Will NASA’s planetary defence test work?

We’ve all seen the movies – a hunk of space rock hurtling towards and a bunch of has-been astronauts strap themselves into rocket, risking their necks to save us all. 

24th September 2022: The Earth has been impacted by a vast number of significant objects from space.  Luckily, there’s no known objects in the Solar System which pose a threat to Earth on a global scale like the Chicxulub meteor that impacted near Mexico some 66 million which contributed to the extinction of the dinosaurs.

A main part of NASA’s Planetary Defense effort is the Near-Earth Object (NEO) Observations Program. This aims to find 90% of NEOs that are 140m or larger which could cause major damage on Earth.  The search is carried out by a combination of ground-based telescopes and spacecraft. You can read more about the program here.

The problem is that there are thousands of small, rocky objects whizzing around the Solar System. Some will approach or hit the Earth unknown to us, like Chelyabinsk meteor. This exploded in the air over Russia in 2013, releasing energy roughly equal to a 400 kiloton nuclear blast that caused widespread injury and destruction. It was certainly a wakeup call to the kind of damage that even a small rocky body travelling at high velocity towards us could cause. It wasn’t spotted beforehand.

Meteor exploding over Chelyabinsk, Russia. Via NASA

But what could we do if we found an object in space headed our way?

There are a few options.  Blowing it up with nuclear weapons springs to mind. This is likely to split a single body into thousands of pieces – all still headed towards Earth. If found early enough, even a small “nudge” might disturb its path enough away from Earth enough to avoid a collision.  This could either take the form of planting rocket motors or other thrusters on the object’s surface. Another approach would be to simply slam something into the body and change its course much like a game of pool.

On the 26th Sep 2022, NASA intends to slam a small space probe into a rocky body to see if its orbit can be changed. The DART (Double Asteroid Redirection Test) mission targets a small near-Earth asteroid orbiting another. Double asteroids are rare, making up less than 15% of those asteroids we know about.

This system is made up of the approx. 780-meter-diameter “Didymos” and the smaller, approx. 160-meter size “Dimorphos,” which orbits Didymos.  (Dimorphos is an irregular shaped, and not round.) While they’re classified as “near Earth”, the system is still some 11 million km from Earth and nowhere near a collision orbit with Earth. The small nudge from DART also won’t be enough to move it towards us either. There won’t be a NASA “whoopsie” moment!

If successful, DART will be humanity’s first movement of a celestial object from its original position.

Illustration of NASA’s DART spacecraft and the Italian Space Agency’s (ASI) LICIACube prior to impact at the Didymos binary system. Image via NASA/John Hopkins

DART will accelerate in the next few days to some 21,000km per hours relative to Dimorphos and if all goes to plan, slam straight into the small asteroid. The impact won’t be enough to destroy or even damage Dimorphos.  What is hoped is that the energy contained in the impact from DART will change the orbit of Dimorphos by about 1%. Dimorphos currently takes 11 hours and 55 minutes to complete an orbit of Didymos – scientists will be keeping a keen eye on the orbit to see exactly how much it will be changed.

We’ll get to see the action via onboard camera on DART called DRACO (Didymos Reconnaissance and Asteroid Camera for Optical navigation). This will help DART navigate and make its final approach. DRACO will stream live images of the approach and collision which will be available on the NASA YouTube channel, as well as other streams.

As DRACO will likely be destroyed by the impact, a small satellite called LICIACube  (Light Italian CubeSat for Imaging of Asteroids) detached itself from DART a couple of weeks ago and will follow DART as it heads for collision. The images from LICIACube won’t be available for a little while after impact.

Other telescopes like the JWST (James Webb Space Telescope) and NASA’s Lucy mission will be trying to spot any immediate changes by the impact. Dimorphos might even brighten slightly as dust is sprayed up from its surface once DART hits. However, it will be ground based telescopes that will actually determine the change in the orbit and how successful the DART mission has been.

Another visitor

HERA mission. Illustration via ESA

Dimorphos and Didymos won’t be alone for long. In 2024 ESA’s HERA mission will launch to return to the system to study it in more detail and get close up observations on the longer-term influence of the DART impact.

Combined with better detection of celestial bodies that could head our way and technologies to nudge them away from Earth, the various space agencies are focused on defending us from threats from above.


Earl White




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