On Monday (Jan. 6), talk at the annual meeting of the American Astronomical Society in National Harbor, Maryland, was all about those strange exoplanets known as “super-Earths” or “mini-Neptunes.” In fact, most of the exoplanets detected so far appear to be of this type: larger than Earth and smaller than Neptune. What’s odd is that this size range doesn’t exist in our own solar system.
According to astronomer Geoff Marcy of the University of California at Berkeley, about 85 percent of planets discovered by NASA’s Kepler space telescope are super-Earths. He said these planets orbit close to their parent stars and that it’s possible scientists eventually will discover smaller, rocky planets at more distant orbits, according to the Washington Post.
Marcy noted that the universe seems to have a preference for these intermediate-sized super-Earths. They also appear to follow a distinct pattern: About twice the diameter of Earth, they are rocky and dense. But larger than that, the density drops sharply, indicating that these larger worlds are enveloped in gas.
This observation is consistent with the theory of planet formation, in which there’s a limit to how large a rocky planet can get. That’s because the force of gravity keeps compressing the dirt, now matter how much of it is thrown at the planet, Marcy said.
The Kepler telescope, launched in 2009, was able to detect the presence of exoplanets by watching the regular periodic dimming of starlight as planets pass across, or transit, across the face of their parent stars. Since then, scientists have been using other methods to look at the parent stars. For example, Marcy and his colleagues used radial velocity measurements to observe a star’s Doppler shift as it’s pulled by the gravity of its orbiting planets.
As to the question of whether there could be life on super-Earths, Marcy hesitates to speculate. “We know very little about how life got started and in what environments it might flourish,” he said.
Although super-Earths are nothing like our own planet, it’s not impossible that some life-forms could exist under their extremely high atmospheric pressures, similar to the way life exists around deep-sea hydrothermal vents.
University of Chicago graduate student Laura Kreidberg presented data about the planet she called “everybody’s favorite super-Earth,” classified as GJ 1214b. This planet appears to be shrouded in a thick layer of clouds whose composition is as yet unknown. Observations have eliminated the possibility they are made of water, methane, or carbon dioxide.
“I put my money on a layer of haze high up in the atmosphere, made out of soot … kind of like smog, actually,” Kreidberg said.
It’s possible the clouds are composed of potassium chloride which, Kriedberg noted, is pink when in liquid form.
“It could be a pink planet,” she said.