[fusion_text]By Bruce Gavett
As a SciWorks volunteer in the Planetarium, I often get questions about the “dwarf” planets, the round objects that orbit the sun just like the eight major planets, but are not large enough to gravitationally clear their orbital path of most or all other celestial bodies. Pluto, which was once known as the smallest planet in the solar system and ninth from the sun, was downgraded to dwarf planet in 2006 by the International Astronomical Union and is now the best known of the dwarf planets. Ceres, the only dwarf planet in the inner solar system, has also been in the news quite a bit lately.
Dawn at Ceres
Composed of rock and ice, Ceres is the largest object in the asteroid belt, which lies between the orbits of Mars and Jupiter. Last Friday, March 6, the robotic Dawn spacecraft arrived at Ceres, becoming the first spacecraft to orbit a dwarf planet and the first spacecraft to orbit two solar system objects. Dawn spent a year orbiting the asteroid Vesta back in 2011 and 2012.
During Dawn’s approach to Ceres, two mysterious white spots have appeared in the photos. We may have to wait a few more weeks to find out more. Dawn is now “spiraling down” to a lower orbit where it will take more readings and images starting in late April.
New Horizons at Pluto
On Sunday, March 8, NASA’s New Horizons spacecraft burned its engine for 93 seconds to make a slight course adjustment. It essentially “tapped its breaks” to slow down just over one meter per second. It is traveling at a speed of 14 ½ km per second, and it is now taking signals just under 4 ½ hours to reach the Earth!
Emily Lakdawalla of the Planetary Society has provided an overview of what we can expect when New Horizons arrives at Pluto. Information will not arrive back on the Earth in real time. Evidently, the spacecraft cannot take readings of Pluto and send back information at the same time, so information will be downloaded at specific times during the close encounter. New Horizons will let us know that it made it by Pluto around 9 PM on Tuesday, July 14. We’ll get images of Pluto and its moons on Monday (Noon), Wednesday (7 AM and 3:30 PM) and Thursday (3:30 AM) that week.
Want to know more about Pluto? The folks running the New Horizons mission have provided a nice web page on what we know about Pluto. See New Horizons: NASA’s Mission to Pluto. And, NASA’s Space Place also has some fun facts about “Peculiar Pluto.”[/fusion_text]