Venus is not Earth’s closest neighbor (2019) [pdf]

https://fermatslibrary.com/s/venus-is-not-earth-s-closest-neighbor

by BerislavLopac • 3 years ago

243 176 3 years ago

hpaavola• 3 years ago

CPG Grey, Which Planet is the Closest?: https://www.youtube.com/watch?v=SumDHcnCRuU

Blammar• 3 years ago

The most surprising conclusion is that Mercury is on the average closest to ANYTHING that orbits the sun, including (presumably) long-orbit comets!

yreg2• 3 years ago

It's totally unintuitive, but makes perfect sense once you know the answer.

orlp• 3 years ago

This isn't true for two different objects in the same orbit with a small phase difference.

To be fair that arrangement is rather unstable, especially with planet-sized objects.

mr_toad2• 3 years ago

The whirly dirly corollary.

talk about cosmic apotheosis.

m348e912• 3 years ago

Doesn't this also imply that the sun is mostest closest to any planet than any other planet?

ithkuil3• 3 years ago

I had the same thought: if there was another planet inside mercury's orbit, that would be the mostest closest planet to all the planets, stealing mercury's status, and so you keep iterating on that until you reach smallest and smallest orbits around the sun center of mass (which is inside the sun).

So, if you when you say "the sun" you mean the sun surface, then yes, the sun is always the mostest closest celestial body, to all planets

tromp• 3 years ago

Yes, a hypothetical planet located at the centre of the sun would be every planet's closest neighbour, by virtue of never getting as far away as others.

8note• 3 years ago

"Closest the mostest" makes it feel like less of a gotcha

pimlottc• 3 years ago

TL;DR it’s Mercury

The article describes a novel mathematical formula for calculating the average distance between planets orbiting the same star. Using this method (and confirming with computer simulations), the authors determine that Mercury, not Venus, is the closest planet, on average, to Earth.

It’s actually the average closest for all the planets! However it does not really go into the orbital mechanics to offer any intuitive explanation of this surprising result.

eimrine• 3 years ago

because other planets use to appear too far sometimes, as it has been shown by whirly-dirly simulation

nordsieck• 3 years ago

However it does not really go into the orbital mechanics to offer any intuitive explanation of this surprising result.

I think you just need geometry to get an intuitive explanation.

1. Draw the Sun and the orbits of Mercury, Venus, Earth, and Mars.

2. Pick a point on Earth's orbit for where Earth is.

3. Draw a circle around Earth that intersects the Sun.

4. Draw a line, tangent to that circle, that intersects the Sun.

A hypothetical planet that orbits the sun at 0 distance has half of its orbit in the circle and half of its orbit outside the circle.

As planets get further from the sun, an increasing proportion of their orbit sits outside the circle.

xmcqdpt2• 3 years ago

The "paper" looks like a science fair project to me (a very good one though!) They don't really come up with a new method of calculating the distance, more like an explanation that might be more intuitive to some.

The average distance is pretty straightforward to calculate over all times using integration.

MrQuincle• 3 years ago

I guess an even closer neighbor is the sun.

dmurray• 3 years ago

Not as close as the moon.

billpg• 3 years ago

But not as high as maybe dirigibles or zeppelins or lightbulbs. And maybe clouds.

I'm sorry. I'm not sure what happened to me there.

bell-cot• 3 years ago

Yeah - casually ruling out the moon and sun in the article's first sentence feels a bit underhanded. Beyond pedantry, what's the point of the "Planets Only" sign?

varenc• 3 years ago

It’s interesting that Mercury is every planet’s closet neighbor. And of course its orbit is so close to the Sun that that average distance to Mercury is about the same as each planet’s average distance from the Sun. (Which I think is even a closer average neighbor)

pmontra• 3 years ago

Of course it's Mercury but even after I explain it to people and they understand the point, they keep saying that Venus is closest. Probably people are used to think about distance between stationary places so they look at the orbits, not to where planets are on their orbit.

By the way, that probably explains a lot of sci-fi movies where they have to go to Mars first, then Jupiter, then Saturn, then Neptune.

darkwater• 3 years ago

I think that the trick - that it's not automatic for most people - is "on average". I guess people tend to think about the minimum distance rather than the average.

adwn• 3 years ago

Probably people are used to think about distance between stationary places so they look at the orbits, not to where planets are on their orbit.

These people are more correct than you give them credit for.

1. If you look at their orbits (and not momentary positions), then the orbit of Venus is closer (less distance) to the orbit of Earth than the orbit of Mercury is.

2. It takes less delta-v to go from Earth to Venus than to Mercury.

Slow_Dog• 3 years ago

Venus has the smallest average distance from each point of the Earth's orbit to the nearest point on the other planet's orbit. I.e. whenever we're shown a diagram of the solar system, the "circle" that is Venus's orbit is closest (has the most similar size) to that of Earth's. I don't know the correct term for this measure.

