Scientists have long been fascinated with the search for life on other planets. The announcement last month of the discovery of a potentially habitable planet may turn this possibility into a fact.
According to preliminary reports, the newly discovered planet resembles Earth more than any other detected planet does. It is a terrestrial planet three times the mass of Earth. Most importantly, like Earth, it exists within the "Goldilocks zone" with relation to its nearest star: not too hot, not too cool — just right.
"A ‘Goldilocks' planet is one that falls within a star's habitable zone," Danilo Marchesini, an assistant professor of physics and astronomy, said. "A planet following this principle is one that is neither too close nor too far from a star to rule out liquid water on its surface, and thus life on the planet."
The planet, known as Gliese 581g, is the sixth member of the Gliese 581 planetary system and resides within the Libra constellation.
Kenneth Lang, a professor of physics and astronomy, explained that both the distance of a planet to a star and the intensity of that star are of the utmost importance with regard to habitability.
"If the star is dimmer, the planet can be closer to the star, and it can orbit around the star in less time than the Earth takes to orbit our sun," Lang said.
The discovery of Gliese 581g is monumental, Marchesini said, because it is essentially the first ‘Goldilocks' planet we know about, aside from Earth. While it is possible for pools of liquid to form on the planet's surface, scientists say, no actual evidence of pools or any water has yet been found.
"We do not know if Gliese 581g has water, if it is in sufficient amount and if it is in liquid form," Marchesini said.
Although the discovery of a stable planet is exciting news, there are still too many unknowns to conclude that there is life on the planet — or whether the planet itself actually exists.
Steven Vogt, a University of California, Santa Cruz professor who led the team responsible for the planet's discovery, maintains a positive attitude, reportedly saying that chance of life on Gliese 581g is 100 percent.
But a group of Swiss astronomers this week announced that they could not find evidence of the planet's existence.
"It is important to keep in mind that the discovery of this planet has not been confirmed by other groups," Marchesini said. "At the moment, we only know that this planet seems to be in the habitable zone of the star."
The discovery was the work of the Lick−Carnegie Exoplanet Survey, which, through ground telescopes and other more advanced technologies, has been tracking radial velocity measurements for 11 years; the telescopes detect wobbles when observing stars, which indicate that planets are orbiting around them.
An encouraging detail about Gliese 581g for those expecting to discover extraterrestrial life is the prediction that the planet may have an atmosphere. Additionally, the predicted age of its star, Gliese 581, is estimated to be about 4.3 billion years — only slightly younger than Earth's sun. There has been plenty of time, therefore, for life to develop within the system.
But not all scientists are so sure.
"Although the planet is in the habitable zone, whether or not there is life is a matter of speculation," Lang said. "It brings us to the larger question of whether or not you believe in extra−terrestrial life. Both are questions of faith and informed speculation."
Any life that is potentially found, however, will almost undoubtedly be drastically different from the life found on Earth, according to Marchesini.
"Life on Gliese 581g will likely be a bit harsher than on Earth," Marchesini said. "It is very likely that it developed a spin−synchronous configuration, meaning that one hemisphere of the planet is always in perpetual darkness."
Even if no life is found on Gliese 581g, though, the discovery of the planet opens up the possibility of other nearby "Goldilocks planets" that have yet to be discovered.
"This discovery seems to [be] telling us that such planets are actually quite common," Marchesini said. "And so the chances of finding intelligent life in the ‘solar neighborhood' might be higher than we thought."
Lang echoed that sentiment.
"It gives the potential of companionship in a lonely universe," he said.
