Gliese 876 c

Gliese 876 c is an exoplanet exoplanet, meaning a planet that orbits a star outside our solar system. It travels around a small, cool star called a red dwarf red dwarf, specifically the star known as Gliese 876 Gliese 876. This journey takes about 30 days days to complete, which is much faster than it takes Earth to orbit the Sun.

The planet was discovered in April 2001, making it one of the earlier exoplanets to be found. It is the second planet from its star, coming after another planet that is even closer to Gliese 876. Studying planets like Gliese 876 c helps scientists learn more about how solar systems form and how common Earth-like planets might be around stars far from our own.

Discovery

When scientists studied the star Gliese 876, they already knew it had one planet, called Gliese 876 b. Then, on January 9, 2001, they found a second planet, named Gliese 876 c. They discovered this by looking at how the star's movement changed over time, called its radial velocity. The time it takes for Gliese 876 c to go around its star is exactly half the time it takes the farther planet, which made scientists at first think the first planet's orbit was shaped differently than it really was.

Host star

Main article: Gliese 876

The planet Gliese 876 c orbits a small, cool star called Gliese 876. This star is much smaller and cooler than our Sun, with only about a third of the Sun’s mass and radius. It has been shining for 2.55 billion years.

Orbit and mass

Gliese 876 c is in a special pattern called a 1:2:4 Laplace resonance with two other planets, Gliese 876 b and Gliese 876 e. This means that for every orbit planet e makes, planet b makes two orbits and planet c makes four orbits. This pattern was first seen with Jupiter's moons Io, Europa, and Ganymede.

The planet is very close to its star, only about a third of the distance between Mercury and the Sun. Even though it is close, it is still in a place where liquid water could exist because its star is very dim. Scientists think the planet’s mass is about 0.72 times the mass of Jupiter.

Characteristics

Gliese 876 c is likely a gas giant, meaning it doesn’t have a solid surface like Earth. Because we detected it by its effect on its star, we don’t know its exact size, what it’s made of, or its temperature. Scientists think it might have a clear upper atmosphere.

The planet orbits at the inner edge of its star’s habitable zone, which is the area around a star where liquid water could exist on a planet’s surface. Even though gas giants may not support life themselves, a large moon orbiting this planet might have conditions right for life. However, the gravitational pull from the star and planet could prevent such moons from staying stable long enough to be habitable.