Glossary and Selected Acronyms
2008 TC3—An asteroid observed by the Catalina Sky Survey to be on a collision course with Earth; 2008 TC3 exploded in an airburst over Sudan on October 7, 2008.
2009 HC82—A near-Earth asteroid 2 to 3 kilometers in diameter in a retrograde (“backwards”) orbit, discovered in 2009.
absolute magnitude (M)—A specially defined quantity describing a celestial object’s intrinsic brightness.
airburst—An explosion in Earth’s atmosphere of an object entering it at high speed.
albedo—The ratio of the light reflected by a physical object (e.g., planet or asteroid) to that received by it.
AsteroidFinder—A German spacecraft mission and the first payload to be launched under Germany’s new national compact satellite program. AsteroidFinder is planned for launch sometime in 2012, with a 1-year baseline-mission duration, will be equipped with a 30-centimeter-diameter telescope mirror, and will operate in low-Earth orbit. Its primary goals are to estimate the population of near-Earth objects (NEOs) interior to Earth’s orbit, their size distribution, and their orbital properties, along with impact hazard assessment.
blast wave—The pressure and flow resulting from an explosion or airburst that deposits a large amount of energy into a small, localized area.
C3—A measure of the extra energy required over that to escape Earth for a space mission. C3 is given as the square of the required excess velocity, usually in units of (km/s)2.
CCD—charge-coupled device: an electronic memory that records the intensity of light as a variable charge. Widely used in still cameras, telescopes, and other optical devices to capture images, CCDs are analog devices. Their charges equate to shades of light for monochrome images or shades of red, green, and blue when used with color filters.
characterization—The determining of various characteristics of a celestial object, including but not limited to orbit, rotation, size, composition, and albedo.
chemical energy—The energy released in a chemical reaction, measured here in terms of the energy released when TNT (trinitrotoluene) is detonated.
Chicxulub Crater—An approximately 200-kilometer-diameter impact crater formed 65 million years ago in the Yucatan Peninsula and associated with the extinction of the dinosaurs.
civil defense—A mitigation option, civil defense entails protecting the population by taking precautions on the ground, such as advanced warning, evacuations, and the provision of protective shelter. It is already used for natural disasters such as hurricanes.
contact forces—A force exerted through physical contact with an object.
CSS—Catalina Sky Survey, a system of three telescopes located at the Mount Lemmon Observatory in Arizona, the Mount Bigelow Observatory in Arizona, and the Siding Spring Observatory in Australia (funded by NASA). CSS currently discovers NEOs at the highest rate of any operational telescope system.
CSS+—Catalina Sky Survey Binocular Telescopes, a proposed series of three binocular telescopes fully dedicated to discovering NEOs, based on using six existing 1.8-meter-diameter primary telescope mirrors. CSS+ is currently not funded.
ΔV—“Delta-V”: Change in velocity.
Deep Impact—A NASA mission during which a spacecraft collided with comet Tempel-1 in July 2006; an example of a kinetic impact (see impactor).
Deep Space Network—A network of three deep-space communications facilities placed approximately 120 degrees apart around the world that supports interplanetary spacecraft missions and radio astronomy observations as well as selected Earth-orbiting missions. Facilities are located at Goldstone in California’s Mojave Desert; near Madrid, Spain; and near Canberra, Australia.
Discovery Channel Telescope (DCT)—A telescope with a 4.2-meter-diameter mirror under construction in Arizona. A collaborative effort between Lowell Observatory and Discovery Communications, the telescope is designed to contribute to multiple astronomical projects, including searches for NEOs. Its approximately $14 million camera is not yet funded.
dissipative surface—In the context of this report, a low-density, porous surface (e.g., of an asteroid) on which the energy from an impact or explosion is dissipated across the surface rather than transferring to the interior of the body.
Don Quijote—European Space Agency mission that is not funded. The proposed mission involved an NEO impactor and an observation spacecraft.
