The Impact

Credit of the illustration: European Space Agency – ESA .

At this point, the spacecraft weighing about 285 kilograms - 200 kg of aluminum in its body of 1m3, 3 kg of N2H4 hydrazine, 0,26 kg of Xenon, epoxi, two solar carbon fiber panels and solar stacks AsGa with 6.5 meters each, will slam against the lunar surface at a speed of 7200km an hour, in a descending oblique angle of only 1 degree in an ascending inclination of 2.5 degrees, originating a lengthened crater (similar in format to the ones of Messier A and B) with a size of between 5 to 10 meters.

The kinetic speed of the SMART-1 spacecraft will be lower than the speed of a 1kg meteorite, which reaches the Moon in natural speed of 144.000 km/h or, even lower than the speed of the most massive lunar modules which slammed during the Apollo missions. Due to this low speed and the obliquity of its orbit, its effects will be even more localized.

The adopted models foresee that the resultant flash of the impact will last for only 20 Milliseconds approximately.

The kinetic energy will be of about 600 MJ, and the depth of penetration might be of about one meter. The thermal magnitude of the flash would reach 7.4 if half of the kinetic energy were converted into heat. Anyway, for the adopted model of a 2km speed prediction, an estimated magnitude around 16 will be more realistic (Koschny and Gruen, Koschny 2006).

A volume of 10 to 80m3 of excavated material is expected to result of this impact – 80% lighter and colder, constituted basically of dust of about 15 microns in size (normalized by area) – will be ejected and will be extended through a 25km square area, which will result in a complete darkening of the reached surface and will result after the first minute in signals of partial darkening.

This material, in its totality, is expected to be observed by the reflection of the Earthshine with a magnitude of around V=17 by square kilometer, therefore, only accessible to big instruments. Smaller telescopes will detect only additional brightness the reached area, which due to its raised albedo, will have an additional magnitude of around 13 to 14.

With the normal component of the speed in the order of 130 m/s, it is expected that a small amount of the ejected material (about 1%) may have a vertical speed higher than 280 m/s, which will be sufficient to reach the solar light and become visible. That corresponds to a 100-degree angle of solar phase with a V=11.5 magnitude or smaller , therefore, more easily detectable by the small telescopes. [To see the item: The Observations.]

The lack of more precise data of the lunar topography (the used topographical information has a grid of only 1 kilometer, captured by the Clementine Spacecraft, of the Science and Technology Operations Centre - STOC) also allows the possibility of occurrence of the impact either in the previous orbit or in the subsequent orbit calculated for the nominal impact.

This happens because the spacecraft might slam against some high lunar mount of unknown altitude, located in the way of the calculated trajectories or will either move between these mounts, slamming in a posterior orbit.