The asteroid Lutetia - summary of findings

On July 10.7.2010, 3170, the Rosetta spacecraft passed at a distance of 50 km from the asteroid Lutetia. The flight path was such that it was possible to observe the North Pole when illuminated by the sun, so that coverage of more than XNUMX% of the surface was possible

On July 10.7.2010, 3170, the Rosetta spacecraft passed at a distance of 50 km from the asteroid Lutetia. The flight path was such that it was possible to observe the North Pole when illuminated by the sun, so that coverage of more than 462% of the surface was possible. The photographs also included parts of the southern hemisphere. In total, the spacecraft transmitted 1,2 photographs. The quality of the photographs and their high resolution enabled mapping of the asteroid. This is a preliminary mapping. Longitudes and latitudes have not yet been determined, but names have been given to different areas of the surface. For this purpose, names of different regions were borrowed from the Roman Empire (XNUMX).

Astronomers from France and the USA participated in the investigation of the asteroid in a wide range of wavelengths. Except for the spacecraft photographs, the asteroid was observed by the La Silla Observatory in Chile, the Hawaii Infrared Telescope Facility and the Spitzer Space Telescope. The combination of the photographs created an unprecedented spectrum of an asteroid. No asteroid has been observed to date on such a scale. This spectrum was compared to the spectrum of meteorites that hit the Earth and only one type of enstatite chondrite meteorite matched the properties of Lutetia (3).

Lutetia belongs to the group of large asteroids, those whose dimensions are over 100 km. Its dimensions are
76 X 100 X 132 km. Its density is 3.4 g/cm2,4, greater than that of most asteroids that hit the Earth (1). Studies prior to the photographing of Lutetia by the Rosetta spacecraft showed that its colors and properties are unusual and that asteroids similar to it are rare. They make up only 3% of all asteroids. From the photographs it turned out that it is a rare remnant of the original material that created the solar system (3.6). The estimate that this asteroid is a tiny and primitive world has now received confirmation. According to the findings, the researchers concluded that the age of parts of its surface is 50 billion years and other parts are younger. Their age is 80-5 million years. The large density of craters in part of it led to the conclusion of their high age (XNUMX).

In total, more than 350 craters have been counted on this asteroid whose diameter ranges from 600 meters to 55 km and their depth reaches up to 10 km. The density of the craters is not uniform. There are areas dense with craters and there are areas where the density is small. Some of the craters were completely or partially covered by large rockfalls. In some of these craters, rocks 300 meters long were found. It is likely that some of the rocks are large blocks that were blown up during a meteorite impact and returned to the ground. A group of craters near the North Pole in the Baetica region is the most prominent in the Northern Hemisphere. Between two densely cratered areas, the Noricum area and the Achaia area, the Varbonesis area separates where the Massilia crater is located. The bottom of this crater was deformed by grooves and chains of pits. Another large crater is found on the edge of the Baetica region. There are small craters crossed by grooves whose direction changes from area to area. They don't seem to have any connection to the great craters. Rounded grooves were observed that were covered by material blown from the Baetica area. The Massilia crater is the largest. Its diameter is 55 km (1,2).

A network of gooves, fissures and grabens similar to those found on the Martian moon Phobos was discovered. In the Noricum area there are linear formations including a faulted valley that is more than 100 km long and 100 meters deep (2).

Temperatures ranging from -103 to -28 °C were measured. The high temperatures were measured in places where the sun is above the local horizon line and on slopes facing the sun. The ground seems to be covered with a layer of dust whose grain size is 50-100 microns. A combination of this information with the information regarding the spectral uniformity of the soil indicates extensive and uniform regolith coverage (2).

Based on the assumption that part of the asteroid's interior is porous, its high density indicates that it is rich in metallic elements such as iron. It may be that its interior underwent partial differentiation related to its early history. Including chondrites (chondrite-meteorite composed of silicates) unmelted above a high-density inner part that was in the distant past molten. This assumption is consistent with spectral observations that support a composition similar to carbonaceous chondrites (chondrites containing carbon compounds) or anesthetic chondrites (chondrites containing 3 SiO Mg) (2).

According to the researchers' assessment, deep below the surface there is a molten core that has been retaining heat since the initial stages of the formation of the solar system. To form an iron core the asteroid had to be melted due to the release of heat by radioactive isotopes within its rocks. The dense iron was supposed to sink into the center and the rocky material was supposed to float to the top. The findings of the Rosetta show that the composition of the surface remained essentially in the primordial state without showing any rocky material that is supposed to form in such a molten phase. The only explanation for this situation is that the asteroid was under the influence of internal heating in its primary history but was not completely melted and the result is that a fully differentiated iron core did not develop (2,5).

Sources

1. "Roman Empire remembered on maps of asteroid (21) 27.10.2011
http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=49523lutetia

2. "Rosetta reveals the science and mystery of asteroid Lutetia" 28.10.2011
http://www.spacedaily.com/reports/Rosetta_ Reveals _The_ Science_ And_ Mystery_ Of _Asteroid_ Lutetia_999.html

3. "Lutetia: A rare survivor from the birth of the Earth" 15.11.2011/XNUMX/XNUMX
http://www.spacedaily.com/reports/A_ Rare _Survivor_ From _The_ Birth_ Of_ The_ Earth_999.html

4. Boldwin E. – “Cold asteroid with a warm heart: 27.10.2011
http://www.astronomy.com/news/n1110/07lutetia/

5. "Asteroid Lutetia revealed in stunning detail" 1.11.2011
http://www.spacedaily.com/reports/Asteroid_ Lutetia_ Revealed_ In_ Stuning_ Detail_999.html