NASA's Dawn spacecraftrecently marked its one-year anniversary of becoming the first man-made object to enter orbit around a dwarf planet. Join us as we takea look at the spacecraft's many achievements in shedding light onwhat had previously been a little known member of our solar system,Ceres.
Launched on Sep. 27, 2007, Dawn was tasked with rendezvousing and characterizing theasteroid Vesta and the dwarf planet Ceres, with the primary goal ofproviding insights into the nature of our solar system and theprocess by which it was created. The spacecraft utilizes threeidentical zenon-fuelled ionengines for propulsion, and is sustained by a twin solar array thatwhen deployed gives the spacecraft an impressive 65 ft (19.7 m)wingspan.
These systems, and manyothers, kept Dawn operational over the course of a 3.1 billion-mile(4.9 billion-km) journey that included a helpful gravity assist fromJupiter, and a historic visit to Vesta, culminating in arrival atits final target and eventual resting place, Ceres.
The successful journeyto not one, but two distinct solar system bodies stands as testamentto the skill of every engineer and scientist involved in theambitious program. Since launch, Dawn has been under the care of ateam of dedicated mission specialists based on the eighth floor ofthe Jet Propulsion Laboratory's building 264 in Pasadina, California.
Following the loss oftwo of the probe's four initial reaction wheels, theteam was forced to improvise a fuel saving method of orientating thespacecraft relying heavily on Dawn's hydrazine supply. Despite thisunexpected complication, Dawn's mission operators were able tonavigate the void of space, manipulating the spacecraft into Ceres' gravitational embrace.
Prior to achievingorbit, Dawn was already making history by providing mankind withviews of Ceres far surpassing any previous image snapped by theHubble Space Telescope. As the spacecraft sped towardsthe dwarf planet, one feature in particular began to move in tosharper focus.
Previous Hubbleobservations had highlighted the presence of an unusual bright spotmarking the surface of Ceres, but the resolution of the telescopewasn't high enough to determine its nature. As Ceres drew nearer, thephenomenon revealed itself as a series of bright spots located inwhat is now known as the Occator crater. The featurenaturally sparked widespread debate as to the source of thebrightness, and of course drew the attention of more than a fewconspiracy theorists.
On Mar. 6, 2015,roughly seven and a half years after lift-off, Dawn finally achievedorbit around Ceres. However, whilst captured in orbit, the momentumof the spacecraft approaching the dwarf planet left it in a highlyeccentric orbit, requiring the probe to adjust its orbit. Around fiveand a half weeks of manouvering later, Dawn was sitting in its itsfirst mapping orbit some 8,400 miles (13,500 km) above the surface ofthe dwarf planet.
Once established inthis initial science orbit, the spacecraft set about transmittingdata harvested by the probe's sophisticated suite of onboardinstruments, allowing NASA scientists to set about compiling thefirst detailed maps of Ceres' surface. These maps highlighted thebarren, cratered surface of the wandering planetoid, hinting at asurprisingly active geological history.
An early analysis ofCeres led scientists to estimate that 25 percent of the mass of theplanetoid was comprised of water ice. Furthermore the formation ofcraters on Ceres in terms of depth and diameter shared manycharacteristics with the two icy Saturnian satellites, Dione andTethys.
Meanwhile, scientistscontinued to pour over increasingly detailed views of the 130-pluswhite spots that are now known to sporadically mark Ceres' surface.The patches observed in the Occator crater during Dawn's approachremained the brightest examples of the phenomena, with theories ontheir composition ranging from the presence of cryovolcanoes to vast,sunlight-reflecting salt deposits.
A later study published in the online journal Naturein Dec. 2015 would identify the bright material as type ofmagnesium sulfate called hexahydrite. The researchers assertedthat there could be a global subsurface layer of briny water-ice,which either sublimated leaving behind the bright residue, or was dugup by meteor impacts.
Anotherpaper pubished in the same journal focussed on the detection ofammonia rich clays by Dawn's Visible and Infrared MappingSpectrometer. The detection of the clays suggested that either Ceresoriginated outside of the main asteroid belt between Mars and Jupiter(where it is located today), or that the material originated fromfarther out and subsequently was transferred to Ceres via asteroidstrikes.
Over the course of theyear Dawn would spiral ever closer to the dwarf planet, firstdropping to a height of 2,700 miles (4,400 km), and then into itsthird mapping orbit 900 miles (1,500 km) above Ceres. Dawn settledinto its fourth and final mapping orbit in mid-December last year ata height of 235 miles (380 km), where it remains today.
In mid-June, as Dawnprogressed through its second orbit, NASA scientists were taken abackby the discovery of a solitary peak towering over thesurrounding terrain. The formation reached an impressive 3 miles (5km) towards space, and was marked on its sides by an uneven coveringof bright material bearing a striking resemblance to the depositsphenomena first discovered in the Occator crater upon Dawn's initialapproach to Ceres.
As Dawn moved closer to the surface, it became apparent that the mountain,tentatively named Ahuna Mons, may not be the only exampleof a peak-like formation. Dawn's science team and planetaryscientists across the globe have yet to figure out the geologicalprocess responsible for creating Ahuna Mons and its somewhat lessdefined cousins.
In its third mappingorbit, Dawn took 11 days and 14 complete orbits toimage the entirety of Ceres' surface at a resolution of roughly 450ft (140 m) per pixel. In its final mapping orbit, also known as theLow Altitude Mapping Orbit (LAMO), the probe was capable of imaging theplanetoid with a far superior resolution of 120 ft (35 m) per pixel.
In much the same waythat image resolution has increased with proximity, the spacecraft'sother instruments, such as Dawn's Visible and Infrared MappingSpectrometer, have been able to collect more accurate data concerningthe distribution of minerals across the surface of the dwarf planet.
Furthermore, sinceachieving orbit, Dawn has been engaged in continuously observing thequirks of Ceres' electromagnetic field, while images from thespacecraft's framing camera have allowed the science team to create aseries of 3D representations and fly-overs of the planetoid'ssurface.
Whilst there are stillmany mysteries surrounding Ceres, the data collected by Dawn willundoubtedly succeed in shedding light on the composition andformation of our solar system, and maybe, just maybe we can figureout what created the (at this point annoyingly enigmatic) brightspots.
Dawn's primary missionis set to continue up until the end of June this year. The limitingfactor to the probe's lifespan lies with its quickly diminishingsupply of hydrazine fuel. Once fully expended, the spacecraft will beunable to control its orientation in space. Having run dry, the theninert probe would be incapable of pointing its antenna to Earthin order to receive or relay information, or to angle its solararrays to collect the nourishing sunlight that has thus far kept itoperational for three quarters of a decade.
Once this inevitabilityoccurs, Dawn's batteries will run dry within a matter of hours,leaving the derelict spacecraft to orbit Ceres for a further 50 yearsbefore finally smashing into the surface of the dwarf planet.
What will remain isDawn's undying legacy – a veritable treasure trove of data, andthousands upon thousands of breathtaking images of a strange littleworld that, before the spacecraft's arrival last year, had beenlittle more than a blur.
Source: NASA