The order of the planets is something most of us learn in school: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and (until 2006) Pluto.
So you would be forgiven for thinking that as Earthlings, our closest planetary neighbor is Venus. And in a way, you’d be right – at its closest, Venus approaches Earth closer than any other planet in the solar system. Likewise, its orbit is closer to our orbit than any other. However, in another sense, you would be wrong. At least that’s the argument made in an article published in Physics Today.
To identify our nearest neighbor, engineers affiliated with NASA, Los Alamos National Observatory, and the U.S. Army’s Engineering Research Development Center built a computer simulation to calculate the average proximity of the Earth in relation to its three nearest planets (Mars, Venus and Mercury) over a Period of 10,000 years. Due to the way the planets line up in their respective orbits, the model shows that Earth spends more time closer to Mercury than Venus or Mars.
“In other words, Mercury is closer to Earth, on average, than Venus because it orbits the Sun more closely,” the authors explain.
Indeed, it is not only the Earth. Other calculations suggest that the seven planets in the solar system (minus Mercury) spend most of their orbits closer to the “winged messenger” than any other planet. Sound impossible? This is how they worked.
The results are based on a technique called the Point-Circle Method (PCM) – essentially, a mathematical equation that takes the orbits of two planets as circular, concentric and coplanar, and calculates the average distance between two planets orbiting the Sun. .
“From the PCM, we noticed that the distance between two orbiting bodies is at a minimum when the inner orbit is at a minimum,” the authors explain.
“This observation results in what we call the swirling corollary (named after an episode of the cartoon rick and morty): For two bodies with roughly coplanar, concentric, and circular orbits, the average distance between the two bodies decreases as the radius of the inner orbit decreases.”
“It is clear from this corollary and the table that Mercury (mean orbital radius 0.39 AU), not Venus (mean radius 0.72 AU), is the closest planet to Earth on average.” (AU is astronomical units, the distance between the Earth and the Sun.)
To test their hypothesis, they built a computer simulation that tracked the positions of the four planets over a period of 10,000 years and calculated the average distance between them. The results of this simulation differed from traditional calculations (determined by subtracting the average radius of the inner orbit from the average radius of the outer orbit) by an incredible 300%. Yet differed from PCM calculations by a relatively insignificant percentage of 1%.
He found that the average distance between Earth and Venus was 1.136 astronomical units (0.28 on the “old method”). By comparison, the average distance between Earth and Mercury was 1.039 astronomical units (0.61 on the “old method”).
The hypothesis has not yet been submitted to a peer-reviewed article and will no doubt be subjected to extensive cross-examination by experts in the field, but the authors have already noted some possible uses for their new PCM equation. .
“With the right assumptions, PCM could eventually be used to get a quick estimate of the average distance between any set of orbiting bodies,” the authors write.
“Perhaps this can be useful for quickly estimating satellite communication relays, for which the signal strength decreases with the square of the distance. In any case, at least we now know that Venus is not our nearest neighbor – and that Mercury belongs to everyone.”
[H/T: Physics Today]
This article was originally published in March 2017