Meteorites
Definition
A meteorite is a body of space debris that enters the atmosphere of a planet and survives the friction with surrounding atmospheric gases to impact the surface energetically. Impact causes planetary cratering, ejecta and dust (forming a layer of regolith on planets with low geological activity such as Mars). This poses an obvious risk to life on the surface of Earth, but due to the tenuous atmosphere of Mars, smaller debris have the greater chance to impact the Martian surface.
Observations of Meteorite Impacts on Mars
[Image:Moc_impact.jpg|thumb|right|200px|Mars Global Surveyor images of the same site in 1999 and 2006 - Impact from meteorite is obvious.]
On January 9, 2006 the Mars Global Surveyor MOC science operations team came to the realization that their camera (used primarily to map the Martian surface) may be able to locate and characterize fresh impact craters on the surface of Mars. Such a survey would provide useful information about the current meteorite impact rate. This survey would be the first of its kind ever carried out on a Solar System body (including the Earth-Moon system) due to the unprecedented number of high resolution cameras inserted into Mars orbit.
In results gathered on January 6, 2006, the MOC had acquired a new feature on the Martian surface in Arabia Terra in one of its images. The feature was circular and very dark. At the time, the camera was capturing images at a resolution of 240 meters/pixel, so there were some ambiguities as to what the blurred feature was. The team began exploring the possible scenarios, but after proving shadows of the two moons, Phobos and Deimos were not to blame, they quickly realized that something in the area was new when compared with images taken by Mariner 9 (in 1971) through to the Mars Express mission (in 2003). There was still the possibility that the dark circular object may have been caused by the removal of sand and dust due to high winds in the region so better observations had to be carried out.
To increase the resolution in the images, a technique known as Roll-Only Targeted Observation (ROTO) was employed. This massively improved the images for analysis, the new resolution registered at 1.5 meters/pixel allowing the team to see the main impact crater and several smaller craters arcing away from the large dark spot. Another observational technique – compensated Pitch and Roll Observation (cPROTO) – was used to improve the images further until the evidence was indisputable. A fresh impact crater had been discovered.
Mars Odyssey's THEMIS instrument and Mars Express' High Resolution Camera (HRSC) were able to provide supplementary observations of the area to constrain the impact date to some time between November 12, 2004 and January 6, 2006. Since this first discovery in January 6, 2006, another 20 new impact craters have been discovered by the MOC.
Meteors
Meteorites should not be confused with meteors however. Debris that is too small or too light to survive friction with surrounding atmosphere will burn up very quickly, not reaching the planetary surface. Known as meteors, they are short-lived and will emit a flash of light as they burn. Terrestrial meteors are also known as shooting stars.
