It's official: NASA confirms its DART planetary defense test was a success

Breathe a sigh of relief.

NASA confirmed that its Double Asteroid Redirection Test (DART) mission — which purposefully crashed a spacecraft into an asteroid last month to alter its path — was a success.

Since the DART spacecraft's impact on September 26, scientists have been carefully measuring and observing the target asteroid Dimorphos' trajectory. Yesterday, October 11, NASA announced that the spacecraft impact significantly altered the asteroid's motion in space, meaning we have a working method for planetary defense.

NASA's DART mission is a success

The DART mission was designed to test a planetary defense method that could one day be used against a hypothetical hazardous asteroid headed towards Earth — Dimorphos and Didymos pose no danger to our planet. Now, thanks to numerous observations made from Earth-based telescopes, NASA's scientists were able to confirm a change in the orbit of the 160m-wide (520ft) Dimorphos asteroid.

Dimorphos is part of a binary asteroid system. It orbits around a larger asteroid called Didymos (780m or 2,550ft wide) located some 7 million miles (11 million km) from Earth. Astronomers on Earth measured Dimorphos' orbital period around Didymos to ascertain the change in motion. They measured the orbital period by observing the time it would take for Dimorphos to be obscured by Didymos' shadow — as illustrated in the Gif below.

Before the impact event, NASA explains, Dimorphos would make one orbit of Didymos in 11 hours and 55 minutes. Ground observations show that post-spacecraft crash, the orbital period has now been reduced to 11 hours and 23 minutes for a total change of 32 minutes. This equates to Dimorphos moving closer to Didymos by "tens of meters".

This may seem like a small nudge in the great scheme of things, but taken over the immense distances that asteroids travel, a change of tens of meters would significantly alter the eventual path of an asteroid over weeks, months, and years.

In other words, we should be able to use the same technology to avert a hazardous asteroid on a collision course with Earth, if we catch it early enough.

NASA is a serious "defender of the planet"

NASA defined the minimum successful period change of Dimorphos as a 73-seconds alteration in its orbital period. The results released by NASA show DART surpassed the minimum benchmark by more than 25 times.

It's worth noting that NASA calculates the probability of an asteroid with a 3-6 mile (5-10 km) diameter, like the one that wiped out the dinosaurs, hitting Earth as incredibly small. It currently stands at 0.000001 percent every year. That's not to say we shouldn't be prepared.

"This mission shows that NASA is trying to be ready for whatever the universe throws at us," said NASA Administrator Bill Nelson. "NASA has proven we are serious as a defender of the planet. This is a watershed moment for planetary defense and all of humanity, demonstrating commitment from NASA's exceptional team and partners from around the world."

Alongside the announcement of a successful mission, the U.S. space agency also released more data from DART, including new images from Hubble Space Telescope and from a small Italian satellite, or CubeSat, called LICIACube that traveled alongside DART before detaching as the impact time grew nearer.

NASA does provide a word of caution, saying these preliminary results may not apply to asteroids of all shapes and sizes. And scientists aren't ready to stop observing Didymos and Dimorphos just yet. In four years time, the European Space Agency (ESA) plans to have three spacecraft — from a mission called Hera — carrying out follow-up investigations at the binary asteroid system whose path has been forever altered by human beings.