A transit of Mercury will take place on November 23, 2005, 6:00 UT. Unfortunately it is only seen from Mars. During the transit, Mercury will pass directly between the Sun and Mars and any Martian will see a small black disc moving across the face of the Sun.
Transits of Mercury from Mars are much more common than transits of Mercury from Earth: there are several per decade. From Earth, there are either 13 or 14 transits of Mercury every century. All Mercury transits fall within several days of 8 May and 10 November. The next transits of Mercury seen from Earth is on Nov 08 2006.
Future Mars colonists may be able to observe such a transit of Mercury from Mars. The Mars Rovers Spirit and Opportunity are unable to see the transit because use the only camera available for this has insufficient resolution. The Mercury-Mars synodic period is 100.8882 days. It can be calculated using the formula 1/(1/P-1/Q), where P is the orbital period of Mercury (87.969 days) and Q is the orbital period of Mars (686.98 days).
The inclination of Mercury's orbit with respect to Mars' ecliptic is 5.16°, which is less than its value of 7.00° with respect to Earth's ecliptic.
Transits of Mercury from Mars December 18, 2003 January 12, 2005 November 23, 2005 May 10, 2013 June 4, 2014 April 15, 2015 October 25, 2023 September 5, 2024 January 26, 2034 February 21, 2035