Sat. May 28th, 2022

A NASA spacecraft the size of a golf cart has been sent to smash into an asteroid with the intention of knocking it a little off course. The test aims to demonstrate our technological readiness in the event that an actual asteroid threat is detected in the future.

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

The mission will travel to the asteroid Didymos, a member of the Cupid group of asteroids. Every 12 hours, Didymos orbits a minimal moon, or “moon”, Dimorphos. This smaller half of the pair will be DART’s goal.

Are we facing an extinction threat from asteroids?

We have all seen disaster movies where an asteroid hits Earth and creates an extinction event similar to the one that killed the dinosaurs millions of years ago. Could it happen now?

Well, the Earth is actually often bombarded by small asteroids ranging from 1-20 meters in diameter. Almost all asteroids of this size dissolve in the atmosphere and are usually harmless.

There is an inverse relationship between the size of these objects and the frequency of shock events. This means that we are hit much more often by small objects than larger ones – simply because there are many more smaller objects in space.

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

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

Risk assessment

NASA’s DART mission has been triggered by the threat and fear that a major 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 from 0 to 10, where 0 means that there is a negligible chance of collision, and 10 means impending collision, where the impacting object is large enough to trigger a global catastrophe.

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

With the rise of online news and the ability of individuals to film events, asteroid “near-accidents” tend to create fear in the public eye. NASA is currently keeping a watchful eye on the asteroid Bennu, which is the object with the largest “cumulative hazard rating” right now. (You can also stay updated).

With a diameter of 500 m, Bennu is able to create a 5 km crater on Earth. However, NASA has also said that there is a 99.943% chance that the asteroid will miss us.

Hanger for shock

At some point in their orbit around the Sun, Didymos and Dimorphos come within about 5.9 million km of Earth. This is still further away than our moon, but it is very close in astronomical terms, so this is where DART will hit Dimorphos.

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

The larger Didymos is 780m in diameter and is thus a better target for DART to aim for. Once the DART has detected the much smaller Dimorphos, only 160 m in diameter, it can make a last minute course correction to collide with the moonlight.

The mass of Dimorphos is 4.8 million tons and the mass of DART at impact will be around 550 kg. By traveling at 6.6 km / s, DART will be able to transfer an enormous amount of momentum to Dimorphos, to the point where it is actually expected to change the moonlight’s orbit around Didymos.

This change, of about 1%, will be detected by ground telescopes within weeks or months. While this may not seem like much, 1% is actually a promising shift. If DART were to collide with a solitary asteroid, its orbital period around the Sun would only change by about 0.000006%, which would take many years to measure.

So we will be able to detect the 1% change from Earth, and in the meantime, the pair will continue along its orbit around the Sun. DART will also deploy a small satellite ten days before the crash to capture everything.

This is NASA’s first mission dedicated to demonstrating a planetary defense technique. At a price of $ 330 million, it is relatively inexpensive for space mission purposes. The James Webb telescope, to be launched next month, costs close to $ 10 billion.

There will be little or no waste from the impact of DART. We can think of it in the form of a comparable event on Earth; imagine a train parked on the rails but without brakes. Another train comes and collides with it.

The trains do not break or destroy each other, but run together. The stationary one will gain some speed and the one who affects it will lose some speed. The trains become a new system with different speeds than before.

So we will not experience any impact, ripples or dirt from the DART mission.

Is the effort really worth it?

Results from the mission will tell us how much mass and speed it takes to hit an asteroid that could pose a threat in the future. We are already tracking the vast majority of asteroids coming close to Earth, so we would have early warning of any such object.

That said, we’ve been missing items in the past. In October 2021, the asteroid UA_1 passed about 3,047 km from the Earth’s surface over Antarctica. We missed it because it was approaching from the direction of the Sun. With a size of only 1m, it would not have caused much damage, but we should have seen it coming.

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

A candidate for such a system could be the new technology developed by the American space company SpinLaunch, which has designed technology to send satellites into orbit at high speeds. This device could also be used to fire masses at closely spaced asteroids. The conversation


Gail Iles, Associate Professor of Physics, RMIT University

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

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