Aim of the newly designed DART
The DART mission, which was just launched, is intended to see if colliding with an asteroid with a spacecraft may shift the rock’s trajectory sufficiently to prevent a predicted collision with the Earth if enough time is given. Dimorphos, a satellite of the bigger asteroid Didymos, will be the target of the DART mission. According to mission personnel, no probability of the duo impacting Earth exists, regardless of how well the NASA probe performs.
So Didymos and Dimorphos aren’t a threat, but should most people be concerned about asteroid impacts? “It’s complicated,” as is the case with many things.
According to NASA, a relatively large rock, roughly the size of an American football field and capable of causing substantial local damage upon impact, only hits Earth every 2,000 years or so.
Countless tiny impacts
To begin with, the question isn’t if an asteroid will collide with the Earth:
It has happened before, and it does so very frequently.
Compact rocks bump all the time – as per NASA, something the small car size impacts Earth’s atmosphere nearly once a year, but these objects burn and explode very soon before they touch the ground.
When this happens, no one notices, except possibly to believe it’s a pretty amazing show, because these rocks produce meteors, the “shooting stars” that we like viewing on a dark, clear night. Meteoroids, which are genuine bits of the asteroid that are burning up, produce meteors. A major majority of meteoroids are just a few millimeters or fractions of 1 inch in diameter.
Meteorites are larger objects that fall to Earth’s surface. Only one person is known to have been directly hurt by a meteorite:
Ann Hodges, who was struck in the leg by a 9-pound meteorite in 1954. She didn’t get a life-threatening bruise.
A small risk of a big impact
To determine the relative chance of a serious asteroid impact on Earth, scientists use a variety of methods.
Take look at the most recent major effects. In the Tunguska event of 1908, a massive asteroid or comet erupted over Siberia, causing shock waves that devastated 750 square miles of woodland. The next noteworthy impact happened nearly 100 years later above Chelyabinsk, damaging residences as far as 55 miles (88 kilometers) on each side of its track. The impact in Chelyabinsk resulted in almost 1,200 injuries, the majority of which were caused by windows being blown in by the shock wave.
These incidents took place over a century apart. Although these are only two incidents, they provide some insight into the frequency with which large-scale impacts occur.