Years ago, back when we still had a space program and a government that recognized the importance of science, we launched a probe to the planet Mercury called "MESSENGER." Nowadays we can't even get funding to *built* a spacecraft, much less send it anywhere. I digress:
The only other probe ever to go down that road was in the early 1970s. It wasn't very sophisticated, and it's a tough haul: far more light, heat, and radiation to contend with than if you're going *out* from the sun. All we got that time out was some vague readings, and a low-quality photomontage of about a quarter of the planet. Nothing seemed too interesting, and frankly, no one was really all that interested in being interested in the post-Apollo days. Mostly folks just wanted to sit around, snort coke, lose the Vietnam war, listen to disco, and get crabs. "It looks like the moon. We've already been to the moon. The Moon is dull. Screw it. Did you hear Meatloaf has a new album out? You know 'Meatloaf' refers to his penis, right? He's cool. Let's do another line!"
Flash forward 40 years, and Mr. Loaf is still as boring as ever (Jim Steinman won't return his calls) but MESSENGER has been toodling around in orbit of the innermost planet for a while now, and it's turned out that the planet is way more interesting than the filthy hippies thought:
* It's got water! Yeah, I know NASA's endlessly yammering on about water, and I'm generally disdainful of it, seeing as there's never really been any debate about water on Mars (You can see the poles through a good telescope), but water on Mercury, that close to the sun, *IS* pretty amazing.
* There's crazy amounts of sulphur on the planet. Way more than anywhere else. No one knows why.
* There's next to no iron! This is a shocker, and again, nobody knows why. The other terrestrial plants are piled high with it. I mean, Mars is red because it rusted...
* By volume, Mercury's core makes up about 85% of the planet! The other terrestrials have cores that make up maybe 30% of their volume. Again, no one knows why (But I do of course have a theory: Being so close to the sun, I think the planet has basically boiled away its volatiles over the last 4 billion years, and shrunk. I think it used to be a superterrestrial)