Two parallel lines across an ocean moon
Processed image. Galileo photographed these intersecting ridges on 2 February 1999 during E19, at 90 metres per pixel. Near-infrared, green and violet exposures form this enhanced-colour view; north points towards the lower left. The large curved ridge may reflect changing tidal forces, but its apparently steep edges do not give a measured slope. This 603 × 433-pixel archive product preserves the published view, without adding detail through enlargement.
NASA/JPL image-use policy · credited mission imagery; resized to WebP
· Original image source · Image licenceDouble ridges create an intricate record of crossings.
- World
- Europa
- Case date or period
- Galileo’s ridge observations
Look closer
Europa’s ridges intersect and sometimes overprint one another. Close views reveal that a simple line at low resolution can become a pair of raised structures with a trough between them.
Follow the evidence
Look for interrupted ridges and continuous ridges at intersections. Relative order is something images can help establish even when the exact mechanism that built each structure is uncertain.
An Earth analogue makes a testable proposal
Riley Culberg, Dustin Schroeder and Gregor Steinbrügge studied a Greenland double ridge using ice-penetrating radar and elevation observations from 2015–2017. Refreezing water trapped near the surface pressurized and fractured the ice, raising two crests. They proposed a related mechanism for Europa, while emphasizing that it is one hypothesis among several. Greenland’s surface melt supplies its water; Europa would need another source, such as water injected upward through fractures. Similar geometry supports an analogue, not direct proof of a lake beneath each photographed ridge.
Trace a crossing before explaining its origin
The E19 photograph adds curved ridges to the straight doublets. Follow each line through an intersection before comparing its shape with the Greenland proposal. The published colour view combines filter exposures, while the wider plains composite also combines different encounter dates; neither is a movie of a ridge being built.
Sources & further reading
- Prominent Doublet Ridges on Europa — NASA / JPL; original mission product metadata
- Dark and Bright Ridges on Europa — NASA / JPL; original mission product metadata
- Double Ridges, Dark Spots, and Smooth Icy Plains on Europa — NASA / JPL; original mission product metadata
- Scientists explain formation of abundant features on Europa — Culberg, Schroeder and Steinbrügge (2022) — Stanford / original investigator research account
- Cracks and Ridges on Europa — E19 observation, 2 February 1999 — NASA / JPL; original mission photograph metadata