How NASA and the ESA are preparing for wayward asteroids

28 Jun 2021

Image: © Dabarti/

Prof Alan Fitzsimmons will explain the details of an international trial asteroid deflection at an online event marking World Asteroid Day.

What would happen if an asteroid was spotted hurtling towards Earth? Would we be able to stop it or would we go the way of the dinosaurs?

Prof Alan Fitzsimmons is helping to answer just that. Working from the Astrophysics Research Centre at Queen’s University Belfast, Fitzsimmons is involved in two upcoming space missions that will measure how hard it is to deflect an asteroid.

The Didymos system is actually a pair of asteroids, first noted in 1996, and will be the subject of tests that could one day be used to prevent an asteroid collision.

If an asteroid like those in the Didymos system were to hit the Earth, they could wipe out any cities or towns within tens of kilometres of the impact site.

Didymos – which means ‘twin’ in Greek – is the larger of the binary asteroid system that currently orbits the sun. Dimorphos (also known as Didymoon) is its smaller companion moonlet and will be the focus of the redirection tests over the next few years.

The pair will pass close to Earth in 2022 and, while posing no risk, represent a perfect chance to trial a deflection.

If all goes as planned, Dimorphos will be the first celestial object in the solar system to have its orbit shifted by human effort in a measurable way.

The trial comprises two stages: NASA’s Double Asteroid Redirection Test (DART) and the European Space Agency’s Hera Mission.

DART is the first element and is described as a “kinetic impactor technique”.

The DART spacecraft will deliberately crash itself into the moonlet at a speed of roughly 6.6 kilometres per second. This collision should change the speed of the moonlet in its orbit around the main body by a fraction of 1pc. This, in turn, will change the orbital period of the moonlet by several minutes – enough to be observed and measured using telescopes on Earth.

Fitzsimmons, who is a member of the DART investigation team, commented: “The team at NASA and Johns Hopkins Applied Physics Laboratory have designed a fantastic mission that should change the orbit of Dimorphos.”

While the change can be observed from Earth, the international scientific collaboration wants to know more.

What will the collision site look like? What material is Dimorphos made of? What other changes will have occurred to the 160m-sized moon?

This is where Hera comes in.

Named after the Greek goddess of marriage and roughly the size of an office desk, the second satellite will collect information about Dimorphos after it has been impacted.

Hera will launch from Earth in 2024 and arrive at Dimorphos in 2026, staying there for about a year. While there, the spacecraft will perform a “crash scene investigation”, where it will precisely measure how massive Dimorphos is and how the asteroid responded to being hit by DART.

According to Fitzsimmons, DART and Hera will be humanity’s first practice in planetary defence. Both spacecraft will also carry smaller cubesat spacecraft, to help further understand how to move asteroids.

Fitzsimmons will be explaining all about asteroids and comets in a talk to mark World Asteroid Day on 30 June at 5pm with the Geological Society of London. Attendance is free and is open to the public, but pre-registration is required.

Sam Cox was a journalist at Silicon Republic covering sci-tech news