Gliese 581g, also Gl 581 g or GJ 581 g, is an unconfirmed extrasolar planet of the red dwarf star Gliese 581, 20.5 light-years from Earth in the constellation of Libra. It is the sixth planet discovered in the Gliese 581 planetary system and the fourth in order of increasing distance from the star.
Why is it on the unconfirmed list? Extraordinary claims require extraordinary evidence in science, as late planetary scientist Carl Sagan once said, and that meant extraordinary scrutiny for Gliese 581g. The scrutiny came only two weeks after the world was first announced, from astronomer Francesco Pepe of Switzerland's Geneva Observatory, part of the High Accuracy Radial velocity Planet Searcher (HARPS) team, which had first detected four planets around Gliese 581 in 2009. More data collected by his European team showed no sign of Gliese 581g, Pepe and colleagues said.
Gliese 581g was detected through 11 years of Lick Observatory telescope data collected by Steve Vogt of the University of California-Santa Cruz, and his colleagues, measuring back-and-forth gravitational wobbles that the planet, along with at least four others in its solar system, induced on the star as they orbited. This "Doppler method" isn't perfect, and the Paris Observatory list includes nearly 160 "controversial, unconfirmed or retracted" planets on its list, including the Goldilocks planet, many of them first detected through stellar wobbles.
Contrary to F11’s conclusions, we find that the full 240-point HARPS data set, when properly modeled with self-consistent stable orbits, by and of itself actually offers confirmative support for a fifth periodic signal in this system near 32-33 days, and is consistent with the possibility of having been detected as GJ 581g at its 36-day yearly alias period by V10. The residuals periodograms both of our interacting and non-interacting fits and of the F11 four-planet circular fit reveal distinct peaks near 32 days and 190 days. Both of these residuals peaks are largely simultaneously accounted for by adding a fifth planet at 32.1 days to the system
As regards GJ 581g, they conclude that, from a statistical point of view, given the data sets of M09 and V10, it is not incorrect to state the existence of GJ 581g. However, this requires the assumption that all planets in this system are in essentially circular orbits, an assumption strongly supported by the above-mentioned Bayesian studies.
Vogt [an astronomer at the University of California, Santa Cruz] and his team found 581f and 581g using the so-called radial velocity — or Doppler — method, which looks for tiny wobbles in a star's movement caused by the gravitational tugs of orbiting planets.
To detect such subtle movements, the researchers looked at data from two different instruments: the HARPS spectrograph, on a telescope in Chile, and the HIRES spectrograph, on Hawaii's Keck Telescope.
Another planet in the system, called Gliese 581g, is about three times as massive as Earth, and it's also most likely a rocky world. This planet received a lot of attention when its discovery was announced in September 2010, because it's located right in the middle of the habitable zone. That makes 581g a prime candidate for liquid water and life as we know it — if the planet exists.
The scientists were not clear whether this liquid is frozen and stored under the surface or flowing freely across the planet. [Vogt] said that the planet has “churchly weather”.However the researchers were unable to determine what the surface of the planet is like, Vogt was quoted as saying by The Daily Telegraph.
It is known as a “super earth” due to its ability to hold on to its gassy atmosphere, which increases its chances of retaining liquid. While such claims by lead researcher Professor Vogt from the University of California have been previously reported, a new study, released to News.com.au this week, dismisses calls of balderdash by the international science community, the report said. Vogt said that he has since named it ‘Zarmina’s world’, after his wife.
One of the planets, named Gliese 581g, has a mass of three to four times that of Earth and takes 37 days to orbit the star. Astronomers believe it is a rocky planet with enough gravity to retain an atmosphere
A team of planet hunters spotted the alien world circling a red dwarf star called Gliese 581, 20 light years away.
The planet is in the "Goldilocks zone" of space around a star where surface temperatures are neither too hot nor too cold for liquid water to form.