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NASA’s Astronomy Picture of the Day for Nov. 2, 2026, features a 2018 image of the Arsia Mons Elongated Cloud, a water-ice cloud near a Martian volcano. The cloud appears during spring and summer mornings and can extend more than 1,500 kilometers downwind; its formation process remains uncertain.
NASA’s Astronomy Picture of the Day for Nov. 2, 2026, features a 2018 image of the Arsia Mons Elongated Cloud, a water-ice cloud that forms near a large Martian volcano and can trail more than 1,500 kilometers downwind. The daily feature describes when the cloud appears and outlines what scientists still do not know about how it forms.
The cloud, commonly called AMEC, has been observed near Arsia Mons. NASA’s account says it was first recorded by the Viking Orbiter 2 in 1977, and that ESA’s Mars Express spacecraft has since imaged it in greater detail. The picture selected for the Nov. 2 feature was taken in 2018; the APOD page credits ESA, the German Aerospace Center, Freie Universität Berlin and image processor J. Cowart.
According to NASA’s explanation, AMEC forms during Martian spring and summer, and only in the morning hours. It is made of water ice. After it develops near the volcano, winds carry it downstream, producing the long tail that can exceed 1,500 kilometers. The description does not give a specific measurement for the cloud in the featured 2018 image, so the maximum stated length should not be read as the length shown in that picture.
The mechanism behind its formation remains unresolved. NASA says the familiar process in which ice crystals form around dust particles would not work under the conditions high in the Martian atmosphere, described as thin and lacking dust. The leading speculation is that dust is not involved; the APOD account presents this as a hypothesis, not a settled explanation.
Why the Cloud’s Formation Matters
AMEC offers researchers an unusual case for studying how water-ice clouds form in Mars’ thin atmosphere. Its recurring seasonal and morning pattern, combined with its great length, gives scientists observable features to investigate. But the NASA account does not announce a new discovery or a resolved theory: the value of the image is that it highlights a persistent atmospheric puzzle.
NASA says improved understanding of AMEC may contribute to a more complete view of cloud formation on Earth. That is a possible scientific benefit, not a demonstrated direct application. Comparing cloud processes across planets can help researchers test which mechanisms may operate under different atmospheric conditions, while the specific explanation for this Martian cloud remains open.
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From Viking Orbiter to Mars Express
The Nov. 2 entry is part of NASA’s Astronomy Picture of the Day, a daily feature that pairs an image or photograph of the universe with an explanation written by a professional astronomer. In this case, NASA revisits a cloud known for decades rather than reporting a new observation. The history given on the page begins with its first recording by Viking Orbiter 2 in 1977.
Later observations by ESA’s Mars Express provided more detailed images, according to NASA. The featured image is from 2018, not a newly captured view from the publication date. NASA’s page credits the image to ESA, DLR and Freie Universität Berlin, with processing and licensing credited to J. Cowart. The source does not provide the exact date of the 2018 observation or describe the imaging instrument.
The Cloud’s Formation Remains Unsettled
NASA’s account does not identify a confirmed process that creates the cloud’s ice crystals. It says the familiar dust-related explanation would fail because the upper Martian atmosphere is thin and has little dust, then describes a dust-free origin as speculation. The feature does not provide a proposed alternative mechanism or report evidence that conclusively rules out every role for dust.
The page also gives no new measurements of the 2018 cloud, no precise account of how often it appears, and no forecast for when a further observation will be published. Its statement that AMEC can extend more than 1,500 kilometers describes the cloud’s possible reach, not necessarily the particular image featured on Nov. 2.
Further Observations of AMEC
NASA says efforts to understand Arsia Mons Elongated Clouds will continue, but its APOD entry does not name a scheduled mission, experiment or release date. Further observations would be needed to examine the cloud’s seasonal and morning appearance and test explanations for how water ice forms in the sparse, high atmosphere.
For now, the Nov. 2 feature presents a previously observed Martian phenomenon and summarizes the questions it raises. The next concrete milestone is not specified in the source; readers should distinguish any future findings from the current, qualified suggestion that dust may not be involved.
Key Questions
What is the long cloud on Mars?
It is the Arsia Mons Elongated Cloud, or AMEC, a water-ice cloud that forms near the Martian volcano Arsia Mons and is carried downstream by wind.
How long can the cloud become?
NASA’s APOD explanation says its tail can extend more than 1,500 kilometers. The page does not say that the cloud in the featured 2018 image reaches that length.
When does AMEC appear?
NASA says it forms during spring and summer on Mars and appears only during morning hours.
Do scientists know how it forms?
No confirmed mechanism is given in the APOD account. NASA says the usual dust-related cloud-crystal process would not work under the described upper-atmosphere conditions, and that a dust-free explanation is speculation.
Is the featured image new?
No. The image featured on Nov. 2, 2026, dates to 2018. NASA’s page says the cloud was first recorded by Viking Orbiter 2 in 1977 and later imaged in greater detail by Mars Express.
Source: science.nasa.gov
