Phobos and Deimos: Two Moons, From One Source?

Phobos

Running the clock back on the enigmatic pair of Martian moons Phobos and Deimos gives researchers insight to their possible origin.

A recent study provides crucial clues on the possible ‘origin story’ for the two tiny moons of Mars, Deimos and Phobos.

Modern astronomy provides us with a snapshot, a look at the present state of affairs across the solar system… but what were things like in the distant past? The existence of the two tiny moons seen orbiting Mars presents a particular dilemma for astronomers. Close up, Phobos and Deimos resemble tiny misshapen captured asteroids… but how did they get into the neat, tidy orbits that we see today?

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What Could We Learn From a Mission to Phobos?

According to new research that appeared in the scientific journal Nature Geoscience, the larger of Mars’ two moons (Phobos) has an orbit that takes it through a stream of charged particles (ions) that flow from the Red Planet’s atmosphere. This process has been taking place for billions of years as the planet slowly lost its atmosphere, effectively establishing a record of Martian climate change on Phobos’ surface.

This research has provided yet another incentive for landing a mission on Phobos, something that has never been done successfully. In essence, this mission could gather sample data that would allow scientists to study this record more closely. In the process, they would be able to learn a great deal more about how Mars went from being a warmer world with liquid water to the extremely arid and cold environment it is today.

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New Pictures of Phobos, Seen in the Infrared

NASA’s Mars Odyssey Orbiter doesn’t get a lot of headlines lately. It was sent to Mars in 2001, to detect the presence of water and ice on Mars, or the past presence of it. It also looked at Mars’ geology and radiation. It’s been doing its job without a lot of fanfare.

Now Odyssey’s infrared camera has given us three new images of Mars’ moon Phobos.

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Curiosity Looked up and Saw Phobos During the Daytime

For fans and enthusiasts of space exploration, the name Kevin Gill ought to be a familiar one. As a software engineer at NASA’s Jet Propulsion Laboratory who specializes in data visualization and analysis, he has a long history of bringing space exploration to life through imagery. Among his most recent offerings is a very interesting pic taken by the Curiosity rover early in its mission.

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Mars Express Takes Photos of Phobos as it Flies Past

Much of Phobos' surface is covered with strange linear grooves. New research bolsters the idea that boulders blasted free from Stickney crater (the large depression on the right) carved those iconic grooves. Image Credit: NASA/JPL-Caltech/University of Arizona

The ESA’s Mars Express Orbiter is no stranger to the Martian moon Phobos. The spacecraft was launched in June 2003 and has been in orbit around Mars for 16 years. During its long time at Mars, it’s captured detailed images of Phobos, and helped unlocked some of that Moon’s secrets.

In a new sequence of 41 images captured during a recent fly-by, the Mars Express’ High Resolution Stereo Camera imaged Phobos from different angles, capturing images of the moon’s surface features, including the Stickney crater.

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Want To Explore Mars? Send Humans To The Moons Of Mars First: Phobos And Deimos

Humans to Mars. That’s the plan right? The problem is that sending humans down to the surface of Mars is one of the most complicated and ambitious goals that we can attempt. It’s a huge step to go from low Earth orbit, then lunar landings, and then all the way to Mars, a journey of hundreds of millions of kilometers and 2 years at the least.

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Mars Odyssey Reveals Phobos Using THEMIS

Phobos THEMIS

Welcome to the moons of Mars, as you’ve never seen them.

NASA’s aging 2001 Mars Odyssey orbiter recently snapped some unique views of the twin moons Phobos and Deimos, in an effort to better understand their texture and surface composition. The images are courtesy of the spacecraft’s THEMIS (the Thermal Emission Imaging System) heat sensitive instrument, and show the thermal gradient across the surface of the moons in color. Odyssey has been studying the moons of Mars since September 2017. The recent images of Phobos taken on April 24, 2019 are especially intriguing, as they occurred during full illumination phase.

