Cosmic Ray Exposure Age

Time interval that a meteoroidSmall rocky or metallic object in orbit around the Sun (or another star). was an independent body in space. In other words, the time between when a meteoroid was broken off its parent bodyThe body from which a meteorite or meteoroid was derived prior to its ejection. Some parent bodies were destroyed early in the formation of our Solar System, while others like the asteroid 4-Vesta and Mars are still observable today. and its arrival on Earth as a meteoriteWork in progress. A solid natural object reaching a planet’s surface from interplanetary space. Solid portion of a meteoroid that survives its fall to Earth, or some other body. Meteorites are classified as stony meteorites, iron meteorites, and stony-iron meteorites. These groups are further divided according to their mineralogy and – also known simply as the “exposure age.” It can be estimated from the observed effects on a meteorite by bombardment by cosmic raysHigh-energy subatomic particles mainly originating outside the Solar System that continuously bombard the Earth from all directions. They represent one of the few direct samples of matter from outside our solar system and travel through space at nearly the speed of light. These charged particles – positively charged protons or from the SunOur parent star. The structure of Sun's interior is the result of the hydrostatic equilibrium between gravity and the pressure of the gas. The interior consists of three shells: the core, radiative region, and convective region. Image source: http://eclipse99.nasa.gov/pages/SunActiv.html. The core is the hot, dense central region in which the and the rest of the GalaxyConcentration of 10 to 10 stars, dust and gas, that are gravitationally bound. Our galaxy contains ~2 × 10 stars. There are four main types of galaxies: • Elliptical
• Lenticular
• Spiral
• Irregular
. As these cosmic rays strike the meteoroid in space, they produce both radioactive isotopes, such as ³He, ²¹Ne, and ³⁸Ar, and stable isotopes. The longer a meteoroid has been exposed to cosmic rays, the more of these new isotopes are formed. Further  dating information comes from an analysis of the fissionBreaking apart of a body into smaller fragments. In nuclear physics, fission refers to splitting of a heavy atomic nucleus into two or more lighter nuclei with an associated release of energy. The mass of the nucleus before fission is greater than the combined masses of the resulting fragments; the tracks (thin trails left in a substance by a fast-moving atomic nucleusCore of an atom, where nearly the entire mass and all positive charge is concentrated. It consists of protons and neutrons.) that cosmic rays cause. Exposure ages range typically from 1-100 Ma.