Nasa sets date for mission to practise saving Earth from deadly asteroids

On 26 September, at 7.14pm EDT, Nasa will slam a speeding spacecraft into a massive asteroid.

It’s a test run for future missions to redirect dangerous asteroids, should the need arise. And the space agency will let the world watch live.

Nasa launched the Double Asteroid Redirection Test mission, or Dart, in November 2021, with a mission to slam into the asteroid Dimorphos at high speed in an attempt to alter its orbit. Dimorphos does not, and will not pose a threat to Earth, but Dart’s impact will provide scientists with the data they need to construct a similar mission to change the course of any large asteroid that actually threatens Earth.

It’s a proof of concept important to Nasa’s planetary defence initiative, which aims to identify and mitigate threats to life on Earth from near Earth asteroids.

Here’s what you need to know about the Dart mission and what it means for everyone and everything on planet Earth.

What is Dart?

Dart is a relatively small spacecraft, about the size of a small car, designed to slam into an asteroid at high speed and change that space rock’s trajectory with the energy of the impact.

Launched on 24 November 2021, Dart used solar electric propulsion to fly a trajectory that will intercept the asteroid Dimorphos around 6.8 million miles from Earth on 26 September. Solar electric propulsion uses electricity generated with solar arrays to propel charge particles — in this case, xenon atoms — from the rear of a spacecraft, generating thrust.

Dart will hit Dimorphos head on at around 4 miles per second, or 14,400 miles per hour, transferring enough kinetic energy from the roughly 1,200 pound spacecraft to noticeably alter the orbit of Dimorphos. A small satellite carried by Dart and released before the impact will photograph the impact and the immediate after effects, while the European Space Agency’s HERA mission will arrive at Dimorphos in 2027 to assess whether Dart changed the asteroid’s orbit.

Dart is a collaboration between Nasa and the Johns Hopkins Applied Physics Laboratory (APL), in Laurel, Maryland, and APL operates the spacecraft. The spacecraft and mission are funded through Nasa’s Planetary Defense Coordination Office.

When will Dart impact its target and how can I watch?

Dart will impact the asteroid Dimorphos at 7.14pm EDT on Monday 26 September. Live coverage will begin at 6pm ET on Nasa’s website, Nasa TV, and the space agency’s social media accounts on Youtube, Twitter and Facebook.

What is Dimorphos?

Dimorphos is a near Earth asteroid about 525 feet in diameter that orbits the larger asteroid Didymos.

The pair of asteroids orbit the Sun on a path that ranges from around half an astronomical unit from the Sun to a full three astronomical units; an astronomical unit is equivalent to the distance from the Sun to Earth, about 93 million miles. Didymos and Dimorphos occasionally pass close to Earth — they came within 4.3 million miles in 2003— but never pass so close to our planet to be a threat.

Dimorphos’s orbit around Didymos, and the larger orbit of Didymos around the Sun relative to Earth, make Dimorphos a good target for the Dart mission. While a true asteroid deflection mission would attempt to push an asteroid headed to Earth onto a different orbit around the Sun, Dart will test the feasibility of such a mission by attempt to slow Dimorphos in its orbit around Didymos, bringing the asteroid closer to its larger partner.

Why is Dart important?

Scientists know that the impacts of large asteroids have wreaked havoc on Earth’s ecosystems in the distant past: An asteroid or comet around six to 12 miles in diameter that struck what is now the Yucatan region of Mexico 65 million years ago may well have caused the extinction of the dinosaurs and many other life forms.

In 2005, the US Congress passed a law requiring Nasa to catalog at least 90 per cent of all asteroids large enough to cause similar destruction should they strike the Earth, and the space agency has now charted an estimated 95 percent of such massive space rocks. Following the creation of Nasa’s Planetary Defense Coordination Office in 2016, the space agency has set a similar goal to chart at least 90 per cent of all asteroids 500 feet in diameter or larger, an ongoing project.

But knowing which asteroids may become hazardous is only part of the project of planetary defence — scientists and political leaders would like to do more than simply know ahead of time if an asteroid will cause widespread destruction on Earth, they would like to be able to avert that disaster.

Dart represents an early test of the types of technologies and mission profiles that could help protect Earth from a large asteroid impact once the ongoing survey’s of potential hazardous asteroids would discover an asteroid on a definite collision course for Earth.