14 DAY TRIAL // Ever since the first extrasolar planets were discovered and analyzed, astronomers have been wondering as to what the most common type of planet in the Universe is. The conclusions of a recent analysis suggest that worlds known as super-Earths may be the most widespread type of exoplanet out there.
Our own solar system does not really adhere to the norm when it comes to planet distribution, composition and properties. We have worlds ranging from tidally-locked and hot, like Mercury, and gas giants like Saturn and Jupiter, to habitable planets like Earth and Mars, and ice giants like Neptune.
However, for most star systems out there, such planetary diversity is unheard of. Usually, other stars only feature a handful of planets in their orbit, oftentimes just one or two. Astronomers say that hot giants (Saturn-sized worlds in Mercury-like orbits) and super-Earths are the most common.
A super-Earth is defined as a world that is 2 to 10 times heavier than our planet, and which has up to twice its radius. By definition, such a planet is smaller and lighter than ice giants such as Uranus and Neptune, which weigh in at 15 and 17 times the mass of Earth, respectively.
Recent astronomical surveys have determined that super Earths orbiting M-class stars have the highest chance of being, or becoming, habitable. These stars are significantly cooler than the Sun, which means that the exoplanets, even though located close to the suns, could still hold liquid water on their surfaces.
Stellar maps developed over the years show that stars smaller than the Sun appear to be the norm in the Milky Way, especially in the solar neighborhood. This implies that super-Earths are some of the most widespread exoplanets out there, Astrobiology Magazine reports.
“That super-Earths in short-period orbits around cooler and smaller stars are easier to detect has set the ground for this becoming fashionable, and now there's a great deal of attention in using radial velocity and transit photometry techniques to find such planets in the habitable zones of M stars,” expert Nader Haghighipour says.
The scientist, who is based at the University of Hawaii in Manoa (UHM) Institute for Astronomy, also holds an appointment with the NASA Astrobiology Institute. He explains that observatories such as the NASA Kepler Space Telescope can easily detect super-Earths around nearby stars.
However, surface-based telescopes can be equally accurate in their findings. For example, the European Southern Observatory (ESO) 3.6-meter (141-inch) telescope in La Silla, Chile, features the High Accuracy Radial Velocity Planet Searcher (HARPS) instrument, which has already confirmed numerous exoplanets.
The High Resolution Echelle Spectrograph (HiRES) instrument on the W. M. Keck Observatory, in Mauna Kea, Hawaii, is equally capable of discovering super-Earths, having already proven this multiple times.