for National Geographic News
In the search for habitable planets around nearby stars, the greenhouse effect blamed for global warming on Earth may not always be bad news.
A French-led group of planetary researchers recently modeled the theoretical effects that a cocktail of "super-greenhouse" gases might have on a recently discovered giant planet.
The team found that the theoretical mixture may warm the planet Gliese 581 d to the right temperature for permanent liquid water, the major criterion of any habitable zone.
"Because this detection came very fast, big terrestrial planets seem to be abundant around red dwarf stars," said Franck Selsis at the University of Lyon, the lead author on the study. (Related: Record-Setting Fifth Planet Found Orbiting Nearby Star" [November 6, 2007].)
Combined with the new research, he said, soon "more planets will be found in the habitable zone of [red dwarfs]."
The new study is slated to appear in an upcoming issue of the journal Astronomy & Astrophysics.
Like Early Mars
The greenhouse effect can have negative consequences—it has made Venus an inhospitable inferno, for example.
But the heat-trapping effects of atmospheric gases helped make life on Earth possible. And if early Mars had been more massive, it might have had enough gravity to hold onto an atmosphere long enough to warm to habitable temperatures. (See a virtual solar system.)
To explore this issue, the team took a look at the three outermost planets circling the cool red dwarf star Gliese 581, which is located in the constellation Libra about 20.5 light-years away.
The group ran simulations of the possible warming effects on the three planets of carbon dioxide ice clouds, water, methane, and even ammonia—all potent greenhouse gases.
The most interesting results had to do with the "super Earth" called Gliese 581 d, which is at least 8.3 times the mass of Earth.
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