by Final preparations are underway to send a European spacecraft to an asteroid to find out what happened when a NASA probe intentionally crashed into the space rock two years ago.
The European Space Agency’s Hera mission will study the impact site and take detailed measurements of the shattered rock Dimorphos to help researchers refine their strategies to defend Earth if a wayward asteroid ever threatens the planet in the future.
Hera is scheduled to launch on Monday at 10:52 a.m. local time (3:52 p.m. BST) aboard a SpaceX Falcon 9 rocket from Cape Canaveral in Florida. If everything goes well, the probe will fly past Mars in March next year and reach the asteroid, which is more than 177 m from Earth, in December 2026.
“It’s a series of breathtaking moments,” Paolo Martino, lead engineer and deputy project manager, said of the mission from ESA’s base in Noordwijk, the Netherlands. “The first one survives the start.”
Aside from the routine risks of bad weather and technical problems that can prevent missions from remaining on the launch pad, there have been uncertainties about whether the SpaceX rocket will be allowed to fly. Last week, the Falcon 9 was grounded by the Federal Aviation Administration for the third time in three months after an upper stage malfunctioned during its fall back to Earth.
Named after the Greek goddess of marriage, women and family, Hera will report on the state of Dimorphos, a 150-meter-wide asteroid orbiting a larger, 780-meter-wide parent body called Didymos. In September 2022, NASA’s Double Asteroid Redirection Test (Dart) probe crashed into Dimorphos at 14,000 miles per hour, ejecting millions of tons of rock into space and changing the asteroid’s orbit.
As the first test of Earth’s planetary defenses, the Dart mission was declared a success. But scientists need more information about the impact and Dimorphos itself to ensure that the knowledge gained can be used to deflect asteroids of different sizes and structures that could one day threaten Earth.
“Dart managed to change the orbit of Dimorphos very efficiently, even beyond all expectations, and now scientists need to know in detail what happened and what effects the impact had on the asteroid,” Martino said.
When Dart hit Dimorphos, the probe’s momentum and the force of the debris ejected from the asteroid shortened its orbital period around Didymos by 33 minutes. The collision reshaped the asteroid and ejected a cloud of dust and rock thousands of kilometers into space.
Hera’s instruments will record the exact size, shape, mass and orbit of Dimorphos, allowing researchers to find out how efficiently the momentum from the Dart probe was transferred to the space rock and in what state the asteroid was left.
To take a closer look at Dimorphos, Hera will release two shoebox-sized probes called cubesats. These will map the surface in great detail, measure dust around the body and use ground-penetrating radar to assess the asteroid’s internal structure. The cubesats will then attempt to land on the asteroid and take further measurements.
“The Dart mission was a spectacular success as a demonstration of asteroid deflection technology, but as a scientific experiment it raised as many questions as it provided answers,” said Prof. Gareth Collins, a member of the Hera science team at Imperial College London. “We hope Hera answers these questions and more.”
A mystery is how Dart changed Dimorphos’ orbit so much. Scientists expected NASA’s probe to drill a 20-meter crater into the asteroid and shorten its orbital period by just over a minute. The larger shift in the orbit suggests that the impact completely changed the asteroid. “We think this could be because Dimorphos has an internal structure made up of debris piles, but we only have a few close-up images of its surface to work with,” Collins said.
Of the more than 1,600 near-Earth asteroids on ESA’s risk list, none are gigantic planet killers that could destroy Earth in the next century. Of more concern are the smaller and far more numerous space rocks that have the potential to destroy cities, countries and continents. If one of these were discovered years in advance, scientists would launch a reconnaissance mission to confirm its trajectory, composition and mass, and if it posed a real threat, launch another mission to throw it off course.
Using data from the Hera mission, researchers will figure out which asteroids can be deflected by colliding spacecraft and which space rocks may require more drastic intervention. “If we ever face a real threat in the future, we will be able to choose the best technology,” Martino said.
