Experts call for scientists to establish a clear definition of "habitable planets" to make the search easier. They recommend researchers to take a conservative approach when looking for these planets.
According to James Kasting, an American geoscientist and well-known professor at Penn State University, a clear definition of "habitable planets" include the presence of water and solid surfaces just like Earth's body of waters and land. Therefore, they should not be wasting time looking at Jupiter and Saturn which are impossible to sustain life due to its hydrogen and helium atmospheric conditions. He believes that once a clear definition was made, scientists will be able to design spacecrafts that are more effective in locating other habitable planets than checking each planet encountered only to find out it is impossible to sustain life.
"It's one of the biggest and oldest questions that science has tried to investigate: is there life off the earth?" Kasting said in a press release. "NASA is pursuing the search for life elsewhere in the Solar System, but some of us think that looking for life on planets around other stars may actually be the best way to answer this question."
An earlier study Kasting co-authored with Ravi Kopparapu found that the frequency of habitable planets in M-dwarfs star is only 0.4 to 0.5. This means that there are 10 cool stars which scientists still need to explore. Their findings were backed up by NASA's Kepler Space Telescope.
M-dwarfs stars, or red dwarfs, are dim and bigger compared to our Sun. Scientists have studied the possibility of it housing Earth-like planets especially during the discovery of a super-Earth in a M-dwarf star the GJ 667C. Its size is 4.5 times of our planet and is located on a habitable zone which has a temperature that is not too cold or hot that it can sustain liquid.
"All life that we know of is carbon-based and depends on the presence of liquid water during at least part of its life cycle," Kasting notes in the paper. "Hence, if we see a planet that shows evidence for liquid water, we can immediately think about the possible presence of carbon-based life."
The study was published in the Nov. 25 issue of the Proceedings of the National Academies of Science.
