Dawn Spacecraft Poised to Enter Orbit at Vesta Asteroid
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By Ron Cowen of Nature magazine
The Dawn spacecraft had a difficult birth: it was threatened by cost overruns and technical concerns, cancelled, reinstated and scaled down. Now, after a four-year journey spiraling out from Earth's orbit, the probe is set to explore the beginnings of the Solar System.
On 16 July, Dawn will enter orbit around Vesta (see 'Dawn patrol'), an asteroid that, at 500 kilometers wide, is the second largest in the Solar System. It will spend a year there before flying on to Ceres, the Solar System's largest asteroid at nearly 1,000 kilometers wide. There are hundreds of thousands of bodies in the main asteroid belt, which sprawls between the orbits of Mars and Jupiter and is a storehouse of material that formed early in the Solar System's history. But because Vesta and Ceres have apparently survived in one piece since then, "they are like time capsules telling us about the earliest stages of planet formation", says Carol Raymond, deputy principal investigator of the mission and a planetary scientist at NASA's Jet Propulsion Laboratory in Pasadena, California.
Dawn's comparative study of the two bodies should also help to show how similarly sized objects can evolve very differently. Glimpses of Vesta suggest that its structure is like that of a miniature Earth, with a metallic core and a rocky mantle and crust, but that its growth was halted when Jupiter's far-reaching gravitational influence prevented asteroids in the belt from coalescing any further. Vesta's composition, deduced from afar through its spectral properties, suggests that after its formation, the asteroid was initially hot enough for lava to ooze out onto its surface. By contrast, Ceres contains many water-bearing minerals, and with an average density lower than that of Earth's rocky crust, it may be one-quarter ice beneath its dust-coated surface. The asteroid could even hold a subsurface ocean, long frozen or perhaps still liquid.
Dawn will use three instruments to probe those differences. A camera will image surface features as small as 10 meters across; a spectrometer will map crustal minerals at various electromagnetic wavelengths; and a γ-ray and neutron detector will reveal the quantities of elements by detecting radiation and particles produced when cosmic rays hit atomic nucleii on the surface of the asteroids.
This information, together with models of where in the early Solar System Ceres and Vesta originated, might confirm one theory as to why the asteroids are so different: that Vesta formed a few million years before Ceres. That would have given Vesta enough time to incorporate the radioactive isotope aluminium-26, which was abundant in the earliest years of the Solar System but decayed before most of the asteroids in the belt formed. The radioactivity could have provided enough heat to drive volcanic eruptions, changing the character of Vesta's surface.
Tectonic upheavals erased evidence of early heating on Earth and the other rocky planets--but not on Vesta. "Vesta is telling us what the planet-formation process looked like after the first 10 minutes in the oven," says Richard Binzel, a planetary scientist at the Massachusetts Institute of Technology in Cambridge and a long-time observer of Vesta, who first tracked the asteroid as part of a school project in 1973.
Dawn will also take advantage of a window into Vesta's interior, notes Christopher Russell, lead scientist of the mission and a geophysicist at the University of California, Los Angeles. Pictures taken by the Hubble Space Telescope in 1996 revealed an impact crater 13 kilometers deep, gouged into the asteroid at its south pole. Dawn will peer into that hole to discern any geological diversity exposed by the impact. Three types of meteorite found on Earth--eucrites, howardites and diogenites--are thought to be chips of Vesta, blasted away by the collision. Linking these convenient specimens to particular internal layers of Vesta is a key driver of the Dawn mission, notes Binzel.
"It's a little bit like the Humpty Dumpty problem--we've got a lot of pieces of Vesta and we'd like to see how they all fit together," he says.
After its tour of Vesta, Dawn will fire up its ion thrusters--solar-powered jets that supply a weak but long-lasting push--and set a course for Ceres, which it will inspect over five months in 2015.
Before launch, budget issues caused the mission team to drop two instruments originally meant to fly aboard Dawn; one of them, a magnetometer, will be especially mourned once the craft reaches Ceres. The magnetometer could have looked for fluctuations in the strength of the asteroid's magnetic field that might have provided clues as to whether the body harbors a briny ocean. Losing the instrument "was a big blow", says Raymond.
Although Dawn has so far survived the ravages of budget changes, politics and four years in interplanetary space, Russell says that he won't relax until the craft enters orbit around Ceres. Casey Lisse, a planetary scientist at Johns Hopkins University's Applied Physics Laboratory in Laurel, Maryland, agrees. "We've learned most of what we can from remote observations of Ceres, and we need an up-close and personal look," he says.
