Every Physics classroom has a Solar System line like this.

Or… like this. (Sorry, Pluto.)

Looking at the line, which planet is closest to Earth: Venus or Mars?

To answer, you need first know that, like many things in school, the line is a lie.

Planets are not people queuing for coffee, but rather spheroids scattered in space,

always in motion, not in simple circles either, but in ellipses at untidy angles.

In the cold, dark expanse, this is the coziest Venus gets to Earth,

but only about once a year and a half-ish.

Starting close, she orbits far, then comes back, needs some space -- on the other side of the sun.

This means when Venus is away, Mars can be the closest to play.

So because of orbits, there isn’t one answer to, “Who is the closest?”

It's really, “Who is mostly the closest?”

The mostest closest.

When Mars and Venus are both on the other side of the Sun, it leaves little Mercury the closest.

Each of Earth’s inner three planet friends are at one time the farthest and the closest.

And Mercury, with his smallest orbit, makes him never that far from Earth.

At least on planetary scales.

Giving the little guy a uniquely close relationship with Terra.

In fact, watching the planets spin, because of his small orbit, Mercury, not Mars or Venus, is the closest planet most of the time.

Looking at the line, that seems unpossible.

But nonetheless, in the way of actual orbits,

if we keep measuring the distance to all the planets as they spin,

Mercury is Earth's mostest closest neighbor.

Which is delightfully unexpected.

But wait, if Mercury is the mostest closest to Earth, he has to be the mostest closest to Venus as well, right?

Because her orbit is smaller than Earth's.

And running the numbers, it's true.

Making Earth's special relationship with Mercury less special.

But at least this is one time where the line provides the obvious answer.

Mercury is closest to Venus.

While we’re here, who is Mars’s mostest closest?

On his other side is the asteroid belt, so it should be Earth.

But, maybe it's Venus?

Maybe the rule is the second closest is the mostest closest.

Watching the results, aaaand…

Oh my Celestia, it's Mercury again.

Mercury is the mostest closest to Earth, Venus, and Mars, for the same reason each time.

Bigger orbits make farther average distances for longer times.

So, mercurial Mercury is the constant-est companion.

No, no. It can't be true for Jupiter too.

Enormous, far away Jupiter.

But, it is!

Once again, Mercury’s small orbit means he never goes as far away as the other planets with their bigger orbits.

Thus, are you ready for this?

The orbital math that shows Mercury is the mostest closest to Jupiter is the same for all the planets and everything that orbits the sun.

(You too, Pluto.) [high-five]

For each of the planets, Mercury is the mostest closest.

[soft ambient music]