How a moon slows the decay of Pluto's atmosphere
http://phys.org/news/2017-01-moon-pluto-atmosphere.html
Pluto's relationship with its moon Charon is one of the more unusual interactions in the solar system due to Charon's size and proximity.
It's more than half of Pluto's diameter and orbits only 12,000 or so miles away. To put that into perspective, picture our moon three times
closer to Earth, and as large as Mars.
A new study from the Georgia Institute of Technology provides additional insight into this relationship and how it affects the continuous
stripping of Pluto's atmosphere by solar wind. When Charon is positioned between the sun and Pluto, the research indicates that the moon
can significantly reduce atmospheric loss.
"Charon doesn't always have its own atmosphere," said Carol Paty, a Georgia Tech associate professor in the School of Earth and Atmospheric
Sciences. "But when it does, it creates a shield for Pluto and redirects much of the solar wind around and away."
This barrier creates a more acute angle of Pluto's bow shock, slowing down the deterioration of the atmosphere. When Charon doesn't have an
atmosphere, or when it's behind or next to Pluto (a term scientists call "downstream"), then Charon has only a minor effect on the interaction
of the solar wind with Pluto.
The study's predictions, performed before the New Horizons probe collected and returned data to Earth, is consistent with the measurements made
by the spacecraft about Pluto's atmospheric loss rate. Previous estimates at the time of the study were at least 100 times higher than the actual
rate. The research is currently published in a special Pluto issue of the journal Icarus.
