NASA | GSFC | STScI | HubbleSite | 2019 Dec 19
"Super-Puffs" may sound like a new breakfast cereal. But it's actually the nickname for a unique and rare class of young exoplanets that have the density of cotton candy. Nothing like them exists in our solar system.
New data from NASA's Hubble Space Telescope have provided the first clues to the chemistry of two of these super-puffy planets, which are located in the Kepler 51 system. This exoplanet system, which actually boasts three super-puffs orbiting a young Sun-like star, was discovered by NASA's Kepler space telescope in 2012. However, it wasn't until 2014 when the low densities of these planets were determined, to the surprise of many.
The recent Hubble observations allowed a team of astronomers to refine the mass and size estimates for these worlds — independently confirming their "puffy" nature. Though no more than several times the mass of Earth, their hydrogen/helium atmospheres are so bloated they are nearly the size of Jupiter. In other words, these planets might look as big and bulky as Jupiter, but are roughly a hundred times lighter in terms of mass.
How and why their atmospheres balloon outwards remains unknown, but this feature makes super-puffs prime targets for atmospheric investigation. Using Hubble, the team went looking for evidence of components, notably water, in the atmospheres of the planets, called Kepler-51 b and 51 d. Hubble observed the planets when they passed in front of their star, aiming to observe the infrared color of their sunsets. Astronomers deduced the amount of light absorbed by the atmosphere in infrared light. This type of observation allows scientists to look for the telltale signs of the planets' chemical constituents, such as water.
To the amazement of the Hubble team, they found the spectra of both planets not to have any telltale chemical signatures. They attribute this result to clouds of particles high in their atmospheres. ... However, unlike Earth's water-clouds, the clouds on these planets may be composed of salt crystals or photochemical hazes, like those found on Saturn's largest moon, Titan. ...
Behold the Super-Puffs: Planets as Fluffy as Cotton Candy
University of Colorado, Boulder | 2019 Dec 19
The Featureless Transmission Spectra of Two Super-Puff Planets ~ Jessica E. Libby-Roberts et al
- arXiv.org > astro-ph > arXiv:1910.12988 > 28 Oct 2019