Sat 29th Nov

Are Recent Gullies on Mars Formed by Water? New PGR blog post!

Are Recent Gullies on Mars Formed by Water?

Blog post by Varsha Natarajan, PhD Researcher, Ulster University

Our recent study investigates how gullies form and evolve in a mid-latitude crater on Mars, offering new insights into the planet’s recent climate and the possible role of water and ice.

The Penticton Crater (38.35° S, 263.35° W) is an 8 km wide impact crater in the Hellas region of Mars. Unlike many other mid-latitude craters where gullies are found mainly on slopes that face the poles, Penticton contains gullies on its north, north-east and south facing crater walls (Fig. 1). This unusual distribution hints at a more complex set of surface processes.

Fig 1: Geomorphological map of Penticton crater showing different types of gullies based on Auld and Dixon (2016) classification overlaid on CTX image: B07_012223_1413_XI_38S263W. The arrow indicates the north direction.

A detailed examination of the crater interior revealed several features that point to a glacial origin (GLF), especially in the pole-facing slope. Strong geomorphic evidence suggests that the crater once hosted the Latitude Dependent Mantle (LDM), a mixture of dust and ice that accumulates during high obliquity periods (Fig. 2). Previous studies have shown that many Martian gullies cut into ice rich deposits, which supports the idea that this mantle once covered the slopes inside Penticton. Mars experienced a major obliquity shift around 5 million years ago, decreasing from about 35° to the current value of about 25°. During high obliquity, snow and ice accumulated at mid-latitudes. When obliquity decreased, this stored ice began to sublimate, leaving the surface material unstable. This shift is believed to have produced paraglacial features, including gullies. Penticton Crater is relatively very young and is around 5.5 million years old, placing it within this exact climate transition period.

Fig 2: Boundary of glacial features in Penticton crater on CTX image (B07_012223_1413_XI_38S263W). The blue outline marks layers of LDM flowing into the crater, the green line demarcates the glacial features inside the crater, and the red line represents the uneroded and sharp crater boundary. The arrow points towards the north.

On the equator-facing wall, the study identified typical examples of alcove-apron features and linear gullies. Alcove-apron systems do not contain well defined channels, which indicates formation by dry mass wasting rather than flowing water. Linear gullies, which are narrow and elongated with very small aprons, commonly form on dunes through dry granular processes. In addition, the equator-facing slopes have apex slopes between 21° and 32°, which further supports a dry origin (Fig. 1).

These results reveal that two different gully forming processes were active within the same crater.

  • The pole-facing slopes likely accumulated snow and ice during high obliquity. Later, basal melting followed by sublimation destabilised the loose surface material and helped carve the gullies.
  • The equator-facing slopes, which lacked ice-rich mantling, developed gullies through dry processes such as carbon dioxide frost removal, thermal stress or possibly seismic activity. The exact trigger could not be finalized because of the limited mineralogical data.

The morphometric parameters of the gullies do not exhibit any seasonal variations, and they are now inactive.

Acknowledgements:

Varsha would like to thank her co-authors, Kusuma K N and Lekshmi Nandana, for their valuable contributions to this work. This study was conducted as part of Varsha’s master’s thesis at Pondicherry University, India, and was later published in the Elsevier journal Planetary and Space Science.

 

~ Edited by Adam Hartley, 29th November 2025