Phil Plait, I submit for your approval two heart-shaped volcanic depressions on Io. The volcano on the left is Inti Patera, observed by Voyager 1 on March 5, 1979. The volcano on the right is unnamed and located at 8.5°N, 71.5°W. This feature was observed by Galileo on February 22, 2000.
Both are somewhat cardioid-shaped. Interestingly enough, both volcanoes have similar characteristics. Both paterae have evidence of multiple floor levels, with the lowest portion (to the upper right on Inti, to the left on the other volcano) showing the most signs of activity. Activity at both features tends to also be confined to the outer margins of the paterae, though the volcano on the right has a lower floor that is covered almost entirely by a dark lava flow or lava lake. The majority of both volcanoes have an albedo similar to that of their surroundings, suggesting that lava has not flowed over their floors (except for the lower portions of the floor) in a very long time (>100 years, I'd say). Finally, both show evidence for structural control, pre-existing faults that for part of the boundary for the volcano. This is particularly evident in the volcano on the right, with has a number of straight margins.
Again, tip of the hat to Phil Plait. And Happy Valentine's Day!
Link: Happy Valentine’s Day. Love, Rhea [blogs.discovermagazine.com]