Pluto

Pluto's Orbital Mysteries
The June 23 occultation will also reveal precisely where Pluto and Charon are relative to one another in the sky.
The data should help astronomers solve an orbital mystery that was revealed by the discovery of the two smaller moons Nix and Hydra almost six years ago.
"We once thought that Pluto and Charon orbited in simple ellipses. But, with the discovery of the small moons, we found they all pull on each other and affect each other in subtle ways," Young said.
Pinpointing the orbits more exactly will reveal the objects' masses—and will help astronomers plan observation strategies for the New Horizons spacecraft.
"Knowing the orbits better will help us refine where we aim our cameras—you don't want an image with half of an object out of the frame," explained NASA's Stern.
"Knowing the orbits more accurately will also make us more efficient, so we have time to do more things—and we're only going to be there once."
(Related: "Pluto is the Biggest Dwarf Planet After All?")
The June 27 Hydra occultation is especially exciting, team member Young added, because the small moon has been an elusive target for the past six years. With this round of observing, her team is hopeful that they'll finally be able to pinpoint Hydra's size.
"It's been very hard to do, because until recently we didn't know the orbit of Hydra relative to Pluto very well, and because the object is so small that we have a very small chance of being in Hydra's shadow" to observe it from the proper place on Earth, Young said.
Recent work with Hubble Space Telescope images has narrowed Hydra's position relative to Pluto to within tens of kilometers. With that information in hand, observations from the June 23 occultation can be analyzed in time to pinpoint where in Australia to place a telescope to be in Hydra's shadow four days later.
"By the time [astronomer] Marc Buie starts driving out of Alice Springs two days before the second occultation, we'll be able to tell him and his army of amateurs where to go."
Even with all the planning, NASA's Stern added, part of the allure is that no one's quite sure exactly what they'll see during the Pluto occultations.
"That's the great thing about astronomy," Stern said. "Sometimes when you unwrap a present, you really get a surprise gift."
(The Pluto occultation research is supported by the National Geographic Society's Committee for Research and Exploration, NASA's Planetary Astronomy program, NASA's New Horizons Mission, and the Southwest Research Institute.)