[meteorite-list] Comet's Dust Clouds Hit Stardust 'Like Thunderbolt'

[Ron Baalke]

http://spaceflightnow.com/news/n0406/17stardust/

Comet's dust clouds hit NASA probe 'like thunderbolt'
UNIVERSITY OF CHICAGO NEWS RELEASE
June 17, 2004

Two swarms of microscopic cometary dust blasted NASA's Stardust 
spacecraft in short but intense bursts as it approached within 
150 miles of Comet Wild 2 last January, data from a University 
of Chicago instrument flying aboard the spacecraft has revealed.

"These things were like a thunderbolt," said Anthony Tuzzolino, 
a Senior Scientist at the University of Chicago's Enrico Fermi 
Institute. "I didn't anticipate running into this kind of show." 
Tuzzolino and Thanasis Economou, also a Senior Scientist at the 
Fermi Institute, will report their findings in the June 17 issue 
of the journal Science.

The materials streaming from a comet range in size from particles 
that could fit on the head of a pin to boulders the size of a 
truck. Stardust mission planners correctly estimated that their 
spacecraft could safely avoid the hazardous larger objects by 
passing the comet at a distance of approximately 150 miles and 
using very effective dust particle shields.

Based on the data collected by the Dust Flux Monitor Instrument, 
Tuzzolino and Economou estimate that NASA achieved its goal of 
collecting at least 1,000 samples measuring at least one-third 
the width of a human hair or larger during the flyby.

The Stardust spacecraft is scheduled to return the samples to 
Earth in January 2006. Scientists will study the samples, the 
first ever returned to Earth from a comet, for insights into 
the early history of the solar system.

The Dust Flux Monitor Instrument collected data for 30 minutes 
when the spacecraft passed closest to the comet last Jan. 2. 
Stardust encountered the first swarm of dust particles when 
the spacecraft passed within 146.5 miles of the comet's nucleus. 
The monitor detected a second intense swarm after passing the 
comet when the spacecraft was approximately 2,350 miles from 
the nucleus.

"We believe that we see fragmentation of large dust lumps into 
swarms of small particles after they are coming out from the 
nucleus," Economou said.

In between the particle swarms, the impact of which lasted 
just a few seconds each, the dust monitor went for periods 
of several minutes before it detected another particle.

This isn't Tuzzolino's first encounter with a comet, though 
it is by far the closest. He helped design, build and test 
the Dust Counter and Mass Analyzer instrument that passed 
Comet Halley at a distance of 5,000 miles or more in 1986 
aboard two Soviet Vega spacecraft. Halley had emitted a 
spray of dust "much smoother" than that of Wild 2, 
Tuzzolino recalled.

"In general, one thinks of a comet as emitting gas and dust 
in a nice, uniform steady state, sort of like a hose," he 
said. Halley did show fluctuations, "but not to this extent."

The dust monitor detected its first impact when Stardust 
was 1,010 miles from the cometary nucleus. The last impact 
was recorded at a distance of 3,500 miles as the spacecraft 
sped away. During one intense event, the dust monitor 
detected more than 1,100 impacts in one second. The largest 
particle measured during the cometary flyby measured an 
estimated 500ths of an inch in diameter.

A similar instrument to the University of Chicago Dust Flux 
Monitor Instrument is a component on NASA's Cassini mission 
to Saturn. Cassini's High-Rate Detector, which Tuzzolino 
also built, is part of a larger instrument, Germany's Cosmic 
Dust Analyzer, which will study the ice and dust particles 
that form the major components of Saturn's ring system. 
Cassini is scheduled to become the first spacecraft ever to 
orbit Saturn on June 30.