Definition
An M-type asteroid is a category of asteroids whose main composition is metallic. These bodies are identified by their spectra showing an abundance of iron, nickel, and sometimes heavy elements. They belong to the differentiated asteroids, evidencing a separation between metal and silicates during formation.
Composition
The primary material consists of iron-nickel alloys, with possible traces of cobalt, iridium, and other metals. The surface shows medium reflectivity, indicating the absence or scarcity of silicate minerals. Oxidation and space weathering sometimes alter the metallic shine.
Internal structure
These asteroids are often interpreted as remnants of metallic cores of ancient protoplanetary bodies that fragmented. Their interior is presumed dense and homogeneous, dominated by crystallized metal. The original silicate crust may have been partially or completely lost during collisions.
Dynamic functions
Due to their high density, these asteroids follow stable trajectories influenced by strong gravitational forces. Their mass provides significant inertia, and their metallic properties allow them to reflect radar signals, facilitating detectability.
Evolution
The evolution of M-type asteroids is marked by erosion caused by impacts and solar radiation. Over time, their surface may darken, though the internal structure remains metallic. These objects represent archives of early planetary differentiation.
Limitations
Precise knowledge of their composition relies on spectroscopic and radar observations, but the lack of direct samples limits the understanding of the exact proportions of metals and minor elements. Their classification may sometimes be confused with that of other highly reflective asteroids.