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Quaoar is one of the so-called trans-Neptunian objects, small planets orbiting beyond the solar system's outermost planet Neptune. Quaoar is a proud owner of its own moon, the 100-mile-wide Weywot. And a recent observation campaign revealed that it also has a ring of material in its orbit. Quaoar's ring is at a very unusual distance from its parent body. In fact, before astronomers discovered Quaoar's ring in observations from several telescopes conducted between 2018 and 2021, they had thought that it was impossible for a ring to exist at such a distance. With a radius of about 2,420 miles from...

Explanation: Stickney Crater, the largest crater on the martian moon Phobos, is named for Chloe Angeline Stickney Hall, mathematician and wife of astronomer Asaph Hall. Asaph Hall discovered both the Red Planet's moons in 1877. Over 9 kilometers across, Stickney is nearly half the diameter of Phobos itself, so large that the impact that blasted out the crater likely came close to shattering the tiny moon. This stunning, enhanced-color image of Stickney and surroundings was recorded by the HiRISE camera onboard the Mars Reconnaissance Orbiter as it passed within some six thousand kilometers of Phobos in March of 2008. Even...

HiRISE image of Stickney Crater on Phobos. Credit: NASA/JPL/University of Arizona. Stickney crater is almost half the diameter of Phobos itself. Why did the impact not shatter this small moon? The color picture above is a composite from two pictures taken about 10 minutes apart in order to give the 3-dimensional aspect. A recent Picture of the Day described some of the large-scale formations on Phobos, especially Stickney Crater, but this more dramatic picture, which has recently become available, deserves another showing because it portrays the distinctive features of an Electric Discharge Machining (EDM) event with greater clarity. The...

Jafar Arkani-Hamed of McGill University discovered that five impact basins--dubbed Argyre, Hellas, Isidis, Thaumasia and Utopia--form an arclike pattern on the Martian surface. Three of the basins are well-preserved and remain visible today. The locations of the other two, in contrast, were inferred from measurements of anomalies in the planet's gravitational field... a single source--most likely an asteroid that was initially circling the sun in the same plane as Mars--created all five craters. At one point the asteroid passed close to the Red Planet... and was broken apart by the force of the planet's gravity. The resulting five pieces subsequently...

New Theory: Catastrophe Created Mars' Moons By Leonard David Senior Space Writer posted: 07:00 am ET 29 July 2003 PASADENA, California – The two moons of Mars – Phobos and Deimos – could be the byproducts of a breakup of a huge moon that once circled the red planet, according to a new theory. The capture of a large Martian satellite may have taken place during or shortly after the formation of the planet, with Phobos and Deimos now the surviving remnants. Origin of the two moons presents a longstanding puzzle to which one researcher proposed the new solution at...

Asteroid Vesta: The 10th Planet? Discovery Brightens Odds of Finding Another Pluto Nemesis: The Million Dollar Question HOUSTON, TEXAS -- Our solar system may have had a fifth terrestrial planet, one that was swallowed up by the Sun. But before it was destroyed, the now missing-in-action world made a mess of things. Space scientists John Chambers and Jack Lissauer of NASA's Ames Research Center hypothesize that along with Mercury, Venus, Earth, and Mars -- the terrestrial, rocky planets -- there was a fifth terrestrial world, likely just outside of Mars's orbit and before the inner asteroid belt. Moreover, Planet V...

Phobos and Deimos are both small for moons — about 14 and 7.7 miles (22.5 and 12.4 kilometers) wide, respectively — and sort of potato-shaped. Compared to other satellites in the solar system, they look more like asteroids. As a result, astronomers previously hypothesized that these moons were asteroids captured by Mars' gravitational pull. ...previous research suggested that Phobos and Deimos would have relatively irregular orbits. In reality, these moons have nearly circular orbits positioned near the Martian equator. ... huge impact that previous research suggested created the gigantic Borealis basin in the northern lowlands of Mars, which covers two-fifths...

Phobos survived a giant impact early in its history, but damage from the crash left the moon weak, say Benjamin Black and Tushar Mittal, planetary scientists with University of California at Berkeley. Their study shows that in 20 million to 40 million years, Phobos will break apart, leaving a cloud of debris that will relatively quickly assembly into a ring around Mars. Initially, the ring will be as dense as Saturn's rings today, and it will last for up to 100 million years, the study shows.

Explanation: This moon is doomed. Mars, the red planet named for the Roman god of war, has two tiny moons, Phobos and Deimos, whose names are derived from the Greek for Fear and Panic. These martian moons may well be captured asteroids originating in the main asteroid belt between Mars and Jupiter or perhaps from even more distant reaches of the Solar System. The larger moon, Phobos, is indeed seen to be a cratered, asteroid-like object in this stunning color image from the robotic Mars Reconnaissance Orbiter, recorded at a resolution of about seven meters per pixel. But Phobos orbits...

