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Mars solar eclipse accompanied by strange phenomenon that may help understand Red Planet better, says study

Recording the strange phenomenon is NASA's Insight Lander, which is tasked with studying Mars interiors
Mars and its moon (Getty Images)
Mars and its moon (Getty Images)

The solar eclipse on Mars is quite unlike the ones seen on Earth. NASA's InSight lander has recorded something strange happening during the phenomenon, according to a new study. This odd signal could help experts plan future missions to Martian moons and learn about the planet's interior structures.

During a solar eclipse, scientists have detected a slight tilt on an instrument aboard the InSight lander called a seismometer, which records quakes. In other words, when the Martian moon named Phobos moves in between the Sun and the Red plant, the instrument tips slightly to one side, puzzling the team.

Mars has two moons: the larger Phobos and Deimos. Both of them leave a cone-shaped shadow every time they pass in front of the Sun. “However, the eclipses on Mars are shorter – they last just 30 seconds and are never total eclipses,” said Simon Stähler, a seismologist at ETH Zurich’s Institute of Geophysics, in a statement. In fact, Phobos passes from west to east every five hours.

Insight's solar cells can detect Earthquakes. "When Phobos is in front of the Sun, less sunlight reaches the solar cells, and these, in turn, produce less electricity,” Stähler explained. During an eclipse, there is a 30% decline in the amount of sunlight.

Researchers were expecting to record some changes typically seen on Earth. “When Earth experiences a solar eclipse, instruments can detect a decline in temperature and rapid gusts of wind, as the atmosphere cools in one particular place and air rushes away from that spot,” Stähler explained. However, InSight did not detect them on the Red Planet.

If the moon Phobos obscures the sun, the seismometer tilts to the side, hardly measurable, and thus registers the transit of the moon in front of the sun. (Nasa/JPL)

But in a surprise discovery, InSight's seismometer and the magnetometer recorded an effect during the eclipse. The signal from the magnetometer is most likely due to the decline in the solar cells’ electricity, Anna Mittelholz, who is also part of ETH Zurich’s Mars team, pointed out. The more surprising part was the seismometer's slight tilt in a particular direction, according to the team.

The team tried to find answers to the unusual effect on the seismometer. They speculated that it could be due to Phobos’s gravity. But the theory did not hold water because the signal should appear every five hours when Phobos makes its pass, instead of only during eclipses. 

The slight tilt in the instrument could be due to a dip in surface temperature during an eclipse. It may have deformed the ground unevenly, leading to the changed angle, according to Martin van Driel from the Seismology and Wave Physics research group. 

The small tilt has applications for future missions. It can tell scientists about Phobos' orbit. For example, Japan’s space agency JAXA is planning to send probes to Martian Moons in 2024 and bring samples from Phobos back to Earth. “To do that, they need to know exactly where they’re flying to,” says Stähler.

There is more. Information on Phobos' orbit can provide insights on Mars' interior. Phobos is moving closer to the planet and is expected to crash into the surface in the next 30 to 50 million years. “We can use this slight slowdown to estimate how elastic, and thus, how hot the Martian interior is: cold material is always more elastic than hot,” Amir Khan, from ETH Zurich’s Institute of Geophysics, explained.

The research is published in Geophysical Research Letters.