Dust plucked from Comet Wild 2 surprises scientists

Science’s long-held beliefs that Comets are just conglomerations of ice, dust and gases, and originate only in the frigid, outer reaches of the solar system, are disproved by a NASA-funded study which observed the first comet samples returned to Earth and revealed that Comets were also formed partly by the heat of the sun.

After a detailed study of dust fragments from Comet Wild-2, captured by NASA's Stardust spacecraft and brought to Earth in January 2006, scientists’ team led by astronomer Don Brownlee from the University of Washington in Seattle, found Comet Wild 2 certainly is made up of components with a more complex history than imagined.

They found a wide range of primordial material, as if the solar system had turned itself inside out, and size in the Wild 2 samples.

The findings, reported in the Dec. 15 issue of the Science Express, the online edition of the journal Science, indicate the formation of at least some comets may have included materials migrated out from the inner solar system to the far and cold outer edge of the solar nebula.

Scientists used spectroscopy technology which does not damage the mineral content of the particles, and discovered that the dust plucked from Comet Wild-2 is made up of a diversity of high- and low-temperature minerals instead of a single dominant one.

"We have found very high-temperature minerals, which supports a particular model where strong bipolar gas jets coming out of the early sun propelled material formed near to the sun outward to the outer reaches of the solar system," said Michael Zolensky, NASA cosmic mineralogist and Stardust co-investigator at the Johnson Space Center (JSC), Houston.

"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."

The findings are the first scientific results from NASA's Stardust mission, a $212 million project launched in February 1999 that sent a spacecraft through the tail of the comet Wild 2 to excavate grains of dust, minerals and organic compounds.

Stardust met comet Wild 2 beyond the orbit of Mars in January 2004. It zoomed close to Earth and ejected a capsule containing the rare samples. The capsule safely parachuted down to the Utah desert Jan. 15.

Comets, which are relatively small extraterrestrial bodies consisting of a frozen mass that travels around the sun in a highly elliptical orbit are among the oldest objects in the Solar System. Scientists from Imperial College London and the Natural History Museum believe the study of the dust brought from the oldest solar body can enable them to find out how Earth and other planets came to be formed.

"We're doing things no one ever imagined we could do, even at the time we launched the mission," said Donald Brownlee, the University of Washington astronomer who is principal investigator, or lead scientist, for Stardust.

"We've taken a pinch of comet dust and are learning incredible things."