A Nod to Mercury (The Planet, Not Freddie)

Just in time for Earth Day.

Howdy! Joey here, back for more Fun Fact Friyay. Earth Day is on Monday, but today another planet is getting some shine.

Photo by NASA on Unsplash

On average, Mercury is the closest planet to every other planet.

It’s a common lesson in just about every elementary or middle school: the order of the planets.

There’s the sun—which, to the surprise of some baseball broadcasters, is not a planet—and then Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

(And, depending on your age, Pluto, though that is no longer the case. RIP, Pluto’s planetary status.)

NOT SO FAST.

As Physics Today lays out, if we only look at the planets by measuring their radii at their closest points, Venus is the closest planet to Earth because it has the nearest approach at a certain point during its orbit—which is pretty unique itself!

Another reading believes all planets orbit on the same plane and that those orbits are roughly circular. Researchers call this point-circle measurement, or PCM for short, and it measures the average distance between planets for every point along their orbits.

By that measurement, Mercury, despite staying relatively close to the sun, is closer to Earth nearly 50% of the time. Mars and Venus split the rest.

Using PCM for every other planet, Mercury’s average distance again comes out as the closest each time. In fact, this method of measurement actually puts Uranus as the furthest planet from Neptune.

Of course, this is simply one way to calculate the distance between planets. If you say that Jupiter and Saturn are next to each other, you would not be wrong by the classic measurement.

It’s yet another way space is truly out of this world! *hold for applause at this unprecedented wordplay*

Prefer a visual demonstration of PCM? Here you go!