Sibling world may be the lightest and wettest known

Gliese 581d



A planet orbiting a red dwarf star 20 light years away could be the first known water world, entirely covered by a deep ocean.

The planet, named Gliese 581d, is not a new discovery, but astronomers have now revised its orbit inwards, putting it within the "habitable zone" where liquid water could exist on the surface. "It is the only low-mass planet known inside the habitable zone", says Michel Mayor of Geneva Observatory.

Mayor and his team used the European Southern Observatory's 3.6-metre telescope in Chile to observe the low-mass star Gliese 581, and a precise spectrometer called HARPS to analyse its light.

That turned up the faint footprints of four planets, since the orbiting planets make the star wobble slightly, giving its light a slight Doppler shift. Three of the planets had been identified previously.

The outermost planet had been thought to have a period of 83 days, putting it too far away from the small star's gentle heat to bear liquid water. But that was a mistake. "We only had a limited number of observations", Mayor told New Scientist. Now with three times as much data, he finds an orbital period of 66 days, putting the planet closer to its star – about a quarter of the Earth-Sun distance – and just inside the red dwarf's habitable zone.
New class

Gliese 581d is about seven times as massive as Earth, so it is much too small to be a gas giant like Jupiter, but probably too big to be a rocky world like our own. "Around such a small star, it is very difficult to have so much rocky material at such a [large] distance," says Mayor. Instead, the planet is likely to have a makeup similar to Neptune or Uranus, which are dominated by ices of water, ammonia and methane.

In the warmth of the habitable zone, these substances should form a sea thousands of kilometres deep. "Maybe this is the first of a new class of ocean planets. That is my favourite interpretation," says Mayor. "Whether there is life or not, I don't know."

The same set of observations also revealed a new world, Gliese 581e, with only 1.9 times the mass of Earth. That is the lowest published mass of any exoplanet around a normal star – although preliminary results have hinted that another exoplanet may weigh just 1.4 Earth masses. Gliese 581e is very close to the star, however, and probably far too hot for liquid water.

The results were announced on Tuesday at the European Week of Astronomy and Space Science meeting in Hatfield, UK.

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This makes me wonder what kind of life other than our planet is out in the vast universe.
I was recently observing the size of the Earth compared to the Sun, and the size of the Sun compared to a Hyperstar:




It's really astounding.

Whatever is out there... They better not be a bunch of queers.

I added the thread to the front page. Unfortunately, as far as I know, the radial velocity detection technique doesn't give enough data about an exoplanet for one to determine its surface gravity. Its lowest mass is approximately 7.09 M⊕[3] (Earth masses). Assuming its mean density to be that of Mars (approximately 3934 kg/m³, while Earth's mean density is approximately 5519 kg/m³), then its surface gravity is approximately



So with a reasonably low estimate for the density of Gliese 581 d and the current lowest estimate for its mass, its gravitational field will still make everything 54% "heavier" than on Earth. While health effects of long-term exposure to high gravity are not known, it will be more difficult to perform most kinds of work.

Now, if its actual mass turns out to be that of the highest estimate (22 M⊕) and its mean density is that of Earth (one of the most dense terrestrial planets in our solar system), its surface gravity becomes That is equivalent to 281% of Earth's surface gravity, or roughly the total acceleration subjected to the crew of the space shuttle-carrying rocket during launch[2].

That's really cool. Makes me wonder if our definition of habitable would be the same for another species out there, though...

I love this kind of stuff.

I added the thread to the front page. Unfortunately, as far as I know, the radial velocity detection technique doesn't give enough data about an exoplanet for one to determine its surface gravity. Its lowest mass is approximately 7.09 M⊕[3] (Earth masses). Assuming its mean density to be that of Mars (approximately 3934 kg/m³, while Earth's mean density is approximately 5519 kg/m³), then its surface gravity is approximately So with a reasonably low estimate for the density of Gliese 581 d and the current lowest estimate for its mass, its gravitational field will still make everything 54% "heavier" than on Earth. While health effects of long-term exposure to high gravity are not known, it will be more difficult to perform most kinds of work. Now, if its actual mass turns out to be that of the highest estimate (22 M⊕) and its mean density is that of Earth (one of the most dense terrestrial planets in our solar system), its surface gravity becomes That is equivalent to 281% of Earth's surface gravity, or roughly the total acceleration subjected to the crew of the space shuttle-carrying rocket during launch[2].

Hushahaw-haw-haw what~?
This is what I get for leaving the "talk like a retard thread" ain't it? I'm so lost...