On September 26 at 23:15 UTC, NASA’s DART mission (Asteroid double redirect test) will be the first to deliberately and measurably alter the motion of a major body in our solar system.
In other words, it will crash into a asteroid.
The mission will provide the first test of a technique that could be used in the future – to redirect any asteroids we detect onto a collision course with Earth.
You can watch a livestream below:
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A binary pair of space rocks
DART was launched on November 24, 2021, its destination is a pair of asteroids orbiting each other, 11 million kilometers (nearly 6.84 million miles) from Earth.
The larger asteroid of the pair is called Didymos and is 780 meters (just under half a mile) in diameter. The smallest asteroid, just 160 meters wide, is called Dimorphos. The two orbit each other at a distance of 1.18 kilometers and one orbit takes almost 12 hours.
These asteroids pose no risk to Earth and were chosen as the target for DART in part for this reason. But also, and above all, because the asteroids form a binary pair, it will be possible for astronomers on Earth to assess the results of the impact.
As asteroids orbit, the sunlight reflected from them increases and decreases, systematically varying over the 12-hour cycle of the orbit.
Astronomers using powerful telescopes from Earth can monitor this variation and see how it changes, from before to after the collision.
The physics is simple, the mission is not
The physics sounds simple, and it is. Hit a thing with another thing to change its movement. But the execution of the mission is very complicated.
When DART reaches the asteroids, it will be 11 million kilometers from Earth after a 10-month journey. The spacecraft must use autonomous targeting, using asteroid images he acquires as he approaches.
DART must recognize asteroids on its own, automatically lock onto Dimorphos, and adjust its trajectory to hit it. All this while moving at a speed of nearly 24,000 kilometers (nearly 15,000 miles) per hour!
Impact outcomes, while fairly simple to measure, are difficult to predict. The size, shape, and composition of Dimorphos, and exactly where DART hits and how hard, will affect the outcome.
All of these factors are uncertain to some degree. Full computer simulations of the impact have been undertaken, and comparisons of simulations, predictions, and measured results will be the primary outcomes of the DART mission.
In addition to measurements from telescopes on Earth, a closer view of the impact itself will be possible, from an Italian space agency CubeSat (a small type of satellite) called LICIACube it was deployed from a spring box aboard the craft on September 11. LICIACube will follow and photograph the collision and its consequences.
The results will tell us a lot about the nature of asteroids and our ability to alter their motions. In the future, this knowledge could be used to plan planetary defense missions that seek to redirect asteroids deemed to threaten Earth.
What is the threat level?
An asteroid as small as 25 meters (82 feet) in diameter could cause injury in an airburst if it hit the atmosphere above a populated area. It is estimated that there are 5 million such objects in our solar system and that we have discovered about 0.4% of them.
It is estimated that such a blow occurs once every 100 years. Although quite frequent, the overall risk is low and the risk of impact is also relatively low.
However, it is predicted that there are 25,000 Dimorphos-sized objects in the solar system, of which 39% are known, that strike Earth every 20,000 years. Such an object would cause massive casualties if it hit a populated area.
The asteroids that could challenge the existence of human civilization belong to the size category over one kilometer, of which there are less than a thousand in the solar system; they might only hit Earth every 500,000 years. We have already found 95% of these objects.
Thus, potential asteroid collisions with Earth range from frequent but benign to very rare but catastrophic. DART tests are undertaken in a very relevant and interesting size range for asteroids: those over 100 meters.
If DART is successful, it could set the stage for future missions targeting asteroids, to steer them out of the way of collisions with Earth.
When an asteroid is far from Earth, it only takes a little nudge to get it out of our way, so the sooner we can identify asteroids that pose a potential threat, the better.
In the near future, the well-worn premise of so many “an asteroid is coming, we have to deflect it!“The films could well become a reality.
Steven TingayProfessor Emeritus John Curtin (Radio Astronomy), Curtine University.
This article is republished from The conversation under Creative Commons license. Read it original article.