Mission Elapsed Time:
(Beginning 1/19/06 19:00:00 UTC)
2727 (7.47 yrs.) Days 08 Hours 14 Minutes
Pluto Closest Encounter Operations Begin:
( 4/12/15 00:00:00 UTC)
614 Days (1.68 yrs.) 20 Hours 14 Minutes
Pluto Closest Encounter Begins:
(7/14/15 11:49:59 UTC)
735 Days (2.01 yrs.) 08 Hours 33 Minutes
This week the New Horizons mission team is celebrating the 35th anniversary of the discovery of Pluto’s largest and “first” moon, Charon. This discovery was made in 1978 by U.S. Naval Observatory astronomers James Christy and Robert Harrington, working in Flagstaff, Ariz., and Washington, D.C.
Charon discovery images: In mid-1978 U.S. Naval Observatory astronomer James W. Christy noticed something unusual – a bump to the side of Pluto which turned out to be Charon. These discovery images were taken while he was making routine measurements of photographic plates of Pluto taken in June 1978 with the 1.55-meter (61-inch) Kaj Strand Astrometric Reflector at the Observatory’s Flagstaff Station in Arizona.
Charon, whose discovery was first announced on July 7, 1978, orbits about 19,400 kilometers (12,500 miles) from Pluto and has a diameter of about 1,207 kilometers (750 miles) — about the width of Texas. At half the diameter of Pluto, Charon is the largest moon relative to its planet in our solar system.
Note that the colors do not indicate the colors of Pluto and Charon, but the brightness of light (in the same way that contours show height on a topographic map). And because the light from Pluto and Charon is scattered by the Earth's atmosphere above the telescope, the images of Pluto and Charon are also blurred - their actual sizes are much smaller than they appear in this image.
Keck Observatory’s view of Pluto and Charon’s reflective but almost colorless surface is covered by water ice, and may contain traces of ammonia as well. Its interior is much less rocky than Pluto (which is nearly 70-percent rock). By contrast, Charon’s interior exhibits a nearly 50-50 combination of rock and water ice. And unlike Pluto, Charon has no substantial atmosphere.
Until only very recently, images taken by ground-based telescopes always showed Pluto and Charon blurred together since their maximum separation is only 0.9 arcsec as seen from the Earth. Thanks to the excellent quality of its 8.3-meter primary mirror and the stability of the atmosphere above Mauna Kea, Subaru Telescope has been able to provide clearly separated images of the two bodies using its Cooled Infrared Spectrograph / Camera (CISCO). With their light cleanly separated, subsequent infrared spectroscopy using CISCO reveals dramatically different surface compositions for Pluto and Charon.
The historic discovery of Charon ushered in the modern understanding of Pluto as both a double planet and the product of a giant collision that formed the system in much the same way as the Earth-Moon system was formed. We now know that Charon, once thought to be Pluto’s only moon, orbits Pluto with at least four much smaller moons: Nix, Hydra, Kerberos and Styx, all of which, like Charon, orbit in circular paths and in Pluto’s equatorial plane. From Charon, Pluto looms large in the sky—more than 14 times as wide and 200 times as big of an area as the Earth’s moon appears in our sky. And at “full Pluto,” Charon’s night side is about 50-percent brighter than a full moon in Earth’s nighttime sky.
New Horizons is on course to fly by and make the first reconnaissance of the Pluto system just two years from now, in July 2015. When it does, the spacecraft will turn these moons and their parent planet Pluto from points of light into well-mapped worlds, chart their compositions in exquisite detail, explore Pluto’s atmosphere, search for other moons and rings, and make many other observations as well.
Present Course and Position of New Horizons in 3 Dimensions: