Year of the Dwarf Planets: Ceres 2015

In 2015, Pluto won't be the only dwarf planet that will receive a visit from an electronic ambassador. NASA's Dawn mission is currently on its way to Ceres.

Dawn was launched in 2007 to study the two largest celestial objects in our solar system's asteroid belt: asteroid Vesta and dwarf planet Ceres. Dawn studied Vesta from July 2011 to September 2012 and is now headed for Ceres. The dwarf planet is of particular interest since it is the asteroid belt's largest object, accounting for 25% of its total mass. In addition, Ceres is differentiated, with a rocky core, like Earth and Mars, and a water ice layer below a thin outer crust, like some of the moons of the gas giants Saturn and Jupiter. 

In January 2014, using observations from the Herschel Space Observatory, astronomers discovered that Ceres was releasing water vapor into space from two points near its equator, at a rate of about 5 kg (11 lbs) / second. At the time these observations were made, the 950-km-wide (590 mi) dwarf planet was closest to the sun (perihelion) during its 4.5-year-orbit around the sun. This was an unexpected and exciting finding. The presence of water on Ceres raises the possibility of alien life. In addition, water vapor plumes have never been observed escaping from an asteroid belt object. 

Ceres thus poses a number of intriguing questions. In coming months, scientists will likely be able to answer many of them.

Image credit: NASA

Artist's impression of dwarf planet Ceres outgassing water vapor into space from two sources near its equator. This suggests the presence of water and the possibility of alien life.

Image credit: William K. Hartmann Courtesy of UCLA

Artist's rendition of Dawn in the asteroid belt between Mars and Jupiter, marking the boundary between our solar system's inner and outer planets. Vesta is the largest, potato-shaped asteroid on the left, and the dwarf planet Ceres - almost shperical in shape - is at the right.

Image credit: NASA

Ceres is a dwarf planet in the asteroid belt with a rocky inner core, a trait it shares with inner planets like Mars and Earth, and a sub-surface water-ice layer, a feature it has in common with some of the moons of the outer planet gas giants Saturn and Jupiter.

This is the highest resolution image we have of Ceres to date, taken by the Hubble Space Telescope. Dawn will arrive at Ceres in late March / early April 2015 and start to return images with a higher resolution than the above in about six weeks. That event will mark the first time humans will get a close-up look at a dwarf planet. New Horizons will arrive at Pluto several months later. The differences and similarities between the two dwarf planets will provide a wealth of information about the formation of our solar system. 

Dawn will initially orbit Ceres at an altitude of 13,500 km (8,400 mi), and descend to about 1,500 km (950 mi) in August 2015 to resolve Ceres' surface in 3D. Dawn's closest passes to the surface will be at an altitude of 375 km (230 mi) in November 2015, where the craft will remain for three months.