Cosmic-ray exposure (CRE) age - This is an age for a meteorite that is based on the decay of certain short-lived radioactive isotopes that are generated by the interaction of a meteoroid with cosmic rays. As cosmic rays do not penetrate more than a few m in solid rock, CRE ages date the time a meteoroid was roughly m-sized or smaller. CRE ages vary greatly, from ~500 Ma (million years) for most iron meteorites, to ~10 Ma for most ordinary chondrites, to <10 Ma for most carbonaceous chondrites. This is attributed to differences in strengths of meteoroids made of different materials, with iron bodies being fairly strong and carbonaceous bodies fairly weak.
IDP - Interplanetary Dust Particle.
These are dust-sized particles beleived to be derived from comets and the
interstellar medium. They can be collected in Earth's stratosphere
as they float down to the surface by using a special collector attached
to a U2 plane.
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Example of IDP (bright object) collected in the Earth's
stratosphere. This particle is about 10 microns arcoss.
http://stardust.jpl.nasa.gov/science/sd-particle.html
Inclination - This is the angle (abbreviated "i")
made between the plane of an object's orbit around the sun and a reference
plane known as the ecliptic. The ecliptic corresponds to the Earth's
orbital plane around the sun.
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http://faculty.erau.edu/ericksol/courses/sp215/ch4/orbits_ch4.html
Eccentricity - This is a measure of the ellipticity
of an orbit (abbreviated "e"), with 0 being a perfectly circular orbit,
and 1 being a parabolic, unclosed orbit.
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Examples of orbits with 4 different eccentricities.
The sun would be located at the dot (focus).
http://hyperphysics.phy-astr.gsu.edu/hbase/kepler.html
Main belt asteroid - An asteroid that has a relatively
low-eccentricity orbit between Mars and Jupiter with a semi-major axis
of ~2.2 to 3.2 A.U.
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Locations of asteroids at a particular instant.
Most asteroids are concentrated in the Main Belt with
semi-major axes of ~2.2 to 3.2 A.U. Secondary
concentrations occur at the Trojan points.
Hilda and Trojan asteroids - These are asteroids
that have roughly circular orbits with semi-major axes of ~4.0 and 5.2
A.U., corresponding to 3:2 and 1:1 resonances with Jupiter. At these
locations, Jupiter stabilizes the orbits and there are concentrations
of asteroids, rather then Kirkwood Gap depletions. The Trojans orbit
a constant 60 degrees in front of and behind Jupiter.
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Number of asteroids plotted as a function of semi-major
axis. The main belt extends from
~2.2 to 3.2 A.U. Resonance positions with Jupiter
and names of asteroid families are also shown.
http://www.physics.uc.edu/~sitko/Fall2002/16-Asteroids/asteroids.html
nu-6 resonance - This is a resonance caused by gravitation interaction with Mars which defines the inner edge of the main asteroid belt. This edge is defined both by semi-major axis and inclination (see Fig. 3 of Burbine et al.).
3:1 resonance - This is a particularly strong resonance caused by gravitation interaction with Jupiter. It is located within the asteroid belt at a semi-major axis of ~2.5 A.U. An object in this resonance will orbit the sun 3 times for every 1 orbit that Jupiter makes around the sun. This resonance condition will perturb the object's orbit by decreasing its value of "a" and increasing its value of "e", effectively moving it out of its initial orbit. Similar resonances are responsible for producing the Kirkwood Gaps. This type of resonance is what Burbine et al. refer to as the "main resonances" in the asteroid belt. It can result in transforming a Main Belt asteroid to an NEA asteroid or a meteorite-producing source object.
Yarkovsky Effect - This is an effect that causes rotating m-sized objects to gradually spiral into or away from the sun, depending on the sense of rotation. It is caused by greater emission of thermal energy from the "afternoon" side of a rotating body, which causes a small additional thrust.
Short-lived radionuclide - These are isotopes that decay so fast that none of the original parent isotope remains. A good example is 26Al, which has a half-life of ~0.72 Ma.
Magnetic induction heating - This is a speculative heating mechanism that could have arisen in the presence of a very strong magnetic field in the early solar system. Newly-formed stars have strong magnetic fields and this could have caused heating of any solid bodies present at the time. This type of heating is calculated to increase with decreasing distance to the star and with decreasing size of the solid body.
T-Tauri star - This is a type of star that is about to begin H-burning fusion reactions. These stars are known to have strong magnetic fields and strong stellar winds.
Poynting-Robertson Effect - This is an effect which causes dust-sized objects to spiral inwards to the sun as a result of photon pressure from the sun. Think of what happens when you drive through a rainstorm. As your car moves forward the rain hits the front windshield preferentially. This causes the car to experience a drag force. If your car had the mass of a dust grain (or if the raindrops were moving closer to the speed of light), your car would eventually come to a stop even if it were moving fast initially and if there were no friction with the ground.
Fischer-Tropsch reaction- This is a type of catalytic reaction that some think was important in forming organic molecules in meteorite parent bodies. We'll say more about these later.