stripping away its atmosphere.
Characteristics GJ 3378 has a mass of about and a radius of . It has a luminosity of 2.1 solar luminosity and an effective temperature of . It was measured to have an average density of 17.7 g/cm3. It was initially given a rotational period of days however Sabotta et al. (2021) reported a slower rotational period of 83.4 days. It has a metallicity that is close to the solar value, with an M/H dex of . The magnetic field of GJ 3378 has been clearly detected. It is small-scaled and has a mean strength of , making it a very quiet and cool star. Because GJ 3378 is a star with a mass lower than 0.35 solar masses, it is a fully-convective star.
Planetary system
Moutou et al. (2024) proposed evidence for an exoplanet and obtained data on its orbit and mass using observations from the SPIRou (Spectropolarimètre infrarouge) located at the Canada–France–Hawaii Telescope (CFH) in Hawaii, United States. They reported that this planet has an eccentric orbit and an orbital period of days. They proposed a minimum mass of 5.26 Earth masses making it a sub-Neptunian or Super-Earth type planet. Robertson et al. (2026) conducted a survey of fully convective stars within the Solar neighborhood using the near-infrared spectrograph HPF on the Hobby-Eberly Telescope (HET) at McDonald Observatory in Texas, US. They refined the planet's orbital period down to days and its minimum mass down to Earth masses. They also gave estimates for its orbital distance and equilibrium temperature of and respectively.
Even with the reduced orbital period presented by Robertson et al. (2026), GJ 3378b would orbit within the conservative habitable zone (HZ) of the star where water could be present in its liquid state. Their reduced mass estimates would also make it more likely that this planet has a terrestrial composition. This could mean that it is a potentially habitable exoplanet. However GJ 3378b has been placed near the cosmic shoreline meaning that its atmosphere may have been lost due to radiative stripping by the parent red dwarf star.
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