Mercury -- Not Venus -- is the Closest Planet To Earth on Average, New Research Finds (gizmodo.com)

That's the finding presented by a team of scientists who have published their results this week in an article in the magazine Physics Today. From a report: They explain that our methods of calculating which planet is "the closest" oversimplifies the matter. But that's not all. "Further, Mercury is the closest neighbor, on average, to each of the other seven planets in the solar system," they write. Wait -- what?

Our misconceptions about how close the planets are to one another comes from the way we usually estimate the distances to other planets. Normally, we calculate the average distance from the planet to the Sun. The Earth's average distance is 1 astronomical unit (AU), while Venus' is around 0.72 AU. If you subtract one from the other, you calculate the average distance from Earth to Venus as 0.28 AU, the smallest distance for any pair of planets. But a trio of researchers realized that this isn't an accurate way to calculate the distances to planets. After all, Earth spends just as much time on the opposite side of its orbit from Venus, placing it 1.72 AU away.

One must instead average the distance between every point along one planet's orbit and every point along the other planet's orbit. The researchers ran a simulation based on two assumptions: that the planets' orbits were approximately circular, and that their orbits weren't at an angle relative to one another.

Comments

Link to the Physics Today Article

[mykepredko]

https://physicstoday.scitation...

Interesting work with the best message to get out of this; don't rely on what's obvious, test what you think is true.

Re:Link to the Physics Today Article

[Hillie]

Let me repeat myself for the retarded folks:

Science: You have studies to figure out how something works or what outcome you get from a hypothesis

Liberal pseudo-science: You rig studies in favor of coming out with your chosen outcome. If it doesn't you simply do not publish that study.

Liberalism isn't a conspiracy, it's just fucking stupidity incarnate.

So next time don't try to apply conspiracy theories to where there are none you hack.

Re:Link to the Physics Today Article

[MachineShedFred]

Anybody that understands that all the planets aren't always in a single synchronized line could have inferred this - all the planets do not have the same orbital period, so there will always be a distribution around the Sun. This means that some of them may be on the opposite side of the Sun from us, and even though their average distance from the Sun is close to Earth's average distance from the Sun, they are not close to each other at that point in time.

I didn't know there was opportunity for publishing papers that spell out common sense and grade school two-dimensional geometry, though.

Distance doesn't matter

[jeti]

It's all about the delta-v.

Obvious to anyone who observes them

[jfdavis668]

Amatuer astronomers love to observe Mars. The problem is Mars is on a close, but outside orbit. Unlike Jupiter and Saturn, which the Earth passes every year in thier orbits, it is a different story with Mars. It is only really close for two months every 2 years. It spends most of its time on the far side of its orbit until the Earth can chase it down again, and then quickly races away. Even though you can view it through most of its orbit, it is small and normally far away. Venus, even when near the far side of its orbit, it is fairly easy to observe. At least once it rises far enough out of the Sun's glare. Mercury would be even better, but due to the small orbit it doesn't get far from the Sun from our point of view before it dives back down into the glare.

Re:Obvious to anyone who observes them

[dissy]

It is only really close for two months every 2 years. It spends most of its time on the far side of its orbit until the Earth can chase it down again, and then quickly races away.

It's because of this that make some interesting "artifacts" show up when plotting the path of Mars from the point of view on Earth when doing so on a 2d "map" of the night sky.

On such a map, one sees Mars following a line as one would expect, then that path curves back around and it looks as if Mars is orbiting in the opposite direction for a time (roughly those two months), before it loops back around to continue in the original direction but along a path slightly offset from the original "tail" for the rest of those two years.

If instead your 2d map is from the point of view of a hypothetical camera view above the plane of the solar system but with Earth at the center of that map, the orbit of Mars would plot out with these loops such that it looks like the line was drawn with a Spirograph.

Every two years you get one of these misaligned circles containing a two month backwards loop in it.
Just like with Spirograph if you keep going around, that is multiple orbits around Earth, you get the famous Spirograph "flower", or loopy loop (technical term) pattern.

Amatuer astronomers love to observe Mars.

The above does cause unfortunate timing issues for amateur astronomy too.
Not only do you want to catch it during those two months while it is closest to Earth, but each two year period brings Mars close to a different vantage point on the Earth.

Presuming as an armature you are not going around Earth to chase this ideal view and instead are waiting for it to happen overhead where you are at, you have to not only wait for the right two month period it is close, but also the right two year period it is closest to where you are looking from.

Fortunately this pattern repeats on a scale that is just under 20 years or so, but assuming you live most of your life in the same place on Earth, this does limit the number of opportunities is a single lifetime to catch the ideal position of Mars to observe.

Unfortunately for my experience the "ideal" view was different only in that I could see there were different shades of color compared with the usual smudged spec of blur.
That was back in the late 80s and I haven't personally had another opportunity since, so I'm very thankful for all the amazing professional imagery from far superior sources that are so easily available to see today.

My prediction

[necro81]

Well, shit, I need to recalculate my horoscope again.

