Dwarf planet Pluto's atmosphere

Dwarf planet Pluto is the smallest Solar System body with atmosphere. It is thin - atmospheric pressure on the surface is 100 000 times less than on Earth, but this is enough to effectively reshape surface features, such as, for example 500 meters high sharp spires from my previous post. Moreover, Pluto has no magnetic field. Modern theory says that solar wind  (flow of charged particles) must effectively blow off atmosphere molecules in the short time, but this does not happen. Pluto's  atmosphere is clearly seen on this beautiful photo from New Horizons spacecraft, taken hours after flyby.

Possible solution of this mistery is offered in the Icarus magazine.

It says that protector of Pluto's atmosphere is its satellite, or rather companion - Charon. Pluto has diameter 2300 kilometers, Charon - 1200 km and distance between them is only 19 000 km. Just imagine our Moon is 4 times closer to Earth and is of Mars size. So, when Charon is on the line between Sun and Pluto, it partially shields its companion from the solar wind.

Modeling results also demonstrate more compex mechanism:  sometimes Charon can 'borrow" temporary atmosphere from Pluto - it can capture methan molecules, blown from Pluto surface. Part of these molecules condenses near Charon north pole; in the dark area, unofficially named Mordor Macula. Another part is ionized in result of interaction with solar wind, and creates ionosphere - mush stronger shield from solar wind because it has bigger size than satellite's diameter and more effectively deflects solar plasma flow.