A big asteroid will fly by Earth Wednesday, but don't panic. It won't hit us.

1998 OR2 will stay 3.9 million miles away from our planet.

Don't be fooled by any hyped-up headlines you may have read: This week's asteroid flyby poses no threat to Earth or anything on it.

The big asteroid 1998 OR2 will zoom within 3.9 million miles (6.3 million kilometers) of our planet early Wednesday morning (April 29). While that's a close shave in the context of the visible universe, which is more than 90 billion light-years wide, there's zero chance that the space rock will hit Earth on this pass, scientists stress.

Indeed, at its closest approach, the roughly 1.5-mile-wide (2.4 km) 1998 OR2 will still be about 16 times farther from us than the moon is from the Earth. (The moon orbits Earth at an average distance of 239,000 miles, or 385,000 km.)

And you can let relief keep washing over you, for we know of no big asteroids that could harm us in the foreseeable future.

"There are no asteroids which have any significant chance of hitting the Earth that are of any significant size," Paul Chodas, manager of NASA's Center for Near-Earth Object Studies at the agency's Jet Propulsion Laboratory in Pasadena, California, said during a pre-recorded "NASA Science Live" webcast today (April 27). "There are none on our list."

That list is pretty comprehensive. NASA scientists think they've found and tracked more than 90% of the near-Earth asteroids (NEAs) that are least 0.6 miles (1 km) wide, big enough to pose a global threat to humans should they line Earth up in their crosshairs.

But such relief should not breed complacency, said both Chodas and Lindley Johnson, NASA's Planetary Defense Officer and program executive of the Planetary Defense Coordination Office. After all, the number of NEAs out there is enormous, so some big dangerous ones may still lurk out there undetected. 

And asteroids commonly get jostled this way and that by the gravitational pulls of other objects, making it very difficult to model their orbits over the very long term. Given enough time, these jostles will eventually send a big space rock screaming toward Earth, as the dinosaurs' demise can attest.

"Impact of the Earth by an asteroid large enough to do damage at the surface is an extremely rare event, but it's an inevitable event," Johnson said during today's webcast.

That inevitability makes asteroid discovery and tracking efforts incredibly important, both he and Chodas said, because we're not as helpless as the dinosaurs. We can do something about an incoming asteroid if we spot it far enough in advance.

For example, a lead time of five to 10 years is probably the minimum needed for humanity to mount a kinetic-impactor deflection mission, which would send a spacecraft out to knock the hazardous space rock off course, Chodas said. 

If we have considerably more time than that, we might be able to employ the nonviolent "gravity tractor" method, slowly nudging the rock away from Earth with a fly-along probe. And if we have very little time at all, we might have to quite literally employ the nuclear option.