Before we get started, I want to mention that if you’re ever bored online (really, how is that even possible?) you should check out solarsystem.nasa.gov. They have all sorts of cool things like an interactive display of Jupiter that you can send spinning, live counts of how far each planet is away from the sun, and a bunch of other fascinating information. On a planet like Mercury, that distance from the sun is clicking up and down like nobody’s business as it whirls around in its tight orbit. There’s a reason they call it the swiftest planet and named it after the fastest of the Roman gods!
Ok, so let’s talk a little more about Mercury. As you might intuit from it being the swiftest planet, Mercury is the planet that is closest in to the sun, and therefore the most affected by its gravity as it zooms around and around.
It takes 88 Earth days for Mercury to go around the sun, and 59 Earth days for it to rotate completely on its axis, which is what we consider a day on Earth. But a day on Mercury is quite different, in that the sun doesn’t exactly rise and set evenly. In fact, the sun might rise, fall and rise again in close to the same position as Mercury turns closer to the sun and whips around in orbit. The same thing happens at sunset in reverse in other places on Mercury’s surface. So a solar day, where the sun rises, crosses the sky and sets, is equal to 176 Earth days, meaning if you wanted to travel to Mercury to see the sun rise and set, you’d be there for two Mercury years.
What’s it like on Mercury? Extreme. Similar to Mars, Mercury’s atmosphere has been blown away by the solar wind from the sun, which means it has nothing to keep heat in for any type of temperature regulation. So while it may be blazing hot on the side of the planet facing the sun (up to 801 degrees Fahrenheit), it’s freezing cold on the night side (down to -290 Fahrenheit). And remember, that’s not a quick day and night; each are about as long as a Mercury year.
The lack of atmosphere also means that Mercury has no protection against the severe radiation coming off the sun, and no protection against meteoroids and comets. Its surface is therefore quite pocked and marked by impact craters. The theme of naming craters on Mercury uses famous, dead musicians, authors or artists, which includes greats like Beethoven, Bach, Dickens, Lennon, Disney, Monet, Picasso, Seuss, Shakespeare, and many more (yes, I quite enjoyed lumping together Dr. Seuss and Shakespeare here).
Is there life on Mercury? Not that we’ve found, obviously, but if we look toward indicators of water, astronomers believe that it’s possible Mercury has water ice at its north and south poles. These patches would have to be deep inside of craters, in places of permanent shadow that would keep cool enough to prevent it from boiling off the planet as steam.
Even with the possibility of water ice, it would be tough for life as we know it to live on Mercury, considering the extreme swings in temperature and the radiation coming off the sun.
Poor Mercury is a moonless wonder; even at a third the size of Earth, it has had no luck attracting a friend, making it and Venus the only two planets in our solar system to go without. Astronomers have hypothesized this is due to their proximity to the sun, seeing that its gravitational pull would make it quite difficult for the planets to keep a moon at their side.
Next week, we’ll talk about the limited exploration we’ve done of Mercury — and how that’s about to change.
LOOKING UP THIS WEEK — Mercury will be reappearing in our morning sky this week, and its brightness will provide the best opportunity to see it all year. Remember, it always sticks close to the sun because of that proximity. You’ll also find a bright Venus in the eastern sky at dawn. In the evening, Mars is continuing to grow dimmer as it heads west, with Saturn low in the same sky.