International Monitoring System—An international network of seismic, infrasound, radionuclide, and hydroacoustic stations deployed by the Department of Defense and the Comprehensive Test Ban Treaty Organization. In addition to monitoring for violations of the treaty, its microbarograph sensors also detect airbursts from cosmic objects striking Earth’s atmosphere.

iron meteorite—A meteorite consisting primarily of metallic nickel-iron alloys.

keyholes—Small regions of space near Earth where Earth’s gravitational pull changes an NEO’s orbit just enough that the NEO hits Earth on a future approach.

kinetic energy—The energy of motion.

kinetic impactor—See impactor.

kinetic yield—See impact energy.

Lagrangian points—Discovered by Italian-French mathematician Joseph Louis Lagrange, the Lagrangian points mark positions where the gravitational pull of two large, mutually orbiting masses precisely equals the centripetal force required to keep a small body there rotating at the same angular speed as the massive ones. Objects placed near the Lagrangian points would orbit around them.

LEO—Low-Earth orbit, commonly between 160 and 2,000 kilometers in altitude above Earth’s surface.

LINEAR—Lincoln Near-Earth Asteroid Research Program, operated by the Massachusetts Institute of Technology’s Lincoln Laboratory and funded by the U.S. Air Force and NASA. It was the most successful NEO search program from 1997 to 2004. The program was intended to demonstrate application of technology designed for the surveillance by Earth-orbiting satellites for detecting NEOs.

LONEOS—Lowell Observatory Near-Earth-Object Search, operated by the Lowell Observatory, is a 0.6-meter-diameter telescope that can scan the entire sky accessible from Flagstaff, Arizona. Project funding from NASA began in 1993 and ended in 2008.

LSST—The Large Synoptic Survey Telescope is a survey project under development by a consortium of institutions. It is centered on an 8.4-meter-diameter mirror and will operate in Chile, scanning the entire sky every few days in visible and infrared wavelength bands. The major science goals for the LSST include the cataloging and characterizing of all moving objects in the solar system, including the identification of NEOs.

mass driver—A mechanism placed on the surface of an object that ejects mass from the object as propellant (see also contact force).

Meteor Crater—An approximately 1.2-kilometer-diameter crater located in Arizona.

momentum transfer—The amount of momentum that one object gives to another upon collision.

Monte Carlo simulations—A class of computational algorithms that use random numbers; useful for simulating complex systems with a large number of unknown quantities.

MOPS—Moving Object Processing System.