[meteorite-list] Stardust Team Reports Discovery of First Potential Interstellar Space Particles

[Ron Baalke]

August 14, 2014
     
Stardust Team Reports Discovery of First Potential Interstellar Space Particles

Seven rare, microscopic interstellar dust particles that date to the 
beginnings of the solar system are among the samples collected by scientists 
who have been studying the payload from NASA's Stardust spacecraft since its 
return to Earth in 2006. If confirmed, these particles would be the first 
samples of contemporary interstellar dust.

A team of scientists has been combing through the spacecraft's aerogel and 
aluminum foil dust collectors since Stardust returned in 2006.The seven 
particles probably came from outside our solar system, perhaps created in a 
supernova explosion millions of years ago and altered by exposure to the 
extreme space environment.

The research report appears in the Aug. 15 issue of the journal Science. 
Twelve other papers about the particles will appear next week in the journal 
Meteoritics & Planetary Science.

"These are the most challenging objects we will ever have in the lab for 
study, and it is a triumph that we have made as much progress in their 
analysis as we have," said Michael Zolensky, curator of the Stardust 
laboratory at NASA's Johnson Space Center in Houston and coauthor of the 
Science paper.

Stardust was launched in 1999 and returned to Earth on Jan. 15, 2006, at the 
Utah Test and Training Range, 80 miles west of Salt Lake City. The Stardust 
Sample Return Canister was transported to a curatorial facility at Johnson 
where the Stardust collectors remain preserved and protected for scientific 
study.

Inside the canister, a tennis racket-like sample collector tray captured the 
particles in silica aerogel as the spacecraft flew within 149 miles of a 
comet in January 2004. An opposite side of the tray holds interstellar dust 
particles captured by the spacecraft during its seven-year, 
three-billion-mile journey.

Scientists caution that additional tests must be done before they can say 
definitively that these are pieces of debris from interstellar space. But if 
they are, the particles could help explain the origin and evolution of 
interstellar dust.

The particles are much more diverse in terms of chemical composition and 
structure than scientists expected. The smaller particles differ greatly from 
the larger ones and appear to have varying histories. Many of the larger 
particles have been described as having a fluffy structure, similar to a 
snowflake.

Two particles, each only about two microns (thousandths of a millimeter) in 
diameter, were isolated after their tracks were discovered by a group of 
citizen scientists. These volunteers, who call themselves "Dusters," scanned 
more than a million images as part of a University of California, Berkeley, 
citizen-science project, which proved critical to finding these needles in a 
haystack.

A third track, following the direction of the wind during flight, was left by 
a particle that apparently was moving so fast -- more than 10 miles per 
second (15 kilometers per second) -- that it vaporized. Volunteers identified 
tracks left by another 29 particles that were determined to have been kicked 
out of the spacecraft into the collectors.

Four of the particles reported in Science were found in aluminum foils 
between tiles on the collector tray. Although the foils were not originally 
planned as dust collection surfaces, an international team led by physicist 
Rhonda Stroud of the Naval Research Laboratory searched the foils and 
identified four pits lined with material composed of elements that fit the 
profile of interstellar dust particles.

Three of these four particles, just a few tenths of a micron across, 
contained sulfur compounds, which some astronomers have argued do not occur 
in interstellar dust. A preliminary examination team plans to continue 
analysis of the remaining 95 percent of the foils to possibly find enough 
particles to understand the variety and origins of interstellar dust.

Supernovas, red giants and other evolved stars produce interstellar dust and 
generate heavy elements like carbon, nitrogen and oxygen necessary for life. 
Two particles, dubbed Orion and Hylabrook, will undergo further tests to 
determine their oxygen isotope quantities, which could provide even stronger 
evidence for their extrasolar origin.

Scientists at Johnson have scanned half the panels at various depths and 
turned these scans into movies, which were then posted online, where the 
Dusters could access the footage to search for particle tracks.

Once several Dusters tag a likely track, Andrew Westphal, lead author of the 
Science article, and his team verify the identifications. In the one million 
frames scanned so far, each a half-millimeter square, Dusters have found 69 
tracks, while Westphal has found two. Thirty-one of these were extracted 
along with surrounding aerogel by scientists at Johnson and shipped to UC 
Berkeley to be analyzed.

NASA's Jet Propulsion Laboratory, Pasadena, California, manages the Stardust 
mission for NASA's Science Mission Directorate, Washington. Lockheed Martin 
Space Systems, Denver, developed and operated the spacecraft.

For information about the Stardust mission on the Web, visit:

www.nasa.gov/stardust 

For information about NASA and agency programs on the Web, visit:

http://www.nasa.gov/home 

-end-

J.D. Harrington
Headquarters, Washington
202-358-5241
j.d.harrington at nasa.gov 

William Jeffs
Johnson Space Center, Houston
281-483-5111
william.p.jeffs at nasa.gov