Pluto, the little planet discovered at Lowell Observatory by Clyde Tombaugh in 1930 and named by British schoolgirl Venetia Burney. It became our solar system’s ninth planet, yea! Pluto, the Roman mythological ruler of the underworld. Makes it seem a little creepy.
Pluto enjoyed planetary status until astronomers realized it had siblings out there orbiting the Sun as well. Some of them are nearly a big as Pluto. This orbital space, called the Kuiper Belt, is beyond the orbit of Neptune and way bigger than the asteroid belt. So, Pluto’s planetary moniker was stripped away by committee during the 2006 International Astronomical Union conference. It became just another member of the Kuiper Belt, but big enough to be called a “minor planet” or a “dwarf planet”.
We did not know what Pluto was up to or much about its make-up, it was so far out even the Hubble Telescope couldn’t get good shot of it. The best Hubble could do was show that Pluto has a mottled appearance, bright, and dark patches. Interesting. None of Earth’s space exploration agencies had sent a probe to Pluto. Didn’t seem to be a worthy candidate, I guess. Pluto would remain a creepy, unknown world, that is, until NASA approved the New Horizons project.
New Horizons was the first exploratory vehicle sent to Pluto, ever! Not everyone was optimistic, however. Pluto was still getting disrespected by a lot of astronomers, who had other priorities. Anyway, New Horizons was funded, built, and finally launched in, what a coincidence, 2006! It would take nine years for New Horizons to reach Pluto, even at a record 36,400 miles per hour! Pluto is far-out, really. In 2015 astronomers got their first close-up views of this enigmatic minor planet and they were blown away!
After all the po-pooing, Pluto served up a first-class experience. Pluto has it all; mountain ranges that look like sharp fish scales on edge, a vast heart-shaped nitrogen and carbon monoxide (CO) ice field, cryovolcanic features, and large areas of reddish-brown organic stuff. Oh, and a tenuous atmosphere too.
How can an atmosphere exist on cold, cold Pluto? Its axis of rotation is tilted at 120 degrees with respect to its orbital plane, resulting in continuous sunlight for one hemisphere, while the other is in continuous darkness. This situation reverses during Pluto’s 248-year orbit. The sunlit side gets just warm enough for nitrogen/CO to sublimate from ice and form a thin atmosphere. Right now, the vast ices of Sputnik Planitia sublimate/outgas and Pluto’s rotation causes winds. Those nitrogen/CO winds travel to the dark side, producing telltale streaks on the ice of Sputnik Planitia, and then freeze out as snow.
Nitrogen snow falls gently on the windless, silent dark side.
What’s in the Sky?
Jupiter and Saturn are in the southeastern late-night sky
Venus is a pre-sunrise planet
July 3-6; 10pm; southeast: The Moon slips through Sagittarius then meets Jupiter and Saturn