Perseverance captures the transit of Phobos in the shape of a ‘bulging eye’

Oct. 31 () –

From its position on the western wall of Mars’ Jezero Crater, NASA’s Perseverance rover recently sighted a “bulging eye” that looked down from space.

The pupil of this celestial gaze is the Martian moon Phobos, and the iris is our Sun.

The event, captured by the rover’s Mastcam-Z on September 30, the 1,285th Martian day of the Perseverance mission, took place when the potato-shaped moon passed directly between the Sun and a point on the surface of Mars, obscuring a large part of the solar disk. At the same time that Phobos appeared as a large black disk moving rapidly across the face of the Sun, its shadow, or antumbra, moved across the planet’s surface, NASA reports.

Astronomer Asaph Hall named the potato-shaped moon in 1877, after the god of fear and panic in Greek mythology; The word “phobia” comes from Phobos. (And the word for fear of potatoes, and perhaps potato-shaped moons, is potnonomicaphobia.) He named the other moon of Mars Deimos, in honor of the mythological twin brother of Phobos.

With a diameter approximately 157 times smaller than Earth’s Moon, Phobos is only about 27 kilometers at its widest point. Deimos is even smaller.

Because Phobos’ orbit is almost perfectly aligned with the Martian equator and relatively close to the planet’s surface, transits of the moon occur most days of the Martian year. Due to its fast orbit (about 7.6 hours to make a complete revolution around Mars), A Phobos transit usually lasts only 30 seconds or so.

This is not the first time a NASA rover has seen Phobos blocking the Sun’s rays. Perseverance has captured several transits of Phobos since it landed in Mars’ Jezero Crater in February 2021. Curiosity captured video in 2019 and Opportunity captured an image in 2004.

By comparing the different images, scientists can refine their understanding of the moon’s orbit to see how it is changing. Phobos is approaching Mars and is expected to collide with it in about 50 million years.