Near-Earth object NEO
An asteroid or comet whose orbit enters Earth's neighborhood. This describes an orbit, not an impact prediction.
Research / reference
Terminology, clearly.
Short definitions for the terms behind asteroid impact risk. Start with the five distinctions below, or find a specific word.
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Five distinctions that matter.
Potentially hazardous describes a screening category. It does not predict an impact.
Orbit distance compares two orbital paths. It is not the distance between two objects at a given time.
Impact corridor maps possible impact locations. It is not the full damage area.
Fragmentation changes an object's shape and path. It does not erase its mass or energy.
DART demonstrated a kinetic impact. It does not establish a ready response for every object or warning time.
THE REFERENCE
Find a term.
Definitions are simplified for orientation. Follow the source links for technical use.
Browse the terms below.
01
The threat
Near-Earth asteroid NEA
A near-Earth object that is an asteroid rather than a comet.
Potentially hazardous asteroid PHA
A screening category based on orbital closeness and brightness. It does not mean the asteroid is on a collision course.
Warning time
The time between credible detection of an impact threat and the possible impact. Useful response time may be shorter.
Absolute magnitude H
A measure of an asteroid's brightness under standard viewing conditions. It helps estimate size, but diameter also depends on reflectivity.
Minimum orbit intersection distance MOID
The smallest separation between two orbital paths, such as Earth's and an asteroid's. It does not say where both objects will be at the same time.
Impact probability IP
The estimated chance of impact under the current observations and model. It can change as new observations improve the orbit.
Torino scale
A 0–10 public communication scale for the likelihood and possible consequences of a future impact.
Palermo scale
A technical scale comparing a predicted impact threat with the background impact risk over the same time period. It is not the Torino scale in different units.
02
Orbit & uncertainty
Observation arc
The span of time over which an object has been measured. More useful observations often narrow the range of possible orbits.
Orbit solution
An orbit estimated from measurements. It comes with uncertainty, so the reported path is not the only possible path.
Nominal orbit
The best-fit orbit from the available data. Risk analysis must also consider other orbits allowed by measurement uncertainty.
Virtual impactor
A possible orbit within the uncertainty range that leads to an Earth impact. It is a model case, not a newly discovered object.
Line of variations LOV
A way to sample an important direction of uncertainty around a best-fit orbit when searching for possible impact paths.
B-plane
A reference plane used to map possible close approaches to a planet. It helps researchers see how orbital uncertainty relates to an encounter.
Impact corridor
The band of possible impact locations produced by uncertain trajectories. It is not a map of where effects would be felt.
Sentry
NASA CNEOS's automated system for monitoring possible future Earth impacts from known near-Earth objects.
03
Physical response
Kinetic impactor
A spacecraft designed to strike an asteroid and change its motion through momentum transfer.
DART
NASA's Double Asteroid Redirection Test. Its collision with Dimorphos demonstrated asteroid deflection by kinetic impact in a test, under circumstances unlike a short-warning emergency.
Deflection
Changing an object's trajectory enough to avoid or lessen a future impact. Even a small change can matter when there is enough time.
Delta-v Δv
A change in velocity. For planetary defense, its effect depends on direction, timing, orbit, and the object's properties.
Momentum enhancement β
A measure of how material thrown off during an impact can add to the push delivered by the impacting spacecraft.
Interception
Meeting an incoming object at a chosen point. An intercept alone does not show that its path or consequences improved.
Disruption
Breaking an object into pieces. The fragment paths, atmospheric effects, and remaining risk must all be assessed.
Fragmentation
Breaking into multiple pieces, naturally or through intervention. Smaller pieces can still cause airbursts or surface damage.
Stand down
Decide against physical action when evidence, safety, time, or authorization is insufficient. It can be the responsible choice.
04
Effects & decisions
Atmospheric entry
An object passing into Earth's atmosphere. Heating, pressure, and breakup can change the effects before it reaches the surface.
Airburst
A release of energy in the atmosphere when an incoming body breaks up or explodes. A surface impact is not required for harm.
Damage footprint
The area that could experience harmful effects such as blast, heat, or falling fragments. It may extend beyond the impact corridor.
Transferred risk
Risk shifted toward another population or state by a changed trajectory or intervention. It is a scientific and governance issue.
Residual risk
Danger that remains after a response, including uncertainty about whether the action worked.
Expected harm
A comparison of possible losses weighted by their estimated likelihood. TURAI's proposed decision rule asks whether action lowers this overall measure.
Civil protection
Warnings, evacuation or shelter plans, emergency services, and recovery actions that protect people whether or not an asteroid is physically altered.
05
Organizations & systems
Minor Planet Center MPC
The international clearinghouse for observations and designations of small Solar System bodies.
Center for Near Earth Object Studies CNEOS
NASA JPL's center for calculations about near-Earth object orbits, close approaches, and impact probabilities.
Near-Earth Object Coordination Centre NEOCC
ESA's center for near-Earth object observations, orbit analysis, and risk information.
International Asteroid Warning Network IAWN
An international collaboration that coordinates asteroid observations, threat analysis, and warning communications.
Space Mission Planning Advisory Group SMPAG
An international group that plans and coordinates options for possible space missions in response to an asteroid threat.
United Nations Office for Outer Space Affairs UNOOSA
The UN office that supports international cooperation in peaceful uses of outer space and hosts information on the planetary-defense coordination framework.
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PRIMARY REFERENCES
Go deeper at the source.
NASA CNEOS / object classes ↗NASA CNEOS / Sentry ↗NASA CNEOS / Torino scale ↗NASA / DART ↗ESA / planetary defence ↗UNOOSA / IAWN & SMPAG ↗
These are independent, plain-language explanations for the TURAI research site. For precise definitions, models, or current risk data, use the cited institutions directly.