On Mars, insects are not common, and neither are "butterflies". However, from orbit, we sometimes spot a form that somewhat resembles wings – it is a special type of elliptical crater formed by the oblique impact of a meteorite. When a space rock hits the surface at a very shallow angle, the ejected material does not spread evenly in all directions but spills out into two main lobes, resembling wings extending to opposite sides from the central "body" of the crater. Such structures do not testify to life, but to the dynamics of the impact and how much water and ice were present beneath the ground at the moment of impact.

Where the "butterfly" is located: Idaeus Fossae and the northern lowlands

An example of a "butterfly crater" is noticeable in the Idaeus Fossae region on the northern lowlands of Mars. It is a transitional area on the edge of the Tempe Terra highlands and the vast plains of Acidalia Planitia, intersected by deep, parallel faults and grabens – typical consequences of crustal stress. In such a geological context, a shallow-angle impact shaped an oval depression with two unequal wings of ejected material. The wings are irregular and in places poorly defined, but they are distinguished as slightly raised belts extending from the main rim ring of the crater.

Low-angle impact and "fluidized" ejecta

Why does the ejected material spill out like liquid? The explanation lies in volatile substances, primarily water in the form of ice. The impact releases heat and mechanical energy that melts or pulverizes the ice, so the mixture of dust, sand, and water briefly flows like a mud avalanche. The result is rounded edges and continuous, uniform curtains of ejecta, rather than the jagged blocks we usually see on dry, rocky surfaces. Mars is full of such "fluidized" craters, which indirectly teaches us where and how much ice was beneath the surface at the time of impact.

Mesas, layers, and traces of volcanism

The Idaeus Fossae region itself is interesting even without the crater. It is a network of linear valleys and troughs oriented approximately northwest–southeast. They mark the contact of one of the most faulted parts of the Martian northern highlands – Tempe Terra – with lower terrains towards Acidalia Planitia. The faults were formed by crustal stretching, and subsequent tectonic compression and cooling of the planet's interior left a mark in the form of "folds" known as wrinkle ridges. Such low, long elevations form when surface layers fold under compression; they are often associated with thrust faults hidden beneath the surface.

Rocky elevations with flat tops – classic mesas – also attract attention in the frame. These are remnants of higher plateaus that wind has unevenly worn down over millions of years. Where the layers are more resistant – for example, when cemented by volcanic ash or lava rich in iron and magnesium – upright "table mountains" with sharp, dark stripes on the edges remain. Such layering suggests that the region repeatedly received deposits of ash and thin lavas, then sand and dust, and then volcanic material again. Later erosion stripped these edges and opened a cross-section through the history of the deposits.

Geometry as a clue to impact direction

The geology of the "butterfly crater" also offers a story about the direction of impact. In oblique impacts, the ellipticity of the crater and the orientation of the ejecta lobes point to the direction from which the projectile came. If the "wings" are most pronounced along the north–south axis, the meteoroid likely arrived from an east–west direction, gliding low over the horizon before burying its energy into the substrate. Precise determination of the geometry requires measurement analysis of digital terrain models and high-resolution images, but even a visual impression shows that it is an asymmetry typical of low-angle impacts.

Mars Express and HRSC: how "flyovers" and 3D mosaics are created

Such structures are clearly visible on materials recorded and processed over the last two decades by the European Mars Express mission. Its High Resolution Stereo Camera (HRSC), developed by the German Aerospace Center (DLR) in cooperation with Freie Universität Berlin, enables three-dimensional depictions of terrains and precise measurement of slopes, heights, and layer thicknesses. Through public archives and regular releases, color mosaics, digital terrain models, and "flyovers" over selected areas are available, recreating the experience of flying over the crater and surrounding mesas.

Comparison: the "butterfly" in Hesperia Planum

"Butterflies" on Mars are not an isolated phenomenon. In the southern highlands, above the plains of Hesperia Planum, a large elliptical crater is known whose rims and ejecta lobes are a textbook example of a shallow impact. It shows how the substrate and the amount of ice affect the symmetry of the wings: in dry, harder rocks, the wings are sharper and layer boundaries clearer, while in ice-richer areas, the edges are more spread out and "slushy". Comparison with the example from Idaeus Fossae gives geologists the opportunity to map changes in composition and volatiles from one side of the transition zone to the other.

Tharsis, Tempe Terra, and "wrinkles": the broader geodynamic picture

In the broader picture, the contact between Tempe Terra and the northern lowlands shows more than mere tectonics. It is also the edge of the immense volcanic provinces of Tharsis. Distant supervolcanoes and their prolonged activity over billions of years bent the lithosphere, loaded the crust, and indirectly triggered the creation of fault networks like Idaeus Fossae. When lavas flooded the surface and cooled, contraction and regional compression left "wrinkles". Later, winds stripped the layers, and sand and dust filled the valleys, so the landscape today looks like a tapestry of repeated flows, deposits, and erosional phases.

Why the "butterfly" is important: layers of data that complement each other

Such places are particularly useful because they sum up multiple independent "records": impact structures reveal instantaneous conditions at the moment of impact (e.g., presence of ice beneath the surface), wrinkles speak of long-term tectonic and thermal development, and mesas of the history of erosion and sedimentation. Together, they help reconstruct how Mars cooled, how it lost water and atmosphere, and where underground ice reservoirs survived until the geologically recent past.

HiRISE and details: from "spots" to grooves

In more recent times, alongside HRSC, the role of confirmation and "magnifier" is taken over by high-resolution cameras from other missions, such as HiRISE on the Mars Reconnaissance Orbiter. They nibble at individual details – say, small grooves within crater walls or spotted surfaces where melting ice caused collapse – and thus complement wide-angle mosaics. When all layers of data are piled up, a consistent picture is obtained: on the border of Tempe Terra and the lowlands, around Idaeus Fossae, underground ice and former volcanic activity together shape the terrain, and oblique impacts depict these processes in the form of ejecta "wings".

Glossary for quick checks

Fluidized ejecta: curtains of material that behaved like a thick flow due to mixing with volatiles; in images, it looks like a smooth, continuous blanket with rounded edges and often with multiple "lobes".

Wrinkles / wrinkle ridges: low, tectonic ridges formed by the folding of surface layers under compression; they generally follow the direction of regional stresses and sometimes hide thrust faults underground.

Mesas: flat-topped, steep-sided hills (table mountains) that remain as relief "islands" after long-term differential erosion of layered deposits.

How to read the landscape: a guide for a virtual "flyover"

All this is not just a catalog of exotic terms, but a guide to reading that same reddish-brown surface we have been watching in photos for decades. With new data processing, virtual "flyovers", and three-dimensional terrain models, it is easier than ever to imagine what it would be like to orbit over the "butterfly crater" and its surroundings, trace the transitions from lighter, sandy plains to wrinkled darker belts, or glide along the edges of mesas where dark layers break out into the daylight. Teams processing HRSC data often publish sequences that faithfully convey this dynamic and help scientists and the public "read" the terrain without specialized instruments.

Interactions that shape the "butterfly"

Finally, the "butterfly" in Idaeus Fossae reminds us how common and crucial meteoroid impacts are in shaping Mars, and how important it is to observe them in context. In places rich in ice, the effects are different than in dry rocks; near tectonic boundaries, ejecta flows meet relief that directs and deforms them; above old volcanic plates, erosion is selective and subsequently highlights more resistant layers. From this interaction arises a landscape that, at least at first glance, resembles something familiar and fragile – a butterfly – but is fundamentally a record of the history of ice, fire, and impact in one of the most interesting transition zones of the Martian northern hemisphere.