The Sudbury Star is the City of Greater Sudbury’s daily newspaper.
A city known for its rock and snow may well have been formed, nearly two billion years ago, by a giant ball of rock and snow.
New research by Laurentian PhD candidate Joe Petrus suggests the Sudbury basin was the work of a comet, which blasted through the atmosphere at a speed of about 50 km/second and struck with such force that debris rained down as far away as Thunder Bay and Minnesota.
Scientists have understood since the 1960s that the area owes its shape and geology to the impact of a celestial object, but exactly what type of object — asteroid or comet — has remained an open question.
It was a puzzle that Petrus, who earlier studied physics, couldn’t resist probing. “‘Why hasn’t somebody done this?’ ” he recalls thinking. “It seemed a glaring question, especially since Sudbury is one of the most important impact craters on Earth.”
The doctoral student also felt the timing was right. While there had been some earlier speculation about a comet being the cause of Sudbury’s crater, more sophisticated technology was now available to test the theory.
Petrus’s study, undertaken with the support of PhD supervisor Balz Kamber, formerly affiliated with Laurentian University, and geologist Doreen Ames relied largely on chemical analysis of rocks in the impact zone.
On a stratified planet like Earth, iron-loving elements are found deep below the crust, Petrus notes, whereas asteroids and comets aren’t so “differentiated,” or separated into layers. When they strike, melting and/or vaporizing on contact, “these elements are mixed in with the rocks formed during the impact, creating a detectable signature that can be traced back to the type of asteroid or comet that was involved.”
While Petrus says the chemical signatures he and his team analyzed showed an obvious “extraterrestrial” influence, differentiating between a comet and an asteroid can be tricky.
A comet is composed largely of ice, but can also contain plenty of rock and dust — hence the common comparison to a “dirty snowball.” Asteroids are large chunks of rock that can consist of both silicates and metals.
They hail from different areas of the solar system — asteroids typically orbit a zone between Mars and Jupiter, while comets come from as far away as the Kuiper Belt, beyond Neptune, or from even farther, in the Oort Cloud — but if similar in size could create the same sort of splash that occurred at Sudbury.
“It’s like trying to tell the difference between a birthday cake being hit by a hard-boiled egg or a potato,” analogizes David Pearson, a professor in the School of the Environment at the university.
In its initial form, the Sudbury crater stretched about 20 km in depth and 250 km in circumference.
For the rest of this article, click here: http://www.thesudburystar.com/2014/11/24/research-shows-comet-as-cause-of-sudbury-crater