Final preparations are underway to send a European spacecraft to an asteroid to discover what happened when a Nasa sin deliberately slammed into the space rock two years ago.
The European Space Agency’s Hera mission will survey the impact site and take detailed measurements of the battered rock, Dimorphos, to help researchers hone their strategies to defend Earth should a wayward asteroid ever threaten the planet in the future .
Hera will be launched on Monday at 10.52am local time (3.52pm BST) aboard a SpaceX Falcon 9 rocket from Cape Canaveral in Florida. If all goes well, the probe will fly past Mars in March next year and reach the asteroid more than 110m miles (177m km) from Earth in December 2026.
“It’s a series of breathtaking moments,” Paolo Martino, the chief engineer and deputy project manager, said of the mission from ESA’s base in Noordwijk, the Netherlands. “The first one survives the launch.”
Beyond the routine risks of bad weather and technical problems that could keep missions on the launch pad, there were uncertainties about whether the SpaceX rocket would be allowed to fly. Last week, the Falcon 9 was grounded for the third time in three months by the US Federal Aviation Administration after experiencing an upper stage malfunction as it fell back to Earth.
Hera, named after the Greek goddess of marriage, women and family, will report back 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) probed crashed into Dimorphos at 14,000 miles per hour, throwing millions of tons of rock into space and changing the asteroid’s orbit.
As a 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 lessons learned 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 effectively, even beyond expectations, and now the scientists need to know in detail what happened and what kind of effect the impact had on the asteroid,” said Martino.
When Dart slammed into Dimorphos, the momentum of the probe and the force of debris ejected from the asteroid knocked 33 minutes out of its orbital period around Didymos. The collision the asteroid reformed and sent a plume of dust and rock thousands of kilometers into space.
Hera’s instruments will record the exact size, shape, mass and orbit of Dimorphos so researchers can work out how efficiently momentum was transferred from the Dart probe to the space rock and what state the asteroid was left in.
For a closer look at Dimorphos, Hera will release two shoebox-sized probes called cubesats. It will map the surface in fine detail, measure any dust around the body, and deploy a ground-penetrating radar to determine the asteroid’s internal structure. The cubesats will then attempt to land on the asteroid and take further measurements.
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“The Dart mission was a spectacular success as a demonstration of asteroid deflection technology, but as a science experiment it generated as many questions as it provided answers,” said Prof Gareth Collins, a member of the Hera- science team at Imperial College London, said. “Our hope is that Hera will answer those questions and more.”
One mystery is how Dart Dimorphos’ orbit changed so much. Scientists expected the Nasa probe to hit a 20-metre crater in the asteroid and shave just a minute off its orbit. The more substantial shift in orbit suggests that the impact completely reshaped the asteroid. “We think this may be because Dimorphos has a junk-heap internal structure, but we only have a few close-up images of its surface to work with,” Collins said.
Of more than 1,600 near-Earth asteroids on ESA’s risk listneither are gigantic planet killers that can destroy the earth in the next century. More worrying are the smaller and much more space rocks that have the potential to take out cities, countries and continents. If one of these was spotted years in advance, scientists would aim to launch a reconnaissance mission to confirm its orbit, composition and mass, and if it posed a real danger, launch another mission to knock it off course .
Armed with data from the Hera mission, researchers will work out the range of asteroids that could be deflected with impacting spacecraft and which space rocks might need more dramatic interventions. “If we ever have a real threat in the future, we will be in a position to choose the best technique,” Martino said.