One of the most striking features we see on images of Phobos is the parallel sets of grooves on the moon’s surface. They were originally thought to be fractures caused by an impact long ago. But scientists now say the grooves are early signs of the structural failure that will ultimately destroy this moon. "We think that Phobos has already started to fail, and the first sign of this failure is the production of these grooves," said Terry Hurford, from NASA’s Goddard Space Flight Center. ... Mars' gravity is pulling in Phobos closer by about 2 meters (6.6 feet) every...

Explanation: What does the Martian moon Phobos look like? To better visualize this unusual object, images from ESA's Mars Express orbiter have been combined into a virtual rotation movie. The rotation is actually a digital illusion -- tidally-locked Phobos always keeps the same face toward its home planet, as does Earth's moon. The above video highlights Phobos' chunky shape and an unusually dark surface covered with craters and grooves. What lies beneath the surface is a topic of research since the moon is not dense enough to be filled with solid rock. Phobos is losing about of centimeter of altitude...

On March 25, 2010, the European Space Agency (ESA) announced on their blog that ESA’s study of the mass of Phobos had been accepted for publication in the scientific journal Geophysical Research Letters. The announcement excerpted startling conclusions of ESA’s findings: “We conclude that the interior of Phobos likely contains large voids. When applied to various hypotheses bearing on the origin of Phobos, these results are inconsistent with the proposition that Phobos is a captured asteroid.” (1,2) Since that time, a number of prominent ancient astronaut blogs have had plenty to say about the findings. The ESA findings were most...

Explanation: This moon is doomed. Mars, the red planet named for the Roman god of war, has two tiny moons, Phobos and Deimos, whose names are derived from the Greek for Fear and Panic. These martian moons may well be captured asteroids originating in the main asteroid belt between Mars and Jupiter or perhaps from even more distant reaches of the Solar System. The larger moon, Phobos, is indeed seen to be a cratered, asteroid-like object in this stunning color image from the Mars Reconnaissance Orbiter, recorded at a resolution of about seven meters per pixel. But Phobos orbits so...

Astronomy Picture of the Day Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer. 2004 January 4 Deimos: A Small Martian Moon Credit: Viking Project, JPL, NASA Explanation: Mars has two tiny moons, Phobos and Deimos. Pictured above is Deimos, the smaller moon of Mars. In fact, Deimos is one of the smallest known moons in the Solar System measuring only nine miles across. The diminutive Martian moons were discovered in 1877 by Asaph Hall, an American astronomer working at the US...

Astronomy Picture of the Day Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer. 2003 November 29 Phobos Over Mars Credit: Viking Project, JPL NASA Explanation: Hurtling through space a mere 3,000 miles above the Martian surface, the diminutive moon Phobos (below and left of center) was imaged against the backdrop of a large shield volcano by the Viking 2 Orbiter in 1977. This dramatic picture looks down from the Orbiter's viewpoint about 8,000 miles above the volcano, Ascraeus Mons. Phobos itself...

Astronomy Picture of the Day Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer. 2003 October 24 Mars Moons Credit & Copyright: Johannes Schedler (Panther Observatory) Explanation: This year's record close approach of Mars inspired many to enjoy telescopic views of the red planet. But while Mars was so bright it was hard to miss, spotting Mars' two diminutive moons was still a good test for observers with modest sized instruments. Mars' moons were discovered in August of 1877 by Asaph Hall...

Astronomy Picture of the Day Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer. 2003 July 1 Martian Moon Phobos from MGS Credit: Malin Space Science Systems, MGS, JPL, NASA Explanation: Why is Phobos so dark? Phobos, the largest and innermost of two Martian moons, is the darkest moon in the entire Solar System. Its unusual orbit and color indicate that it may be a captured asteroid composed of a mixture of ice and dark rock. The above picture was captured recently...

Astronomy Picture of the Day Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer. 2003 April 6 Phobos: Doomed Moon of Mars Credit: Viking Project, JPL, NASA; Image mosaic by Edwin V. Bell II (NSSDC/Raytheon ITSS) Explanation: This moon is doomed. Mars, the red planet named for the Roman god of war, has two tiny moons, Phobos and Deimos may well be captured asteroids originating in the main asteroid belt between Mars and Jupiter or perhaps from even more distant reaches of...

Astronomy Picture of the DayDiscover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer. 2003 March 29 The Shadow of Phobos Credit: Malin Space Science Systems, MGS, JPL, NASA Explanation: Hurtling through space above the Red Planet, potato-shaped Phobos completes an orbit of Mars in less than eight hours. In fact, since its orbital period is shorter than the planet's rotation period, Mars-based observers see Phobos rise in the west and set in the east - traveling from horizon to horizon in about...