Solar eclipses of Phobos and Deimos observed from the surface of Mars

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The small martian satellites Phobos and Deimos orbit in synchronous rotation with inclinations of only 0.01° and 0.92°, respectively, relative to the planet's equatorial plane. Thus, an observer at near-equatorial latitudes on Mars could occasionally observe solar eclipses by these satellites (see ref. 1, for example). Because the apparent angular diameter of the satellites is much smaller than that of the Sun, however, such events are more appropriately referred to as transits. Transit data can be used for correcting and refining the orbital ephemerides of the moons. For example, Phobos is known to exhibit a secular acceleration that is caused by tidal dissipation within Mars2,3,4. Long-term, accurate measurements are needed to refine the magnitude and origin of this dissipation within the martian interior as well as to refine the predicted orbital evolution of both satellites5,6. Here we present observations of six transits of Phobos and Deimos across the solar disk from cameras on Mars aboard the Mars Exploration Rovers Spirit and Opportunity7,8. These are the first direct imaging observations of satellites transiting the Sun from the surface of another planet.

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Figure 1: Summary images of the transits observed by Spirit and Opportunity.
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These observations were made possible by the hard work of the engineers and scientists working with the Mars Exploration Rovers Spirit and Opportunity. We thank D. Limonadi, S. Spohn and J. Swift for their assistance with MER clock drift corrections. We also thank B. Bills for critical comments that improved this paper. This research is supported by grants and contracts from the NASA Mars Exploration Rover project.

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Correspondence to J. F. Bell III.

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Bell, J., Lemmon, M., Duxbury, T. et al. Solar eclipses of Phobos and Deimos observed from the surface of Mars. Nature 436, 55–57 (2005) doi:10.1038/nature03437

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