Dimorphos is easily one of the least interesting objects in the solar system. It’s a rock – a moon, in fact – measuring just 160m (525ft) in diameter, orbiting the asteroid Didymos, which itself is just 780m (2,560ft). Located 11 million km (6.8 million mi) from Earth, the Didymos-Dimorphos system is just a tiny part of the river of rubble that circles the sun in the asteroid belt between Mars and Jupiter. .
But on Monday, September 26 at precisely 7:14 p.m. ET, the attention of much of the astronomical community will be directed to Dimorphos. This is when NASA’s DART (short for Double Asteroid Redirection Test) spacecraft will hit the moon In the nose – deliberately hitting it at a speed of around 28,200 kph (17,500 mph). The results of this cosmic crisis could go a long way in determining how NASA and other space agencies around the world can protect the planet from incoming asteroids: destroy or deflect them before they can cause the kind of cataclysmic damage that has occurred. when a 10 to 15 km (6.2 to 9.3 mi.) space rock crashed off the Yucatan Peninsula 65 million years ago, causing the global extinction that sounded the death knell dinosaurs.
The risk to Earth today is real. NASA’s Center for Near Earth Object Studies (CNEOS) maintains a running account of what it calls near-Earth asteroids (NEAs), defined as space debris that is not locked in the asteroid belt, but is rotating around the sun in an orbit that brings it within 45 million km (28 million miles) of Earth. That would seem like a pretty safe miss distance, but there’s always a chance that another piece of free-flying space junk could collide with an NEA, altering its course and sending it flying in our direction. According to the CNEOS census, there are 855 known NEAs measuring at least 1 km (0.62 mi) and more than 10,000 measuring at least 140 m (460 ft) in diameter. In total, there are 29,801 known NEAs of all sizes in the CNEOS database.
Interception and deflection are our best defense against NEAs, and as a first test of the as yet unproven technique, NASA built DART and launched it towards the Didymos-Dimorphos pair on November 23, 2021. The spacecraft is actually two spaceships. The main body of the DART is 2.6 m (8.5 ft) in diameter and weighs 600 kg (1,320 lb). It is accompanied by a small, toaster-sized spacecraft built by the Italian Space Agency (ISA), dubbed the Light Italian CubeSat for Imaging Asteroids (LICIACube). It is DART itself that will collide with Dimorphos; the job of LICIACube, which split from DART on September 11, is to fly close and take images of the moon before and after impact.
“We are working with ASI to bring LICIACube within 25-50 miles [40 to 80 km] of Dimorphos just two to three minutes after the DART impact – close enough to get good images of the impact and the ejecta plume, but not so close that LICIACube could be hit by the ejecta,” said the NASA’s LICIACube navigation director, Dan Lubey, in a statement from the space agency.
LICIACube’s work will be important when it comes to gathering evidence about what kind of physical damage an impacting spacecraft can cause to an asteroid. But the real indicator of the mission’s success will come from measurements of how drastically DART alters Dimorphos’ orbit around Didymos. This will be determined by an array of ground-based telescopes, including NASA’s Deep Space Network of radio telescopes in Barstow, California; Madrid, Spain; and Canberra, Australia.
For now, NASA’s best estimate is that DART will speed up the moon’s 11.9-hour orbit around Didymos by several minutes. This seemingly small difference is actually very large, as even a slight change in an asteroid’s speed or trajectory when it is millions of miles from Earth could send it flying far away from us when it finally reaches our planetary neighborhood.
Space has always been a dangerous place. The DART mission could help make it safer. How much safer will be known as early as next week.
This story originally appeared in TIME Space, our weekly newsletter covering all things space. You can register here.
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