Thursday, April 24, 2014
(Continued from page 1)
Space Probe: Location of the New Horizons spacecraft on Dec. 10, 2013.
Image courtesy of NASA
Third, out beyond the Kuiper Belt and Sedna is the Oort Cloud, where an unknown abundance of comets slow-orbit the sun. No one has ever seen anything in the Oort Cloud because what’s out there is too small and distant for telescopes — 1,000 to 100,000 AU out. But the Oort Cloud is thought to be the origin of long-period comets, meaning the ones that come streaking into our view just once, to return near Earth only after thousands of years, or possibly never.
New Horizons is on its way out, scheduled to fly by Pluto in July 2015 and then proceed into the Kuiper Belt. It will take pictures of whatever comes into range and send back detections of molecular and atomic activity in space for hopefully another five years or so. When New Horizons reaches about 55 AU out, its signals will not be strong enough to make it back to Earth intact.
These spectacularly lonely seeming distances are actually, in a way, neither far out, nor in deep. The most distant spacecraft we still hear from is Voyager 1, about 127 AU away (radio signal: 17.6 light-hours). The nearest bright star is the Alpha Centauri system, whose light takes 4.3 light-years to get here. The nearest large galaxy to us is 2.5 million light-years away. Far out. But when did the farawayness of the horizon ever stop anyone on the beach from keeping watch?
Dana Wilde lives in Troy. His writings on the stars and planets are collected in “Nebulae: A Backyard Cosmography,” available from Booklocker.com and online book sellers. Backyard Naturalist appears the second and fourth Thursdays each month. You can contact him at firstname.lastname@example.org.