Launched by NASA on February 7, 1999 Stardust was a 300-kilogram robotic space probe, whose main mission was to gather dust samples from the coma of comet Wild 2–as well as samples of cosmic dust–and bring them back to Earth for scientists to study. Since 2006, when the spacecraft finally delivered its aerogel and aluminum foil dust collectors back to our planet, scientists have been combing through the collectors in search of rare, microscopic motes of the dust that swims around in the space between stars. Stardust was the first sample mission of its kind, and on its long journey to meet up with Comet Wild 2, the craft also flew past and studied the asteroid 5535 Annefrank. In August 2014, the team of scientists combing through the microscopic particles carried back to Earth by Stardust, report that they have detected seven dust motes that very likely originated from beyond our own Solar System, perhaps born in the wake of a supernova blast millions of years ago and altered by eons of exposure to the extremes of space. If so, these seven motes of captured stardust would be the first confirmed samples of contemporary interstellar dust.
“They are very precious particles,” commented Dr. Andrew Westphal in an August 14, 2014 University of California at Berkeley Press Release. Dr. Westphal, a physicist at UC Berkeley’s Space Sciences Laboratory, is the lead author–with 65 coauthors–of a report describing the particles appearing in the August 15, 2014 issue of the journal Science. Twelve other papers concerning the precious particles of captured stardust are available online, and also appear in August 2014 in the journal Meteoritics & Planetary Science.
Dr. Westphal cautioned, however, that additional tests had to be performed before the team can say definitely that these seven dust motes are tiny bits of debris from interstellar space. But if, indeed, they are, the particles could help explain the origin and evolution of interstellar dust–that up until now could only be guessed at, based on distant astronomical observations.
These little motes of dust are considerably more diverse in terms of their structure and chemical composition than scientists had previously believed. Indeed, the smaller ones are very different from the bigger ones, and they may have different histories. For example, many of the big ones have a fluffy structure, reminiscent of snowflakes, according to Dr. Westphal.
“The fact that the two largest fluffy particles have crystalline material–a magnesium-iron-silicate mineral called olivine–may imply that these are particles that came from the disks around other stars and were modified in the interstellar medium. We seem to be getting our first glimpse of the surprising diversity of interstellar dust particles, which is impossible to explore through astronomical observations alone,” Dr. Westfhal continued to explain in the August 14, 2014 UC Berkeley Press Release.
A mission extension of Stardust, that was codenamed NExT, culminated in February 2011, with Stardust intercepting comet Tempel I, a small Solar System object that had previously been visited by Deep Impact in 2005. Stardust ended its operation in March 2011.
Stardust was launched fifteen years ago to fly through the debris shed by Comet Wild 2, and capture cometary dust with aerogel tiles and aluminum foils mounted on the front of a two-sided collector. Aerogel, sometimes called “frozen smoke,” is a synthetic, porous extremely light-weight material derived from a gel, in which the liquid component has been replaced by a gas.
Collectors that had been mounted on the rear were created to capture particles from the “snowstorm of interstellar dust streaming through the Galaxy,” explained Dr. Anna Butterworth in the August 14, 2014 UC Berkeley Press Release. Dr. Butterworth is a Berkeley research physicist. She went on to add that “This dust is relatively new, since the lifetime of interstellar dust is only 50 to 100 million years, so we are sampling our contemporary Galaxy”.
Stardust was competitively chosen in 1995 as part of NASA’s Discovery Program of relatively inexpensive missions with dedicated, highly focused scientific goals. Comet Wild 2 was chosen as Stardust’s main quarry, providing a rare chance for astronomers to observe a long-period comet that had wandered in close to our Sun. The comet became a short-period comet after an occurrence back in 1974, when its orbit was altered by the powerful gravitational pull of the gas-giant planet Jupiter. This gravitational interaction moved Wild 2’s orbit inward, and closer to the fiery heat of our Star. In planning Stardust, it was expected that most of the original material–from which the comet had been born–would still be preserved on that frozen object.
