It looks like Mercury might be the planet that is closest to Earth
Most of the time, we think of Venus as our closest sibling in the Solar System. In size, mass, and make-up, it’s the most like Earth. And we thought it was the closest in terms of how far away it was, but it looks like Mercury might be closer.
No, the order of how the planets move around the sun hasn’t changed. Mercury is still the closest planet to Earth, and Venus is still the planet whose orbit is closest to Earth’s. But new calculations show that Mercury is, on average, closer to Earth than our old best friend.
It doesn’t make sense, doesn’t it? And maybe that’s how the misunderstanding started in the first place.
“Science popularizers have spread information based on a flawed assumption about the average distance between planets,” engineers Tom Stockman, Gabriel Monroe, and Samuel Cordner write in a commentary that was published in Physics Today.
“By using a more accurate way to estimate the average distance between two orbiting bodies, we find that this distance is proportional to the relative radius of the inner orbit.
In other words, Mercury is closer to Earth than Venus is, on average, because it orbits the Sun closer than Venus does.
The team, whose members work at Los Alamos National Observatory, the US Army’s Engineer Research Development Center, and NASA, hasn’t published their calculations in a peer-reviewed paper yet, but the authors say they’re excited for the scientific community to look at them closely.
The team points out that the way we usually figure out how far apart the planets are is based on how far apart they are from the Sun. The average distance between Earth and the Sun is one astronomical unit (AU). Venus is 0.722 AU. Mercury is at 0.387 AU.
But if you take the distance between Venus and Earth and subtract it from the distance between Earth and Venus, you get the average distance between their orbits, not the distance between the planets themselves. Since the planets move at different speeds, they spend a lot of time on the opposite side of the Sun.
Because Mercury is closer to the Sun than Venus, the distance between them when they are farthest apart is much smaller than the distance between Earth and Venus when they are farthest apart.
The team came up with the “point-circle method” or PCM equation to figure out the average distance between two planets in circular orbits that are concentric and coplanar, which means they move in the same plane.
Based on what they found, it’s not just Earth. Mercury is also, on average, the planet that is closest to every other planet. Yes, even Neptune, which is on the very edge of the Solar System. And yes, even Pluto in the far distance (although its highly elliptical orbit complicates the maths).
The group has called their find the… Whirly-Dirly Corollary: “The average distance between two bodies whose orbits are roughly coplanar, concentric, and circular decreases as the radius of the inner orbit decreases.”
To test it, they made and ran a simulation that tracked the positions of all the planets in the Solar System over a period of 10,000 years. They then compared the results with the traditional distance measurements and the PCM results. With the PCM, the simulation only changed by 1%, but with the old distances, it changed by up to 300%. Yikes.
“As far as we know, no one has ever thought of a way to compare orbits like PCM,” the engineers write.
“PCM could be used to quickly estimate the average distance between any set of orbiting bodies if the right assumptions were made. It might be helpful for quickly estimating satellite communication relays, since the strength of the signal decreases with the square of the distance.
Whatever happens, we now know that Venus is not our closest neighbor and that Mercury belongs to everyone.
Still, you can never have too many friends on another planet. We all agree that Mercury should be added to the club of best friends instead of Venus. We still love all of our neighbors, even those who live far away. Even you, distant dwarf planet Pluto.
