Last week, NASA's Perseverance Rover captured a gorgeous view of Phobos eclipsing the Sun, from the surface of Mars. From the point of view of any Martian microbes lurking out there, the eclipse may have seemed more ominous (yeah ok, there might not be living organisms up there, let alone ones sentient enough to grasp the concept of an eclipse) as the moon is destined by physics to one day slam into the red planet.
Phobos – the closest of Mars' two moons – is set to get ever closer to the planet, before its final descent, while Deimos will drift ever outwards until it leaves Mars' orbit.
"Phobos is nearing Mars at a rate of six feet (1.8 meters) every hundred years; at that rate, it will either crash into Mars in 50 million years or break up into a ring," says NASA's page on the Martian moon.
"Scientists already know that Phobos is doomed," NASA said in a statement discussing the recent eclipse captured by Perseverance. "The moon is getting closer to the Martian surface and is destined to crash into the planet in tens of millions of years. But eclipse observations from the surface of Mars over the last two decades have also allowed scientists to refine their understanding of Phobos’ slow death spiral."
Our own Moon, perhaps tired of our shenanigans, is moving away from us at the rate of about 3.78 centimeters (1.5 inches) per year, meaning that in the future our distant descendants (should they still be around) will not see a total solar eclipse. It will be too small from our perspective to cover the Sun.
"Over time, the number and frequency of total solar eclipses will decrease," lunar scientist at NASA's Goddard Space Flight Center Richard Vondrak said in 2017. "About 600 million years from now, Earth will experience the beauty and drama of a total solar eclipse for the last time."
The fact that our Moon currently eclipses the Sun in its entirety is a happy accident. The Sun and the Moon look about the same size in the sky as the Sun is about 400 times further away from the Earth than the Moon, and about 400 times bigger in diameter. 4 million years ago, before the Moon drifted to its current orbit, it would have appeared about three times as big as it is now in the sky.
Fortunately, depending on your outlook, the Sun will become a Red Giant and engulf the Earth before we are properly separated from the Moon's influence. We shall go down together.