Watch: A Martian moon passing by Jupiter and the Galilean satellites

The European Space Agency's Mars Express probe has caught a golden moment of Mars' small moon Deimos eclipsing Jupiter and its Galilean moons.

At the time, Mars Express was almost 750 million kilometers from the moons of Jupiter. Nevertheless, on 14 February 2022, the alignment of these astronomical bodies was caught on camera, and the resultant images, 80 of them, were stitched together and animated.

"Such an alignment is extremely unusual because Deimos must be exactly in the orbital plane of Jupiter's moons for the alignment to occur," ESA said in a statement released Thursday.

Mars Express arrived in orbit at the Red Planet in 2003. Ever since, it has been regularly observing the planet's chemical composition and its two moons, Phobos and Deimos, and traced the history of water across the globe. This observation demonstrated that Mars once harbored conditions that might have been suitable for life.

A rare celestial event

Mars Express's observations of the moons and occultations with other Solar System objects have permitted a correction of 0.62-1.24 miles (1-2 km) in our knowledge of where the moons are located.

The orbits of these moons fluctuate perpetually, owing to the strong tidal forces from Mars. While Phobos orbits close to Mars at just 3,728 miles (6,000 km), Deimos moves away from it.

Now, their orbits cannot be measured from Earth due to the brightness of Mars when compared to the small moons. But, the "fortuitous alignment of Deimos passing in front of Jupiter on 14 February 2022 enabled the position and orbit of Deimos to be more accurately pinpointed." By measuring the duration of the occultation – when the light from one celestial body is blocked by another – the orbit can be calculated, said the statement.

In the video, one can see the 'bumpy' surface of the small nine-mile-wide (15 km) Deimos as it passes in front of the icy moon Europa. At the time, Ganymede, the largest moon in the solar system, is then concealed from view. Jupiter, which appears as a large white spot in the center, then disappears behind Deimos.

Next, Deimos is seen covering the active volcanic moon Io, and finally, the cratered moon Callisto is obscured from view.

The moon appears to be swaying up and down in the animation, which is caused by the movements of Mars Express as it rotates to keep the High-Resolution Stereo Camera in position.

Future missions will dive deep into Mars' moons

Not much is known about Mars' moons. However, future missions like the JAXA-led Martian Moon eXploration mission (MMX) could help scientists learn more about the moons. MMX will place a lander on Phobos to collect and return a sample from the surface and observe Deimos.

Meanwhile, the ESA-led JUpiter ICy moons Explorer (Juice) mission will launch in 2023 to arrive in the Jupiter system in 2031. Juice will conduct flybys of the moons Ganymede, Callisto, and Europa. In June 2022, an occultation of a star helped refine Europa's orbital data for the Juice mission. The ESA's Gaia mission helped predict the occultation.