The Flybys of Asteroids 2867 Steins, 21 Lutetia, and 4179 Toutatis

Abstract

Three flybys of asteroids have occurred in the period between 2008 and 2012. (2867) Šteins and (21) Lutetia have been observed by the European Space Agency's Rosetta spacecraft, and (4179) Toutatis was observed by the Chinese National Space Agency's Chang'e-2. The properties of these three bodies are very different from other asteroids visited to date. Šteins seems to have been subject to a combination of various processes, including collisions and significant reshaping as a result of rotational forces (the YORP effect). Lutetia has a high density, which has led to speculation that it is a partially differentiated body. Images display a surface with complex morphology exhibiting different structures: pits, craters, crater chains, scarps, and vast younger terrains have been observed. The shape of Toutatis shows two major lobes, suggesting a contact binary object. A comparison with data obtained by previous asteroid flybys is presented. Limitations of flyby results, in particular interpretation of the composition, are also discussed.