Scientists have searched for years for a suitable planet for life. But now, it seems as though the very first planet capable of supporting life has been discovered.
In April, 2007, scientists used the High Accuracy Radial Planet Searcher (dubbed HARPS) to discover a planet in the Libra constellation. The star it was revolving around was named Gliese and this planet, the fourth in line to go around the star, was dubbed Gliese 581 d. The scientists used a technique called radial velocity technique to determine the mass and size of the planet. This technique uses the minute wobble and changes in orbit of the star created by the orbiting planet to estimate the planet’s diameter and mass. The estimates on radius and mass are 1.5 and 6 times that of Earth respectively.
Although, soon after discovery, the planet was said to be on the outer limit of habitability, it was in 2009 that astronomers found out that the planet revolved Gliese 581 much closer than they actually estimated. This would put the planet in the habitable zone, a zone in space near the star where liquid water and suitable climate can actually develop to support life.
This has sparked interest in scientists, who believe they have actually discovered what they believe to be the first exosolar planet among several others to actually have a chance to support life. Not only that, they also believe that they have found the first planet other than Earth in the universe that is a serious “Ocean Planet” candidate, being covered by an ocean rivalling that on Earth, large and deep.
Regarding starlight, Gliese 581 d recieves about 30% of the light recieved here on Earth. To emphasize on how small this is, Mars, our solar neighbour, recieves 40% of the light recieved by us. That puts the temperature of Gliese 581d at very cold, in fact colder than Mars. But scientists have said that Gliese 581d, unlike Mars, lies in the habitable zone. It is also much heavier than Mars. This, as scientists say, can be very influential in creating one thing that is very vital for survival – atmosphere.
Planets which are heavy have a higher gravitational pull. So it is much more likely that Gliese 581d has retained any gases it has trapped, unlike Mars. When there is an atmosphere, there is also something which is currently in excess in Earth, threatening life – The greenhouse effect.
The greenhouse effect has rocketed into fame so fast in recent years, and not without reason. I don’t need to repeat the effects that global warming is causing that is causing the ice caps to melt. Scientists have calculated that if greenhouse effect were not present, then our planet would be about -18°C (this is a piece of knowledge distributed to the general public). The very fact that greenhouse effect boosts the temperature from below freezing to causing the ice caps to melt, is the same that has the capability to make Gliese 581 d very much habitable.
Its parent star is the Gliese 581, located in the Libra constellation, about 20.3 light years away from Earth. It is a red dwarf and its mass is one-third that of the Sun. It has atleast four planets, Gliese 581b, c, d and e.
Although Gl 581 c was first thought to be within the habitable zone, scientists have since then come to the conclusion that Gl 581c would have a runaway greenhouse atmosphere, rather like Venus. A runaway greenhouse atmosphere means that the possible vast resources of greenhouse gases in the crust or in any other form were released abruptly, causing intense greenhouse effect. In contrast, Gl 581d is thought to be in the habitable zone much more firmly. Given below are the comparitive sizes of the Sun and Gliese 581. The smaller star is Gliese.
From this, we can quite easily see the difference in the intensity of light. The sun is comparitively very young, while Gliese 581 is atleast a billion years old. The Sun emits radiation primarily in the visible part of the spectrum in the yellow region, while Gl 581 emits radiation primarily in the infrared region, thus the red coloration in the image.
While Gliese 581 holds much promise for the presence of life, we’ll have to wait and observe as the nature of the atmosphere is the deciding factor for the presence of any form of life.