by S. Prasad Ganti

For the first time in human history, we sent a spacecraft and jammed it into a space rock and the trajectory of that piece got nudged as a result. It was a great attempt and a great result, and this will mean a lot for our future. 

Dimorphous is a small rock about 500 feet wide which orbits a larger asteroid called Didymos in the asteroid belt between Mars and Jupiter. It is more of a binary asteroid system than a main asteroid and its satellite. DART (Double Asteroid Redirection Test) is a simple refrigerator sized spacecraft which slammed into Dimorphous recently. A companion cube satellite (a micro satellite in form of a cube shape) called LICIACube went along with DART and separate out from DART before it went on a suicidal mission to strike Dimorphos. LICIACube recorded the impact. 

DART used advanced technologies like an ion engine called a xenon-thruster powered by advanced  solar arrays. It took about 10 months for the spacecraft to reach its target. The navigation was totally autonomous as no one was driving the spacecraft into the asteroid. 

Neither Didymos nor Dimorphous posed any risk to Earth. They were not on a collision course with Earth. This was just a demonstration mission to prove what is possible to defend against any intruders in future. There was no dearth of such planetary collisions in the past. Such collisions played a major role in Earth’s history. The impacts are very well documented in a book titled “Impact” by Greg Brennekca. 

About 150 million years ago  after the formation of the solar system, a Mars sized body named “Theia” collided with Earth and the  ejected material is supposed to have formed the moon. It is a plausible theory but yet to be proved. Lots  of smaller impacts in the form of meteorites have taken place and continue to take place to this day. It is possible that organic molecules came from outside in a meteorite. Every day about 100 tons of meteoritic material falls to earth, most of it is dust in the form of micro meteorites. 

Some of the bigger meteorites are supposed to have  brought the  metals found in the Earth’s crust and organic materials as well as water. Because the original metals from the formation of Earth sunk to the molten core. Whatever we extract today from the crust is supposed to have been brought to us courtesy of the meteorites. In fact, life on Earth may owe its existence to organic material and water which may have been delivered by these couriers from outer space.

All such collisions may not be so benign. An asteroid about 6 miles across smashed into the Earth about 65 million years ago and created a huge crater which lies beneath the water in Gulf of Mexico near the Yucatan peninsula. It led to the extinction of many species, notably the dinosaurs. There were several other extinctions in the past which may or may not be attributed to collision of larger meteors and asteroids. 

The collisions are not specific to Earth alone. Other planets and moons experience it too. At a cosmic level, merger of galaxies and black holes within neutron stars happen too. There are likely to be many such major collisions with the Earth in the future. Humanity’s endeavor is to detect and prevent such collisions as a self-preservation measure. We do have a monitoring process which identifies and catalogs all such rocks which are likely to collide with Earth at some point in future. The most probable candidates are watched very carefully. 

There are two strategies to encounter such collisions. One is to send a missile with a warhead to destroy an object. The risk with such an attempt is that the multiple resulting pieces could cause more dangers than the original one. Second strategy is to nudge the trajectory of the object so that it moves out of our way and prevents harm. Something like a nudge of a ball on the  billiards table. 

The second strategy was at work with the recent DART collision of Dimorphous. Some material from the asteroid was dislodged and erupted. But it still remained as one piece. But its orbit around Didymos has changed. It used to take  11 hours and 55 minutes for each orbit before. Now, the orbit is shorter by 32 minutes. This is better than expected improvement. The momentum of the slamming spacecraft got transferred to the orbiting asteroid and caused it to speed up. 

Lot of work still needs to be done to fine tune the strategy and be ready for the doomsday. But a great beginning for the future of humanity !