Monitoring surface evolution of Apophis during its 2029 Earth flyby: the role of HAMLET on ESA's Ramses Mission

On April 13, 2029, near-Earth asteroid (99942) Apophis will make an exceptionally close approach to Earth, passing at a distance of approximately six Earth radii. This rare event offers a unique opportunity to study the effects of tidal forces on a small body during a planetary flyby. The European Space Agency’s Ramses (Rapid Apophis Mission for Space Safety) mission will rendezvous with Apophis and monitor it throughout this encounter.

Apophis is classified as an Sq-type asteroid, spectrally similar to LL ordinary chondrites, with an estimated olivine abundance of 63 ± 3 vol.% [1,2]. Its moderately weathered surface may undergo significant changes during the close approach, including regolith displacement due to tidal forces or spin state alteration [3] .These effects could lead to observable spectral changes, potentially shifting Apophis from an Sq-type to a Q-type asteroid, indicative of fresh, unweathered material [4].

A key instrument aboard Ramses is HAMLET (HyperScout for Apophis MultispectraL Exploration and Taxonomy), a hyperspectral camera designed for detailed surface characterization. It is an advanced version of the HyperScout-H spectral imager, which is currently flying as part of the Hera mission (ESA) (Fig.1) [5].

Fig.1: HyperScout-H current payload volume

HAMLET features a high-resolution CMOS sensors and operates across two spectral channels (Fig.2): Channel 1 (650–960 nm) and Channel 2 (960–1500 nm), providing a wide field of view and high spatial resolutions at the same time.

Fig.2: HAMLET’s CH1 and CH2 on Apophis spectra by Reddy et al., 2018.

This spectral coverage enables precise mapping of surface composition, including modal abundances of olivine, orthopyroxene, and clinopyroxene, and their Fe, Mg, and Ca content. Key absorption features (e.g., Fe²⁺ at ~0.9 and ~1.1 μm; Fe³⁺ in hydrated minerals around 0.7 μm; OH in hydroxylated phases near 1.4 μm) will be analyzed to assess mineralogy and surface maturity.

HAMLET also provides insights into physical properties such as grain size, porosity, and surface roughness. By detecting spectral slope variations and absorption depth changes, the instrument can identify space weathering effects before and after the Earth flyby. Additionally, it will investigate regolith dynamics—such as gardening and mass wasting—revealing how surface processes are modulated by gravity and close encounters.

Overall, HAMLET’s high-resolution, multi-wavelength observations will offer unprecedented data on Apophis’ surface evolution, with broader implications for planetary defense and small body science.

 

References:

[1] Reddy et al., 2018; The Astronomical Journal, 155:140 (8pp)

[2] Binzel et al., 2009; Icarus Volume 200, Issue 2, April 2009, Pages 480-485

[3] Scheeres et al., 2005; Icarus, Volume 178, Issue 1, p. 281-283.

[4] Binzel et al., 2010 Nature, Volume 463, Issue 7279, pp. 331-334

[5] Popescu et al., EPSC2024-586