Saturday, October 16, 2010

Gliese 581 d and Gliese 581 g

Gliese 581 d or Gl 581 d is an extrasolar planet orbiting the star Gliese 581 approximately 20 light-years away in the constellation of Libra.
It is the third planet discovered in the system and the fifth in order from the star.
Because of its mass, at least 5.6 times that of Earth, the planet is classified as a super-Earth. In late April 2009, new observations by the original discovery team concluded that the planet is on the outskirts of the habitable zone where liquid water may exist.

It was originally thought that Gliese 581 d orbits outside the habitable zone of its star. However, in 2009 the original discovery team revised its original estimate of the planet's orbital parameters, finding that it orbits closer to its star than originally believed. They concluded that the planet is within the habitable zone where liquid water could exist. According to St├ęphane Udry, "It could be covered by a 'large and deep ocean'; it is the first serious ocean planet candidate."

Gliese 581 g is probably even better though:
Studies indicate that the planet is situated near the middle of the habitable zone of its parent star, where temperatures are neither too hot nor too cold. If it is a rocky planet, favorable atmospheric conditions could permit the presence of liquid water, a necessity for all known life, on its surface. With a mass 3.1 to 4.3 times Earth's, Gliese 581 g is considered a super-Earth, and is the planet closest in size to Earth known in a habitable zone. This makes it the most Earth-like Goldilocks planet found outside the Solar System and the exoplanet with the greatest recognized potential for harboring life.

Gliese 581 g has an orbital period of 37 days, orbiting at a distance of 0.146 AU from its parent star. It is believed to have a mass of 3.1 to 4.3 times that of the Earth and a radius of 1.3 to 2.0 times that of Earth (1.3 to 1.5 times Earth's if predominantly rocky, 1.7 to 2.0 times Earth's
if predominantly water ice). Its mass indicates that it is probably a rocky planet with a solid surface. The planet's surface gravity is expected to be in the range of 1.1 to 1.7 times Earth's,
enough to hold on to an atmosphere that is likely to be denser than Earth's.

Obviously both Jan and I texted them out there in the Gliese system:

As part of the 2009 National Science Week celebrations in Australia, Cosmos Magazine launched a website called Hello From Earth to collect messages for transmission to Gliese 581d. The maximum length of the messages was 160 characters, and they were restricted to the English language.
In total, 25,880 messages were collected from 195 countries around the world. The messages were transmitted from the DSS-43 70 m radio telescope at the Canberra Deep Space Communication Complex at Tidbinbilla, Australia on the 28th of August, 2009.



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