Science

Could we really deflect an asteroid heading for Earth? An expert explains NASA’s DART mission

This article originally appeared on The Conversation. The post contributed the article to Space.com’s Expert Voices: Op-Ed & Insights.

Gail Iles, Senior Lecturer in Physics, RMIT University

A golf cart-sized NASA spacecraft has been ordered to crash into an asteroid, with the intention of slightly diverting it from its course. The test aims to demonstrate our technological readiness in the event that a real asteroid threat is detected in the future.

The Double Asteroid Redirection Test (DART) took off aboard a SpaceX rocket from California on November 23 and will arrive at the target asteroid system in September of next year.

The mission will travel to the asteroid Didymos, a member of the Amor asteroid group. Every 12 hours, Didymos orbits a mini-moon, or “moon,” Dimorphos. This smaller half of the pair will be the target of DART.

Related: If an asteroid really threatened Earth, what would a planetary defense mission look like?

Are we facing an extinction threat from asteroids?

We’ve all seen disaster movies in which an asteroid hits Earth, creating an extinction event similar to the one that killed dinosaurs millions of years ago. Could that happen now?

Well, the Earth is frequently bombarded by small asteroids, which vary between 1 and 20 meters in diameter. Almost all asteroids of this size disintegrate in the atmosphere and are usually harmless.

There is an inverse relationship between the size of these objects and the frequency of impact events. This means that small objects hit us much more often than large objects, simply because there are many more small objects in space.

Small asteroid impacts showing daytime impacts (in yellow) and night impacts (in blue).  The size of each point is proportional to the radiated optical energy of the impact.

Small asteroid impacts showing daytime impacts (in yellow) and night impacts (in blue). The size of each point is proportional to the radiated optical energy of the impact. (Image credit: NASA JPL)

Asteroids with a diameter of 1 km hit Earth every 500,000 years, on average. The most “recent” impact of this size is believed to have formed the Tenoumer impact crater in Mauritania, 20,000 years ago. Asteroids with a diameter of approximately 5 km impact the Earth approximately once every 20 million years.

The 2013 Chelyabinsk meteoroid, which damaged buildings in six Russian cities and injured some 1,500 people, was estimated to be about 20 meters in diameter.

Assess the risk

NASA’s DART mission has been triggered by the threat and fear that a large asteroid will hit Earth in the future.

The Turin scale is a method of categorizing the impact hazard associated with a near-Earth object (NEO). It uses a scale of 0 to 10, where 0 means there is a negligible probability of collision and 10 means imminent collision, with the impacting object being large enough to precipitate a global disaster.

The Chicxulub impact (which is attributed to the extinction of non-avian dinosaurs) was a Torino 10 scale. The impacts that created the Barringer crater, and the Tunguska event of 1908, both correspond to the Torino 8 scale.

With the rise of online news and the ability of people to film events, asteroid “near misses” tend to create fear in the public. NASA is currently closely monitoring the asteroid Bennu, which is the object with the highest “cumulative risk rating” at this time. (You can also keep up to date).

With a diameter of 500 m, Bennu is capable of creating a 5 km crater on Earth. However, NASA has also said that there is a 99.943% chance that the asteroid will not reach us.

Prepare for impact

At one point in their orbit around the sun, Didymos and Dimorphos lie about 5.9 million kilometers from Earth. This is still further away than our moon, but very close in astronomical terms, which is when DART will hit Dimorphos.

DART will spend about ten months traveling towards Didymos and when it is close it will change direction slightly to hit Dimorphos at a speed of approximately 6.6 km per second.

This animation shows the path of DART around the Sun. Rosa = DART |  Green = Didymos |  Blue = Earth |  Turquoise = 2001 CB21 |  Gold = 3361 Orpheus.

This animation shows the path of DART around the Sun. Rosa = DART | Green = Didymos | Blue = Earth | Turquoise = 2001 CB21 | Gold = 3361 Orpheus. (Image credit: NASA)

The largest Didymos is 780m in diameter and therefore a better target for DART. Once DART has detected the much smaller Dimorphos, only 160m in diameter, it can make a last-minute heading correction to collide with the moon.

The mass of Dimorphos is 4.8 million tonnes and the mass of DART at the time of impact will be about 550 kg. Traveling at 6.6 km / s, DART will be able to transfer a large amount of momentum to Dimorphos, to the point where it is expected to actually change the moon’s orbit around Didymos.

This change, of the order of 1%, will be detected by ground-based telescopes in weeks or months. While this may not sound like much, the 1% is actually a promising change. If DART were to crash into a lone asteroid, its orbital period around the sun would change by only 0.000006%, which would take many years to measure.

DART mission dates and timeline events.

DART mission dates and timeline events. (Image credit: Johns Hopkins University)

Then we will be able to detect the 1% change from Earth and meanwhile the pair will continue along its orbit around the sun. DART will also deploy a small satellite ten days before impact to capture everything.

This is NASA’s first mission dedicated to demonstrating a planetary defense technique. At a cost of 330 million dollars, it is relatively cheap in terms of space mission. The James Webb telescope, due to launch next month, costs about $ 10 billion.

There will be little to no debris from the DART impact. We can think of it in terms of a comparable event on Earth; imagine a train parked on the tracks but without brakes. Another train approaches and collides with him.

The trains will not break or destroy each other, but will move together. The one that is stopped will gain some speed and the one that hits it will lose some speed. The trains combine to become a new system with different speeds than before.

Therefore, we will not experience any impacts, ripples, or debris from the DART mission.

Typical asteroid orbits remain between Mars and Jupiter, but some with elliptical orbits can pass close to Earth.

Typical asteroid orbits remain between Mars and Jupiter, but some with elliptical orbits can pass close to Earth. (Image credit: Pearson)

Is it really worth the effort?

Mission results will tell us how much mass and speed it takes to hit an asteroid that may pose a threat in the future. We already track the vast majority of asteroids approaching Earth, so we would have an early warning of any such object.

That said, we have lost items in the past. In October 2021, the asteroid UA_1 passed about 3,047 km from the Earth’s surface, over Antarctica. We lost it because it approached from the direction of the sun. At only 1 meter in size, it wouldn’t have caused much damage, but we should have seen it coming.

It would be difficult to build a deflection system for a possible major asteroid threat. We would have to act quickly and hit the target with very good aim.

A candidate for such a system could be new technology developed by the American spaceflight company SpinLaunch, which has engineered technology to launch satellites into orbit at fast speeds. This device could also be used to shoot masses at asteroids that pass nearby.

Read more: Where do meteorites come from? We tracked hundreds of fireballs across the sky to find out.

This article has been republished from The Conversation under a Creative Commons license. Read the original article.

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