Grooves across a battered little moon
Processed image. The second HiRISE observation on 23 March 2008, within ten minutes of the first, from about 5,800 kilometres. Blue-green, red and near-infrared channels are combined; this is processed camera colour, not a mineral map. Native sampling is 5.8 metres per pixel, with features roughly 15 metres across resolvable in the full source. Stickney’s bluer rim prompted a freshness interpretation by analogy, not a directly measured age. Catalogue PSP_007769_9015.
NASA/JPL image-use policy · credited mission imagery, resized to WebP
· Original image source · Image licenceStickney crater provides a landmark for exploring Phobos’s surface.
- World
- Phobos
- Case date or period
- Camera observations · 1998 & 2008
Look closer
Phobos’s irregular outline, large crater and networks of grooves invite connections between shape and impact history. Orbital views give different perspectives on the same small moon.
Follow the evidence
The colour image is processed; the sharper monochrome frames offer their own view of the relief. Keep geometry and resolution in mind when matching a groove across observations.
Two mechanisms make different predictions
Terry Hurford and colleagues modelled grooves as fractures in a surface layer stretched by changing tides as Phobos moves inward. Kenneth Ramsley and James Head instead simulated Stickney ejecta boulders rolling and bouncing across the irregular moon, producing intersecting tracks and skipped regions. Both approaches compare predicted patterns with observed grooves, and depend on assumed internal structure or boulder trajectories. Neither is a recording of grooves forming. Differences among groove families and their relationships to crater ejecta provide tests; a resemblance to one model does not establish a single origin for every groove.
Two viewpoints, one encounter
Compare the first and second HiRISE views using Stickney’s rim as a landmark. Their changed perspective comes from camera geometry within ten minutes, not measurable groove growth. The older monochrome details belong to the same 1998 observing encounter as each other; they sample the far wall and near-rim terrain. Their native sampling differs from the resized previews. Track specific groove families before comparing rival tidal-fracture and rolling-boulder predictions; colour alone neither dates a surface nor selects a mechanism.
Sources & further reading
- Phobos from 5,800 Kilometers Color — NASA Image and Video Library / JPL
- High-Resolution MOC Image of Phobos Stickney Crater — NASA Image and Video Library / JPL
- High-Resolution MOC Image of Phobos Face — NASA Image and Video Library / JPL
- Tidal disruption of Phobos as the cause of surface fractures — Hurford and colleagues — Original investigator research paper
- Mars moon got its grooves from rolling stones — Ramsley and Head investigation — Brown University / original investigator account
- Phobos · first HiRISE view — NASA Photojournal / credited mission imaging team