From Stone to Ice

Changes with distance from the Sun in the early Solar System are recorded in the locations of asteroids and comets. Asteroids, which are composed mainly of silicate minerals and metals, are located mainly between the orbits of Mars and Jupiter, whilst comets, which are rich in water ice, are mainly located further out in the Solar System. Evidently temperatures decreased outwards from the Sun in the Solar Nebula during the formation of these objects.

In more detail changes with distance from the Sun are observed within the asteroid belt. The inner asteroid belt appears to be dominated by asteroids that were strongly heated at an early stage, whilst the outer belt contains asteroids that retain elements easily lost during heating, the volatile elements. Asteroids are thought to have been heated by short-lived radioactive nuclides such as 26-aluminium, which were present when these bodies formed and heated their interiors. The change in asteroids through the asteroid belt may, therefore, be due to differences in the amount of these heat-producing isotopes.

Although some information can be obtained on the nature of asteroids using telescopes, detailed information on their degree of heating and the abundance of isotopes such as 26-aluminum can only be obtained from samples which can be studied in the laboratory.

Many samples of asteroids come to us each year as meteorites, however, it is usually impossible to exactly determine from where in the asteroid belt these rocks are derived. Only when meteorites are observed to fall can their orbits be traced back to their sources in the asteroid belt.

Watching for Meteorites

Meteorites with known orbits are exceedingly rare since meteorite fireballs are infrequently observed with sufficiently accurately to determine their trajectories. Meteorites with known orbits, however, are valuable samples of the asteroid belt since they provide us with detailed information on changes in the Solar Nebula with distance from the early Sun.

An important goal of the Origins Network is to recover more meteorites from known locations in the asteroid belt. A network of cameras, operated by Imperial College London, has been established in the Nullabor Desert of Australia, this Desert Fireball Camera Network, is being used by the Origins Network to identify the trajectories and orbits of fireballs, and recover resulting meteorite falls. The Desert Fireball Camera Network is expected to provide a signficant number of meteorites with known orbits. The orbits of the meteorites are being calculated by the Ondrejov Observatory.

Once recovered meteorites recovered by the Origin Network will characterised by a variety of analytical techniques. Special attention will be given to analyses of short-lived radionuclides. In addition to meteorites, extraterrestrial dust found on Earth, known as micrometeorites, and dust particles recovered from the NASA Stardust mission, will also be analysed since these are thought to have formed at greater distances from the early Sun than asteroids.

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