Devil Girl from Mars (1954)
The moons of Mars are not quite like our Earth’s Moon. Phobos, the larger of the two, is much closer to its planet; compared to the Moon’s 27-day orbit, Phobos swings around Mars in line with the planet’s equator thrice every Martian day (sol).
Solar eclipses, therefore, are much more frequent than those here on Earth. Phobos passes in front of – but never entirely covers – the Sun for an annular or partial eclipse somewhere on Mars most sols. Because Phobos is moving so fast, it never transits for more than 30 seconds…
To the surprise of Mars scientists, during Phobos eclipses, the lander’s seismometer – the instrument that records ground motions to monitor possible quake activity – tilts, just an infinitesimal little bit, towards one side.
Take a guess at why this occurs. Then, RTFA, and get the real scoop. [Cripes…I almost said “nitty-gritty”. How’s that for dating myself?]