Perihadean Achieved

The New Horizons spacecraft made its closest approach to the planet Pluto today, following a nine year voyage. New Horizons has been sending back a stream of pictures of Pluto and its largest moon, Charon, over the past week and will resume sending out more images over the next couple of months.

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Name That Moon

In 2011 and 2012, two new moons were discovered in orbit around Pluto. Called P4 and P5, the scientists who discovered the moons have put up a poll asking internet users to select from one of twelve names (or to write in a suggestion) as to what the moons should be called. The choices, all of which have a mythical tie to the underworld, are Acheron, Alecto, Cerberus, Erebus, Eurydice, Hercules, Hypnos, Lethe, Obol, Orpheus, Persephone, and Styx.

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Pluto + 4

Scientists have announced the discovery of a fourth moon in orbit around Pluto. Pluto’s first discovered moon, Charon, was found in 1978. Two more moons, Nyx and Hydra, were identified in 2005. The new moon, which is currently called P4, is believed to be between 13 and 34 km in diameter and orbits Pluto every 32 days at a distance of about 59,000 km, between the orbits of Nyx and Hydra.

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Change Among the Plutoids

Recent measurements of Eris, the dwarf planet discovered in 2005 which led to the reclassification of Pluto, indicate that the object may be smaller than originally believed. Eris’s high density means that the plutoid is most likely smaller, although more massive, the Pluto, which may now be the largest of the dwarf planets. The new measurements of Eris were conducted during an occultation by the plutoid of a star in Cetus, observed in the Chilean Andes on November 6.

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Dwarf Planet Definition Offered

Although astronomers created a definition for a Dwarf Planet in 2006, the definition only dealt with the upper size limit. Now, astronomers Charles Lineweaver and Marc Norman at the Australian National University in Canberra, have offered a definition for the lower end of dwarf planets, stating that a dwarf planet must have a circumference of at least 200 miles. Lineweaver and Norman selected that figure because anything larger will naturally form into a sphere, while anything small will retain a lumpier shape. The IAU has yet to debate and vote on the issue.

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Obituary: Venetia Phair

Venetia Phair (b.1918) died on April 30. Born Venetia Burney, in 1930, she suggested to her grandfather, Falconer Madan, that the new planet discovered by Clyde Tombaugh should be named Pluto, after the god of the underworld. Madan passed her suggestion on to astronomer Frederick Hall Turner and the name was eventually adopted.