Slope Lineae as Potential Geologic Markers of Recent Devolatilization on Mercury

Slope lineae are bright, elongated streaks on Mercury’s slopes. Along with hollows, lineae are considered one of the youngest geologic features on Mercury. Past surveys suggested a qualitative relation between lineae and subsurface volatiles, implying that lineae could be geologic markers of the recent – and potentially ongoing – release of subsurface volatiles on Mercury. However, lineae have not been systematically mapped across Mercury and no quantitative analysis of their abundance, distribution, and geostatistical properties has been conducted. In [1], we use a deep learning-driven approach to scan through ~112,000 MESSENGER images and catalog slope lineae across Mercury to a) characterize their spatial distribution as well as their morphometric and spectral properties and b) use geostatistical and change detection approaches to explore whether lineae are active today – and whether they could be tied to recent or ongoing devolatilization on Mercury. Our analysis presents several arguments for a direct link between lineae formation and devolatilization: 1) lineae appear to feature a blue spectral slope, like hollows, 2) lineae largely source from hollows and hollow-like features, 3) lineae are predominantly hosted by small, young impact craters that penetrated volcanic deposits, i.e., in a geologic context that facilitates (vertical and lateral) access to subsurface volatiles, 4) lineae tend to cluster on equator-facing slopes, 5) lineae appear to be hosted by terrain with slightly higher (modelled) bi-annual peak temperatures at the surface and at shallow depth, and 6) several lineae occur on shallow slopes well below the angle of repose of dry regolith, suggesting the presence of volatiles as a fluidizing agent (more details are presented in [1]). We do not observe any lineae activity between 2011 and 2015, such as changed or newly formed lineae, implying that lineae activity occurs below MESSENGER’s spatial resolution and/or on timescales longer than ~4 years. Devolatilization-driven lineae activity is a hypothesis that will be scrutinized by the ESA/JAXA (European Space Agency, Japanese Aerospace Exploration Agency) BepiColombo spacecraft and the SIMBIO-SYS instrument suite (Spectrometer and Imaging for MPO BepiColombo Integrated Observatory SYStem) that are expected to initiate their science investigations in early 2027.

 

[1] Bickel et al. (2026). Slope lineae as potential indicators of recent volatile loss on Mercury. Communications Earth & Environment (in press).