APOD: 2026 October 9 – Stickney Crater

Meta Title: Stickney Crater on Phobos: Why Mars’s Largest Moon Has a Giant Scar
Meta Description: NASA’s Astronomy Picture of the Day highlights Stickney Crater, the enormous impact feature on Phobos. Learn how it formed, why it matters, and what it reveals about Mars’s inner moon.
URL Slug: stickney-crater-phobos-mars-moon
Excerpt: Stickney Crater dominates the surface of Phobos, Mars’s larger and innermost moon. Its immense size, unusual grooves, and possible role in Phobos’s future make it one of the Solar System’s most intriguing impact sites.

# Stickney Crater: The Enormous Impact Scar on Mars’s Moon Phobos

NASA’s Astronomy Picture of the Day (APOD) for October 9, 2026 is titled “Stickney Crater,” directing attention to the most prominent feature on Phobos, the larger of Mars’s two small moons.

The source summary identifies the featured object but does not provide the full APOD image caption or image-credit details. What is well established, however, is that Stickney Crater is an enormous impact crater on a remarkably small world. It is a dramatic example of how collisions have shaped the surfaces—and perhaps the long-term survival—of moons across the Solar System.

Stickney is not merely a striking hole in the ground. Its size relative to Phobos raises questions about the moon’s internal structure, the origin of its long grooves, and whether Phobos could eventually break apart as Mars’s gravity continues to pull it inward.

## A crater almost too large for its moon

Phobos is an irregular, potato-shaped moon measuring roughly 27 kilometers (17 miles) across at its widest point. It orbits Mars at an exceptionally low altitude, circling the planet about three times every Martian day.

Stickney Crater is about 9 kilometers (5.6 miles) wide. On a body as small as Phobos, that is a colossal feature. If a comparably proportioned crater existed on Earth, it would span a substantial fraction of the planet’s diameter.

The impact that created Stickney excavated a large volume of material and left steep crater walls, a broad interior floor, and a visual imprint that dominates many spacecraft views of Phobos. The collision was powerful enough that scientists have long considered whether it came close to shattering the moon completely.

Rather than being a solid, uniform rock, Phobos may be a fractured body or a loosely bound “rubble pile” made of broken material held together by gravity. That possibility helps explain how the moon survived such an extreme impact while retaining its overall form.

## Who was Stickney Crater named after?

The crater is named for Chloe Angeline Stickney Hall, the wife of American astronomer Asaph Hall. In 1877, Hall discovered both Martian moons—Phobos and Deimos—while observing from the U.S. Naval Observatory.

The International Astronomical Union, which oversees official planetary naming, approved the name Stickney in 1973. It is a rare and fitting connection between an important astronomical discovery and the person who encouraged the discoverer during a difficult observing campaign.

Phobos itself takes its name from the Greek personification of fear, while Deimos represents dread. In Greek mythology, Phobos and Deimos accompanied their father, Ares—the Greek counterpart of Mars—into battle.

## The grooves of Phobos remain an important clue

One of the most recognizable aspects of Phobos is its network of long, shallow grooves. Many run across the moon’s surface, and some appear to radiate outward from the region around Stickney Crater.

For decades, a leading explanation was that the grooves formed as fractures created by the Stickney impact. In this view, the collision sent stresses through Phobos’s interior, cracking and weakening its outer layers.

More recent research has complicated that picture. Some scientists argue that at least many of the grooves may instead be chains of small pits produced when loose material slid across the surface. Phobos has very weak gravity, so boulders and debris disturbed by impacts can travel long distances. As they move, they may create repeated marks or collapse features in the dusty regolith.

It is possible that more than one process is involved. Stickney’s impact likely altered the moon substantially, while later landslides, secondary impacts, and surface movement may have modified the grooves over time.

This uncertainty is scientifically valuable. Phobos offers a natural laboratory for studying how impact damage behaves on low-gravity objects, including asteroids and small moons.

## Why Stickney matters for the future of Phobos

Phobos is gradually getting closer to Mars. Tidal interactions between the planet and moon are lowering Phobos’s orbit by a small amount each year. Over tens of millions of years, the moon may reach a point where Mars’s tidal forces overcome its structural strength.

Scientists generally expect one of two broad outcomes: Phobos could break apart and form a temporary ring around Mars, or some of its material could eventually fall toward the planet. The exact timing and outcome depend on the moon’s strength and internal composition.

Stickney Crater is relevant because large impacts can leave deep fractures and zones of weakened material. If Phobos is heavily fractured or loosely consolidated, its response to Mars’s tidal pull could differ significantly from that of a dense, solid moon.

The crater therefore provides more than evidence of an ancient collision. It may preserve clues about whether Phobos can endure the gravitational stresses it faces today.

## An unusual target for future exploration

Phobos has been visited or photographed by several spacecraft, including NASA’s Mariner and Viking missions, the Mars Global Surveyor, Mars Reconnaissance Orbiter, and ESA’s Mars Express. These missions have shown a dark, heavily cratered object whose surface is covered in fine dust and scattered boulders.

Yet major questions remain. Scientists do not know with certainty whether Phobos formed from material associated with Mars, whether it was a captured asteroid, or whether its history combines elements of both scenarios.

Japan’s Martian Moons eXploration mission, known as MMX, is designed to investigate Phobos in much greater detail and return samples to Earth. Laboratory studies of that material could help determine the moon’s composition, its relationship to Mars, and the age and history of its surface.

A sample from Phobos might also contain dust blasted off Mars by ancient impacts. That makes the moon a potentially useful archive of Martian material, including rocks that may no longer be accessible on the planet’s heavily altered surface.

## A reminder that small worlds have dramatic histories

Stickney Crater illustrates a basic truth of planetary science: small objects can preserve outsized records of Solar System history.

On Earth, erosion, oceans, plate tectonics, and vegetation erase or obscure many ancient impact sites. Phobos has no atmosphere, no rain, and no active plate tectonics. Its battered surface remains exposed to space, retaining evidence of impacts and slow gravitational change over immense spans of time.

The APOD feature is a useful prompt to look beyond Mars itself. Its moons are not simple satellites in the background of the Red Planet’s story. Phobos, and Stickney Crater in particular, may help researchers understand impacts, rubble-pile physics, orbital evolution, and the eventual fate of planetary moons.

## What is known—and what is not—from the APOD listing

The available source information confirms that NASA’s APOD entry is titled “Stickney Crater” and is dated October 9, 2026. The provided summary does not include the complete explanatory text, the featured image’s mission or telescope, or the specific observation date.

That missing context matters because images of Stickney have been acquired by multiple missions under very different lighting conditions. Regardless of the image source, the crater’s scientific importance is clear: it is the defining impact feature of Phobos and a major target for research into the origin and evolution of Mars’s innermost moon.

## Authority sources (external links):

– [NASA Solar System Exploration overview of Phobos](https://science.nasa.gov/mars/moons/phobos/)
– [NASA’s Astronomy Picture of the Day archive](https://apod.nasa.gov/apod/astropix.html)
– [ESA Mars Express mission and Phobos observations](https://www.esa.int/Science_Exploration/Space_Science/Mars_Express)
– [JAXA’s Martian Moons eXploration (MMX) mission](https://www.mmx.jaxa.jp/en/)
– [International Astronomical Union Gazetteer of Planetary Nomenclature](https://planetarynames.wr.usgs.gov/)

## Internal links (ProductVortex):

– Suggested anchor text: **How Mars became the Solar System’s most studied planet**
– Suggested anchor text: **Phobos and Deimos: the strange moons of Mars explained**
– Suggested anchor text: **What asteroid