In the year 69163, approximately 3,360 generations from now, there should be a simultaneous transit of Venus and Mercury across the Sun as seen from Earth. Not sure where on Earth but I don't think this *really* matters.
Due to the 'evolution of planetary orbits' this event cannot occur with the current planetary configuration.
Take a look at Quarter Million Year Canon of Solar System Transits by John Walker for a nice write up. The entire quarter million year canon of transits can be downloaded in Comma Separated Value (CSV) format from the download center at the end of the document.
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