* Astronomy

Detailed observations from the first comet samples returned to Earth are debunking some of science’s long-held beliefs on how the icy, celestial bodies form.
Scientists expected the minute grains retrieved from a comet Wild 2 to be made up mostly of interstellar dust — tiny particles that flow through the solar system thought to be from ancient stars that exploded and died.
Instead, they found an unusual mix of primordial material as if the solar system had turned itself inside out. Hot particles from the inner solar system migrated out to the cold, outer fringes beyond Pluto where they intermingled and congealed to form a comet.

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NASA's Stardust Findings May Alter View of Comet Formation

Samples from comet Wild 2 have surprised scientists, indicating the formation of at least some comets may have included materials ejected by the early sun to the far reaches of the solar system.

Scientists have found minerals formed near the sun or other stars in the samples returned to Earth by NASA's Stardust spacecraft in January. The findings suggest materials from the centre of the solar system could have travelled to the outer reaches where comets formed. This may alter the way scientists view the formation and composition of comets.

"The interesting thing is we are finding these high-temperature minerals in materials from the coldest place in the solar system" - Donald Brownlee, Stardust principal investigator from the University of Washington, Seattle, US.

Scientists have long thought of comets as cold, billowing clouds of ice, dust and gases formed on the edges of the solar system. But comets may not be so simple or similar. They may prove to be diverse bodies with complex histories. Comet Wild 2 seems to have had a more complex history than thought.

"We have found very high-temperature minerals, which supports a particular model where strong bipolar jets coming out of the early sun propelled material formed near to the sun outward to the outer reaches of the solar system. It seems that comets are not composed entirely of volatile rich materials but rather are a mixture of materials formed at all temperature ranges, at places very near the early sun and at places very remote from it" - Michael Zolensky, Stardust curator and co-investigator at NASA's Johnson Space Centre, Houston.

One mineral found in the material brought back by Stardust is olivine, a primary component of the green sand found on some Hawaiian beaches. It is among the most common minerals in the universe, but scientists were surprised to find it in cometary dust.
Olivine is a compound of iron, magnesium and other elements. The Stardust sample is primarily magnesium. Along with olivine, the dust from Wild 2 contains high-temperature minerals rich in calcium, aluminium and titanium.

Stardust passed within 240 kilometres of comet Wild 2 in January 2004, trapping particles from the comet in an exposed gel. Its return capsule parachuted to the Utah desert on January 15, 2006. The science canister with the Wild 2 sample arrived at Johnson on January 17. Samples have been distributed to approximately 150 scientists for study.

"The collection of cometary particles is greater than we ever expected. The collection includes about two dozen large tracks visible to the unaided eye." - Stardust Deputy Principal Investigator Peter Tsou of NASA's Jet Propulsion Laboratory, Pasadena, California, US.

The grains are tiny, smaller than a hair's width. Thousands of them appear to be embedded in the glass-like aerogel. A single grain of 10 microns, only one-hundredth of a millimetre, can be sliced into hundreds of samples for scientists.
In addition to cometary particles, Stardust gathered interstellar dust samples during its seven-year journey. The team at Johnson's curatorial facility hopes to begin detailed scanning of the interstellar tray within a month. They will initiate the Stardust at Home project. It will enable volunteers from the public to help scientists locate particles.
After registering, Stardust at Home participants may download a virtual microscope. The microscope will connect to a server and download "focus movies." The movies are images of the Stardust Interstellar Dust Collector from an automated microscope at the Cosmic Dust Lab at Johnson. Participants will search each field for interstellar dust impacts.

Stardust science team members presented their first findings this week at the annual Lunar and Planetary Science Conference in League City, Texas, US.

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January 29th marks the 2-week anniversary of the picture perfect landing of the STARDUST Sample Return Capsule in Utah. The first of four cycles of sample harvesting (removing aerogel cells from the comet Wild 2 flight tray) for the Preliminary Examination of returned samples reached its peak last week. The pace of sample processing (removing and preparing the particles from the aerogel cells) has ramped up considerably. Six particles have been removed from the aerogel. Most of these particles were 'potted' in epoxy and the epoxy was then sliced into very thin wafers.
Additionally, researchers also separated particles along with their tracks in small pieces of aerogel. Infrared spectroscopy has been performed on the removed particles, and half of one of the removed aerogel cell has been examined with a X-Ray beam from a synchrotron.
The soil samples taken from the Utah landing site of the Sample Return Capsule are been examined for their chemical composition.
One piece of the removed aluminium foil will be examined under a Scanning Electron Microscope to observe very small particle impacts. Some of the sliced wafers are being readied for a Transmission Electron Microscope to reveal the particle's mineralogy and petrology. As more of these processed samples reach the hands of eagerly awaiting analysts around the world, the pace of Wild 2 sample analyses - the central focus of this Preliminary Examination - will accelerate along with the revelation of breathtaking results. Stay tuned!

Source

Stardust Capsule Reentry Movie