A NASA probe is orbiting a dwarf planet for the first time ever

"We feel exhilarated," said Chris Russell, principal investigator of the Dawn mission at the University of California, Los Angeles (UCLA). "We have much to do over the next year and a half, but we are now on station with ample reserves, and a robust plan to obtain our science objectives."

Dawn's journey began in 2007, when the fridge-sized probe was launched from Cape Canaveral on a Delta II rocket. The spacecraft is equipped with cameras, infrared spectrometers, and both gamma ray and neutron detectors — all of which have been used to study Vesta in 2011 and 2012, and will now be trained on Ceres.

Ceres was made a dwarf planet in the same reshuffle that demoted Pluto

Ceres was first spotted in 1801 by Italian astronomer Giuseppe Piazzi, who claimed it was a planet. Rival astronomer William Herschel pointed out that it was too small to be a planet and coined the term "asteroid" — meaning 'star like' — to describe it. Ceres was then bumped up to dwarf planet status in the same 2006 planetary reshuffle that saw Pluto lose its planet license. Scientists hope that Dawn's observations of Ceres (and Vesta) will help advance our knowledge of how solar systems form.

"Both Vesta and Ceres were on their way to becoming planets, but their development was interrupted by the gravity of Jupiter," said Carol Raymond, deputy principal investigator at JPL Caltech. "These two bodies are like fossils from the dawn of the solar system, and they shed light on its origins."

Although Vesta and Ceres may seem like undifferentiated lumps of rock orbiting the Sun between Mars and Jupiter, the two dwarf planets have very different compositions. While Vesta has a dry, rocky mantle that suggests it was once molten, the surface of Ceres is full of ice, with scientists estimating that as much as a quarter of its mass could be comprised of water.

This suggests that Ceres might been formed further out in the cold depths of space, before being pulled inwards by the gravity of a large planet. This would support the most recent theories about how solar systems develop, with scientists now suggesting that the positions of planets (and dwarf planets) are more mutable than we previously believed.

"By studying Vesta and Ceres, we will gain a better understanding of the formation of our solar system, especially the terrestrial planets and most importantly the Earth," said Raymond. "These bodies are samples of the building blocks that have formed Venus, Earth and Mars. Vesta-like bodies are believed to have contributed heavily to the core of our planet, and Ceres-like bodies may have provided our water."

Ceres might be home to cryovolcanoes — volcanoes that spew water and gas

It's possible that the water ice on Ceres is what is creating the bright spots that Dawn spotted on the dwarf planet's surface earlier this month. Although there are many theories as to what created the spots (impacts by smaller asteroids is one explanation), it's possible that they're the result of cryovolcanoes — volcanoes that spew water and gas rather than molten rock. This might suggest the presence of subsurface seas on Ceres and — at a stretch — a possible home for extraterrestrial life.

All images are from NASA/JPL-Caltech unless otherwise stated.