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TOPIC: Gl581 planet


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According to the European Southern Observatory, a team of French and Swiss astronomers working at the La Silla observatory in Chile discovered a planet about the size of Neptune located some 20.5 light years from our solar system.

The still unnamed planet is located in the Libra constellation and has about 17 times the mass of the Earth. It takes only 5 days to complete its orbit around a star that has about a third the mass of the Earth's sun.
The star Gliese 581, (G1 581), is a red dwarf, a small, cool, and faint star that is the most common type in our galaxy. Since 80 of the 100 stars closest to the sun are red dwarfs, astronomers are interested in discovering if they have planets orbiting them.

Position(2000): RA: 15 19 26.8 Dec: -07 43 20
Size 12'9 x 12'9

"Our discovery could mean that planets orbiting small stars are common. This tells us that red dwarfs are key in the search for exoplanets" - Xavier Delfosse, member of France's Grenoble Astrophysics Laboratory.

Of the currently known 170 planets circling other stars, only five of them are smaller than this newly discovered planet.
The discovery was made possible by a high precision instrument called HARPS that astronomers installed in the telescope of the observatory in north central Chile.
The planet was revealed by the wobble it induces on the host star. With the HARPS very precise measurements, the astronomers found the star to move back and forth with a maximum velocity of 13 metres/second, or a little bit less than 50 km/h.

This image shows the radial velocities of the red dwarf Gliese 581 as a function of the orbital phase. The amplitude of the detected variation is 13.2 m/s and the curve is consistent with a circular orbit. The orbital period is 5.366 days.

The planet orbits at only 3.7 million miles from its star, which leads scientists to estimate its surface temperature at about 302 degrees Fahrenheit (150 degrees centigrade).
Mercury, the planet closest to the sun, by comparison is 36 million miles from the sun and its orbit takes 88 days.

Read More (French)



Posts: 131433
Gl581 planet

Researchers have discovered a Neptune-mass planet around the M dwarf star Gl 581 (Spectral Type M3V, 0.31 solar masses), using precise Doppler measurements with the HARPS spectrograph at the La Silla Observatory.
The observed radial velocities reveal a circular orbit with a period of 5.366 (± 0.001) days and semi-amplitude K1 = 13.2 m/s. It has an orbital Semi major axis of 0.041 AU.
The resulting minimum mass of the planet is only 0.052 Jupiter masses or 0.97 Neptune masses.
This makes Gl 581b one of the lightest extra-solar planet (16.6 earth masses) known to date.

The Gl 581 planetary system is only the third centred on an M dwarf, joining the Gl 876 three-planet system and the lone planet around Gl 436.
Its discovery reinforces the emerging tendency of such planets to be of low mass, and found at short orbital periods. The statistical properties of the planets orbiting M dwarfs do not seem to match a simple mass scaling of their counterparts around solar-type stars.

The star system lies 20.4 light years away in the constellation libra

Position(2000): RA =15 19 26 Dec = -07 43 20

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