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http://www.examiner.com/astronomy-i...-earth-exoplanet-habitable-zone-of-gliese-581
Astronomers discover Super-Earth exoplanet in habitable zone of Gliese 581
* September 30th, 2010 11:31 am ET
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On September 28, 2010 a team of astronomers led by Steven S. Vogt announced the discovery of the first Earth-like exoplanet orbiting in the habitable zone of another star. The star, Gliese 581, is about 20 light years away in the constellation Libra. The newly discovered exoplanet is the most Earth-like planet discovered to date.
The new extrasolar planet Gliese 581g (aka GJ 581g) is about 0.146 astronomical units (just under 22 million kilometers or 14 million miles) from Gliese 581. GJ 581g has a 36.6 day orbital period and a minimum mass of 3.1 times Earth's mass. Astronomers have not yet measured GJ 581g's diameter, however if it has a density similar to Earth's it would have a diameter about 1.2 to 1.4 times Earth's diameter. The gravitational force on the surface would be at most just slightly higher than Earth's.
Gliese 581 is an M spectral class main sequence star with about 30% the mass and diameter of the Sun and about 1.3% the Sun's luminosity. Because it is cooler, smaller, less massive, and less luminous than the Sun it's habitable zone is much closer to the star than the Sun's habitable zone. GJ 581g is near the center of the habitable zone despite being closer to its parent star than Mercury is to the Sun.
Using the temperature of Gliese 581 and the distance to Gliese 581g, allows astronomers to calculate the equilibrium temperature of the planet, which is the temperature the planet would have with no atmosphere. Gliese 581g has an equilibrium temperature of 228 Kelvins (-45° C), which is about 27 Celsius degrees cooler than Earth's equilibrium temperature. An atmosphere would trap heat and increase the temperature above the equilibrium temperature. GJ 581g has a temperature that could support liquid water and life, if other conditions are right. Astronomers do not yet know if other conditions are right.
Vogt's team discovered GJ 581g using very high resolution spectra from the 10 meter Keck I telescope and the HIRES (High Resolution Echelle Spectrometer) spectrometer, which Vogt designed. The HIRES spectrometer can measure radial velocities (velocities moving directly towards or away from Earth) of stars to an accuracy of about 1 meter/second (an easy walking speed). Doubling the amount of data on Gliese 581, the astronomers collected 122 radial velocity measurements of Gliese 581 over 11 years and combined their data with 119 previously published radial velocities.
When a planet orbits a star, the star also wobbles ever so slightly as it orbits the mutual center of mass of the star and planet. A star with multiple planets, such as Gliese 581, will have the wobbles for each of the planets superposed on each other. Astronomers must sort out the individual wobbles from the sensitive radial velocity measurements to find the periodic wobbles corresponding to each planet. These data then allow astronomers to calculate the mass and orbital period for each of the planets.
With their new data, Vogt's team confirmed four previously discovered planets orbiting Gliese 581. They also discovered two Super-Earth planets in this system. A Super-Earth planet is an exoplanet with less than 10 times the Earth's mass. In addition to Gliese 581g, they discovered Gliese 581f orbiting 0.758 astronomical units (about 110 million kilometers or 70 million miles) from Gliese 581 every 433 days. Gliese 581f a minimum mass of about 7 times earth's mass. Gliese 581f is too far from the parent star to be in the habitable zone.
The new Earth-like planet is officially designated either Gliese 581g or GJ 581g. Vogt has however unofficially named the planet Zarmina's World in honor of his wife.
Vogt's team will publish their results in a paper in the Astrophysical Journal.
Suggested by the author:
* NASA Kepler mission discovers two planets like Saturn orbiting the sun-like star Kepler-9
* NASA Kepler mission discovers hot stellar companions possible new class of astronomical objects
* Astronomy 101: How astronomers discovered the water planet GJ 1214b
* Astronomers discover planet outside solar system similar to Jupiter and Saturn
* Astronomers discover water ice, organic molecules on asteroid 24 Themis
Astronomers discover Super-Earth exoplanet in habitable zone of Gliese 581
* September 30th, 2010 11:31 am ET
Do you like this story?