The Stardust spacecraft was designed, constructed and operated by Lockheed Martin Astronautics as a Discovery-class mission in Denver Colorado. The Jet Propulsion Laboratory (JPL) in Pasadena, California, provided mission management for the NASA division for mission operations. The principal investigator of the mission was Dr. Donald Brownlee from the University of Washington.
Comet Wild 2 And Other Flashing, Frozen Wanderers
Comets are delicate, transient bodies–strange and alien visitors from afar, flashing into Earth’s warm inner region of the Solar System with their fiery, flickering tails. These mysterious, beautiful visitors travel in from their remote, frigid home beyond the outermost major planet Neptune, where our Sun appears to be no more than just an especially bright star suspended in the darkness. Comets bear within their frozen hearts the pristine traces of primordial ingredients that formed our Solar System. These ancient ingredients have been kept pure in the frigid, dark “deep freeze” that exists at the edge of our Solar System. Obtaining an understanding what makes up the mysterious compositions of comets translates into an understanding of the identity of the primordial ingredients that cooked up our Sun’s entire family of planets, moons, comets, asteroids and other smaller objects.
The frozen, “dirty snowballs” that we call comets are icy planetesimals, meaning that they are the lingering population of the building blocks of the quartet of giant gaseous planets inhabiting the outer Solar System–Jupiter, Saturn, Uranus, and Neptune, as well as their enchanting retinues of mostly icy moons. Rocky planetesimals, on the other hand, such as the asteroids, are the lingering building blocks of the quartet of rocky terrestrial planets dwelling in our Solar System’s toasty inner regions closer to our Star–Mercury, Venus, Earth, and Mars.
Comets fly into Earth’s warm, golden inner region of the Solar System from two dark and frigid domains. The first is termed the Kuiper belt, which circles our Star beyond the orbit of Neptune, and it is the source of short-period comets. The short-period comets zip into the inner Solar System more frequently than every two hundred years. The second domain of comets is called the Oort cloud, which is an immense sphere of icy objects that surrounds our entire Solar System. The Oort cloud is the very dark and frigid home of the most remote comets, the long-period comets, which take at least two hundred years to flash into Earth’s inner solar neighborhood. Because we are located comparatively close to the Kuiper belt, short-period comets have played a more influential role in Earth’s history.
The core of a comet is called its nucleus, and it is made up mostly of dust and ice encased within a dark coating composed of organic material. The ice is mostly frozen water, but other frozen ingredients may also exist–such as carbon dioxide, carbon monoxide, ammonia, and methane. As the comet zips in towards our Star, the ice on the surface of its nucleus becomes a gas, and creates a cloud called a coma. The Sun’s radiation pushes the dust motes away from the coma, thus creating the thrashing, flashing bright dusty tail that comets are so famous for. Charged particles fleeing from the Sun ionize some of the comet’s gases, creating an ion tail. Because the thrashing tails of comets are shaped by our Sun’s glare and the solar wind, they always point away from the Sun.
The fragile microscopic motes of space dust obtained by the Stardust spacecraft are, perhaps, the first to be directly captured that originated from beyond our Solar System. These seven tiny particles could help scientists understand the building blocks not only of our own planet and its siblings but also planets that dwell around stars other than our Sun. The sample comes after years of collecting dust and more years of thousands of people analyzing the spacecraft’s take.
Two dust motes, each only about two microns (thousandths of a millimeter) in diameter, were separated from the fluffy, light aerogel detectors after their impact tracks were detected by volunteers, calling themselves “Dusters,” who studied over a million images through a UC Berkeley citizen-science project called “Stardust At Home”. “Stardust At Home” proved to be of the utmost importance in finding these “needles in a haystack.” A third track was formed by a particle zipping from the right direction–the flow of the interstellar wind–but seemed to be traveling so speedily, over 10 miles per second, that it had vaporized! An additional 29 tracks, also detected by the volunteers, were determined to have been booted out of the spacecraft itself into the waiting snare of the collectors.