Mercury’s #1

Hello, friends!

I love Mercury.  He’s the planet closest to the Sun, which makes him the first planet of our Solar System.  Sadly, that seems to be the limit of what the average person knows about Mercury, so today I’d like to share just a few other ways Mercury wins first place.

First off, if there were a footrace among all the planets of the Solar System, Mercury would win.  Easily.  Mercury is the #1 fastest moving planet in the Solar System.  This has a lot to do with Kepler’s laws of planetary motion and Netwon’s law of universal gravitation, but I think I can explain this without digging into Kepler or Newton’s math.  Imagine you’re a planet and you don’t want to fall into the Sun.  You’ll need to keep moving to maintain your orbit.  The closer you are to the Sun, the more you’ll have to fight the Sun’s gravity, and thus the faster you’ll have to move.  Mercury is the closest planet to the Sun; ergo, he’s the fastest.  (If you’d like to learn more about the math behind planetary motion, click here.)

Since Mercury is the planet closest to the Sun, you might assume Mercury is also the hottest planet.  But no, Venus is hotter than Mercury (how that happened is a story for another time).  However, Mercury does have the #1 most extreme difference between daytime and nighttime temperatures.  Daytime temperatures climb as high as 430 degrees Celsius (800 degrees Fahrenheit).  At night, the temperature rapidly drops as low as -180 degrees Celsius (-290 degrees Fahrenheit).  Why?  Because Mercury has virtually no atmosphere.  Atmospheres are like insulating blankets for planets.  Without an atmosphere, Mercury can’t retain heat at all, so all the extreme heat Mercury gets during the day is immediately lost to the vacuum of space at night.  (To learn more about Mercury’s daytime vs. nighttime temperatures, click here.)

There are plenty more ways Mercury is #1, but I’m only going to share one more with you today.  Mercury is the #1 most heavily cratered planet in the Solar System.  How did that happen?  Well, once again, Mercury has no atmosphere, which means all the smaller meteoroids that would burn up in the atmospheres of other planets make it straight through to the ground on Mercury.  Additionally, there’s very little geological activity on Mercury.  No volcanic eruptions, no major earthquakes (mercuryquakes?)… at least not in the last 3.5 billion years.  On other worlds, geologic activity helps erode and erase old impact craters, but that’s not happening on Mercury.  So Mercury gets hit more easily and has a harder time erasing old impact craters.  Those two facts add up to Mercury having more impact craters today than any other planet in our Solar System.  (To learn more about Mercury’s overabundance of craters, click here.)

In my humble opinion, Mercury doesn’t get as much love as he deserves.  I don’t know why that is, but I hope this post has piqued your curiosity and helped you appreciate Mercury a little bit more.  At the time of this writing, the BepiColombo space probe (a joint venture by the European and Japanese space agencies) has completed several flybys of Mercury.  If all goes according to plan, BepiColombo should settle into orbit around Mercury in November of this year (2026).  Here’s hoping BepiColombo will discover even more reasons to love the first planet from the Sun.

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