An asteroid made a fly-by Friday, coming within 17-thousand miles of earth. That's closer than some of the satellites in orbit right now.
We watched the fly-by with an ASU professor.
There hasn't been an asteroid this big and this close to earth in recorded history. NASA put together an animation showing its path. It crosses Antarctica, which is why you wouldn't be able to see it from here.
In fact, it's so far away you can only see it with a telescope.
"Even though 45 meters in size, sounds very big in the grand scheme of things, it is pretty small," says Professor Dave Williams.
In this NASA image taken from an earth telescope, you can see the asteroid moving across the sky. It's more than 17,000 miles away from earth and that big line is a satellite passing by.
Here another image showing its path. It's actually closer to earth than some satellites.
It's believed to be as big as the meteor that created Arizona's Meteor Crater 50,000 years ago.
"It happens to be the largest asteroid that has flown by in historical times, that people have been able to actually study and be here to actually see," says Williams.
ASU professor Dave Williams is part of a team that sent a spacecraft to study two large objects, known as protoplanets, in the asteroid belt between Mars and Jupiter.
He says having one pass by earth this closely could be a boon to scientists who are looking to protect earth from any future impacts.
"For any asteroid, I think particularly all of the near earth objects, of which there are 10,000 or so, there are probably 4,700 that are in potentially hazardous orbit, so any opportunity to study one of these is important," says Williams.
"These things can be a threat but there is also the potential for them to be a resource. There has been a couple of companies formed with the last year whose objective is go out identify and mine these near earth asteroids for resources."
Professor Williams is part of an ASU and U of A team that is developing a spacecraft that will actually travel to asteroids and collect a sample.
It is a 14-year mission that is expected to launch in 2016.