This article is reproduced with permission from the magazine Nature. The article was first published on July 13, 2011.
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11 Comments
Add CommentInteresting but is this journey necessary when we should be first researching the deepest oceans and what life is present within earth
Reply | Report Abuse | Link to thiswhy would there be any dependency one the progress of the effort to explore the oceans and the effort to explore space?
Reply | Report Abuse | Link to thisYou might as well be asking: is it necessary to wash my face if my fingernails keep growing?
Question: what is an " �-ray and neutron detector"?
Reply | Report Abuse | Link to thisWhen are we going to go grab an asteroid and bring it back to be the anchor of a space elevator?
Reply | Report Abuse | Link to thisIt may be a lot easier to deal with deep space than extreme pressures involved in deep dives. Besides at this point unless Freeman Dyson was right the asteroids are dead objects that we have had serious issues with in the past. Ask the birds about their cousins and 65 million years ago. I do hope that the missions goal is not to bring one of these back with them.
Reply | Report Abuse | Link to thisConsidering our ocean how much more damage should we cause as we investigate and exploit it. I heard today that blue tuna may be extinct. What I am pretty sure of is the ocean is critical and the patient is crashing.
You may want to also reconsider life at the bottom of the ocean meaning much. It has been posed that 90% of the biomass on Earth is under the first 10 miles of the crust and there is a complete ecosystem on the first millimeter of the oceans water. Study the earth all you want but you are now looking at a patient in ICU and if we keep exploiting it the patient will flat-line long enough to get rid of us.
Reply | Report Abuse | Link to thisSounds like an gamma ray and neutron detector. What is not really stated is that the magnetic field of Jupiter probably has more influence than all the asteroids put together. I think they are trying to get a better picture of actual material the asteroids are made of. It was only recently we realized that the asteroids may not be solid objects at all which would quickly change any approach to manipulating one of these objects.
Reply | Report Abuse | Link to thisWe may be also able to exploit some of the minerals on these objects and that could make space travel not only fun but productive. There are now projections of China having both moon bases and space stations for manufacturing purposes.
Well, it ain't much but I'll take it ! Where is my " Warp Drive " ?
Reply | Report Abuse | Link to thisRead 'Project Orion' by George Dyson. His father Freeman Dyson one of the greatest physicist in the world was part of the project and it provided 10% light speed for an object the size of several football fields.
Reply | Report Abuse | Link to thisThat means closest star in 40 years not 40,000 years or better at the speeds we go at.
Oh, they didn't pack a magnetometer for Ceres. Bummer.
Reply | Report Abuse | Link to this@ exodus88:
There is no "should first" in science. We can prioritize, but if we don't, synergy between fields and results makes everything go faster.
@ Atlanta-Terry:
1. Presumably a "gamma-ray" (γ-ray) et cetera, with code fail.
2. Space elevators is a technology question, not a research interest.
@ David Russell:
There has been only one impactor causing mass extinctions during history, and it did so because it rather unluckily hit calciferous and sulfurous minerals which are garbage piles that _life_ are responsible for. (Humans are young and amateurish in producing waste compared to some other life forms. [Which is rather ironic btw, seeing your later discussion.])
Have you seriously looked at the number of times we have had impacts inluding the one that caused the moon which more than likely set us up for life instead of environments like venus. In addidtion to the heavy metal core, change in angular velocity, stability of orbital angle and creation of magnetic field the moon has probably protected us as well as Jupiter as a impact catcher.
Reply | Report Abuse | Link to thisRegarding other extinction events it has been stated that we take a good hit about everby 20 to 60 million years and if not for erosion the evidence would be more obvious. It has recently been stated that there was an event over North America around 13,000 years ago wiping out most of the mega fuana here, createing serious freezing problems in Siberia (Mamoths with fresh food in their mouth in a flash frozen state) and some talk of the Permian being brought on by a strike.
I hope that clarifies the statement. Regarding Freeman Dyson, I have to admit a special love for him, Einstein, Bohr and Feynman. Together with Groucho, Dali and Lennon our world has been given the answers and the questions required to evolve to a better level. If I was a betting man I would agree with Hoffner, Ardley and White in that we are animals, we are teritorial and we tend to be true belivers meaning I don't think we will ever admit how wired we really are which is required to start fixing the world we were given dominion over. The thing to always remember life is special and the environment for life is short lived. In a billion years the sun will end up boiling the water off the earth and then we can study the whole ocean.
My point really is appreciate the current state, that we got as far as we did and we became aware that our actions have consequences. I thank God we got that far.