A giant asteroid as wide as a football field is set to zoom past the region Friday afternoon at 37,000 mph with no evidence of its presence here on Earth.
Still, Jay Melosh, a Purdue University professor and international crater expert, wants people to know what might happen if asteroid 2012 DA14 were to hit Chicago, so they can learn more about the connection between our planet and space.
"I think what we're learning is not to be so Earth-centered," Melosh said. "Stars are not little lights in the sky with little to do with us other than astrology. The sky has a direct impact on us and has sculpted our planet.
"We owe our existence and dominance as mammals to a big rock that hit the planet and killed the dinosaurs."
Melosh, a professor of earth, atmospheric and planetary science, physics and aerospace engineering, has worked with NASA, the Federal Emergency Management Agency and the Department of Homeland Security.
The asteroid passing by the Earth Friday is significant, he said, because "it's the closest fly-by we've ever seen of an object this size in recent history."
The asteroid is 50-meters wide, is traveling at 37,000 mph and weighs about 200,000 tons, nearly half the weight of a loaded supertanker.
"We saw it a year ahead of time thanks to a group in Spain," he said. "They are part of an international group of scientists concerned about impacts."
The good news with learning early of this asteroid's arrival, Melosh said, is scientists have been able to accurately predict its trajectory and determine it is not aimed toward Earth.
Still, Melosh explained what might happen if it were to hit a large city like Chicago.
The energy would be the equivalent of 4 megatons of a mid-sized thermonuclear bomb, Melosh said.
"It's coming into the atmosphere at 37,000 miles per hour, so it hits the air like a brick wall," he said. "It would break up into a bunch of fragments."
At 30,000 feet, the height used for flying aircraft, it would be at the optimum point for a significant burst, he said.
"It would topple buildings and flatten the downtown," Melosh said. "It would blow out windows and defoliate trees for a 20-mile radius."
The human casualties, he said, would likely be in the millions with the asteroid hitting during the lunch hour on a work day in the Loop.
The last time an asteroid hit the Earth was in 1908 in a remote area of Siberia. That asteroid was twice as big as the one passing by Friday, Melosh said.
"It evaporated a herd of reindeer and blasted the trees 20 miles away," he said.
Melosh created a Web site called Impact: Earth! which allows users to input various scenarios to see the results of projectiles of various sizes and densities and hitting targets with specific chemical properties.
"Whenever we get events such as these, we get calls asking the what-ifs," Melosh said. "It seemed we could automate that and let everyone have a chance to see the results with different variables."
Australia and Indonesia will have the best viewing points for the asteroid Friday, where it will be nighttime at the time is races past earth. Astronomers there will study its path closely, Melosh said.
Here, most won't know it ever came close.
"The most we could expect is a brief interruption of a cell phone call," he said. "So, if you're on a cell phone tomorrow and want to hang up on someone, you can blame the asteroid."