A Martian Origin for the Mars Trojan Asteroids

TL;DR

This paper presents evidence that the Mars Trojan asteroids, including Eureka, originated from impact debris excavated from Mars's mantle, supported by spectral analysis and numerical simulations linking them to Martian material.

Contribution

It provides new near-infrared spectral data of Trojans and demonstrates through simulations that these asteroids are likely impact ejecta from Mars rather than captured main-belt asteroids.

Findings

Eureka and two other Trojans have olivine-rich spectra similar to Martian mantle material.

Spectral data supports an achondritic, impact origin for the Trojan cluster.

Simulations favor impact ejecta origin over capture from the asteroid belt.

Abstract

Seven of the nine known Mars Trojan asteroids belong to an orbital cluster named after its largest member 5261 Eureka. Eureka is likely the progenitor of the whole cluster, which formed at least 1 Gyr ago. It was suggested that the thermal YORP effect spun-up Eureka resulting with fragments being ejected by the rotational-fission mechanism. Eureka's spectrum exhibits a broad and deep absorption band around 1 {\mu}m, indicating an olivine-rich composition. Here we show evidence that the Trojan Eureka cluster progenitor could have originated as impact debris excavated from the Martian mantle. We present new near-infrared observations of two Trojans (311999 2007 NS2 and 385250 2001 DH47) and find that both exhibit an olivine-rich reflectance spectrum similar to Eureka's. These measurements confirm that the progenitor of the cluster has an achondritic composition. Olivine-rich reflectance spectra are rare amongst asteroids but are seen around the largest basins on Mars. They are also consistent with some Martian meteorites (e.g. Chassigny), and with the material comprising much of the Martian mantle. Using numerical simulations, we show that the Mars Trojans are more likely to be impact ejecta from Mars than captured olivine-rich asteroids transported from the main belt. This result links directly specific asteroids to debris from the forming planets.