Complex Numbers

Millimeters of Mercury

There are several articles in my queue, from various sources, about planets in our solar system. Fittingly, though randomly, the one about Mercury (from Vox) shows up here first.

Mercury was a total mystery for centuries. We're finally learning its secrets.  

It's still a mystery to me. I've never knowingly seen it in the sky.

All the other visible planets, sure, no problem. Venus, when it's visible at all, is very visible, usually the brightest thing in the night sky apart from the Moon. Mars is generally easy to spot for its color; Jupiter, like Venus, tends to be bright, but isn't limited to just after sunset or just before sunrise. Saturn, while you can't see its rings with unaided eyes, is generally recognizable.

I've even seen the next planet out, through a telescope that someone else pointed. No, I won't name it until its article comes up, lest someone make a worn-out, juvenile joke about it.

But Mercury? Its visibility is even more limited than that of Venus, always close to the twilight horizon if it's visible at all, not to mention much dimmer, and that makes it tough if you don't know exactly what to look for. And despite my interest in astronomy, I never could be arsed to get one of those cellphone apps that tells you what everything is.

It's entirely possible that I've seen it and mistaken it for a star near the horizon, where some constellational context is missing.

Anyway, that's not what the article is about. Thanks to space robots (we have SPACE ROBOTS), we've seen Mercury quite a bit.

On Friday, the US Geological Survey released the most comprehensive topographical map of Mercury ever created, depicting its craters, ridges, volcanoes, and mountains — some rising more than 2 miles high — in fine detail:

You'll have to go to the link to see the map. Also, "on Friday" refers to a long-ago Friday in early 2016, as the article is pretty old now.

Because Mercury is so small and close to the sun, it's tricky to send spacecraft to visit it — before NASA's MESSENGER probe, the only craft that had come close was Mariner 10, which made a series of quick flybys in the 1970s.

The difficulty of getting to Mercury may seem counterintuitive. Woudn't a probe just fall toward the Sun? Well, no, for the same reason Earth (much to our relief) doesn't; you have to cancel a lot of angular momentum, and that takes fuel, careful planning, and lots and lots of math.

So, the rest of the article consists of some of the stuff we managed to figure out thanks to fuel, careful planning, and lots and lots of math.

1) Mercury is shrinking

And no, not because of #2 here:

2) Mercury has water ice

This has long been theorized, but lots of things were theorized that turned out not to be the case. The brief explanation for how ice can exist on the surface of a planet that's famously close to a giant perpetual fusion bomb is that Mercury has no real atmosphere to distribute heat, and the ice is in shadowed craters at the poles.

3) Mercury had a violent, volcanic past

While, again, it's good to get evidence, this isn't exactly surprising given that other terrestrial planets (and the Moon) have or had volcanic activity.

4) We can't quite figure out how Mercury formed

To be fair, we're a little fuzzy on the details of how any planets formed.

What's cool is that we're able to figure out things like how big a planet's core is and what it's made of, and that we have the technology to send robots there in the first place.

5) Mercury has a weird, off-center magnetic field

"Weird" meaning "No, we don't understand that yet, either, but it'll help us do more science."

So, there it is: stuff we didn't know before, or suspected but didn't have proof of. Always more to find out.