Gliese 581 is a cool, dim M-type main-sequence star (M3V), located about 20 light years away from Earth in the constellation of Libra. It is the 89th closest star to the Sun.
History[]
Gliese 581 has been known to astronomers since at least 1886, when it was included in Eduard Schönfeld's Southern Durchmusterung (SD), with a designation of "BD -7 4003".
The current name, Gliese 581, refers to its number from the 1957 survey "Gliese Catalogue of Nearby Stars", a catalog containing 965 stars that were located within 20 parsecs (65 light years) from Earth. The star does not have a proper name.
Characteristics[]
Gliese 581 is an M3V red dwarf, and has an estimated mass of almost a third (~31 percent) of the Sun's mass. Because of its lower mass, the core region of the star fuses hydrogen at a significantly lower rate than the Sun. The size of Gliese 581 is about 29% that of the Sun. Based on its apparent magnitude and distance, the estimated temperature of the star is about 3200 K, and has a visual luminosity of 0.2 percent of that of the Sun. To receive the same amount of energy that Earth does from the Sun, a planet orbiting a star like Gliese 581 would need to be fairly close to it. The region of space around a star is sometimes referred to as the "Goldilocks zone", but is more frequently called the "habitable zone". The extent of such a zone is not fixed and is highly specific for each planetary system.
Gliese 581 is a relatively "inactive" star, with a rotational period of about 94.2 days. Gliese 581's kinematic characteristics, magnetic activity, and sub-Solar metallicity indicate that Gliese 581 is, at minimum, 2 billion years old. The Canadian Space Agency's MOST satellite monitored Gliese 581 for a month and a half in 2007, and found that the brightness of the star varied by only a few tenths of a percent, which suggests that the star is several billions of years old. It is likely around 7 billion years old, possibly as old as 11 billion, based on current knowledge of the star.
Gliese 581 is classified as a variable star of the BY Draconis type, and has been given the variable star designation "HO Librae". This is a star that exhibits variability because of the presence of star spots combined with the rotation of the star. However, the measured variability is close to the margin of error, and, if real, is most likely a long term variability. Its brightness is stable to 1%. Gliese 581 is known to emit X-rays.
Planetary system[]
- See Gliese 581 planetary system for more information.
| Planet | Mass | Semimajor axis | Orbital period (days) | Eccentricity | Inclination | Radius |
|---|---|---|---|---|---|---|
| b | ≥15.8 Earth mass | 0.0406 AU | 5.37 days | 0.00-0.03 | N/A | N/A |
| c | ≥5.5 Earth mass | 0.073 AU | 12.9 days | 0.00-0.06 | N/A | N/A |
| d (unconfirmed) | ~6.98 Earth mass | 0.218 AU | 66.7 days | 0.00-0.25 | N/A | N/A |
| Debris disk | N/A | 25 ± 12 AU->60 AU | N/A | N/A | N/A | N/A |
| e | ≥1.7 Earth mass | 0.0285 AU | 3.15 days | 0.00-0.06 | N/A | N/A |
| g (unconfirmed) | ≥2.2 Earth mass | 0.13 AU | 32 days | 0.00 | N/A | N/A |
| Inner H.Z. edge | N/A | ~0.11 AU | N/A | N/A | N/A | N/A |
| Outer H.Z. edge | N/A | ~0.28 AU | N/A | N/A | N/A | N/A |