NASA’s 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
Dawn then signalled its mission controllers at NASA’s 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 System’s main asteroid belt between
Ceres is seen from NASA's Dawn spacecraft on March 1, just a few days before the mission achieved... [+]
The latest pictures phoned home by Dawn show Ceres as a crescent that’s 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 didn’t just choose Ceres and Vesta for study because of their massive size, they’re 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. It’s more like
By studying both bodies with the same instruments, Dawn hopes to build up an idea of where their evolutionary paths diverged and help add to our picture of how our Solar System was formed.
Because of Ceres’ potential water content, it’s also sparked the inevitable speculation that it may play host to primitive life. That speculation has been fuelled by better images of the bright spot on the surface of the planet as Dawn drew nearer.
First seen in Hubble pictures, the relatively bright patch turned out to be two spots as Dawn got closer and they remain a mystery to scientists. It’s possible that the spots are scars from recent impacts, minerals deposited by active geysers, erupting water ice from “cryovolcanoes” or even plumes of water vapour.
"Ceres' bright spot can now be seen to have a companion of lesser brightness, but apparently in the same basin,” said the University of California’s Chris Russell, principal investigator for the mission, of the most recent images of the spots, sent back by Dawn late last month.
“This may be pointing to a volcano-like origin of the spots, but we will have to wait for better resolution before we can make such geologic interpretations.”
Researchers will be hoping that Dawn discovers more over the coming months.
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