The DART probe, which was launched by NASA and SpaceX on Earth‘s orbit last year, is finally ready to collide with the 168-meter asteroid Dimorphos to try and knock it off course.

Dimorphos orbits the larger asteroid Didymos with a size of 780 meters, and does not threaten to collide with the Earth, but is a convenient target for an experiment, which, if successful, can grow into a full-fledged system to protect our planet from asteroids.

NASA's DART probe to deflect the asteroid. How and when to watch.

The results of the collision will be watched by observatories from all over the world, including the James Webb Space Telescope, the Hubble Space Telescope and the asteroid-bound LICIACube spacecraft.

The collision is expected to change Dimorphos’ speed by a fraction of a percent, changing the time it takes to complete its orbit by several minutes. It may not seem like much, but for planetary defense scientists, these minutes are monumental.

“This demonstration is extremely important to our future here on Earth,” Lindley Johnson, NASA’s Planetary Defense Officer,, said at a press briefing before the mission’s launch.

According to Johnson, this moment in history is unique: for the first time, people are not only aware of the threat posed by asteroids, but also have the technology to do something about it. In case we ever find a giant rock hurtling toward a planet, having a plan or two in place to stop that rock is good, and having a few practice launches under your belt might be even better.

“Dart is demonstrating what we call the kinetic impact technique for changing the speed of the asteroid in space and therefore changing its orbit,” Johnson said.

There are other options in the arsenal of planetary defense tools, including a “gravity tractor” – a spacecraft that can fly next to an asteroid, gently pulling it to a safer path. There is also the possibility of bombarding an asteroid with an ion beam for a long time, pushing it into another orbit. DART will try a more direct method: crash into the asteroid at full speed.

During final approach, the DART will be driving itself. About 44 people will be in the control room monitoring telemetry and data, but starting about four hours before impact, “the spacecraft has to do everything on its own,” said Elena Adams, a DART mission systems engineer at the Johns Hopkins Laboratory for Applied Physics during press conference. It has an intelligent navigation system on board that directs it to the Didymos/Dimorphos system. It discovered Didymos earlier this summer, but won’t be able to see Dimorphos, the actual target, until about an hour before impact.

NASA's DART probe to deflect the asteroid. How and when to watch.

When the probe spots Dimorphos, the 168-meter-wide asteroid will appear only as a pixel. This will be enough for the navigation system to start tracking the stone itself, and not its satellite asteroid. Two and a half minutes before impact, the navigation systems that guided the spacecraft to that point will shut down, Adams says. “We’re just going to point the camera and take the most amazing pictures of this asteroid that we’re going to see for the first time.”

In addition to observatories in space and on Earth that will monitor the mission, DART’s own camera will send images up until the last minute, beaming them back to Earth so people can watch as the mission reaches its dramatic conclusion.

In addition, a small spacecraft-satellite will document events in space. Italy’s LICIACube (Lightweight Italian Asteroid Imaging Satellite) was launched with DART and separated from the larger spacecraft on September 11. It is following its companion and will document the effects of the experiment, flying past Dimorphos about three minutes after impact. It will also be able to see another side of Dimorphos that a larger spacecraft will never see.

“This mission has two parts. The first part is hitting the asteroid, the next part is actually measuring what happens afterwards,” Adams says. The team expects the asteroid to start moving faster after the collision and will monitor this over time.

NASA will begin its coverage of the DART collision at 6:00 p.m. ET on Monday, September 26 (1 AM on September 27 Kyiv time). The collision is expected at 7:14 p.m. Eastern time (02:14 a.m. on September 27, Kyiv time). You can watch the live broadcast of the impact on the NASA website or on the space agency’s YouTube channel.