Nasa 'asteroid crash' helps plan to keep Earth safe
- Published
In 2022, scientists carried out an unusual experiment in space.
A spacecraft called Double Asteroid Redirection Test (DART) was deliberately crashed into a small asteroid.
It was Nasa's first planetary defence mission: To see if they could successfully change the path of an asteroid away from Earth, if they needed to.
This asteroid was never a threat to Earth, but new research shows that the mission did slightly change the path of two asteroids.
Now scientists have been explaining why a little nudge can go a long way.
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The experiment took place on 26 September 2022 when the spacecraft smashed into an asteroid called Dimorphos.
Dimorphos is not alone in space. It orbits a larger asteroid named Didymos.
Before the crash, Dimorphos orbited Didymos every 12 hours. Earlier studies showed that after the impact, that orbit became 33 minutes shorter.
But scientists have now discovered something even more surprising.
The crash also changed the way the asteroid pair travel around the Sun.
Their journey around the Sun takes about 770 days, and the new study found that this time changed by a tiny amount - just 0.15 seconds.
Even though that sounds incredibly small, scientists say it is very important.
"This is a tiny change to the orbit, but given enough time, even a tiny change can grow to a significant deflection," said Thomas Statler, lead scientist for solar system small bodies at Nasa.
'It can make the difference between an object hitting or missing our planet'
The Italian Space Agency's LICIACube spacecraft traveled alongside Nasa's DART to capture the spacecraft's collision with Dimorphos. In this LICIACube image, taken moments after impact on Sept. 26, 2022, rocky debris can be seen fanning out from the smaller asteroid below its larger partner, Didymos
When the spacecraft struck Dimorphos, the impact blasted a huge cloud of rocky debris into space. The asteroid is about 160 metres wide, that's roughly the length of one and a half football pitches.
As the debris flew away, it pushed the asteroid slightly, like a rocket thrust. Scientists call this effect momentum enhancement - the escaping debris gave the asteroid an extra push, making the impact about twice as powerful as the spacecraft alone.
The study found that the speed of the asteroid system changed by only 11.7 microns per second - about 1.7 inches per hour.
"Over time, such a small change in an asteroid's motion can make the difference between a hazardous object hitting or missing our planet," said Rahil Makadia, the study's lead author at the University of Illinois.
The Hubble Space Telescope observed two tails of dust ejected from the Didymos-Dimorphos asteroid system several days after Nasa's DART spacecraft impacted the smaller asteroid.
To measure these tiny changes, astronomers watched special events called stellar occultations. This happens when an asteroid passes directly in front of a star and briefly blocks its light. By timing these tiny "blinks," scientists can calculate the asteroid's position and speed very precisely.
Dozens of volunteer astronomers around the world helped make the observations.
"When combined with years of existing ground-based observations, these stellar occultation observations became key in helping us calculate how DART had changed Didymos' orbit," said Steve Chesley, a senior research scientist at NASA's Jet Propulsion Laboratory.
The DART mission was the first time humans have deliberately changed the motion of an object in space - in what experts say is an important step toward protecting Earth from dangerous asteroids in the future.
