Pluto and moons, pretty much at scale.*
It’s been a big year for our tiniest former planet. Last month, Pluto’s new moon, tentatively called P4, made news (and lame jokes about Disney characters), and now astronomers are predicting that Pluto also has a faint ring.
Ringed planets aren’t especially uncommon, as it turns out. We know about Saturn’s impressive multi-ring feature because it’s so visible, but fainter rings have also been discovered around Uranus, Neptune and Jupiter. Now, Pryscilla Maria Pires dos Santos and colleagues from UNESP-São Paulo State University in Brazil say Pluto may have a faint ring as well, created by wayward dust from its moons Hydra and Nix following micrometeorite activity on their surfaces.
When small objects strike the planet’s satellites, dust should be expelled into Pluto’s orbit. Pires dos Santos and her team modeled such impacts [image at top] and based on their research, predict that Pluto has a very faint ring which initially begins as a 16,000km-wide field of dust; solar winds and gravity disperse about 50% of the debris, leaving a ring with a calculated transparency of 10^-11.
Hubble, which has never detected anything like a ring around Pluto, can see transparencies of as low as 10^-5. Not low enough for this prediction, alas, but in 2015 when New Horizons reaches Pluto, an on-board dust counter will let us (and Pires dos Santos and team) know if an icy dust cloud does encircle the planet, thereby making Pluto the most interesting non-planetary body in the solar system.