'Cotton Candy' Planet Mysteries Unravel in New Hubble Observations
Release date: Dec 19, 2019 1:00 PM (EST)
When astronomers look around the solar system, they find that planets can be made out of almost anything. Terrestrial planets like Earth, Mars, and Venus have dense iron cores and rocky mantles. The massive outer planets like Jupiter and Saturn are mostly gaseous and liquid. Astronomers can't peel back their cloud layers to look inside, but their composition is deduced by comparing the planet's mass (as calculated from its orbital motion) to its size. The result is that Jupiter has the density of water, and Saturn has an even lower density (it could float in a huge bathtub). These gas giants are just 1/5th the density of rocky Earth.
Now astronomers have uncovered a completely new class of planet unlike anything found in our solar system. Rather than a "terrestrial" or "gas giant" they might better be called "cotton candy" planets because their density is so low. These planets are so bloated they are nearly the size of Jupiter, but are just 1/100th of its mass. Three of them orbit the Sun-like star Kepler 51, located approximately 2,600 light-years away.
The puffed-up planets might represent a brief transitory phase in planet evolution, which would explain why we don't see anything like them in the solar system. The planets may have formed much farther from their star and migrated inward. Now their low-density hydrogen/helium atmospheres are bleeding off into space. Eventually, much smaller planets might be left behind.
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