One popular sci-fi trope is invasion by alien “bugs” – microscopic organisms from other worlds that could harm life on Earth. But scientists also are concerned about things working the other way around: Earth bugs contaminating other planets. So landers are sterilized to prevent them from carrying any hitchhikers. And when the life of an orbiter ends, it’s targeted to crash into a place where it won’t cause any harm.

One world where that’s not a concern is Mercury. The Sun’s closest planet has no air – only a few atoms captured from the solar wind, or knocked off the surface of Mercury by the solar wind. And even that is a hard vacuum by Earth standards.

Mercury is zapped by solar energy. That heats the dayside to as high as 800 degrees Fahrenheit. And ultraviolet energy would destroy any Earth-like microbes.

So when the only Mercury orbiter to date wrapped up its mission, in 2015, it was allowed to crash into the planet.

The next Mercury mission is scheduled to fly past the planet next week, and enter orbit late next year. It may crash into Mercury when its mission is through as well – gouging a new crater, but leaving the planet uncontaminated.

Mercury is just creeping into the dawn sky. It looks like a fairly bright star. But it’s so low that you need a clear horizon to spot it. It’ll be a bit easier to see tomorrow because it’ll perch close to the right of the “fingernail” crescent Moon.

Script by Damond Benningfield