Solved the mystery of the Mars moon Phobos: an important discovery for a space mission

The two moons of Mars Phobos and Deimos.

Photo: NASA / JPLA-Caltech / University of Arizona

Something already Phobos heard? The ancient Greek word for “fear” also refers to one of the planet’s two moons Mars. Along with the smaller Deimos, Phobos turns to Mars. The new findings from the Vienna University of Technology provide important insights. Soon a space mission will take rock samples.

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The surface of the Mars moon Phobos is severely altered. But what does it bring us? Viennese researchers are addressing this question. The small moon was discovered by the American astronomer Asaph Hall in 1877. The awareness that Mars has two moons puts him in “fear” (Phobos) and “horror” (Deimos). In Greek mythology, these are the two horses pulling the chariot of the war god Ares. Both Martian moons were first photographed from a relatively short distance by Viking orbiters in the 1970s.

Space: time does not exist in our sense

Let’s go back to the present: the moon of Mars Phobos is in a very special situation. It is so close to Mars that not only the solar wind but also the bombardment of particles from Mars plays a decisive role there. A research group from TU Vienna has now been able to demonstrate this in laboratory experiments. In a few years, a Japanese space mission to Phobos is expected to take rock samples and bring them back to Earth.

Of course, there is no time in space in our sense of the word – however, rock can “hold up” even in the vacuum of space if it is constantly bombarded with high-energy particles emitted from the sun, for example.

The research team in the laboratory.

Photo: Vienna University of Technology.

How was the Mars moon Phobos born?

There are very different theories about the origin of the Mars moon, as confirmed by Paul Szabo, who is working on his dissertation in Friedrich Aumayr’s research group at the Institute of Applied Physics of the Vienna University of Technology.

“It is conceivable that Phobos was originally an asteroid that was later captured by Mars, but it could also have formed when a larger celestial body collided with Mars.”

When examining such celestial bodies, researchers must always take into account the fact that their surfaces have changed completely over billions of years due to the bombardment of cosmic particles. The rock on earth remains unaffected, because our atmosphere protects the particles. However, science can understand the geology of celestial bodies without an atmosphere – such as our moon or Phobos – only if “spatial alteration” can be correctly evaluated. The Vienna University of Technology makes a vital contribution to this.

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Developing experiments at the Vienna University of Technology

The TU Wien team spared no effort and conducted numerous experiments. “We used rock material like the one found on Phobos and bombarded it with various charged particles in vacuum chambers,” explains Paul Szabo. “With extremely precise scales you can measure how much material is removed and which particles affect the rock and how much.”

In principle, there are many of the minerals found on celestial bodies such as Phobos, the moon, etc., also on earth and can therefore be used as analog rocks, according to our editorial staff. “The raw material for our investigations was specifically made available by our cooperation partners at the University of Bern, who are experts in this field,” says Szabo.

The special properties of the moon Phobos were taken into account for the experiments. Its distance from the surface of Mars is less than 6,000 kilometers, which is not even two percent of the distance between our moon and the earth. Just like our moon, Phobos is in a constrained rotation around its planet: it always turns the same side towards Mars.

Lunar Mars Phobos: The Solution to Weather

“Due to the extremely short distance between Mars and Phobos, not only the particles emitted by the sun play a role on the surface of Phobos, but also the particles of Mars,” says Paul Szabo.

Furthermore, the Martian atmosphere is mainly made up of carbon dioxide. Greater amounts of oxygen are also found in the outer regions of the atmosphere. If solar wind particles penetrate it with great force, oxygen ions can form, which in turn hit Phobos at high speed and change the rock there.

The 2024 space mission benefits from research results

“With our measurement methods, we were able to estimate erosion much more accurately than was previously possible,” says Friedrich Aumayr. “Our results show that the effect of oxygen ions from the Martian atmosphere should definitely not be overlooked.

Aumayr also stresses the importance of distinguishing between the two sides of Phobos. While the solar wind dominates on the opposite side to Mars, on the other hand, when the sun is shielded from Mars, the bombardment from the Martian atmosphere predominates, according to the researcher.

Real Phobos samples may soon be obtained, which will then be evaluated by the researchers. In 2024, as part of the Japanese space mission “MMX (Martian Moon eXploration)”, a spaceship will reach Phobos and bring rock samples to Earth.

You can find the original publication here.

Read more about NASA’s mission to Mars here.