Astronomers have announced the discovery of 50 (yes, five-zero) exoplanets, the largest group of alien worlds announced at one time. Sixteen of these worlds are “super-Earths” — exoplanets that possess masses larger than Earth, yet much smaller than the gas giants.
This time, however, the announcement doesn’t come from NASA’s orbital exoplanet hunter, the Kepler Space Telescope, it comes from the European Southern Observatory’s (ESO) High Accuracy Radial velocity Planet Searcher (or HARPS for short).
As with any exoplanet announcement comes the question: are any of these newly discovered worlds suitable for life? And, in this case, the answer is: maybe.
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Enter HD 85512b, an exoplanet with a mass 3.6 times that of the Earth. This “super-Earth” is exciting in that not only can it be considered a jumbo-sized Earth, it also orbits its sun-like star (HD 85512) on the inner rim of the star’s habitable zone.
“This is the lowest-mass confirmed planet discovered by the radial velocity method that potentially lies in the habitable zone of its star, and the second low-mass planet discovered by HARPS inside the habitable zone,” said Lisa Kaltenegger, of the Max Planck Institute for Astronomy, Heidelberg, Germany and Harvard Smithsonian Center for Astrophysics, Boston, who is an expert on the habitability of exoplanets.
HARPS contrasts greatly from the methods employed by Kepler to detect exoplanets. Located at La Silla Observatory in Chile, HARPS is a spectrometer that analyzes the light from stars.
Over a period of time, HARPS may detect a slight shift in a target star’s frequency. If this shift is periodic, it means something is orbiting the star. By precisely measuring the tiny shift, the HARPS team can deduce the orbiting body’s mass and orbital period (its orbital radius can therefore be calculated).
However, one thing HARPS cannot deduce is an exoplanet’s physical size. Therefore, although finding a 3.6 Earth mass world is exciting, we have no idea whether it’s the same size as the Earth, or puffed up like a mini-Neptune. Therefore, we have no idea whether HD 85512b is rocky, or gaseous, or something more exotic.
This is where Kepler is different, it is able to deduce exoplanets’ physical size. When a world passes in front of its parent star, the exoplanet’s silhouette will block a certain amount of light, relating to its physical size.
But Kepler can only see exoplanets if they are orbiting their star “edge-on” — making HARPS’s “radial velocity method” a very powerful tool for detecting worlds that would otherwise remain hidden from Kepler’s “transit method” eye.
Also, HARPS is no newbie to the field of exoplanet hunting. In the last eight years the instrument has detected 150 new exoplanets, and with the help of these new data, it has made a groundbreaking discovery: Approximately 40 percent of sun-like stars possess at least one exoplanet less massive than Saturn.
Also, the majority of exoplanets of Neptune mass or less appear to be in systems with multiple planets.
Needless to say, this finding will reinvigorate the discussions of the potential for life on these low-mass worlds, particularly when super-Earths are pottering around inside their stars’ habitable zones.
But as discussed by Ray Villard in a recent Discovery News article (“Pale Red Dot: Desert Planets as Abodes for Life?“), dry, desert worlds may have a higher likelihood of supporting alien life than worlds drenched in water, like Earth. Desert planets have habitable zones three times wider than Earth-like worlds.
The scope for the existence of extraterrestrial life appears to have widened, too.