Remember when it was decided that Pluto was too small to be a proper planet and our solar system went from nine to eight planets?
Well, keep an eye on Mercury because according to those who ought to know it's ever so slightly shrinking.
This is something we've suspected for around 50 years, as according to IFL Science NASA's Mariner 10 mission flew by the closest planet to the sun and spotted some warning signs.
If you want to know what the tell-tale signs of a shrinking planet look like, they're miles high slopes called 'scarps' all over the surface.
Basically, because Mercury is shrinking on the inside the surface area has less space to cover and one chunk of the surface gets pushed up and over another chunk.
It's basically like the planet getting a set of wrinkles, like how your fruit gets wrinkly and shrinks when it gets older and the skin doesn't need to stretch over quite the same surface area.
Experts have spotted impact craters on the surface of Mercury which have formed on the scarps, which means they much have happened after the scarps were made.
Based off that astute observation, experts reckon that the scarps are about three billion years old, so it's quite a slow process all in all.
Back in 2014, scientists estimated that Mercury had contracted by about 4.4 miles (7 km) since its birth 4.5 billion years ago - so it is shrinking very, very slowly.
Indeed, Mercury is in no danger of plopping out of existence and will still be here by the time the sun expands and consumes it along the way to destroying the rest of the solar system so let that comfort you.
We're getting quite good at this business of looking at things in space so if Mercury does suddenly take a turn for the worse over the next few million years we'll let you know.
While we're on the subject of planets losing things you should look the other way for a bit, especially since looking at the sun is inadvisable, because poor old Saturn is going to lose its rings.
Not permanently, but it's soon to enter a phase where the rings of Saturn will line up in such a way that we won't be able to see them.
We've got about 18 months before we won't be able to see Saturn's rings for a while, but it'll be about 100 million years before they actually disappear in the proper sense of the word.