Solar Eclipses on Mars

The Perseverance rover on Mars recently captured some high resolution imagery of a solar eclipse as the moon Phobos passed in front of the sun from the point of view of the rover. This isn’t the first time that a rover on Mars has captured an eclipse, as they actually happen multiple times per day given the fast 7-hour orbit of Phobos.

The image below compares a past eclipse or transit of Phobos as seen from the Curiosity rover a few years ago with the one taken April 2, 2022 from the Perseverance . The higher resolution image on the Perseverance camera that was used to record the eclipse makes for much more detailed view in which sunspots on the sun are even visible.

Unlike our moon, Phobos is not very large, just over 22km across and it orbits very close to Mars, allowing it to complete one lap around the red planet every 7.66 hours. This provides three chances per day for Phobos to eclipse the sun compared to only one chance per month on Earth with our moon. So, while Phobos may be small, it can be seen passing in the sun frequently, and also can be seen traversing the night sky very quickly as well.

One interesting aspect of the eclipse images taken by the Perseverance rover is that the same sunspot complex was also seen from Earth, but just barely. As seen from Earth, the sunspot complex was on the right hand side of the sun, but it was on the left hand side of the sun as seen from Mars. You can see the locations of the same sunspot group as seen from Mars and from Earth below. Note that the color is simply a function of the solar filter used as the natural color of the sun is essentially white. The image on the right may also have been artificially colored from a monochrome image.

The reason for the different apparent locations of the sunspot group is that in early April, Mars and Earth were at a nearly 90 degree angle with respect to each other and the sun as the diagram below illustrates. So, that results in the right hand side of the sun‘s surface as observed from Earth being the left hand side as observed from Mars. Note that the right hand side of the sun as observed from Mars would be on the backside of the sun as observed from Earth, and thus the sunspots on the right side of the sun in the Mars image were not visible from Earth.

You can watch the video version of this post below, including the full real-time speed animation of the eclipse as recorded from the Perseverance rover.