How do the surfaces of airless bodies in the Solar System evolve?

Feb. 9, 2026 | Aerospace Project Research Associate, ISAS people

Antonin WARGNIER / Dept. of Solar System Sciences

This article introduces the research of Aerospace Project Research Associate at the Institute of Space and Astronautical Science (ISAS). The Aerospace Project Research Associate program is a development opportunity for early-career scientists who aim to hone their research skills through participation in JAXA projects. This program places a strong emphasis on ISAS's unique approach to developing research capabilities.

Research Summary

My research focuses on the evolution of the surfaces of bodies without atmospheres, with the goal of understanding, more generally, how the Solar System evolves. Understanding the evolution of the Solar System is particularly important for understanding the process of formation of the planets and their moons. It may also help to understand the emergence of life on Earth, through the study of the evolution of water and organic matter in the Solar System.

Up to now, I have mainly worked on three small bodies: Phobos, Deimos, and Ryugu. Phobos and Deimos are the two Martian moons, and are the targets of the next JAXA mission, the Martian Moons eXploration (MMX) mission. Despite not being properly small bodies such as asteroids, the two moons share many similarities with primitive asteroids, such as spectroscopic*1 and photometric*2 properties, density, shape, and small size. On the other hand, Ryugu is a primitive asteroid explored by the JAXA Hayabusa2 mission between 2018 and 2019, which also brought successfully a sample from the asteroid surface to Earth in 2020.

Figure 1
Fig. 1: Images of the two Martian moons, Phobos and Deimos, taken by the HiRISE instrument onboard Mars Reconaissance Orbiter (MRO). The blue and red unit on the two moons are defined by variations of the spectroscopic and photometric properties, which may be due to surface alteration. Background image credit: NASA/JPL-Caltech/UArizona.

To understand the evolution of the surface of an airless body through remote-sensing observations, one way is to look at different regions of the surface, such as landslides or craters. For example, for the two Martian moons, I was mainly interested in understanding the reasons for the spectroscopic differences between the so-called “blue” and “red” units (Fig. 1). These two regions are of particular interest in helping to decipher the origins of Phobos and Deimos. Craters also give important information about the surface evolution because their interiors generally expose less altered materials, while the exterior is covered by more evolved material. The surface of airless bodies can be altered by many processes, such as charged particles from the solar wind or micrometeorites bombardment, that can modify the chemical, mineralogical, and textural (such as porosity, grain size, and roughness) properties. To study these effects, I used images and reflectance spectra acquired by spacecraft in the visible and near-infrared wavelength range, and looked at the variations between crater interior and exterior to understand how the surface texture and surface composition varies between the different regions (Fig. 2).

Figure 2
Fig. 2: A crater on Ryugu and the associated footprints from the NIRS3 spectrometer onboard Hayabusa2, from different altitudes over the crater. NIRS3 is used to derive spectroscopic properties at different spatial resolutions in the interior of the crater and, finally, to assess the composition and physical properties of the surface in this region. Background image credit: JAXA, University of Aizu, University of Tokyo, Kochi University, Rikkyo University, Nagoya University,_Chiba Institute of Technology, Meiji University and AIST.

To better constrain the alteration of surface materials, I also perform laboratory experiments to simulate the process of irradiation by particles from the solar wind, using particle accelerators on analogue samples, and study afterwards the modifications using visible to mid-infrared spectroscopy and microscopy. My goal is to finally link results obtained through laboratory experiments and results from spacecraft observation.

In addition, I am also involved in MMX and Hayabusa2# projects. For the MMX project, I am contributing to the operation planning of the MIRS spectrometer and prepare the future data analysis. For the Hayabusa2# project, I help prepare data analysis and data archiving for the various mission phases, with a view on the flyby of the asteroid Torifune in July 2026. It is particularly exciting to be working on these projects at JAXA in such a stimulating environment.

Terminologies

  • *1 Spectroscopy : Reflectance spectroscopy measures how much light a surface reflects at different wavelengths to obtain its reflectance spectrum and study the composition and mineralogy of planetary surfaces.
  • *2 Photometry : Photometry study how the light interacts with the surface in different viewing or illumination conditions. By analyzing the brightness variations, we can infer physical properties such as surface roughness, texture, and particle size.

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