Yuri Milner Breakthrough Starshot - Nano Craft hitting Earth

[Maths_Teacher]

I've been doing some work with my classes around the Yuri Milner Breakthrough Starshot project to send a tiny nano craft of mass around a few grams to alpha centauri. The starchip would travel at 20% of the speed of light. I've had them calculating various properties of the ship including kinetic energy. Since this would be around 10^14 J (about a Hiroshima bomb) it got the class thinking what would happened if little green men on alpha centauri were sending their own nano starchips toward the earth. If one collided with the Earth what would happen? Some suggested it would burn up in the atmosphere and cause no damage (in which case could all this energy really just be dissipated in the atmosphere with no effect?). Some suggested it would reach the ground and cause a massive A-Bomb type explosion. Are there any natural objects this size traveling at the speeds suggested? What physics would be involved if something like this hit our planet. I'd like to give the class more to think about. Any suggestions.

 

[phyzguy]

Check your numbers - I think the kinetic energy is more like 10^12 J for a 1g object traveling at 20% of the speed of light. Make sure you are calculating the kinetic energy and not the total energy, which includes the rest energy. The rest energy is still there after it slows down. This is about 0.4 kilotons of energy, or about equivalent to a meteor less than 1m in diameter hitting the Earth at 20 km/sec. These events are fairly common. For reference, the Chelyabinsk meteor that hit Russia in Feb, 2013 was traveling at about 20 km/sec and had an estimated diameter of about 20m, and an estimated kinetic energy of about 500 kilotons. It shattered a bunch of windows and was spectacular, but was hardly a huge catastrophe.

 

[davenn]

Are there any natural objects this size traveling at the speeds suggested?

not aware of anything