Space Rocks. An attack on planet Earth conjures up images of Martians, alien empires such as those in the film “Independence Day”, and a whole host of other Hollywood movies that have potential human annihilation at the center of their plots. The concept of Earth being threatened from outer space has probably been around for millennia. Potentially hostile aliens, if they exist, are probably too far away to worry us very much but there are severe risks to Earth’s existence that are much closer and demonstrably real: Space rocks.

     The NEO (Near Earth Objects) Observation Program (NEOOP), a project designed to locate and track objects that are 140 meters across and bigger, has concluded that there are at least 25,000 of them out there. The NEOOP has so far catalogued less than half of its goal of identifying 90% of them. It’s bad enough if we know objects that are approaching Earth’s orbit, but much worse when the thousands that are out there maybe on a crash-course with Earth and we don’t know.

     To put the threat in perspective, it is less than a decade since the residents of Chelyabinsk, in Russia, witnessed an explosion of a meteorite in the atmosphere over their heads. No-one was killed but 1,500 people were badly injured, mostly from flying glass….AND THAT METEORITE WAS CALCULATED TO HAVE BEEN 20 METERS ACROSS. We all know the story of how the dinosaurs disappeared but, in general, humans have been very complacent about this very real danger.

     NASA has been working on the problem for quite a while and, recently, they tested a possible solution; they tried to knock a space rock off its orbit by firing a probe into it.

     Dimorphos is a small asteroid (160 meters across), which orbits a larger asteroid, Didymos (780 meters across). NASA fired a 600 kilogram probe into Dimorphos to try and speed up the orbit by about ten minutes. This is about the increase in speed necessary, NASA calculated, to modify the orbit of a rock threatening the earth so it misses us.

     That might sound like a simple solution but hitting something that is only 160 meters across when that object is 11 million kilometers from Earth is quite a feat, and NASA managed it. Even more amazing, since it is impossible to be that accurate from a launch on Earth, the software on the probe had to be programed to interact with the on-board cameras to autonomously guide the probe onto the target. And the probe hit its target. As I said, amazing!    

     However, all that science, mathematics and technology would have been wasted if the experiment hadn’t worked and the orbit of Dimorphos hadn’t been sped up. Weeks of measurements and observation that followed the “bullseye” collision were fraught to anxiety for the NASA project scientists.

     A few weeks ago, they were able to report that the experiment had worked and Dimorphos now had an orbit that was almost thirty minutes shorter.

     One hopes that, if NEOOP does locate and identify an object on a collision course with Earth, and that event is far more likely than most of us would want to consider, NASA will have an answer….at least for reasonable sized space rocks! Bigger ones might require more drastic measures like a nuclear bomb to knock them off course but, then, we have to worry about the size of the debris from that explosion. At least NASA’s latest success shows someone is thinking about our possible extinction.

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