Click For Photo: https://www.sciencedaily.com/images/2018/02/180208131710_1_540x360.jpg
The GJ 9827 star actually hosts a trio of planets, discovered by NASA's exoplanet-hunting Kepler/K2 mission, and all three are slightly larger than Earth. This is the size that the Kepler mission determined to be most common in the galaxy with periods between a few and several-hundred-days.
Intriguingly, no planets of this size exist in our Solar System. This makes scientists curious about the conditions under which they form and evolve.
Key - Planet - History - Composition - Rocky
One important key to understanding a planet's history is to determine its composition. Are these super-Earths rocky like our own planet? Or do they have solid cores surrounded by large, gassy atmospheres?
To try to understand what an exoplanet is made of, scientists need to measure both its mass and its radius, which allows them to determine its bulk density.
Planets - Way - Astronomers - Trend - Planets
When quantifying planets in this way, astronomers have noticed a trend. It turns out that planets with radii greater than about 1.7 times that of Earth are have a gassy envelope, like Neptune, and those with radii smaller than this are rocky, like our home planet.
Some researchers have proposed that this difference is caused by photoevaporation, which strips planets of their surrounding envelope of so-called volatiles -- substances like water and carbon dioxide that have low boiling points -- creating smaller-radius planets. But more information is needed to truly test this theory.
GJ - Planets - Radii - Planet - B
This is why GJ 9827's three planets are special -- with radii of 1.64 (planet b), 1.29 (planet c) and 2.08 (planet d), they span this dividing line between super-Earth (rocky) and sub-Neptune (somewhat gassy) planets.
Luckily, teams of Carnegie scientists including co-authors Steve Shectman, Sharon Wang, Paul Butler, Jeff Crane, and Ian Thompson, have been monitoring GJ 9827 with their Planet Finding Spectrograph (PFS), so they were able to constrain the masses of the three planets with data in hand, rather than...
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