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  Night Sky

Enjoy the starry night skies
Be a considerate neighbor. Reduce nighttime glare.
Shield your outside lights downward.
Let the stars light up the night.

April 2016 night sky

—Charlie Christmann

What’s up with Pluto?

The difference between the two Voyager spacecrafts and the New Horizons is truly amazing. Though the two Voyager crafts sent back amazing data from Jupiter, Saturn, Uranus, and Neptune, it was still using 1960s technologies. Their data was stored using an eight-track tape system (yes, similar to the ones we used to have in our cars that “ate” the cartridges and resulted in long strings of magnetic tape alongside the roadways).

New Horizons, by contrast uses 2000 technologies. Its camera system shoots high-definition and stores its data in solid-state memory. So much data, that since its close encounter on July 14, 2015, nine months ago, it is still sending its data back to Earth. There are several months of data remaining in its memory banks.

Even though the data is still coming in, and New Horizons has been retargeted to a new small body in the Kuiper Belt, scientists are starting to discover that Pluto is much different than they expected.

In 2006, Pluto was demoted from full planet status and reclassified as a Dwarf Planet, along with an object in the Asteroid Belt and several Kuiper Belt objects. Dwarf Planet Eris’ discovery was the death nail for Pluto’s status. When found, Eris was thought to be larger than Pluto, and Eris was no planet. Pluto is smaller than a host of the moons in our solar system; it is smaller than Earth’s moon, the four Galilean moons of Jupiter, Neptune’s moon Triton, and Saturn’s moon Titan. On the surface of Pluto, a two hundred pound man would weigh just seven percent of his Earth weight, or 13.9 pounds.

New Horizons measured the size of Pluto and came up with 1,473 miles across, making it just slightly larger than Eris at 1,445 miles. That is still not big enough to be a full planet, but big enough to retake the title of largest Dwarf Planet. If you placed one edge of Pluto on the California coast, the other side would barely extend past New Mexico into west Texas and the Oklahoma Panhandle. If you walked around the equator, it would be like walking from Denver to London.

Pluto’s rotational axis is tipped on its side, similar to Neptune, and it rotates the opposite direction from the rest of the planets.

But the big surprises are in its system of small moons, five in all. The largest is Charon, named for the ferryman of Hades who carries souls of the newly deceased across the rivers Styx and Acheron, which divided the world of the living from the world of the dead. Charon is 750 miles across—large enough to leave some astronomers to wonder of Pluto could be a dual dwarf planet system. Charon orbits just 12,200 miles from Pluto once every 6.4 Earth days. And like our geosynchronous satellites, it always hovers over the same point on Pluto’s surface.

The Hubble telescope found the next two moons, Nix and Hydra in 2005, while plans were being made for the New Horizons mission. Though these moons were imaged from a distance by the spacecraft, New Horizons saw that Hydra (26 miles in diameter) has a shape resembling a rubber duck with at least two large craters. Nix, 22 miles in diameter, looks like a jellybean and has a surprisingly large impact crater. With a crater that large, it is a surprise that Nix is still in one piece.

Hubble found the moon Kerberos in 2011 orbiting between Pluto and Hydra and Nix. It is tiny, but bright. Its shape may have been the result of two even smaller bodies sticking together. One lobe is about three miles across, the other five miles wide.

Styx is the farthest moon from Pluto, orbiting 59,030 miles away. This moon was found in 2012 and estimated to be about 4.5 miles wide.

The four smaller moons are spinning and tumbling wildly. If Hydra spun any faster, it would fly apart. These rapid rotational rates are surprising. The gravity of Pluto should slow down the spin of the smaller moons into a tidal lock, like our moon, so only one side always pointed toward Pluto. The best conclusion from the contradictory data is that the moons may be the result of a collision between Pluto and some other object. Pluto and Charon coalesced into round objects, the other moons are fragments left over from the collision.

There is still much theorizing to come that might eventually explain Pluto’s geology and its moons. Perhaps the remaining data being sent from New Horizons, already 1.4 million miles past Pluto and requiring almost five hours for its radio signal to reach Earth, will eventually provide enough clues for science to make some educated guesses.

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