NASAs Dawn spacecraft has just made history by becoming the first mission to orbit a dwarf planet.

The probe went into orbit around the icy world of Ceres Ceres at around 7.39am EST today, when it was around 38,000 miles from the planet.

Dawn then signalled its mission controllers at NASAs Jet Propulsion Lab (JPL) to let them know that it was on track and thrusting with its ion engine. The message took around an hour to get through to JPL and indicated that the spacecraft was in orbit around Ceres as planned.

Since its discovery in 1801, Ceres was known as a planet, then an asteroid and later a dwarf planet, said Marc Rayman, Dawn chief engineer and mission director at JPL, in a statement. Now, after a journey of 3.1 billion miles and 7.5 years, Dawn calls Ceres home.

The successful orbit is a double milestone for Dawn, since it also makes the craft the first mission to orbit two different extraterrestrial targets. Dawn has already spent time from 2011 to 2012 exploring the giant asteroid Vesta. Both Vesta and Ceres are the two most massive space rocks in our Solar Systems main asteroid belt between Mars Mars and Jupiter.

Ceres is seen from NASAs Dawn spacecraft on March 1, just a few days before the mission achieved orbit around the previously unexplored dwarf planet. The image was taken at a distance of about 30,000 miles. (Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA)

The latest pictures phoned home by Dawn show Ceres as a crescent thats mostly in shadow because its trajectory has put it on the dark side of the dwarf planet. From mid-April, when Dawn comes out into the sun, it will be sending back nearer and nearer close-ups as it lowers its orbit around the planet.

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.

NASA didnt just choose Ceres and Vesta for study because of their massive size, theyre also interesting because despite growing up in the same part of the early Solar System, they developed into two different kinds of bodies.

Vesta is a dry space rock with a surface that shows signs of resurfacing, much like Earth and other rocky bodies in the inner Solar System. Ceres has a much more primitive surface that contains water-bearing minerals and may have a weak atmosphere. Its more like Titan Titan and the large icy moons of the outer Solar System.

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NASA's Dawn Spacecraft Reaches Dwarf Planet Ceres