Gliese 876
| Epoch 2000 | |
|---|---|
| Constellation | aquarius |
| Right Ascension | 22h 53m 16.73s |
| Declination | -14° 15' 49.3" |
| Distance | 15.4 ly (4.72 pc) |
| Spectral Type | M4V |
| Apparent Magnitude | 10.16 |
| Other Designations | ross 780, HIP 113020, BD-15°6290 |
Gliese 876 is a red dwarf star (spectral type M4V) 15 light years from Earth in the constellation of Aquarius. It is only half the size of our Sun but it has been found to be orbited by at least two large planets which are locked in a 2:1 orbital resonance, as well as one smaller, terrestrial planet. It is so far one of only two red dwarfs with known extrasolar planets, the other being GJ 436.
In June 2005 the National Science Foundation announced the discovery of the first possibly Earth-like sized extrasolar planet in orbit around Gliese 876. The discoverers estimate the minimum mass for the planet of 5.9 Earth masses, with a period of 1.94 days at a distance of 0.021 astronomical units (AU), or 2 million miles, about ten times the distance the Moon is from Earth.
| Contents |
Planets
Gliese 876 d
| Orbital elements | |
|---|---|
| Semi-major axis (a) | 0.021 AU |
| Eccentricity (e) | ? |
| Orbital period (P) | 1.94 d |
| Inclination (i) | ?° |
| Longitude of periastron (ϖ) | ?° |
| Time of periastron (τ) | ? JD |
| Physical characteristics | |
| Mass | 0.023 ±0.003 MJ |
| Radius | ? RJ |
| Density | ? kg/m³ |
| Temperature | ? K |
| Discovery | |
| Discoverers | E. Rivera et al |
| Discovery date | 2005 |
Gl876_planet1_h.jpg
Gliese 876 d is a low-mass extrasolar planet orbiting the star Gliese 876 with a period of 1.94 days at a distance of 0.021 astronomical units (AU), or 2 million miles. At the time of its announcement in June 2005, it was the smallest extrasolar planet found orbiting a normal star. Mass of the planet is estimated to lie between 6 and 8 Earth masses. It is possible that the planet is terrestrial (its low mass precludes it from retaining gas like Jupiter), a very small Neptune-like gas giant, or a mixture of both. This planet whips around its star in a mere two days, and is so close to the star's surface that its temperature probably tops 400 to 750 degrees Fahrenheit (200 to 400 degrees Celsius) — oven-like temperatures far too hot for life as we know it.
Gliese 876 c
| Orbital elements | |
|---|---|
| Semi-major axis (a) | 0.13 AU |
| Eccentricity (e) | 0.27 |
| Orbital period (P) | 30.12 d |
| Inclination (i) | ?° |
| Longitude of periastron (ϖ) | 330° |
| Time of periastron (τ) | 2450031.4 JD |
| Physical characteristics | |
| Mass | >0.56 MJ |
| Radius | ? RJ |
| Density | ? kg/m³ |
| Temperature | ? K |
| Discovery | |
| Discoverers | Butler, Marcy |
| Discovery date | 2001 |
Gliese 876 c is a gas giant half the size of Jupiter, discovered in 2001. It orbits within the star's habitability zone, a region in which the temperature is right for water to be liquid. This means that the planet itself would be partly made up of water clouds. In addition, if the planet has any large moons with atmospheres, life might have the potential to develop on them. However calculations of the hill zone of the planet have found that the maximum mass of any moon in a stable orbit to be far below that of Mars, killing any hope of life supporting moons.
Gliese 876 b
| Orbital elements | |
|---|---|
| Semi-major axis (a) | 0.21 AU |
| Eccentricity (e) | 0.10 |
| Orbital period (P) | 60.02 d |
| Inclination (i) | 84 ± 6° |
| Longitude of periastron (ϖ) | 333° |
| Time of periastron (τ) | 2450106.2 JD |
| Physical characteristics | |
| Mass | 1.89 ± 0.34 MJ |
| Radius | ? RJ |
| Density | ? kg/m³ |
| Temperature | ? K |
| Discovery | |
| Discoverers | Butler, Marcy, Mayor, Queloz |
| Discovery date | 1999 |
Gliese 876 b is a gas giant twice the size of Jupiter. Its orbit sometimes brings it within the outer edges of the star's habitability zone, but water would normally be frozen on the surface of its moons.