DART Closes In

The Double Asteroid Redirection Test — DART — is scheduled to impact the asteroid Dimorphos today at approximately 7:14 pm EDT (23:14 UT). You can see a countdown here. If all goes according to plan, it will alter the orbit of the 170-meter wide asteroid around its binary companion Didymos by about 0.4 mm/s. This will alter the 12-hour orbital period of the asteroid by about 70 seconds. It will take some time to confirm that it its orbit has changed in line with expectations. But all eyes — including the big telescopic ones — will be turned on a little patch of sky to see the impact.

Now 0.4 mm/sec is not a lot. If this asteroid were headed for Earth, we’d have to hit it about 500 years in advance for such a velocity correction to make it miss. But we are playing this one pretty cautiously. We’ve picked a nearby asteroid whose closest approach to the Sun doesn’t cross Earth’s orbit. We’ve chosen a binary asteroid so we’re only adjusting the orbit of one asteroid around another. And we’re making a small impact — about the equivalent of three tons of TNT. The purpose is not to prove we can defend the Earth, it’s to test the technology that could eventually lead to a planetary defense system and especially to test if our expectations for the change are accurate (the velocity change depends on the composition and density of the asteroid).

But … increase the size or especially the velocity of this spacecraft and you could do some serious redirection. This is another step toward, as the President in Armageddon said, being the first species with the means to prevent our own extinction. Or at least prevent a regional catastrophe. So, let’s hope everything goes according to plan. And that we have the wisdom to follow up on this with a genuine planetary defense system.

The odds of a planet-killing asteroid or comet showing up are low. But they are not zero. A planetary defense system might end up being a huge waste of money. But the lack of one could cost us … everything.