Here is a glossary of terms used throughout the NEOShield-2 website. If you come across a term not included here, please contact us.

Your question may also be answered in the FAQs.

Ablation Ablation is the removal of material from the surface of an object by vaporization, chipping, or other erosive processes.
Absolute Magnitude The brightness an object would have if the observer was 1AU away from it.  This value is often used instead of the size of a NEO, as the albedo of the NEO is usually also not known.  Therefore, for most NEOs, it is not possible to determine the difference between a small bright reflective NEO and a large dull dark NEO, which would have the same Absolute Magnitude.
(For those that are interested, the Diameter of a NEO can be obtained using the following formula if the Absolute Magnitude (H) and Albedo (pv) are known:
D=1329km×10-H/5×pv-1/2)
Albedo The ratio light reflected by an object compared to the amount of light that falls on it.  An albedo of 0 means the object absorbs all light and appears pitch black and 1 means it is a perfect reflector.
Aphelion The farthest point of an orbit to the sun
Asteroid Asteroids are small, airless rocky worlds that revolve around the sun and are too small to be called planets
AU Astronomical Unit – the distance between the Earth and the Sun, 149,597,870.691 kilometres
Eccentricity The difference between the perihelion & aphelion of an orbit.  The higher the difference, the higher the eccentricity of the orbit.
Inclination The angle an orbit is inclined compared to the ecliptic
Keyhole As an asteroid passes by a Moon or planet, the gravity of the object will deflect the path of the asteroid. The keyhole is space an asteroid must pass through so that it is deflected the exact amount to bring in on a collision course with Earth in a future orbit.
Mitigation Reducing the severity of an outcome
MOID Minimum Orbit Distance – the minimum distance between the two orbits (circles or ellipses) of two bodies.
Momentum The measure of a moving body, calculated by taking the product of its mass and velocity.  It is also a measure of the impetus of an object and how difficult it will be to stop it.
NEA Near Earth Asteroid
NEO Near Earth Object – an object whose orbit brings it to within 1.3 times the distance between the earth and the sun, 1.3 AU or 200 million kilometres. The objects can either be comets that take less than 200 years to orbit the sun, or asteroids.
Palermo Scale A scale rating the impact hazard of a NEO (see also Torino Scale for another measure), which compares the threat of a given NEO to the so-called background threat of all NEOs of the same size or larger between now and the predicted date of impact.  In this way, the probability of the impact itself as well as the time until the predicted impact are considered.
The scale is logarithmic, so a Palermo Scale of -2 is only 1% as likely as a random background event between now and the time of predicted impact.  A value of 0 indicates that the risk is the same as the risk from the background threats, and therefore NEOs with a Palermo Scale of greater than 0 are considered threatening.
(The Palermo Scale is defined in the paper “Quantifying the risk posed by potential Earth impacts” by Chesley et al. available here.)
Perihelion The closest point of an orbit to the sun
PHA Potentially Hazardous Asteroid – an asteroid that could make a threatening close approach to the Earth. In technical terms a PHA is defined as having anabsolute magnitude of 22 or brighter and an Earth Minimum Orbit Intersection Distance (MOID) of less than 0.05 AU or 7.5 million km.
Semi-major axis Half of the distance across an ellipse, measuring along its longest axis
Torino Scale A scale rating the impact hazard of a NEO (see also Palermo Scale for another measure), which considers the impact energy as well as the probability of impact.  The scale is from zero to ten, and only applies to potential impacts in the next 100 years.
0: No Hazard (White Zone)
1: Normal (Green Zone) – very unlikely collision
2-4: Meriting Attention by Astronomers (Yellow Zone) – 1% or greater chance of impact
5-7: Threatening (Orange Zone) – uncertain but a threat
8-10: Certain Collisions (Red Zone) – certain impact, with different ratings for different damage zones

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