Eccentricity (e)—A measure of how much an orbit’s shape deviates from a circle. For circular orbits, e = 0. As e becomes greater, the orbit’s shape becomes increasingly elongated.
electric propulsion—A method of spacecraft propulsion using charged ions for thrust.
ESRIN—The European Space Agency’s Centre for Earth Observation, located in Frascati, Italy.
flyby trajectory—A spacecraft’s flight path designed to pass in close proximity to an object but not go into orbit around or impact the object.
gamma ray—Very high energy electromagnetic radiation.
George E. Brown, Jr. Near-Earth Object Survey Act of 2005—A congressional act mandating the discovery by 2020 of 90 percent of cosmic objects 140 meters in diameter or greater.
Goldstone Solar System Radar—Located in the Mojave Desert in southern California, a steerable 70-meter-diameter antenna that transmits and receives radio waves. It is part of NASA’s Deep Space Network and is operated by the Jet Propulsion Laboratory under contract with NASA.
gravity assist—Using the gravity of a planet to change the path and/or speed of a spacecraft.
GTO—Geostationary Transfer Orbit, an intermediate orbit used to move a spacecraft from low-Earth orbit to a geostationary orbit where the spacecraft remains stable above a particular point on Earth’s equator.
Hayabusa—A Japanese spacecraft mission that rendezvoused with the subkilometer NEO Itokawa in September 2005.
heliocentric orbit—An orbit around the Sun.
heliocentric velocity—The velocity of a body relative to the Sun.
Human Space Flight Review Committee—Commissioned by President Obama in May 2009 to review current U.S. human spaceflight plans and programs. The committee concluded its review in September 2009. Also konwn as the “Augustine Committee.”
hydrodynamic simulation—A computer model created to simulate the behavior of fluids in motion.
hyperbolic approach—One orbiting body approaching another along a hyperbolic trajectory.
IAU—International Astronomical Union, the international professional society for astronomers; provides guidance for the Minor Planet Center.
imminent impactor—A space object of natural origin whose impact with Earth is imminent.
impact energy—The amount of energy delivered by one body in an impact with another. Units are often given in megatons (MT), which refers to a comparison with the chemical energy release of a million tons of TNT. Also known as kinetic yield.
impactor—A physical object that collides with a target object at a high velocity, transferring momentum (and energy) to alter the target object’s orbit. Also called a kinetic impactor.
inclination—In this report, the angle between the plane of an orbit and the ecliptic (the plane containing Earth’s orbital path).
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.
MPC—Minor Planet Center, a clearinghouse for positional information from observers of minor planets (including all asteroids) from all observatories around the world; operated by the Harvard-Smithsonian Center for Astrophysics, with primary support from NASA.
NASA—National Aeronautics and Space Administration.
NASA PA&E Office—NASA’s Program Analysis and Evaluation Office, established in 2005 to provide objective, transparent, and multidisciplinary analysis of NASA programs in order to inform strategic decision making. The office has also been charged with leading the agency’s strategic planning efforts.
Near-Earth Object Program Office—Charged with coordinating the Near-Earth Object program for NASA; based at the Jet Propulsion Laboratory in Pasadena, California.
NEAR Shoemaker—Near Earth Asteroid Rendezvous−Shoemaker, a NASA spacecraft mission that rendezvoused with the second-largest near-Earth object, Eros, in February 2000.
NEAT—Near-Earth Asteroid Tracking, a program begun in 1995, was initially a collaborative effort among NASA, the Jet Propulsion Laboratory, and the U.S. Air Force. The program converted the 1-meter Ground-based Electro-Optical Deep Space Survey (GEODSS) telescope in Maui, Hawaii, into the world’s first fully automated asteroid-search telescope. NEAT converted other telescopes in Hawaii as well. The program ended in 2007 after having detected more than approximately 20,000 objects, about 430 of which were NEOs.
NEODyS—Near-Earth Objects Dynamic Site, a European data and information-gathering office maintained by the University of Pisa, Italy, with a mirror site at the University of Valladolid, Spain.
