Did you go out and see the Venus transit a couple of years ago? Well, there’s been another transit, but I’m sure you didn’t go out and see it — it was a transit of Mercury, but it was only visible from Mars.
This was taken with the Mars Science Laboratory Curiosity’s MastCam, which takes pictures of the Sun every day for calibration purposes. Since the Sun isn’t its normal target, the result is blurry, but you can easily make out two large sunspot groups. Mercury is harder to see, since it’s quite small and blurry, but the video highlights it for you, and it’s definitely there.
This is the first time a planetary transit has been observed from anywhere other than Earth. So while this is of little scientific value, it is a historic moment all the same.
Mars is a superior planet to us, which means it orbits further away. You can only see transits of inferior planets, so Mars gets to see transits of three different bodies. The next Mercury transit from Mars will be next April; the next Venus transit will be in 2030, and the next Earth transit (yes, Mars gets to see Earth transits) will be in 2163. An Earth transit will be quite significant, in part because from Mars, you’d also see the Moon transiting the Sun. But we must wait a long time. The last opportunity to see an Earth transit came in January of 2005, when Cassini was at Saturn and an Earth transit was visible. Unfortunately, Cassini was not equipped to usefully photograph the event, and was in any case much too busy with its first major Titan flyby and the Huygens drop that day. But it may only be a matter of time. We just barely missed an opportunity a few months ago, when an Earth transit was visible from Jupiter, but there are no assets at Jupiter right now. The next transit visible from Saturn will be in 2020, and the next from Jupiter in 2026. Will we manage to photograph one of these?