This artist’s conception shows the inner four planets of the Gliese 581 system and their host star. The large planet in the foreground is Gliese 581g, which is in the middle of the star’s habitable zone and is only two to three times as massive as Earth. Some researchers aren’t convinced Gliese 581g exists, however.
Nearly two years after spotting Gliese 581g, the celebrated “first potentially habitable” alien world, the planet’s discoverers continue to fight for its existence.
The discovery of Gliese 581g made headlines around the world in September 2010, because the planet was said to orbit in the middle of its star’s “habitable zone” — that just-right range of distances where liquid water, and perhaps life as we know it, could exist.
Just a few weeks later, however, another prominent research team began casting doubt on the find, saying the alien planet didn’t show up in their observations. This group, led by Michel Mayor of the Geneva Observatory in Switzerland, had found the previously known four planets in the Gliese 581 system.
But in a new study that will be published Aug. 1, 581g’s discoverers examine the Swiss team’s since-expanded data set and take issue with their conclusions, saying that the evidence supports the planet’s existence after all.
The data and analyses “point to there being at least one other planet beyond the confirmed 4, a 5th planet, with a period in the 26-39-day regime,” lead author Steve Vogt, an astronomer at the University of California, Santa Cruz, told SPACE.com via email. [The Strangest Alien Planets]
“This 5th planet would have a mass of only 2-3 [times that of] Earth, and would orbit pretty much squarely in the star’s habitable zone,” he added.
The orbits of planets in the Gliese 581 system are compared to those of our own solar system. The Gliese 581star has about 30 percent the mass of our sun, and the outermost planet is closer to its star than we are to the sun. Gliese 581d might be able to sustain liquid water on its surface.
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Remember Gliese 581g? The potentially habitable “second Earth” 20 light years away, also known as Zarmina? It’s been looking dicey for a while, as many astronomers questioned its very existence. But now, Gliese 581g has been re-added to the top five list of exoplanets considered prime candidates for harboring of life.