Asteroid Day: Watch NASA Live Broadcast on How it is Defending Earth From a Space Collision

Geminids meteor shower
A meteor from the Geminids meteor shower (streak at top) enters the Earth's atmosphere above Southold, New York, on December 12, 2009. Asteroids become meteors when they break up and vaporize once they have entered Earth's atmosphere. STAN HONDA/AFP/Getty

It's the one you've all been waiting for. June 30 is International Asteroid Day.

Scientists, including astrophysicist and Queen guitarist Brian May launched the day in 2014 to raise awareness of the risks of an asteroid colliding with Earth. The United Nations Office for Outer Space Affairs inaugurated it as an official global day of note in December 2016.

To celebrate, NASA will run a special television program about its Planetary Defense Coordination Office, which tracks asteroids and other Near Earth Objects (NEOs). The program will explain the damage that could be caused by an asteroid hitting Earth, and how NASA is prepare to avoid such an eventuality—including by potentially using a nuclear explosion to vaporize part of the asteroid before impact.

The program will run at 12 p.m. Eastern Time (ET) on Friday. It is part of a 24-hour Asteroid Day program from Broadcasting Center Europe, which begins at 9 p.m. ET on Thursday. You can watch the stream below:

Asteroids are celestial bodies that orbit the sun like planets. They are made up of metals and rocky materials. This makes them different from comets, which are partly made from rocky material but have an icy core and include dust and organic compounds. Both are formed out of leftovers from when the solar system was formed some 4.5 billion years ago. Asteroids can have unusual orbits and most of them reside in the asteroid belt, a region located between the orbits of Jupiter and Mars.

The date of International Asteroid Day coincides with the biggest asteroid crash believed to have ever occurred in recent history. In 1908, a huge explosion happened in Russia's Eastern Siberian Taiga, a sparsely populated region. The incident flattened 770 square miles; scientists have widely attributed it to the explosion of an asteroid or comet before it hit the Earth.

More than 16,000 NEOs—asteroids and comets—have been discovered so far; about three-quarters of these are over 50 meters in size, meaning that they may not disintegrate before impact and could produce substantial damage were they to collide with Earth, says Paul Chodas, the manager of the Center for Near Earth Object Studies at NASA's Jet Propulsion Laboratory in California.

"The chances that there is a large NEO heading for Earth are very small, but the consequences of a collision could be very large," says Chodas. "In the worst case, we could have an impact that leads to a global catastrophe, but that would take an asteroid larger than about 1 kilometer [0.6 miles] in size."

Chodas says that NASA has found 90 percent of the objects that could cause a global impact were they to hit Earth, and that the agency had prepared techniques for dealing with a potential collision. These include sending a spacecraft to collide with the asteroid before it gets close enough to cause any damage, or using ion beams to send the asteroid off course.

Just three years ago, Russia witnessed the threat of asteroids: An object of approximately 20 meters entered Earth's atmosphere near the town of Chelyabinsk, burning up and creating a light brighter than the Sun. The object was technically a meteor—the name given to small rocks, or meteoroids, when they enter Earth's atmosphere and burn up—and caused more than 1,500 indirect injuries, mostly from flying glass as the meteor shattered windows.