NEOSSat—Canada’s Near-Earth Object Surveillance Satellite, a joint venture between the Canadian Space Agency and Defense Research and Development Canada, currently under construction. NEOSSat will track human-made satellites and orbital debris, as well as discerning and tracking NEOs.
NEOWISE—The Wide-field Infrared Survey Explorer for Near-Earth Objects, a NASA spacecraft mission launched in December 2009. A subset of the overall WISE mission, NEOWISE will produce a high-sensitivity-imaging survey of the entire sky in four infrared wavelength bands, always looking 90 degrees from the Sun.
NESS—Near-Earth Space Surveillance.
NSF—National Science Foundation.
ocean runup—A condition in which the water level on a coastline rises above normal fluctuations.
PanSTARRS (or PanSTARRS 4 or PS4)—Panoramic Survey Telescope and Rapid Response System is planned to consist of four 1.8-meter-diameter mirrors in a single imaging system, each telescope observing the same area of sky at the same time and wavelength. So far, only PanSTARRS 1 has been built on the island of Maui.
perigee—The point of closest approach to Earth of a body in orbit around Earth.
perihelion—The point of closest approach to the Sun of a body in orbit around the Sun.
photon pressure—Pressure exerted on a body by light.
porosity—A measure of the open spaces, or voids, in a material. It is often defined as a fraction: the volume of open space over the total volume.
proximity detonator—A device used to detonate explosives automatically when the distance to the target becomes smaller than a predetermined value.
radiant energy—The energy of electromagnetic waves. Also may be used to refer to the waves themselves.
recovery—A component of a larger response-and-recovery civil defense plan. Planning for recovery should occur before a NEO impact.
rendezvous trajectory—A spacecraft trajectory designed to intersect the trajectory of another body at very slow speed. The spacecraft can then go into orbit around the body or impact it at low speed.
semimajor axis—The semimajor axis of an ellipse (e.g., a NEO orbit) is one-half the length of the major axis, which is the segment of a line passing through the foci of the ellipse with end points on the ellipse itself.
Shoemaker-Levy 9—A comet that broke apart and later collided with Jupiter in 1994.
slow push or pull—A method of mitigation whereby the orbit of a target object is changed by slowly altering its velocity over a long period of time, perhaps decades, and is limited to use on objects of about 100 meters in diameter or smaller.
solar energy—Radiant light from the Sun.
Spaceguard Survey—Mandated by Congress to detect 90 percent of NEOs 1 kilometer in diameter or greater by 2008.
Spacewatch—Established in 1981, Spacewatch is one of the first NEO discovery systems, is run by the University of Arizona, and utilizes two (0.9-meter- and 1.8-meter-diameter) telescopes.
spall—Flakes of material ejected from a larger parent body as the result of an explosion.
standoff detonation—The detonation of an explosive at a distance from a target object such as an NEO.
stony meteorite—A meteorite consisting primarily of rocky material.
technology readiness level (TRL)—A measure used to assess the maturity of evolving technologies (materials, components, devices). TRL 1 is the lowest level of readiness, limited to studies of a technology’s basic properties. TRL 9 is the level for the application of a tested and proven technology.
thermal inertia—A description of how fast an object changes temperature in response to a change in the heat applied.
thermal pulse—An expanding wave of heated air or other material associated with an impact or an airburst event.
TNT megatons—A method of quantifying the energy released in explosions by comparing it to the equivalent energy released by a quantity of TNT. A ton of TNT is a unit of energy equal to 4.184 gigajoules.
trajectory—The path or orbit that a moving object follows through space; usually applied in this report to a spacecraft headed toward an NEO.
Tunguska event—A term referring to the explosion of a cosmic object above Siberia in a region near the Podkamennaya Tunguska River in 1908 in what is termed an airburst.
Vredefort Crater—A 300-kilometer-diameter crater located in South Africa, formed about 2 billion years ago.