Can we really deflect an asteroid by crashing into it? No one knows, but we’re happy to try ThePipaNews

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NASA’s Dual Asteroid Redirect (Dart) spacecraft is designed to be a one-hit wonder. It will end its days by crashing into an asteroid at 24,000 kilometers per hour on September 26. Launched from Earth in November 2021, Dart is about the size of a bus and was created to test and prove our ability to defend Earth from a dangerous asteroid.

Landing a direct hit on a target 11 million kilometers away is not easy. But while this sounds far, the asteroid was actually selected by Nasa because it is relatively close to Earth. This will allow engineers to test the spacecraft’s ability to operate itself in the final stages before impact, as it crashes autonomously.

The target asteroid is called Dimorphos, a body 163 meters in diameter that orbits a 780 meter wide asteroid called Didymos. This “binary asteroid system” was chosen because Dimorphos is in orbit around Didymos, making it easier to measure the results of the impact due to the resulting change in its orbit. However, the Dimorphos system currently poses no risk to Earth.

Regardless, Nasa is attempting nothing less than a full-scale planetary defense experiment to alter an asteroid’s path. The technique used is called “kinetic impact”, which changes the asteroid’s orbit by crashing into it. It’s basically what’s known as a safety shot in snooker, but played on a planetary level between the spacecraft (like the cue ball) and the asteroid.

A small deflection may be enough to prove that this technique can actually change the path of an asteroid on a collision course with Earth.

But the Dart spacecraft will be completely blown up by the collision because it will have an impact equivalent to about three tons of TNT. By comparison, the atomic bomb dropped on Hiroshima was equal to 15,000 tons of TNT.

So, with this level destruction and the distance involved, how are we supposed to see the crash? Fortunately, the Dart spacecraft is not traveling alone on its journey, but is carrying the LICIACube, a shoebox mini-spacecraft known as a cubesat, developed by the Italian space agency and aerospace company Argotec. This little companion has recently separated from the Dart spacecraft and is now traveling on its own to witness the impact from a safe distance of 55 km.

Illustration of how Dart’s impact will change Dimorpho’s orbit around Didymos. Image credit Johns Hopkins University Applied Physics Laboratory.

Never before has a cubesat operated around asteroids so this provides new potential ways to explore space in the future. The impact will also be observed from Earth using telescopes. Together, these methods will allow researchers to confirm whether the operation has been successful.

However, it may take weeks for LICIACube to send all the images back to Earth. This period will be absolutely nerve-wracking – waiting for good news from a spacecraft is always an emotional time for an engineer.

What happens next?

An investigation team will look into the aftermath of the crash. These scientists will aim to measure the changes in Dimorpho’s motion around Didymos by observing its orbital period. This is the time during which Dimorphos passes in front of and behind Didymos, which will happen every 12 hours.

Ground-based telescopes will aim to take pictures of Dimorpho’s eclipse when this happens. To cause a significant enough deflection, Dart must create at least 73 seconds of orbital period change after impact—visible as changes in eclipse frequencies.

These measurements will ultimately determine how effective “kinetic impact” technology is at deflecting a potentially dangerous asteroid—we just don’t know yet.

That’s because we actually know very little about the composition of asteroids. The great uncertainty surrounding how strong Dimorphosis is has made designing a bullet spacecraft a truly enormous engineering challenge. Based on ground observations, the Didymos system is suspected to be a rubble pile made up of lots of different rocks, but its internal structure is unknown.

There are also major uncertainties surrounding the outcome of the impact. Material ejected afterwards will add to the effects of the crash, providing an extra force. We don’t know if a crater will form from the impact or if the asteroid itself will suffer major deformation, meaning we can’t be sure how much force the impact will unleash.

Future assignments

Our exploration of the asteroid system does not end with Dart. The European Space Agency is set to launch the Hera mission in 2024, arriving at Didymos in early 2027 to take a closer look at the remaining impacts.

By observing the deformations caused by the Dart impact on Dimorphos, the Hera spacecraft will gain a better understanding of its composition and formation. Knowledge of the internal properties of objects such as Didymos and Dimorphos will also help us better understand the danger they could pose to Earth in the event of a collision.

Ultimately, the lessons learned from this mission will help verify the mechanics of a high-velocity impact. While laboratory experiments and computer models can already help validate scientists’ power predictions, full-scale experiments in space like Dart are the closest we’ll get to the whole picture. Finding out as much as we can about asteroids will help us understand what force we need to hit them with to deflect them.

The Dart mission has led to a worldwide collaboration of scientists hoping to address the global issue of planetary defense and, together with my colleagues in the Dart Study Group, we aim to analyze the effects. My own focus will be on studying the motion of the material ejected from the shock.

The spacecraft’s impact is scheduled for September 26 at 19:14 Eastern Daylight Time (00:14 British Summer Time on September 27). You can follow the effects on Nasa TV.

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