A team of astronomers have discovered another terrestrial planet around a distant star which could turn out to be suitable for life.
The planet, dubbed HD 85512b, has only recently been found using a special detector called the High Accuracy Radial velocity Planet Searcher (HARPS) spectrograph at La Silla Observatory in Chile.
It is at least three and a half times more massive than the Earth and orbits a K-type star, which is around 1000 degrees Kelvin cooler than our Sun. Also known as Gliese 370, it lies 36 light-years away in the southern constellation of Vela.
This cooler host star means that a planet which orbits relatively close to it can still reside in what is known as the Habitable Zone (HZ), as is the case with HD 85512b. Although it is only a quarter of an Astronomical Unit from its parent star (about 37.4 million km), it orbits just within the HZ meaning it could potentially harbour extraterrestrial life.
Put simply, the HZ is an area around a star where liquid water can exist on the surface of a planet. Water is essential for life as we know it so it is a good starting point to search for water when looking for habitable planets. The HZ lies close to the star for cool stars and at is situated at larger distances from hot stars.
However, there are many other factors which go into defining the HZ other than the region where liquid water can exist. The composition of the atmosphere is important, as the correct combination of gases is needed in order for temperature to be just right on the surface. Excessive greenhouse gases will raise the temperature of the planet beyond that suitable for life.
Astronomer Lisa Kaltenegger and her colleagues used computer models based on the Earth’s atmosphere to determine if HD 85512b could be habitable. “Earth-based models are what we know could provide habitability (we got the Earth), so other models could potentially provide habitability, but we have no sample – like the Earth – that we could use to have a first idea about habitability,” Kaltenegger told Skymania News.
Another thing they considered was the effect of clouds on habitability. As the planet is at the inner edge of the HZ, it is expected to be quite warm. A planet with no low-lying clouds would absorb more light than it reflects and be too warm for liquid water to exist. However if HD 85512b has more than 50 per cent cloud cover, then the clouds will reflect some of the light from the star and make it suitably cool on the surface.
“As to whether it is really habitable, we’ll need a spectrum to tell that – direct imaging would be the ticket. With a direct imaging mission we could detect if it looks habitable. We could detect clouds if we had a big enough telescope in space,” explained Kaltenegger. So the planet is not necessarily habitable simply because it resides in the HZ, but this is certainly an important step towards finding planets like our own.
Astronomers have previously reported other new planets that might be habitable, for example Gliese 581g last year plus a neighbouring world that might even have oceans, an atmosphere and rainfall.