Professor of Mathematics

Paata Ivanisvili

Department of Mathematics, University of California, Irvine

Candidate 16: Medusae Fossae Formation, south of Amazonis Mensa

Strong · roughly 80%

Two CTX close-ups of the same 600 by 600 m of wind-carved ground south of Amazonis Mensa, from April 2012 and July 2025, under a similar sun. A compact dark spot at the arrow is present only in the 2025 image. — The same 600 × 600 m in April 2012 and July 2025, under a similar sun. The arrow marks the new spot. NASA/JPL-Caltech/MSSS.

What changed. A compact dark spot about 45 by 30 m appeared on the wind-carved ground of the Medusae Fossae Formation, south of Amazonis Mensa, between April 2018 and November 2022. It is still there in July and November 2025.

Why it may be a new impact. Images from 2008, 2012 and April 2018 show nothing there, and each of them would have shown it. The spot is in three images from three orbits, with the sun between 33 and 60 degrees from overhead, so it is neither a shadow nor a camera glitch. A new compact dark spot that lasts for years is what a small fresh impact leaves.

Location: 6.744° S, 214.884° E (145.116° W)
Absent: 16 August 2008, 6 April 2012 and 20 April 2018
Present: 12 November 2022, 31 July 2025 and 7 November 2025
Size: Compact dark spot about 45 × 30 m
Confidence: Strong candidate; roughly 80% that it is a new impact.
Caveat: The ground is soft, wind-eroded rock, so wind stripping the dust to expose darker rock remains possible; that is why the confidence is lower. It first shows in a 2022 image, so the camera teams may already have it on their unpublished lists; but it lies outside every footprint of the high-resolution HiRISE camera, and the teams normally photograph a new impact with HiRISE within months of noticing it. Like every candidate here, it is unconfirmed: see the caveat.

Six CTX images of the same 2 by 2 km patch, from 2008 to 2025, two of them blank. An arrow points to the spot, absent in 2008 and 2012 and present in both 2025 images. — All six CTX images of the same 2 × 2 km patch, 2008 to 2025. The April 2018 and November 2022 panels came out blank; the November 2022 image does show the spot, as the independent check below shows. NASA/JPL-Caltech/MSSS.

A 12 by 12 km CTX view from July 2025 of the wind-carved ground around the spot, with a dashed box around the 2 by 2 km patch and an arrow at the spot. — A 12 × 12 km view from July 2025. The dashed box is the 2 × 2 km patch. NASA/JPL-Caltech/MSSS.

The independent check: three columns of the same ground, 2 km wide above and 600 m wide below, with yellow ticks around the spot. The spot is missing in the earlier image, marked BEFORE, and present in the two later images, marked AFTER. — **Independent check.** A second, deliberately sceptical review downloaded every image again and found that the candidate passes every test. Each column is the same ground, north up, 2 km wide above and 600 m wide below. Columns marked BEFORE are earlier images in which the spot would have been visible had it been there; those marked AFTER show it. Each image keeps one contrast stretch in both rows, so the close-up cannot create a spot. NASA/JPL-Caltech/MSSS.