Vesta, image from NASA's Dawn spacecraft
Vesta, image from NASA's Dawn spacecraft

Ion thrusters full! Set us into a standard orbit, Mr. Sulu….

Well, I don’t know if any of the helms-persons at NASA are named Sulu, but we have indeed achieved orbit—that is, NASA’s Dawn spacecraft around the large asteroid Vesta.

I wrote about Dawn and Vesta not long ago, before the spunky little ion-driven robot arrived there. Since then, Dawn has reached its first destination, 117 million miles from Earth, entering a 9,900 mile orbit around Vesta on July 15th. Science observations are expected to begin in early August, but already Dawn has sent back wonderful preliminary images showing details never before seen.

Vesta’s surface may bear features and materials among the oldest in the Solar System. Already we can see that Vesta is pock-marked and scared by impacts incurred over the eons. Similar to how a forensic scientist may determine the sequence of events that occurred at a crime scene by studying the physical evidence left behind, the scars and residues on Vesta will help paint a picture of conditions throughout the Solar System’s history.

Almost as cool as its science mission is Dawn’s propulsion system. To use a term from a certain Smith and Jones movie, it’s “the New Hotness.” Technology first demonstrated on NASA’s Deep Space 1 spacecraft, Dawn’s engine is the first solar electric ion propulsion system used on a purely scientific spacecraft. Using electrical power generated by solar panels, Dawn’s engine ionizes xenon atoms and accelerates them with an electric field, squirting them out the back of the engine to produce thrust–similar to a balloon-powered car or rocket toy propelled by spurting air. And though a conventional chemical rocket can produce much stronger thrust, Dawn’s ion drive, operating with high efficiency and over longer periods of time, achieves up to 10 times the velocity change for an equivalent amount of propellant.

(As a sign of the technological times, in one episode of the original Star Trek series, Scotty was awe-stricken by an advanced alien spacecraft that used ion propulsion. Ironic; what today’s space explorers wouldn’t give for warp drive….)

Dawn will spend a year orbiting and studying Vesta before it moves onto its second target, Ceres, to harvest its secrets.

Vesta is now the largest known asteroid in our Solar System. It was second fiddle to Ceres for a long time, but back in 2006 when Pluto got “demoted” to dwarf planet status, Ceres’ status also changed—promoted or demoted, take your pick. Sure, Ceres is now in the more exclusive club of the dwarf planets, but it’s the smallest of that group, whereas when it was an asteroid, it was the largest, going from big fish in big pond to junior member of the upstairs office team….

So what’s Vesta like—what we know about it at the moment, anyway? Vesta is a mega-mountain of rock and dust, somewhat lumpy and potato-shaped, but approximating a spherical object with a mean diameter of about 330 miles–roughly the distance from Oakland to Los Angeles as the ion-driven robot flies. In terms of surface area, Vesta has about twice the real estate as the entire state of California!

Sounds pretty big—and it is—but you’d still need over 20,000 Vestas to make one planet with the mass of the Earth. And if you stood on the surface of Vesta, you’d weigh little more than 2% what you weigh on Earth. Myself, I’d weigh in at a tad under 5 pounds. Presumably that means I could jump a hundred feet into the sky and land again safely.

I don’t know about the science, but Vesta sounds like a fun place to me!

Dawn of A New Era 12 June,2013Ben Burress

Author

Ben Burress

Benjamin Burress has been a staff astronomer at Chabot Space & Science Center since July 1999. He graduated from Sonoma State University in 1985 with a bachelor’s degree in physics (and minor in astronomy), after which he signed on for a two-year stint in the Peace Corps, where he taught physics and mathematics in the African nation of Cameroon. From 1989-96 he served on the crew of NASA’s Kuiper Airborne Observatory at Ames Research Center in Mountain View, CA. From 1996-99, he was Head Observer at the Naval Prototype Optical Interferometer program at Lowell Observatory in Flagstaff, AZ.

Read his previous contributions to QUEST, a project dedicated to exploring the Science of Sustainability.

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