On September 28, 2010 a team of astronomers led by Steven S. Vogt announced the discovery of the first Earth-like exoplanet orbiting in the habitable zone of another star. The star, Gliese 581, is about 20 light years away in the constellation Libra. The newly discovered exoplanet is the most Earth-like planet discovered to date.
The new extrasolar planet Gliese 581g (aka GJ 581g) is about 0.146 astronomical units (just under 22 million kilometers or 14 million miles) from Gliese 581. GJ 581g has a 36.6 day orbital period and a minimum mass of 3.1 times Earth's mass. Astronomers have not yet measured GJ 581g's diameter, however if it has a density similar to Earth's it would have a diameter about 1.2 to 1.4 times Earth's diameter. The gravitational force on the surface would be at most just slightly higher than Earth's.
Gliese 581 is an M spectral class main sequence star with about 30% the mass and diameter of the Sun and about 1.3% the Sun's luminosity. Because it is cooler, smaller, less massive, and less luminous than the Sun it's habitable zone is much closer to the star than the Sun's habitable zone. GJ 581g is near the center of the habitable zone despite being closer to its parent star than Mercury is to the Sun.
Using the temperature of Gliese 581 and the distance to Gliese 581g, allows astronomers to calculate the equilibrium temperature of the planet, which is the temperature the planet would have with no atmosphere. Gliese 581g has an equilibrium temperature of 228 Kelvins (-45° C), which is about 27 Celsius degrees cooler than Earth's equilibrium temperature. An atmosphere would trap heat and increase the temperature above the equilibrium temperature. GJ 581g has a temperature that could support liquid water and life, if other conditions are right. Astronomers do not yet know if other conditions are right.
Vogt's team discovered GJ 581g using very high resolution spectra from the 10 meter Keck I telescope and the HIRES (High Resolution Echelle Spectrometer) spectrometer, which Vogt designed. The HIRES spectrometer can measure radial velocities (velocities moving directly towards or away from Earth) of stars to an accuracy of about 1 meter/second (an easy walking speed). Doubling the amount of data on Gliese 581, the astronomers collected 122 radial velocity measurements of Gliese 581 over 11 years and combined their data with 119 previously published radial velocities.
When a planet orbits a star, the star also wobbles ever so slightly as it orbits the mutual center of mass of the star and planet. A star with multiple planets, such as Gliese 581, will have the wobbles for each of the planets superposed on each other. Astronomers must sort out the individual wobbles from the sensitive radial velocity measurements to find the periodic wobbles corresponding to each planet. These data then allow astronomers to calculate the mass and orbital period for each of the planets.
With their new data, Vogt's team confirmed four previously discovered planets orbiting Gliese 581. They also discovered two Super-Earth planets in this system. A Super-Earth planet is an exoplanet with less than 10 times the Earth's mass. In addition to Gliese 581g, they discovered Gliese 581f orbiting 0.758 astronomical units (about 110 million kilometers or 70 million miles) from Gliese 581 every 433 days. Gliese 581f a minimum mass of about 7 times earth's mass. Gliese 581f is too far from the parent star to be in the habitable zone.
The new Earth-like planet is officially designated either Gliese 581g or GJ 581g. Vogt has however unofficially named the planet Zarmina's World in honor of his wife.
Vogt's team will publish their results in a paper in the Astrophysical Journal.
Suggested by the author:
* NASA Kepler mission discovers two planets like Saturn orbiting the sun-like star Kepler-9
* NASA Kepler mission discovers hot stellar companions possible new class of astronomical objects
* Astronomy 101: How astronomers discovered the water planet GJ 1214b
* Astronomers discover planet outside solar system similar to Jupiter and Saturn
* Astronomers discover water ice, organic molecules on asteroid 24 Themis
