Today, Monday, September 26, NASA’s Double Asteroid Redirection Test (DART) mission will test humanity's capabilities to alter the path of an asteroid by slamming into Dimorphos, a small moonlet orbiting the larger asteroid Didymos. The asteroids pose no threat to Earth but will allow NASA to test a crucial approach to planetary defense in a way that is safe for our planet, and we can all watch along.
The spacecraft has already had an exciting few weeks. The probe got its first view of Didymos(above), which is roughly 780-meter-wide (2,560 feet) across, and DART released LICIAcube, a secondary spacecraft from the Italian Space Agency, which has a camera to image the impact and document the effect of DART on Dimorphus once it slams into it.
Why is NASA crashing into an asteroid?
Is this payback for the dinosaurs? No, what the mission is doing will help us nudge asteroids away so that we do not end up like all the species that didn’t survive the Chicxulub impact.
NASA is sending a probe to purposely collide with an asteroid to determine if "kinetic impact" is an effective way of changing the course of any hazardous space rocks heading our way. The spacecraft will slam into the 160-meter-wide (525 feet) moonlet at around 24,140 kilometers per hour (15,000 miles per hour) transferring its kinetic energy to the smaller asteroid, pushing it closer to its larger companion. If it works, Dimorphus will orbit Didymos at the very least 73 seconds faster than before.
Just to be clear, there are no known objects with trajectories that take out Earth currently, including the object of this mission, but it’s best to be prepared. As NASA puts it: "Planetary defense is finding asteroids before they find us."
"These objects are hurtling through space and have of course scarred the Moon and, over time, also on Earth have had major impacts, have affected our history," Thomas Zurbuchen, NASA's associate administrator for science, said during a news conference.
"DART is a first mission to try to really bump out of the way an object of threat in a direct experiment."
What will happen when NASA's probe hits the asteroid?
The impact is due to take place on Monday, September 26 at 7:14 pm ET (11:14 pm UTC) and this is how it will unfold.
The spacecraft will continue to take pictures of the approach until two seconds from impact. It is uncertain if this will be shared with the world immediately or after it's done. The whole spacecraft weighs around 500 kilograms (1,100 pounds), about that of a small car, and will be traveling at 6.6 kilometers (4.1 miles) per second.
The goal is to reduce the velocity of Dimorphus by 0.4 millimeters per second, a tiny amount but enough to create an appreciative change over time. By reducing its velocity, the moonlet will move closer to Didymus. The team expects that its eventual orbital period, currently at a very predictable 11 hours and 55 minutes, will be reduced by about 10 minutes
If an asteroid was coming toward us, that could be good enough to avert catastrophe as long as we acted with plenty of time to spare.
How to watch NASA crash into an asteroid
The main event will have live coverage on all NASA's channels, including Youtube, Facebook, and Twitter, where members of the mission will discuss what’s going to happen and share the science and insights of DART and the asteroids. The impact is scheduled for 7:14 pm ET on Monday, Sept. 26 and the televised briefing will begin at 6 pm ET (10 pm UTC).
You can also follow along thanks to our friends at the Virtual Telescope Project as they are running a live telescope observation of the impact, hoping to spot an increase in brightness from the collision.
We can even follow along long after the (hopefully) successful impact. LICIACube will fly past three days after impact and will provide images of the crater and take some initial measurements, but the true follow-up will be the Hera mission from the European Space Agency. It will arrive at the binary asteroid system in 2027 and will provide a detailed analysis of the effect of DART on Dimorphous.
Until then, ground-based telescopes will keep an eye on the system and provide updates on how the orbit alternation is going.