Most mission scientists would cringe at the thought of their spacecraft being blown to bits. But for those behind Nasa’s Dart probe, anything less than total destruction will be counted as a failure.
The $330 million spacecraft is expected to make a head-on impact with an asteroid about 11 million kilometers above the Indian Ocean shortly after midnight Monday. The nearly seven kilometers per second impact will obliterate the half-ton probe, all in the name of planetary defense.
Not that Dimorphos, the asteroid in question, poses any threat to humanity. The Dart or double asteroid detour test is an experiment, the first mission ever, to assess whether asteroids can be deflected should one ever be found on a collision course with Earth. A well-placed nudge could avert Armageddon, it was thought, and spare humans the same fate as dinosaurs.
“It’s a very complicated cosmic billiards game,” said Prof Alan Fitzsimmons, an astronomer and member of Nasa’s darts investigation team at Queen’s University Belfast. “We want to use as much energy as possible [as we can] of Dart to move the asteroid.”
With telescopes constantly scanning the sky, scientists hope to get some notification should an asteroid ever pose a major threat. “If we can see far enough ahead and know that an asteroid could be a problem, getting it out of the way will be a lot safer than the big Hollywood idea of blowing it up,” Catriona said McDonald, PhD student at Warwick University.
The Dart mission launched from Vandenberg Space Force Base in November last year. On Monday evening, mission controllers will hand over control to Dart’s software and let the probe pilot itself into oblivion. The collision on Tuesday at around 0.14am UK time is captured by Dart’s camera and two other cameras on board a small Italian probe called the LiciaCube, which Dart released last week to watch the spectacle from a safe distance.
When playing with the movement of celestial bodies, it pays to exercise some caution. The Dart mission was planned so that it would not inadvertently place Dimorphos on a collision course with Earth. The 160 meter wide rock orbits a second, larger asteroid called Didymos. When Dart collides, the impact will do nothing but kick up a cloud of debris and slow Dimorphos, adding several minutes to its orbit around the larger body.
“There’s no danger in that,” said Prof Colin Snodgrass, an astronomer and member of the science team for Dart missions at the University of Edinburgh. “We’re just changing its orbit around the larger asteroid, we’re not changing its orbit around the sun. It cannot come to earth.”
Astronomers will use ground-based telescopes to observe the asteroids before and after Dart’s collision. Among them, a new telescope installed at the Turkana Basin Institute in northern Kenya is set to capture the moment of the impact and kick-up of the Dart dust cloud. The amount of debris depends on the energy of the impact, the type of rock that makes up Dimorphos, and whether the material is loosely or tightly bound. “The main mission is a test of planetary defenses, but at the same time we can learn a lot about the asteroid,” Snodgrass said.
After the collision, scientists will find out how much Dimorphos was slowed down by the impact. To do this, they monitor the brightness of the larger asteroid Didymos, which dims slightly each time Dimorphos cruises forward to complete a turn. Dimorphos currently takes around 12 hours to orbit Didymos and is expected to take a few minutes longer once Dart has struck.
Astronomers track about 30,000 asteroids and comets passing close to Earth’s orbit. None of the big ones — comparable in size to the 7-mile-wide asteroid that helped wipe out the dinosaurs 66 million years ago — will hit Earth for the next few hundred years. However, smaller ones are harder to spot and can still cause significant damage. The meteor that exploded over Chelyabinsk, Russia in 2013 was less than 20 meters across but created a shockwave that injured 1,600 people, mostly from flying glass and collapsing walls.
Given previous missions to asteroids and powerful computer simulations, do scientists really need to crash a spacecraft into an asteroid to see what happens? Fitzsimmons thinks so. “We know what asteroids are made of, but we often don’t know what they’re made of, and we don’t know how much Dimorphos will move if it’s hit,” he said. “You don’t want to wait for someone to come up to you to see if this approach works.”
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