On October 17th, 2012, a meteorite crashed into the roof of a Novato, California home. Now, an international collaboration of fifty scientists have tracked its history over 4.4 billion years, from before the moon was formed to the present day.
Timeseries of the disintegration of the Novato meteorite on October 17, 2012. Image credit: Robert P. Moreno Jr./Jim Albers/Peter Jenniskens
During a meteor shower on October 17th, 2012, the Cameras for Allsky Meteor Surveillance (CAMS) project captured the disintegration of a single meteorite at 7:44 pm. After calculating where it could land based on its observed trajectory, a team of scientists asked residents to report any likely chunks of rock.
Their call for assistance prompted a pair of homeowners to investigate the odd thump they'd heard during the meteor shower. Astonishingly, they found a piece that crashed into the garage roof of a Novato home, denting the roof where it impacted. As meteorites are named for the location where they were found, it was promptly dubbed the Novato Meteorite, optimistically specified as fragment N01.
Roof dented by Novato Meteorite fragment N01. Image credit: CAMS
From initial observations, it was an unusual and difficult-to-identify meteorite. Normally, a meteorite has a fusion crust, but this one was shock blackened instead. The remaining strangely-dense rock could easily be mistaken for terrestrial weathering rinds. In an email exchange, NASA researcher Peter Jenniskens elaborates:
The Novato meteorite was exceptionally difficult to recognize as a meteorite because it did not hold on to its fusion crust. Only some tiny patches were left. We now understand that this is because the meteorite is shock blackened, whereby shocks melt iron sulfides that make the rock darker.
Consequently, the fragment was identified as a meteorite on October 20th, only to have that identification retracted on October 22nd, then finally re-confirmed as a meteorite on October 24th when a second, similar fragment was found and identified nearby. The discovery didn't stop at just those two fragments: over the next few months, scientists recovered six fragments of the same meteorite!
Since then, an international collaboration of fifty scientists has been working to unravel the meteorites' secrets. Their results will be in the August 2014 issue of Meteoritics and Planetary Science. The history of these fragments of rock goes back a long way — in a NASA press release proceeding the articles, Professor Qing-zhu Yin at UC Davis explains that the parent-meteoroid was smacked by one of the many pieces of debris flung across the solar system during the Big Splat, when the Moon was knocked free of the Earth:
"We determined that the meteorite likely got its black appearance from massive impact shocks causing a collisional resetting event 4.472 billion years ago, roughly 64-126 million years after the formation of the solar system. We now suspect that the moon-forming impact may have scattered debris all over the inner solar system and hit the parent body of the Novato meteorite."
That chunk of rock stuck together for a few billion years, finally fragmenting 470 million years ago into a distinct debris field in the asteroid belt between Mars and Jupiter. That field is the source of all L6 ordinary chondrites, a classification of meteorites that share the same origin and chemical composition. Within that field, the chemistry and orbital dynamics of the Novato meteoroid point at the Gefion asteroid family as a likely place-of-origin.
Roughly nine million years ago, the meteoroid was ejected from the asteroid belt,with only periodic returns to the belt. By backtracking the impact of cosmic rays upon a freshly-exposed surface, it looks like up until a million years ago, the meteoroid may have been encased within a larger object. Finally, just 100,000 years ago, it might have been smacked once again, leaving a mark in its thermoluminosity.
Thermoluminescence is a material property where the material is heated up, releasing stored energy from past electromagnetic and ionizing radiation exposure as light. One of the researchers working on the fragments, meteoriticist Derek Sears, explains that the thermoluminescence of the meteorite fragments indicate some sort of heating event 100,000 years ago, possibly by an impact:
"We can tell the rock was heated, but the cause of the heating is unclear. It seems that Novato was hit again."
Finally, whittled down to just 35 centimeters (14 inches) across and weighing 80 kilograms (176 pounds), the meteoroid hit the Earth's atmosphere. It broke up as it blazed through the thick gas, breaking in spurts marked by bright flashes of light. At least six of those fragments survived to impact the Earth, were recovered, and submitted for study.
Surprisingly, despite all the impacts, burning, and breaking, some organic compounds survived on the fragments to in detectable quantities:
Qinghao Wu and Richard Zare of Stanford University in California measured a rich array of polycyclic aromatic hydrocarbon compounds - complex, carbon-rich molecules that are both widespread and abundant throughout the universe.
Daniel Glavin at NASA's Goddard Space Flight Center in Greenbelt, Maryland, led a team to search the Novato meteorites for amino acids – molecules present in and essential for life on Earth – and detected some unusual non-protein amino acids that are now very rare on Earth but indigenous to the Novato meteorite.
The large number of recovered fragments, the relatively short time between impact and recovery, and the care with which the fragments were handled makes the Novato Meteorite one of the best-studied ordinary chondrites. The first fragment was even recovered before the next rainfall! This is a beautiful outcome for the importance of scientists reaching out to the public, and the role of citizen-scientists in advancing research. While Jenniskens was an active, public voice cajoling people to check their yards for possible rocks, running public lectures, and even hosting rock-identification nights for people to come in with likely suspects, it was the families in Novato, the undergraduate geology student, and the private meteorite-hunters who found the rocks and allowed researchers access to them.
If you do find a suspected meteorite, treat it carefully to preserve its scientific value:
- Photograph the scene as you find it, paying particular attention to any craters or ejecta, no matter how small.
- Protect the meteorite from contamination — don't touch it with bare hands, plastic or gloves; don't talk directly over it (spittle). Handle and store it using aluminum foil.
- Keep magnets away from the rock — even a fridge magnet could destroy the natural magnetism of the meteorite.
- Keep the meteorite dry. For a freshly-collected sample, you can dry it out by storing the meteorite wrapped in aluminum foil, tucked into a glass jar with more aluminum foil as a lid. Put that whole jar into another, bigger glass jar with a desiccant (rice works), and seal the bigger jar with a lid.
Finally, report your find to local researchers.
Read the full articles: Fall, recovery, and characterization of the Novato L6 chondrite breccia and Records of the Moon-forming impact and the 470 Ma disruption of the L chondrite parent body in the asteroid belt from U-Pb apatite ages of Novato (L6).