New videos captured by the High Resolution Stereo Camera (HRSC) on board ESA’s Mars Express orbiter show the rare moment of the Martian moon Deimos passing in front of Jupiter and its Galilean moons as well as the Martian moon Phobos drifting in front of Deimos.
Deimos passing in front of Jupiter and its Galilean moons. Image credit: ESA / DLR / FU Berlin / K.-D. Matz.
Phobos and Deimos were discovered by American astronomer Asaph Hall at the U.S. Naval Observatory in Washington, D.C., in August 1877.
Both moons are named after the sons of Ares, the Greek god of war, who was known as Mars in Roman mythology. Phobos (panic or fear) and Deimos (terror or dread) accompanied their father into battle.
Phobos, Mars’ innermost and largest moon, has an oblong shape with an average diameter of about 22 km (14 miles). It is an unusual satellite, orbiting closer to its planet than any other moon in the Solar System.
The moon orbits Mars about 5,989 km (3,721 miles) from the surface and completes an orbit in just 7 hours and 39 minutes.
It orbits so close to the Martian surface that the curvature of the planet would obscure its view from an observer standing in Mars’ polar regions. Its orbital period is about 3 times faster than the rotation period of the Red Planet, with the unusual result among natural satellites that Phobos rises in the west and sets in the east as seen from the planet.
Deimos has a mean radius of about 6 km (3.7 miles) and is less irregular in shape.
It orbits around Mars with a period of 30 hours at a distance of approximately 23,460 km (14,580 miles).
Among other things, Mars Express monitors Phobos and Deimos to understand more about their surface composition, in particular Phobos’ mysterious grooved terrain, and ultimately the moons’ puzzling origin. This includes tracking their orbits.
“The fortuitous alignment of Deimos passing in front of Jupiter on February 14, 2022 enabled the position and orbit of Deimos to be more accurately pinpointed,” ESA researchers said.
“That is, by measuring the duration of the occultation — when the light from one celestial body is blocked by another — the orbit can be calculated.”
“Such an alignment is extremely unusual because Deimos must be exactly in the orbital plane of Jupiter’s moons for the alignment to occur.”
The animated sequence of 80 Mars Express/HRSC images shows the bumpy surface of Deimos as it passed in front of Jupiter.
“The animation first shows Deimos passing in front of the icy moon Europa,” the scientists said.
“The largest moon in the Solar System, Ganymede, is then obscured from view.”
“The gas giant Jupiter, appearing as a large white spot in the center, then vanishes behind Deimos.”
“Deimos then covers the extremely active volcanic moon Io, which is a similar size to Earth’s moon.”
“Finally, the cratered moon Callisto disappears behind Deimos.”
“Deimos appears to move up and down in the animation due to the small swaying movements of Mars Express while it rotates to place the HRSC camera into position. The motion of the solar wings, which extend 12 m (39 feet) from the spacecraft, as well as two long radar antennas, also contribute to the small vibrations.”
After imaging the alignment with Jupiter, Mars Express observed the moment Deimos was blocked by Phobos.
The animation is pieced together from 19 HRSC images, taken on March 30, 2022 when Phobos was 12,261 km (7.619 miles) away from the camera
From this perspective it is difficult to see the size difference between the Martian moons, as Deimos is further from the camera at a distance of 27,907 km (17,341 miles).
“The new images demonstrate that Mars Express continues to shine a light on Mars, the immediate surroundings of the Red Planet, and beyond,” the researchers said.
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This article is based on text provided by the European Space Agency.
