'Nanodiamond' asteroid tracked from space to desert impact
Rare meteor from mystery ureilite mother-planetoid
An international alliance of astronomers are exceedingly chuffed to announce the first occasion of an asteroid being tracked from space, through impact with the Earth's atmosphere and thence to recovery of fragments on the ground.
"Any number of meteorites have been observed as fireballs and smoking meteor trails as they come through the atmosphere," says Douglas Rumble of the Carnegie Institution's Geophysical Laboratory. "It's been happening for years. But to actually see this object before it gets to the Earth's atmosphere and then to follow it in – that's the unique thing."
Watch the skies, robot.
The space object in question, catchily named 2008 TC3, was first picked up last October by automated sky-watching telescopes belonging to the Catalina Sky Survey near Tucson in Arizona. Observatories and amateur astronomers worldwide then tracked the 80-tonne asteroid until it passed into the Earth's shadow just hours later, refining information on its trajectory. Shortly thereafter, 2008 TC3 ploughed into the atmosphere above northern Africa and exploded, scattering bits of itself all over Sudan's Nubian Desert.
British boffins at the UK government's William Herschel Telescope in the Canary Islands, alerted to the inbound asteroid, managed to get spectroscope readings on it - offering valuable clues as to 2008 TC3's composition.
"These observations were technically quite difficult since the object was moving fast across the sky," according to Dr Gavin Ramsay from Armagh Observatory. "However, the William Hershel Telescope rose to the challenge magnificently and demonstrated just what a versatile telescope it is. There was a keen sense of excitement in the control room."
After the "car sized" space lump blew up, boffins calculated the impact point for any remaining astro-shrapnel. Dr Peter Jenniskens of the SETI institute in California teamed up with Dr Muawia Shaddad and 45 students and staff from the University of Khartoum to mount a desert search for surviving fragments. Some 47 meteorites were found during expeditions which began last December.
Discovering the planetoid home of the Ureilites
They said we were crazy.
Combining information from the Herschel spectrograms with the recovered pieces from the desert revealed that 2008 TC3 was a very rare type of asteroid known as a ureilite "F-type". It's theorised that all ureilites come originally from the same parent body somewhere out in space, broken off it during asteroid collisions in the past.
On the matter of the mysterious extraterrestrial ureilite source, Rumble says "Where that is, we don't know." However, data gleaned during the 2008 TC3 impact might help here: boffins have already done some backtracking. Based on spectrogram readings like that gleaned from the Canaries, they think that the body 1998 KU2  - a Heathrow-airport-sized lump which orbits mostly between Earth and the asteroid belt - might be the ureilite mother-lode.
Apparently ureilite is strange stuff indeed, based on examination of the Nubian impact fragments. It contains "nanodiamonds", a rare form of carbon. Other scientific treats include "very cooked, graphite-like carbon ... of all the meteorites that we've ever studied, the carbon in this one has been cooked to the greatest extent," says Carnegie's Andrew Steele.
Boffins aren't sure if the superheating occurred during far-off space collisions or because of "some other process".
Professor Richard Crowther of the UK gov Science and Technology Facilities Council, who chairs the UN working group on the planetbusting asteroid threat, reckons that the research could be handy in safeguarding Earth and the human race from a space rockopocalypse in future.
"The search for and study of asteroids is extremely important as not all impacts are as harmless as this small one in October," says the prof.
"Larger impacts of the size associated with the Tunguska event of 1908 occur every few hundred years and even larger impacts with asteroids and comets the size of mountains occur every few tens of millions of years. Any extra knowledge we can gain about asteroids will help us mitigate the potential effects of such impacts in the future."