Dawn Makes Its Second Rendezvous at Dwarf Planet Ceres

Three-and-a-half years ago, a sophisticated NASA space probe named Dawn caught up with an asteroid named Vesta. Instead of just collecting images and data as it flew by, it fired its ion thrusters and went into orbit around it for a year of intensive study.

Then in July of 2012 it did something even more unusual -- it fired up its thrusters again and flew off toward another asteroid, Ceres! Now, this may sound routine in the STAR WARS universe, but that’s quite a feat today in this galaxy.

Asteroids are remnants of the early days of the formation of the Solar System. Their study is critical to our understanding of the details of that process. Dawn learned a great deal about Vesta. Before its visit, about all we knew was that it is the second largest asteroid in the Solar System and that it is the brightest asteroid as seen from the earth. Now we know a great deal more. Its surface has now been mapped in great detail, including the composition of its minerals.

Vesta has enough mass to have pulled itself into some approximation of a sphere. Its surface is pitted with the scars of innumerable meteor strikes, some quite large.

It was long assumed that Vesta was entirely dry because the low temperature and pressure at its surface wouldn’t allow it to retain water. However, analysis of Dawn images show signs of short-lived flows of water-mobilized material on its surface. “Nobody expected to find evidence of water on Vesta. The surface is very cold and there is no atmosphere, so any water on the surface evaporates,” says UCLA postgraduate researcher Jennifer Scully. “Vesta is proving to be a very interesting and complex planetary body.”

Ceres will offer new challenges. It is the largest asteroid. Whereas Vesta, the second largest asteroid, is about the size of Arizona, Ceres is about the size of Texas. It has enough mass to have clearly pulled itself into a sphere. Therefore, Ceres is now officially classified as a dwarf planet. Vesta only rates the designation “protoplanet.”

Although Ceres and Vesta are the two largest asteroids, they are quite different, which is why they were the targets of this mission. Vesta resembles the rocky bodies of the inner Solar System, while Ceres more resembles the icy bodies of the outer Solar System, such as Pluto. Ceres may have water-bearing minerals on its surface and even a weak atmosphere. We’ll soon see.

To date, the best images of Ceres have come from the Hubble Space Telescope. Sophisticated enhancements bring out suggestions of areas that may be impact zones, but we really don’t know. In a matter of days, Dawn will be returning images that will leave the Hubble images in the dust.

If all goes well, Dawn will use its ion thrusters to enter orbit around Ceres on March sixth. Should it succeed, Dawn will become the first spacecraft to orbit two different extraterrestrial bodies -- another NASA first!

You can keep up with the latest mission status at http://www.nasa.gov/mission_pages/dawn/main/, and on NASA TV.

Dawn is functioning well after seven years in space, which speaks well of its designers and builders at Orbital Sciences Corporation. Major components were also contributed by German, Italian, and Dutch firms. Caltech’s Jet Propulsion Laboratory in Pasadena is responsible for Dawn’s mission operation, while UCLA is responsible for developing the science from the mission.

New Horizons begins imaging Pluto

Meanwhile, NASA’s New Horizons space probe is awake, alert, and has aimed its cameras at Pluto. Most of its imaging work at present is navigational in nature as the astrogators at Johns Hopkins Applied Physics Lab work to thread the needle that lets them skim the surface of Pluto on July 14th.

Sometime in March, New Horizon’s images of Pluto will become the best ever obtained. We’ll take a close look at that mission soon.

Almanac

Many of us are fascinated by close alignments of the planets in our sky, called conjunctions (including horoscope-casters and soothsayers). There will be plenty of conjunctions this year, with February giving us a fine display. Mars is still low in the west at dusk as we out distance him in our race around the sun. Venus, meanwhile, is rising up to meet him as she catches up with us from inside our orbit. Uranus and Neptune start the month as a backdrop way in the distance, although you’ll need a telescope to see them.

The Zodiacal Light may be visible in the evening to the west as a huge column of diffuse light from the horizon to up near Venus and Mars.

Jupiter still rules the night sky, reaching opposition on February 6th. At that time it will rise at sunset, set at sunrise, and be at its closest and brightest for the year. Winter is also when our sky provides the sharpest views. (Of course, it’s also when it tends to be coldest!)

Saturn rises in the wee hours of the morning. Its rings are tilted 25º, only 2º short of maximum. When Saturn rises at a more civil (and warmer) hour in the spring, its plumage will still be on splendid display.

Sunrise: 6:53 a.m./Sunset: 5:22 p.m.(Feb.1)

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