Discoveries by Cassini `beyond wildest hopes'

Instruments: Sensors designed in Maryland send back a stream of data from Saturn like `a fire hose.'

Medicine & Science

July 12, 2004|By Frank D. Roylance | Frank D. Roylance,SUN STAFF

More than a dozen years after Maryland scientists and engineers began designing it, an instrument package called MIMI has finally reached Saturn - one of 12 aboard NASA's $3.3 billion Cassini spacecraft.

By all accounts, the Magnetospheric Imaging Instrument is working perfectly. On Cassini's first loop past Saturn, MIMI's three sensors sent back reams of data on the invisible swarm of atomic particles that whiz around the planet, trapped in its powerful magnetic field.

"Gosh, it's beyond our wildest hopes," said University of Maryland physicist Douglas C. Hamilton. He led the development of a sensor called CHEMS, which identifies and measures the particles.

MIMI's principal investigator, Stamatios M. Krimigis of the Johns Hopkins University's Applied Physics Laboratory, agreed: "There is such a fire hose of data coming down that we'll need all the help we can get making sense of it, writing up the results and publishing it."

MIMI has already discovered that Saturn's "magnetosphere" is thick with ionized (electrically charged) forms of hydrogen and oxygen, and the radiation-battered remnants of water molecules blasted from the surfaces of Saturn's icy moons and rings.

The $23 million instrument has also confounded theorists who expected to find plenty of ionized nitrogen swirling around the planet - shreds of the nitrogen atmosphere on Titan, Saturn's largest moon. So far, MIMI has found almost none.

Every planet with a magnetic field, including Earth, traps ions - atoms and molecules that have lost electrons, giving them a positive electrical charge.

Some of these atomic bits arrive as "solar wind" blasted off the sun. Others are excavated, under bombardment from radiation, from the surfaces or atmospheres of the planet, its moons or rings. They flow through the magnetic field, forming belts of radiation such as Earth's Van Allen belts.

And that's where MIMI comes in, Krimigis said. By studying the chemistry and physics of particles in Saturn's magnetosphere, scientists are learning about the origins and evolution of its moons and rings.

"It's the next-best thing to landing and getting a sample," he said. Lessons learned can also be applied to our understanding of Earth's magnetosphere and its interaction with the solar wind.

Interplanetary missions are not for the impatient. In the 6 1/2 years since Cassini was launched on its 2 billion-mile voyage, one MIMI scientist has died. Three others have retired, and a host of engineers and graduate students have moved on to other work.

"The whole complexion of how you do work and analysis has changed, said Krimigis, 65, now Cassini's oldest principal investigator. "When we started this program, not everybody had laptops or even computers sitting on their desks."

Now, scientists see MIMI's data online within hours of its arrival from Saturn. "We couldn't live without the Internet," he said.

Cassini itself was state-of-the-art technology at its launch in 1997. But advances in electronics would make it different if built today.

It would have similar sensors, Krimigis said, "but they probably would weigh 10 times less and be consuming probably 10 times less power."

Some things never change. NASA budget constraints forced the elimination of "spin tables" that would have allowed scientists to point their individual instruments. So, they must turn the entire spacecraft.

That led to years of what Krimigis called "wrenching" negotiations over who would control the pointing and how much time each team's instruments would get on a desired target.

"As a consequence, we are behind in being ready to analyze all the data coming back," he said. "It means scientific team members are going to be working nights and weekends to catch up."

"But the thing that counts is our love of the subject ... and the recognition that we are discovering new knowledge," he said. "So we don't mind, I guess."

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