Heavy Metal, and ESA M7 mission proposal

The ESA M7 Heavy Metal mission proposal is presented. The mission will provide detailed and ambitious science investigations to characterize the large M-class asteroid (216) Kleopatra and its two moons, and perhaps explore 1 or 2 additional M-type asteroids with the same mission.

The main goals of Heavy Metal, apart from characterising (216) Kleopatra with a broad science investigation, are to address the following specific science questions:

• What is the origin and evolutionary history of metallic (M-class) asteroids?
• Are the M-class asteroids the parent bodies of magnetized iron-nickel meteorites?
• Are the M-class asteroids the collisional remains of early protoplanetary dynamos?
• How does the potentially unique space environment around M-class asteroids work?
• How do contact binary asteroids form and evolve?
• What is the nature and origin of asteroid satellites?

The proposed investigation therefore provides a unique window into the early epochs of our solar system.

Our proposed mission profile allows a complete characterization of (216) Kleopatra. The combination of electromagnetic and gravity field (radio science) mapping by two spacecraft provides insight into its internal structure. Remote observations of the surface made in the visible, IR, UV, and radar wavelengths by the Main-craft will complement this by providing a geological context for the origin of any magnetization and its cause. We will address the possibility of remnant magnetization occurring in localized regions, or otherwise being ‘disordered’, by making electromagnetic and plasma measurements close to the surface to identify and remove space environment magnetic field variations.

Figure: Possible crustal field configurations of remnant magnetization, providing information of the evolutionary history of the magnetized material, as well as creating the magnetospheric structures around the asteroid.

A close approach (<10 km to the surface) with the main S/C is difficult, at least at the beginning of the orbital phase, due to the potentially complex gravity field and rapid rotation period of 5.4 hours of the irregularly shaped asteroid. We propose instead to use one Sub-craft to be inserted into a lower-altitude orbit for a duration of a month before the Sub-craft makes a controlled crash on the surface. This will facilitate near surface measurements of the electromagnetic and gravity fields, the composition of any volatile products ejected from the surface and produce truly high-resolution pictures of the surface, complementing the remote observations by the main S/C further away (20-200 km TBD). Additionally, simultaneous measurement of the space environment, including the electromagnetic fields, at both the Sub-craft and Main craft will allow a detailed study of the solar wind electromagnetic variations, and the induction of electrical currents in the partly conductive asteroid surface by the solar wind.

The Sub-craft is suggested to be released from low altitude orbit from the Main craft while having an estimated distance of < 200 km from the (216) Kleopatra surface. The Sub-craft will do flybys of the two moons, and approach (216) Kleopatra while doing science measurements and transferring data to the Main-craft. We hope to reach within a km from the surface of the two moons. At the end the Sub-craft can impact the polar surface of (216) Kleopatra.

High resolution hyperspectral imaging on a close flying Sub-craft will also be able to resolve cm-sized structures. This imaging will help us to decipher the grain size of the minerals, their textures, and the degree of brecciation of the surface to get a comprehensive interpretation about the nature of the regions spectroscopically analysed. These will allow us to determine if the asteroid is composed of relatively homogeneous iron- or rocky-iron-like materials, or more complex products of collisional gardening associated with chondritic impactors. The comparison of the detailed surface geology investigation by Heavy Metal with the terrestrial meteorite record will address the possible connections between metallic meteorites and the M-class asteroids. This investigation with a combined Main-craft and a Sub-craft will give a meaningful investigation for the cosmogony of this type of asteroids, and their relationship to meteoric magnetism. Likewise, an investigation of the composition, geology, and magnetization of the two sizable moons will give information regarding their origin, if coming from (216) Kleopatra or being captured.