Of course it's pedantic

[Headw1nd]

I saw some comments on the Physics Today article about this being pedantic, but astronomy is and always has been about pedantry. It's taking into account tiny details and vanishingly small deviations that allows us to do things like observe the composition of faraway stars or compute the age of the universe.

Re:Of course it's pedantic

[Headw1nd]

the important measure of how close something is is how long it takes to get there.

In astronomy? In astronomy the answer how far away something is might depend on how long it takes light to get there, but for most things astronomy the answer to how long it will take you (or any physical object we could launch) to get there is "you won't."

Re:I call bullsht

[abies]

If perfectly circular, average distance from any planet to any planet should be equal to the center of their path circle, which is, drum roll please, the center of the sun.

No? Planet A at 1AU orbit and Planet B at 2AU orbit have distance between 1AU and 3AU. Planet C at 1000AU has distance to planet A between 999AU and 1001AU. Whatever are their periods, some average of 1-3 won't get anywhere close to average of 999-1001.

So, Earth-Mercury average distance shares the first place with any other of 45 planet pair combinations.

Not sure how you came up with number 45. 8 planets give 28 combinations, so it should be 'any other of 27 combinations'. Even if you didn't get memo from 2006 about Pluto, it would be 36-1=35 combinations.

Re:Potato, Potaato

[lgw]

Seriously, there are more important problems to solve. How about something that's actually useful?

Hey, now, this research evelated pedantry to a whole new level! If ever there was a story that belonged on Slashdot...

But I don't get why they "simulated" this. Isn't this just an integral?

Re:I call bullsht

[Solandri]

perfectly circular, average distance from any planet to any planet should be equal to the center of their path circle, which is, drum roll please, the center of the sun.

No. Distance is a scalar, not a vector. So the average distance doesn't work out to the center of the sun. It works out to the the sum of all points along the circular orbit. For Venus' case, since its orbit is bigger, the scalar distance to each equivalent point in Mercury's orbit is on average bigger because it's at a greater angle from the Earth (with Earth-to-sun line being the shortest distance).

e.g. Pretend Mercury is located in the sun, and Venus has the same orbit as Earth. Consider four points on each orbit spaced 90 degrees apart.

• When Earth, Venus, and Mercury are in line with the sun all on the same side, Mercury is as far as the sun from the Earth (call it R), Venus is on top of the Earth, so its distance is zero.
• When Venus and Mercury are on opposite sides of the sun from Earth, Again, Mercury is distance R, Venus is 2R.
• When Venus and Mercury are at 90 degrees to the right of the sun from Earth, this creates a 45 degree right triangle. Mercury is still at R, Venus is at 2sin(45)R, or 1.414R.
• Likewise when Venus and Mercury are at 90 degrees to the left of the sun, you have the same 45 degree right triangle flipped. And Mercury is at R, Venus is at 1.414R.

Average these four points. The first two cancel out (both average a distance R). The second two result in Mercury being at distance R, Venus at 1.414R. And hence Mercury is on average closer than Venus, even though we're pretending Venus has the same orbit as the Earth.

Re:I call bullsht

[habig]

There's no explanation that I can see on why they would believe that assumption of distribution to be a good one in the first place, though; if they did some research that led them to that assumption, that is probably more interesting than their "closest planet" result.

They did. To quote:

The PCM treats the orbits of two objects as circular, concentric, and coplanar. For our solar system, that’s a pretty reasonable assumption: The eight planets have an average orbital inclination of 2.6 ± 2.2, and the average eccentricity is 0.06 ± 0.06. An object in a circular orbit maintains constant velocity, which means that over a sufficiently long period, it is equally likely to be in any position in that orbit.

Then, they pull out an ephemeris and actually integrate the distances from time point to time point, and that answer is within 1% of their "circles" estimate.

Re:You are technically correct.

[fahrbot-bot]

The best kind of Correct.

You're obviously not married.

Re:I call bullsht

[WorBlux]

Not true, as trigonometric functions aren't linear. Do the math. Take venus at a right angle orbit to earth. sqrt(1+0.728^2)= 1.234 AU. Then Take Mercury at the same right angle, sqrt(1+0.39^2) = 1.073 AU. Mecury is closer for at least half of it's orbit.

But a weird thing is that by average closest planet, they don't mean average distance is the least, they mean if you pick a random time, it's most likely that at that moment, mercury will be closer than mars or Venus. The result was about 45% Mercury, 35% Venus, and 20% mars.

Re:I call bullsht

[WorBlux]

Actually they did calculate average distance as well. 1.05 for mecury, 1.15 venus, 1.65 mars

Re:So, pre-Kepler?

[SEE]

Actually, they did pure math with those simplifying assumptions first. Then they ran a simulation using the actual orbital characteristics (PyEphem uses the real orbits) to check.

That simulation then demonstrated that the assumptions in the pure math produced an error of under 1% for relations among the major planets.

Re:Potato, Potaato

[Immerman]

True, but we don't need one - we're not trying to solve for the motion of an N-body system, we're trying to find the average distance between two bodies whose motion has already been well-characterized by observation.

Our current approximations aren't perfect, but I believe they're generally accepted as accurate enough to project planetary positions for several centuries in either direction of the epoch.