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.

New Horizons: All Eyes On Pluto in 2015

On December 6, New Horizons awoke from hibernation for the final time. This amazing outer solar system probe was launched in 2006 and has traversed 3 billion miles. New Horizons is going further than any planetary probe has gone before; only the two Voyagers - designed to leave the solar system - have traveled further from our home planet. The spacecraft is also zooming fast through space - at a clip that equals traveling from Los Angeles to New York every five minutes, since 2006.

Yesterday New Horizons woke up for the 18th and final time. The probe spent most of its journey in hibernation mode, only waking up periodically for instrument and status checks. Now that New Horizons is closing in on the Plutonian system, we can expect to see the dwarf planet and its moons with ever increasing resolution. New Horizons will have its closest encounter with Pluto in July 2015. 

Data sent from Pluto won't arrive at Earth instantaneously. It takes 4.5 hours for the signal to traverse 3 billion miles through the vacuum of space to be received on Earth.

 Image credit: The Planetary Society

Below is an artist's rendering of New Horizons approaching Pluto and its moons. The dwarf planet at the outer edges of our solar system is still the least well known to us here on Earth. Having lost its status as a full planet not too long ago, Pluto is now likely to present us with spectacular images of its surface and a wealth of knowledge. In a way, going to Pluto is like discovering what an exo-planet looks like. We can't see its surface directly, and, until now, we could only guess what its surface may look like. New Horizons will also be able to discern the presence of subsurface oceans similar to those on icy moons further inside the solar system, volcanic activity like we found on Io, or plumes that vent into space as we see it on Enceladus.

One of the questions mission scientists are eager to answer is whether or not Pluto and its current features are primitive - unchanged since the dawn of our solar system - or the result of activity over time, such us tidal heating or subsurface oceans. 

New Horizons' science instruments will also explore Pluto's night side, search for rings, study the atmosphere, look for dust, plasma and hazes, and collect data that will tell us if Pluto has mountains, fault lines, chasms and other geological features. 

 Image credit: NASA

This is a Hubble telescope image of Pluto and its five moons. Charon is the largest and was discovered in 1978. Two of Pluto's smaller moons, Kerberos and Styx weren't discovered until 2011 and 2012, respectively. This poses a unique challenge for New Horizons scientists: Completing science missions at Pluto and Charon while taking into account two moons that were not known to exist when New Horizons launched in 2006.                     

 Image credit: NASA / Hubble

Below is a Hubble telescope image of Pluto and three of its moons. This is the highest resolution image of Pluto and its moons that we have to date. As New Horizons approaches Pluto in coming months, the spacecraft will start to return images that will be better than this in early May 2015. New Horizons scientists have named this threshold "BTH" - Better Than Hubble. After that point, the craft will return images with increasingly finer resolution until its closest encounter with the dwarf planet in July 2015. At its closest approach, New Horizons' camera will resolve Pluto's surface at about 70-80 m / pixel.

 Image credit: NASA / Hubble

New Horizons' mission may not end after visiting Pluto and Charon. NASA scientists are working to secure funding for extending the spacecraft's mission. It can use Pluto's gravity to slingshot out into the Kuiper Belt and examine a Kuiper Belt Object up close. Two possible target objects have already been selected. A close-up look at a KBO is particularly interesting because it will help us understand the nature and state of the very early solar system, long before planets had time to form. KBOs are thought to have changed very little in the billions of years since the formation of the solar system as we know it.