A transit of Deimos from Mars lasts a maximum of about two minutes, due to its relatively rapid
orbital period of about 30.3 hours. Because they orbit Mars in low-inclination equatorial orbits, the shadows of
Phobos or Deimos projected onto the surface of Mars exhibit a seasonal variation in latitude. At any given geographical location on the surface of Mars, there are two intervals in a Martian year when the shadows of Phobos or Deimos are passing through its latitude. During each such interval, no or one transit of Deimos can be seen by observers at that geographical location (compared to about half a dozen
transits of Phobos). The shadow always falls on the "winter hemisphere", except when it crosses the equator during the
March and
September equinoxes. Thus transits of Deimos happen during Martian autumn and winter in the northern hemisphere and the southern hemisphere, roughly symmetrically around the
winter solstice. Close to the equator they happen around the March and September equinoxes; farther from the equator they happen closer to the winter solstice. Because it orbits relatively close to Mars, Deimos cannot be seen north of 82.7°N or south of 82.7°S; such latitudes will obviously not see transits either. On 4 March 2004, a transit was photographed by Mars Rover
Opportunity, while on 13 March 2004, a transit was photographed by Mars Rover
Spirit. In the captions below, the first row shows Earth time
UTC and the second row shows
Martian local solar time. The data in the tables below is generated using JPL Horizons. There is some discrepancy of a minute or two with the times reported for the series of images above. This may be due to imprecision in the ephemeris data used by JPL Horizons; also the JPL Horizons data gives local apparent solar time while the times reported above are probably some form of mean solar time (and therefore some of the discrepancy would be due to the Martian equivalent of the
equation of time).
Note: the data below is valid for the original landing sites. To the extent that the rovers have moved around on the surface, the parameters of the transits as actually observed may be slightly different. Near misses are in italics.
March 5, 2024: NASA released images of transits of the moon Deimos, the moon
Phobos and the planet
Mercury as viewed by the
Perseverance rover on the planet Mars. ==Observation by InSight==