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Match Made in Heaven
August 04, 1999

A ‘Fly-By’ Encounter With A Big Rock

image: JPL/NASA

Late last week a small experimental spacecraft named Deep Space 1 (DS-1) flew within 10 miles of a near-earth asteroid. This is by far the closest encounter ever attempted, and is helping to solve a puzzling phenomenon: How do asteroids from the asteroid belt end up as meteorites on Earth? Braille, it seems, is a missing link.

In the early hours of July 29, DS-1 flew by the Braille asteroid. The team of scientists and engineers assembled to examine DS-1’s data felt that the ‘fly-by’ would not only test the capabilities of DS-1, but provide more data about asteroids—the ‘big rocks’ that cruise through space.

The close encounter with Braille—a rendezvous occurring 117 million miles from Earth—provided far more than scientists had hoped for. Information from DS-1’s fly-by suggests that the mile-long rock is related to a giant asteroid found in the asteroid belt as well as meteorites on Earth.

A Lucky Break in the Cosmic Jig-Saw Puzzle

image: JPL/NASA

Braille appears to be a chunk of Vesta, one of the largest asteroids in the solar system. Scientists believe that about a billion years ago, a cataclysmic event broke Vesta into smaller pieces, flinging fragments all over the system. Tiny pieces of Vesta, which is now about the size of Arizona, have been located here on Earth, as meteorites.

Scientists noted that Braille’s spectral signature—a unique chemical fingerprint captured by DS-1’s infared camera—matched not only Vesta but that of meteorites found on Earth. It was a spectacular coincidence that few researchers expected. Scientists choose Braille for a fly-by only because it was the easiest to reach. They had no idea that the little asteroid would turn out to be so important.

"What’s astounding to me is this wonderful result that we have gotten," says Bob Nelson, DS-1 Project Scientist at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, Ca. "We’ve been able to take this asteroid, link it to another asteroid and link it to a meteorite. I’m sort of regarding getting all three of them at once sort of like winning the triple crown."

A Y6K Problem?

image: Sandia National Laboratory

Could we expect a visit from Braille in the future? Dr. Eileen Ryan, a visiting professor at New Mexico Highlands University, believes Earth could one day be hit by another big asteroid—much like the collision 65 million years ago that wiped out the dinosaurs.

Dr. Ryan likens the study of Vesta’s breakup to a "giant lab impact experiment ... we can learn a lot about how our solar system formed with information like this and ... we’ll know more about collisions, more about how asteroids break up and be better prepared to deal with a situation like that."

The latest estimates are that Braille is likely to pose a potential collision hazard to Earth in the year 6000. "Something two kilometers across would really be a catastrophic impact with the earth; luckily it’s 4000 years before we have to worry about it," Ryan says.

The Little Spaceship That Could

In October 1998, DS-1 was launched into the cosmos. This launch is the first of many planned in NASA’s New Millennium Program, which will test a series of experimental spacecraft designed to try out new technologies. These experimental flights may one day enable humankind to explore the universe.

DS-1’s package of technological wonders include its ion propulsion system, which was first featured on the Star Trek series in 1968. Ion propulsion involves ionizing a gas by electrically charging molecules of xenon, or some other inert gas. The molecules are accelerated through an electromagnetic field to a speed of 30 km/second (25 miles/second). When these charged molecules, known as ions, are emitted from the exhaust of the engine, the spacecraft is pushed in the opposite direction.

image: JPL/NASA

Another new technology torn from the pages of science fiction books is DS-1’s automated navigation system. It is capable of guiding itself across the solar system with only rudimentary assistance from human controllers. DS-1 found its way to Braille by stellar navigation, or "astrogation."

"This would be like having your car find its own way from Los Angeles to Washington, D.C. arrive in a designated parking space and do it all while getting 300 miles per gallon," says JPL Deputy Mission Manager Marc Rayman.

DS-1 used an infrared camera called "MICAS" (Miniature Integrated Camera and Imaging Spectrometer to record the close encounter with Braille. The camera records light beyond the visible part of the spectrum. Scientist can measure those spectrums on graphs. Braille’s unique spectrum, which identifies the chemical "fingerprint" of the asteroid, gave scientists the startling new information linking Vesta and Braille.

"It’s often said that a picture is worth a thousand words, but today in this circumstance, a spectrum is worth a thousand pictures," Nelson says.

What The Future Holds For DS-1

What’s next for the little spaceship with the big brain? Scientists on the project are so pleased with DS-1’s performance, they want to extend the mission. But unless NASA chooses to further fund the project, the mission will end on Sept. 18. Just in case it’s extended, scientists have already aimed DS-1 at two comets for possible encounters in 2001.

Elsewhere on the Web

DS-1 Homepage

Spacer Magazine, "Ion Propulsion Could Fuel Deep Space Boom"

DS-1 Control Room Webcam

Photos and Animations of Vesta



by STN2


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