NASA's Iron Dome? Israeli astronomer talks planetary defense

This illustration depicts NASA's Double Asteroid Redirection Test (DART) spacecraft prior to impact at the Didymos binary asteroid system. DART's target asteroid is the moonlet Dimorphos, which orbits the larger asteroid Didymos; the pair are not a threat to Earth.
(photo credit: NASA/Johns Hopkins APL/Steve Gribben)

Polishook is an astronomer and planetary scientist at Israel’s Weizmann Institute of Science and is a noted expert in asteroids.

NASA’s long-awaited Double Asteroid Redirection Test (DART) Mission finally concluded on Monday when the spacecraft crashed into the asteroid Dimorphous in a bid to test the viability of kinetic deflection. However, according to Israeli astronomer Dr. David Polishook, this is only the beginning.

Polishook is an astronomer and planetary scientist at Israel’s Weizmann Institute of Science and a noted expert in asteroids. It was this reputation and years of work in the field that earned him a spot on the DART Mission’s international investigation team.

The DART Mission

While the DART Mission itself is run by NASA and led by experts from John Hopkins University, the investigation team consisted of experts from around the world who worked tirelessly to design the astronomical observations for before, during and after the impact.

NASA’s Double Asteroid Redirection Test (DART) command team at Johns Hopkins University, Applied Physics Laboratory monitoring the DART spacecraft’s impact into the asteroid Dimorphos. The operation is the first of its kind test to redirect deadly asteroids from hitting Earth. (credit: NASA/Dave C. Bowman)

In other words, this team was responsible for verifying that DART hit the bullseye and impacted the asteroid.

For Polishook, though, this was especially important, as his location in Israel meant that his observatory would be one of the first that could see the impact happen.

“It was so exciting, like a thriller movie,” Polishook told The Jerusalem Post. “We sat in the observatory at the telescopes while also watching it happen live on NASA TV. We saw the asteroid get closer and closer. Then it hit, and everyone watching around the world was happy it was all over. But, for us, our job just started.”

After a while, Polishook and his team, as well as some other observers in Africa, were able to spot an ejector cloud around the asteroid, which was formed by the impact. This cloud of dust reflected brightly in their telescopes, and Polishook immediately notified NASA as the observation work continued.

And for an asteroid expert like Polishook, all of this was incredibly exciting.

“I was excited to take part in the DART Mission because it’s the first kind of mission like this,” he explained. “It’s unique and it’s at the frontier of our field of study.”

NASA's Iron Dome?

Indeed, NASA’s DART Mission is paving the way forward in the field of planetary defense, finding a way to defend the Earth against one of the most devastating kinds of natural disasters – a kind we currently have no means of defense against.

It is no wonder, then, that many in Israel have called the DART Mission “NASA’s Iron Dome,” comparing it to the Israeli missile-defense system that causes incoming rockets to explode before they hit their targets.

For Polishook, the comparison is flattering, but not entirely accurate.

“It’s true in a sense, but the difference is that the Iron Dome destroys missiles, which are much smaller than the asteroid,” he explained. “Say an asteroid that’s 100 meters [328 feet] wide is set to crash above Washington, DC. If that happens, no Iron Dome can help you, because they’re far too weak.”

Another issue is that the Iron Dome still causes missiles to explode, which is not something you should do with an asteroid.

“We don’t want to blow up an asteroid. We want to push them away,” Polishook explained. “It’s really hard to make an object that is 100 meters in diameter explode. Besides, no one can build a missile that is 100 meters wide – and, if they did, it would be very terrifying.” Laughing, he added, “Of course, given the current political climate, I’d be more afraid of missiles from war than an asteroid.”

The way the DART Mission works is by smashing a spacecraft into an asteroid to slightly adjust its orbit. This causes it to change its course and prevents any possible collision through what is known as kinetic deflection.

This is all-new territory, and DART is providing extremely important information for how any of this would work.

“The problem with asteroids is that their structures are only vaguely known. It’s hard for us to anticipate how an asteroid will react to such an impact like DART,” Polishook said. “If we want to move an asteroid from one place to another, we can, but only a little bit. Say an asteroid will impact the Earth in 20 years. We now know how much impact force you need. But what if the asteroid is only two years away? Then you’ll need more force, but we don’t yet know how much. That’s what DART is helping us find out.”

Asteroids and the future of planetary defense

The DART Mission is a big step forward in protecting the Earth from asteroids, but right now, some questions remain. Did it actually work?

Scientists aren’t sure yet. The reason for this, Polishook explained, is because of the ejector cloud of dust around the Dimorphous asteroid.

“The cloud of dust surrounds the body of the asteroid like it’s masking the object there, so we can’t exactly measure the change in orbit. So, we’ll need to wait to see when the ejector cloud disappears,” he said. “Will it happen today? Next week? Next month? We don’t know, but we’ll know soon enough. I and others continue to observe it daily to see what’s going on as the dust cloud slowly dissipates.”

It is true that another upcoming mission, Hera, launched by the European Space Agency (ESA), is set to examine the impact of DART and how it may have changed the asteroid’s orbit, but that won’t be for a few years. As such, waiting for the cloud to dissipate is likely faster.

The field of asteroid study doesn't stop here

This is far from the end for the field of planetary defense and asteroid studies. And while it isn’t clear if NASA has any further planetary defense missions like DART in the works, there are still other upcoming and exciting missions to learn about the many asteroids within the solar system.

“We are waiting for OSIRIS-REx to arrive back from its mission to the large asteroid Bennu, and there’s another mission called Psyche that is going to measure a large iron asteroid that can give us a lot of information, including about asteroid mining,” Polishook explained. “And there’s another called Lucy that’s going beyond the main Asteroid Belt to the Trojan asteroids, which are following the orbit of Jupiter. They’re probably full of ice and other primitive molecules. And, in 2029, we’ll have Apophis, another large asteroid that will fly extremely close to the Earth, and there will probably be many missions relating to it. The field of asteroid study doesn’t stop here.”

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