Many spacecraft are active in the Solar system at present, some in orbit around their targets, some driving around on its surface, some still on their way. Two robots in particular which are still speeding towards their targets, are going to make the biggest headlines this year. This will give us close up views and many details of two Solar system objects that we know almost nothing about, apart from a few vague images. These are two Dwarf Planets that are representative and therefore crucial to our understanding of the make-up of the Solar system, and especially of its formation history. We cannot wait...
This is the lead article of a series of three on our website (with Pluto the Dwarf Planet and Ceres, the nearest Dwarf Planet) that is preparing us for the historic missions to the nearest dwarf planet 1Ceres in the Main Asteroid belt, and the “Trans-Neptunian” Dwarf planet Pluto. Watch the headlines when the Dawn spacecraft reaches 1Ceres on 6 March and when the New Horizons spacecraft makes its flyby of the Pluto system on 14 July.
The dawn spacecraft was launched on 27 September 2007 as a big step in NASA’s Discovery Programme to study the early Solar system and the processes of its formation. It arrived at the asteroid 4Vesta in July 2011 and spent 14 months around this second largest object in the Main Asteroid belt. Dawn is presently on its way to 1Ceres, the largest object in the belt which is classified as a Dwarf planet.
Go to the Mission page here
Watch a lecture on the Dawn mission by Dr. Carol Raymond, Dawn Deputy Principle Investigator, November 2012 (84 minutes).
When travelling in space you need to be patient. Not only are the distances literally astronomical, but you cannot fly from A to B in a straight line, as you would do here on Earth. Most of the trip you are in free fall, in this mission actually in orbit around the Sun.
Launched in September 2007, the spacecraft made a gravity-assist (or fly-by) past Mars one and a half years later. Another two and a half years later it arrived at 4Vesta in July 2011.
Unique in the Dawn mission is the use of an Ion thruster (see below) that gently nudged the spacecraft in the right direction and saved a large amount of fuel, which otherwise would have made this “mission impossible”.
The ion thrusters use Xenon as fuel and an electric charge to propel Xenon molecules (ions). This gives a very small acceleration but the trick is that this thrust can last for a long time and ultimately generate speed changes that would require much larger amounts of fuel with traditional rockets. One mission to two celestial bodies in the Main Asteroid Belt would be impossible without this ion thruster technology.
Watch an interview with Marc Rayman, Dawn Chief Engineer at JPL discussing the advantage of the Ion Thruster and Dawn’s orbit around and departure from 4Vesta using this ground braking technology here.
Dawn carries four science instruments, The framing camera, a spectrometer for visible and infrared light, a Gamma Ray and Neutron detector and a gravity mapper that together will image the Dwarf planet and will determine its surface composition and conditions as well as internal structure. These instruments were successfully deployed when the spacecraft orbited 4Vesta and will do a similar job this year in orbit around 1Ceres.
Results at 4Vesta
Video 1: Fly aboard the Dawn spacecraft over of the 525 km diameter asteroid 4Vesta. Actual images from the mission were used to create this realistic video. Highlights are views of the features Divialia Fossa, Marcia crater, part of the "snowman" feature and Aricia Tholus. Credits: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA.
Video 2: Watch a summary of the mission highlights at 4 Vesta in this 2.5 minute video: Credit: NASA, JPL
More detailed results can be found e.g. here at Space.com
We are now eagerly awaiting the encounter with Dwarf Planet 1Ceres when Dawn arrives at the Dwarf Planet on 6 March 2015.
See main article: Ceres, the nearest Dwarf Planet
Another very historic mission started nine years ago on 19 January 2006 when the New Horizons spacecraft was launched. New Horizons is on its way to the Pluto Dwarf Planet system. We call it a system because its biggest companion is Charon, and quite recently four other moons have been discovered.
New Horizons carries seven science instruments. Jointly these instruments will study the atmospheres, surfaces and interiors of Pluto, Charon, their moons Nix and Hydra and the recently discovered tiny moons Styx and Kerberos. New Horizons will also map Pluto's "far-side," and look for evidence of rings and magnetic fields around Pluto and Charon.
THE LONG TRIP
Early Cruise: The first 13 months included spacecraft and instrument checkouts, instrument calibrations, small trajectory correction manoeuvres and rehearsals for the Jupiter encounter. New Horizons passed the orbit of Mars on April 7, 2006.
Jupiter Encounter: Closest approach occurred February 28, 2007. Moving about 23 kilometres per second, New Horizons flew about 3 to 4 times closer to Jupiter than the Cassini spacecraft, coming within 32 Jupiter radii of the large planet.
Interplanetary Cruise: activities during the approximately 8-year cruise to Pluto included annual spacecraft and instrument checkouts, trajectory corrections, instrument calibrations and Pluto encounter rehearsals.
New Horizons has also crossed the orbits of Saturn (June 8, 2008) ,Uranus (March 18, 2011), and Neptune (August 2014). But it missed these planets as they were somewhere else in their orbits at the time.
Waking up: New Horizons came out of hibernation mode for the last time during its long flight, on 6 December 2014. It now stays awake and prepares for the close encounter in July. The closest approach will be reached on 14 July 2015. The flyby will be very fast because there is no way to slow down. New Horizons is one of the fastest spacecraft ever launched, starting its journey at a speed of about 45 km per second. That will have slowed down to about 14 km per second at closest approach to the Pluto system. The total science observations will last several weeks during its flyby, both on approach and after closest approach, looking back at the side of Pluto that can never be seen from Earth.
THE PLUTO ENCOUNTER
February 2015: Observations begin
mid June: Daily studies begin
14 July 2015: Closest approach at about 10,000 kilometres
50 minutes later: Pluto – Sun occultation to study Pluto’s atmosphere
135 minutes later: Charon – Sun occultation to study Charon’s atmosphere
(information from: pluto.jhuapl.edu)
As soon as more accurate observations are available of the orbits of Pluto’s smaller moons, the science team will decide how to observe these companions.
Plans for an extended mission include encounters with one to two other Kuiper Belt Objects, ranging from about 40 to 90 kilometres in diameter. New Horizons would acquire the same data it collected at Pluto - where applicable - and follow a timeline similar to the Pluto encounter.
Ultimately, New Horizons will leave the Solar system, just like Voyager-1 and -2 and Pioneer-10 and -11. It will be the fifth human made object to cruise towards the stars.
View the collection of podcasts about the New Horizons mission here.
For more about the Pluto-Charon system see our article Pluto, the Dwarf Planet.