First Potentially Habitable Exoplanet Found

[Tormod]

A team of planet hunters from the University of California (UC) Santa Cruz, and the Carnegie Institution of Washington has announced the discovery of a planet with three times the mass of Earth orbiting a nearby star at a distance that places it squarely in the middle of the star's "habitable zone."

 

This discovery was the result of more than a decade of observations using the W. M. Keck Observatory in Hawaii, one of the world's largest optical telescopes. The research, sponsored by NASA and the National Science Foundation, placed the planet in an area where liquid water could exist on the planet's surface. If confirmed, this would be the most Earth-like exoplanet yet discovered and the first strong case for a potentially habitable one.

 

To astronomers, a "potentially habitable" planet is one that could sustain life, not necessarily one where humans would thrive. Habitability depends on many factors, but having liquid water and an atmosphere are among the most important.

 

 

The new findings are based on 11 years of observations of the nearby red dwarf star Gliese 581using the HIRES spectrometer on the Keck I Telescope. The spectrometer allows precise measurements of a star's radial velocity (its motion along the line of sight from Earth), which can reveal the presence of planets. The gravitational tug of an orbiting planet causes periodic changes in the radial velocity of the host star. Multiple planets induce complex wobbles in the star's motion, and astronomers use sophisticated analyses to detect planets and determine their orbits and masses.

 

"Keck's long-term observations of the wobble of nearby stars enabled the detection of this multi-planetary system," said Mario R. Perez, Keck program scientist at NASA Headquarters in Washington. "Keck is once again proving itself an amazing tool for scientific research."

 

Steven Vogt, professor of astronomy and astrophysics at UC Santa Cruz, and Paul Butler of the Carnegie Institution lead the Lick-Carnegie Exoplanet Survey. The team's new findings are reported in a paper published in the Astrophysical Journal and posted online at:

 

http://arxiv.org

 

"Our findings offer a very compelling case for a potentially habitable planet," said Vogt. "The fact that we were able to detect this planet so quickly and so nearby tells us that planets like this must be really common."

 

The paper reports the discovery of two new planets around Gliese 581. This brings the total number of known planets around this star to six, the most yet discovered in a planetary system outside of our own. Like our solar system, the planets around Gliese 581 have nearly-circular orbits.

 

The new planet designated Gliese 581g has a mass three to four times that of Earth and orbits its star in just under 37 days. Its mass indicates that it is probably a rocky planet with a definite surface and enough gravity to hold on to an atmosphere.

 

Gliese 581, located 20 light years away from Earth in the constellation Libra, has two previously detected planets that lie at the edges of the habitable zone, one on the hot side (planet c) and one on the cold side (planet d). While some astronomers still think planet d may be habitable if it has a thick atmosphere with a strong greenhouse effect to warm it up, others are skeptical. The newly-discovered planet g, however, lies right in the middle of the habitable zone.

 

 

The planet is tidally locked to the star, meaning that one side is always facing the star and basking in perpetual daylight, while the side facing away from the star is in perpetual darkness. One effect of this is to stabilize the planet's surface climates, according to Vogt. The most habitable zone on the planet's surface would be the line between shadow and light (known as the "terminator").

 

Source: NASA

 

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[Jay-qu]

Ok lets go, dont forget snacks.

[Boerseun]

Okay, from a practical standpoint, how would the atmospheric dynamics work on a tidally-locked planet? Will such a planet be able to hold on to its atmosphere? The atmosphere on the far side will be frozen and lying on the ground in a thick, solid sheet of ice, with the vacuum of space reaching to the surface, and on the sunward side it will be incredibly hot and boiling. The imagined habitable zone between the two will have to endure permanent gale-force winds coming from the frozen far side as the hot air from the sun side cools down and drops as it crosses the terminator, to be sucked back towards the sun side. I suppose if the planet is a little closer to its star it could be self-sustaining, if a little farther, more and more of the atmosphere will freeze on the far side until the entire atmosphere is frozen on the far side.

 

The biggest issue will be the composition of the atmosphere, I guess. Enough greenhouse gases might warm the far side sufficiently so that the atmosphere don't freeze out - enough heat transfer combined with the greenhouse effect will stabilise it and result in a consistent planet-wide atmosphere with violent heat exchanges between the two sides. Too little greenhouse gases and the whole thing will freeze out on the far side. But either ways, the region around the terminator will be the only viable place for life as we know it, but with the thermal exchange between the sunlit side and the dark side, it will be a thoroughly miserable place to live.

[Jay-qu]

I dont think it would be quite so extreme B, while Earths poles are only in darkness for a few months at a time, the coldest temps are only enough to freeze CO2. So I dont think the dark side of this planet could freeze a significant portion of atmosphere - certainly not the 02 and N2.

[Boerseun]

I dont think it would be quite so extreme B, while Earths poles are only in darkness for a few months at a time, the coldest temps are only enough to freeze CO2. So I dont think the dark side of this planet could freeze a significant portion of atmosphere - certainly not the 02 and N2.

I don't know - the Earth's poles might be in the dark for a few months of the year, true - but the landmass on the far side of a tidally-locked planet haven't seen the sun for millions or even billions of years. It should just get colder and progressively colder. On the winter poles on Earth the sun is also never quite that far away, and thermal input blows in through the air from the not-too-distant terminator, making it relatively mild compared to a landmass which is very far way from the terminator, and have been for ages. I think the livable terminator region should be a seriously nasty place... if only because of serious winds blowing.

 

Bottom line - I don't know. I should be quite different from what we know of terrestrial atmospherics, though.