More commonly, the impacting objects are much smaller, reaching Earth's surface as meteorites.
Given the Earth's surface composition, meteorites have a seventy-one-per-cent chance of landing in water.
A relative few have orbits that bring them into Earth's atmosphere and down to the surface as meteorites.
Precise ages can be obtained on high-level rocks (i.e., those closer to the surface) and meteorites, and imprecise but nevertheless valuable ages can be determined for rocks that have been strongly heated.
But such compounds also could be contamination from the rover itself — or they may have rained onto the surface inside meteorites, said Paul Mahaffy, a mission scientist from NASA's Goddard Space Flight Center in Greenbelt, Md. "It's unclear if the carbon is Martian or terrestrial," Mahaffy said.
Metamorphic processes can also occur at the Earth's surface due to meteorite impact events and pyrometamorphism taking place near burning coal seams ignited by lightning strikes.
Using scanning electron microscopy, they imaged strings of iron-rich flecks draped across the meteorite surface "somewhat like a string of pearls," says Friedmann.
This suggests that neon will be a useful tool in determining cosmic exposure ages of surface rocks and meteorites.
If that bit of cosmic dust burns up in Earth's atmosphere, it's known as a meteor, and any bits of meteor that impact the planet's surface are called meteorites.
During the season, expedition members live in tents on the ice fields where they search, and they get around on foot or snowmobile, taking full advantage of 24 daily hours of sunlight to peer across blue ice (a "meteorite stranding surface") in search of meteorite specimens.