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Strange Grooves on Phobos Were Caused by Boulders Rolling Around on its Surface

Much of Phobos' surface is covered with strange linear grooves. New research bolsters the idea that boulders blasted free from Stickney crater (the large depression on the right) carved those iconic grooves. Image Credit: NASA/JPL-Caltech/University of Arizona

Back in the 1970s, NASA’s Mariner and Viking Missions were sent out to explore other planets in our Solar System. All three of them (there were two Viking missions) captured images of Mars’ moon Phobos during their travels. They were our first images of the tiny, potato-shaped moon, and the images held a mystery: strange linear grooves on the moon’s surface.
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Saturn Photobombs a Picture of the Martian Moon Phobos

The ESA’s Mars Express probe has been studying Mars and its Moons for many years. While there are several missions currently in orbit around Mars, Mars Express‘s near-polar elliptical orbit gives it some advantages over the others. For one, its orbital path takes it closer to Phobos than any other spacecraft, which allows it to periodically observe the moon from distances of around 150 km (93 mi).

Because of this, the probe is in an ideal position to study Mars’ moons and capture images of them. On occasion, this allows for some interesting photo opportunities. For example, in November of 2017, while taking pictures of Phobos and Deimos, the probe spotted Saturn in the background. This fortuitous event led to the creation of some beautiful images, which were put together to produce a video.

Since 2003, Mars Express has been studying Phobos and Deimos in the hopes of learning more about these mysterious objects. While it has learned much about their size, appearance and position, much remains unknown about their composition, how and where they formed, and what their surface conditions are like. To answer these questions, the probe has been conducting regular flybys of these moons and taking pictures of them.

Phobos and background star (circled in red). Credit: ESA/DLR/FU Berlin

The video that was recently released by the ESA combines 30 such images which show Phobos passing through the frame. In the background, Saturn is visible as a small ringed dot, despite being roughly 1 billion km away.  The images that were used to create this video were taken by the probes High Resolution Stereo Camera on November 26th, 2016, while the probe was traveling at a speed of about 3 km/s.

This photobomb was not unexpected, since the Mars Express repeatedly uses background reference stars and other bodies in the Solar System to confirm positions of the moons in the sky. In so doing, the probe is able to calculate the position of Phobos and Deimos with an accuracy of up to a few kilometers. The probes ideal position for capturing detailed images has also helped scientists to learn more about the surface features and structure of the two moons.

For instance, the pictures taken during the probe’s close flybys of Phobos showed its bumpy, irregular and dimpled surface in detail.The moon’s largest impact crater – the Stickney Crater – is also visible in one of the frames. Measuring 9 km ( mi) in diameter, this crater accounts for a third of the moon’s diameter, making it one the largest impact craters relative to body size in the Solar System.

In another image, taken on January 15th, 2018, Deimos is visible as an irregular and partially shadowed body in the foreground, while the delicate rings of Saturn are just visible encircling the small dot in the background (see below). In addition, Mars Express also obtained images of Phobos set against a reference star on January 8th, 2018 (see above) and close-up images of Phobos’ pockmarked surface on September 12th, 2017.

This image of Deimos and Saturn was taken by the Super Resolution Channel of Mars Express’ High Resolution Stereo Camera. Credit: ESA/DLR/FU Berlin

In the future, the Mars Express probe is expected to reveal a great deal more about Mars’ system of moons. In addition to the enduring questions of their origins, formation and composition, there are also questions about where future missions could land in order to study the surface directly. In particular, Phobos has been considered for a possible landing and sample-return mission.

Because of its nearness to Mars and the fact that one side is always facing towards the planet, the moon could make for an ideal location for a permanent observation post. This post would allow for the long-term study of the Martian surface and atmosphere, could act as a communications relay for other spacecraft, and could even serve as a base for future missions to the surface.

If and when such a mission to Phobos becomes a reality, it is the Mars Express probe that will determine where the ideal landing site would be. In essence, by studying the Martian moons to learning more about them, Mars Express is helping to prepare future missions to the Red Planet.

Be sure to check out the time-lapse video of Phobos and Saturn, courtesy of the ESA:

Further Reading: ESA