The news from Nasa about particles of interstellar dust discovered by scientists working on the Stardust mission focused on the scientific discovery, but most didn’t go into much detail about the amateurs who helped make it happen. Two of those amateurs are even listed as co-authors on the latest paper published in the peer-reviewed journal Science.
We’re all starstuff
Stars flare to life in vast molecular clouds of gas and dust. Millions or billions of years later those stars die. Stars like our Sun expand to become red giants while larger, faster-burning stars die in giant supernova explosions. However it happens, the dying star casts vast amounts of microscopic dust particles into interstellar space.
Until recently, scientists could only study the ancient dust particles locked inside meteorites as the Solar System formed 4 billion years ago. Just as pollen grains or insects trapped in amber give biologists a glimpse of Earth’s ancient history, these meteoritic dust grains give scientists a glimpse of the environment around the Sun as it was being born.
Interstellar dust particles break down quickly - at least on a cosmic scale. Within about 100 million years, radiation and reactions with the interstellar medium break the particles down to the molecular level. That means particles embedded in meteorites can’t tell us anything about the Sun’s more recent neighborhood. So Nasa decided to get something a little fresher.
Nasa launched the Stardust mission in 1999 to study the comet Wild 2 (pronounced Vilt 2). Stardust flew through the comet’s coma 5 years later and collected samples or the comet’s vaporized water and dust. When the spacecraft’s orbit slinged it past Earth again in 2006, it dropped a capsule into Earth’s atmosphere. Stardust didn’t just return bits of the comet. As it cruised through interplanetary space, the spacecraft exposed aerogel sample collectors with the hope of capturing dust particles from beyond the Solar System.
Aerogel is like high-tech cotton candy. The fluffy pink carnival treat consists of strands of spun sugar tangled into a lattice with lots of space in between each strand. An aerogel is like that but on a much smaller scale (and much less tasty). Chains of silica or other material form a lattice surrounding empty pores about 100 nanometers across. A particle passing through the aerogel loses a little speed every time it breaks one of the nanoscale strands. As it crashes through millions and millions of strands, the particle slows to a stop within the aerogel, leaving behind a visible cone-like path of destruction that narrows to where the particle came to rest. In pictures taken with an electron microscope you can follow that path to the particle resting at its point.
Ordinarily, scientists would use automated software to scan for the particles’ tracks through the aerogel, but Stardust’s scientists ran into a problem. The violent vibrations and g-forces of Stardust’s launch, the years in the extreme conditions of interplanetary space, and then the fiery high-g re-entry into Earth’s atmosphere left microscopic cracks throughout the aerogel. Robotic scanners produced too many false alarms. The only way to find a real impact tracks was for a human to look at each image. It would take centuries for the handful of scientists to look at each one of the millions of images.
Amateurs to the rescue
The power of crowdsourcing is its ability to bring thousands or millions of people together to perform simple tasks that add up to a monumental achievement. Spotting a particle’s track through the aerogel doesn’t require the specialized knowledge or skills of an astrophysicist - just the innate human ability to recognize patterns. Enlisting amateurs around the world would let the scientists find Stardust’s particles in a fraction of the time.
Stardust@Home invites you to watch simple, 40-frame animations created from electron microscope images of the aerogel. You flag videos that show evidence of a particle impact. Combining your observations with those of thousands of other “dusters”, lets the scientists find the focus movies most likely to show a particle impact.
It took 4 years of work by 27,000 amateur dusters to review 71 million focus movies before they found the first interstellar dust particles in 2010. Stardust’s scientists credited amateur dusters Bruce Hudson of Ontario, Canada, and Naomi Wordsworth of Wexbury, United Kingdom, for the discoveries. Now, four years later, the number of dusters has reached 30,000 and the Stardust science team has completed this first stage of their research.
Hudson recently spoke with the Canadian Broadcasting Company and recalled his feelings when told of the discovery.
"I said, 'Oh my god, really?" said Hudson, recalling that he felt "a little tingling thing going on."
"I was like, 'Cool.' I never thought I would ever get one. There's so many people doing it."
Hudson was recovering from a stroke when Stardust@Home launched. Stuck at home, unable to work, Hudson decided to devote thousands of hours to the search for dust. "It's almost like you put in that $20 bill [in a slot machine], spin it and you don't know what going to be next. The next one might be the winner,” he told the CBC.
Wordsworth, a British circuit designer from Buckinghamshire, told the New York Times in 2010, “I thought it was a wonderful opportunity for anyone to become involved with real space research and I joined straight away.” She told Nature last week that receiving the email with news of her discovery “felt like winning the lottery.”
Stardust@Home rewarded Hudson and Wordsworth for their hard work by letting the two dusters name the particles they discovered. Hudson chose to name his particle “Orion” after the constellation. Wordsworth chose “Hylabrook” after her family home. The two amateur dust-spotters are also listed as co-authors in the Stardust team’s publications.
The most recent of these papers has just been published in the peer-reviewed journal Science. (DOI: 10.1126/science.1252496) You can read it on the Science website if you have access. Easier to get are press releases from Nasa’s Jet Propulsion Laboratory, which oversaw the Stardust mission, and from the University of California Berkeley, which runs Stardust@Home and conducted the research. The paper the researchers presented at this year’s Lunar and Planetary Science Conference is publicly available on Nasa’s Technical Reports Server.
Many in the mainstream media reported that Nasa had discovered 7 interstellar particles, but that isn’t what the scientists said in their paper or in their press releases. The researchers found “evidence” of 7 particles, but they only captured 2 particles within the aerogel. A third was traveling so fast that it disintegrated as it passed through the aerogel. The remaining 4 particles were too small to survive impacts in the collector’s aluminum foil cover, but left residue behind consistent with interstellar dust.
Stardust’s scientists are carefully planning the next steps in the their research. They must conduct more tests to confirm that the 7 particles actually came from beyond the Solar System and to draw conclusions about the stars that created the particles.
“Stardust@home has been an amazing success,” said scientist Anna Butterworth in the UC Berkeley press release. “If we had had one person searching the aerogel 40 hours per week, they would have taken three years to cover once the same area searched multiple times by the Dusters.”
A duster's work is never done
The crowdsourced approach is still the most effective way to search for dust particles within the aerogel collectors. The scientists are still working through another 100 tracks flagged by the dusters. And the dusters themselves are only halfway through Stardust's collector cells. 55 of the 132 aerogel cells remain unexamined.
You still have a chance to make your own contribution to science. Sign up for Stardust@Home now and your name could go down in history as an amateur space explorer.