Meteor Crater National Landmark was caused by a meteor no bigger then a small house.

Meteor CratorAsteroid Impacts Earth

LD means (Lunar Distance) 1 LD = 384,401 km or 238,855 miles, that is the distance between the Earth and Moon. 1 LD also equals 0.00256 Astronomical Units or AU.
Please note that some asteroids are discovered after they have made their close approach. Alerting system will still email you when they are released by NASA JPL and our Algorithm(FlyByAsteroids) picks it up.