NeoTar• 3 years ago

This question came up when I was studying for my PhD, and had access to software with built in solar-centric planetary locations. From what I recall, across the full-range of time available in the software (which was something like 300 years) it did apply that the Mercury-[PLANET] distance was minimal, although possibly not for Pluto since 300 years is only like one-and-a-quarter orbits.

knome• 3 years ago

it is interesting that earth spends more time with mercury closer than venus due to orbital mechanics, but the entire premise of the article is just an annoying "gotcha" twist of language.

the planet earth is ever nearest to is Venus, which is what people will mean by "closest neighbor". if you work from home and your next door neighbor works at the office, it doesn't make the retired lady in the next house over your closest neighbor, regardless of spending more time in closer relative proximity to her.

mercuryftw123• 3 years ago

I don't think that way. It's more like this: your two blocks down the street neighbor drives by you every morning, would you classify it being closer to you? Because that's how we look at the Venus at the moment. Mercury should be the real neighbor.

vertis• 3 years ago

I think a better example is neighbour 1 drives past your house once a day and neighbour 2 drives past 10 times a day on the main road several blocks further from your house. If you needed a lift somewhere (or some other reason to interact), you can either wait patiently for N1 to drive past or you can walk the several blocks to the main road, and then wait less time for N2.

inopinatus• 3 years ago

If we're talking about transportation, well then. The efficient transfer to Mercury is via Venus transfer, so it is farther by such reckoning. In terms of delta-v budget, Venus is actually closer than Mars, unless you wanted to, say, visit the surface.

See https://upload.wikimedia.org/wikipedia/commons/9/93/Solar_sy..., essential information to plan your next interplanetary holiday

davidgrenier• 3 years ago

I had never heard of the concept of closest average neigbor before. When I read it, I assumed it meant: draw a straight line between the two bodies, that is the current distance between the two bodies, now average it over a couple of years of motion of these two bodies in space.

manojlds3• 3 years ago

But in this case the house itself is moving.

If Mercury and Venus had people, which of those people is our closest neighbour?

otabdeveloper4• 3 years ago

Whichever one has smaller delta-v.

adql2• 3 years ago

The one with smallest ping

0xFF0123• 3 years ago

Taking your argument to the extreme, if there was a planet that somehow brushed by extremely closely to Earth every thousand years, that planet would be the closest neighbor? I would argue not. I think the average is more meaningful.

Ensorceled• 3 years ago

To return to the analogy, if once a year my brother-in-law parks their RV in my drive, nobody would be confused about who my closest neighbour is.

I would argue that MOST people would disagree with you and would say Venus is our closest neighbour but once every 1000 years wobbly Erebus returns from the dark to scare the hell out of us.

xwdv• 3 years ago

If I have a house and you have a house next to me yet neither of us are ever home, we are still neighbors no matter where in the world we are.

Similarly, the entire area earth and Venus clear with their orbits is the planet’s “home”, therefore, we only have two neighbors, Mars and Venus, and Venus is probably the closest.

thx-2718• 3 years ago

Both have independently useful meaning.

The average closest planet would be useful for regularly traveling between two places.

The closest at any one time is useful for planning intermittent trips.

Let's say we had to pick 2 equal planets we would travel to. Adding the stipulation that planet A is closer on average to HOME than planet B; Planet B has the shortest distance to HOME.

If travel is cheap then planet A is more useful to travel to since you can afford to do it regularly.

If travel is expensive then planet B is more useful since you can't afford travel all the time and rather need to make sure each trip is worth.

If you live in a city it's more reasonable to go to the grocery every week.

If you live in a rural area it's more reasonable to wait for the Shwan truck (type of grocery delivery) once a month.

tectec• 3 years ago

What kind of orbit would that be? In order for it to be that close so rarely it must spend most of its time even further from earth.

BurningFrog3• 3 years ago

Halley's Comet might fit that description.

dahfizz• 3 years ago

The term "neighbor" here is confusing. Venus has the planetary orbits right next to Earth's. That makes them "neighbors" - they live right next door from each other.

Mercury is the closest planet on average, but calling it the closest neighbor is just confusing.

dreamcompiler• 3 years ago

it doesn't make the retired lady in the next house over your closest neighbor, regardless of spending more time in closer relative proximity to her.

It does matter a lot if you're trying to send a rocket to a particular one of those neighbors at a particular time.

zamadatix2• 3 years ago

In that case you probably want a delta-v not distance.

rini17• 3 years ago

As light flies yes. But not closest to get stuff there (delta-v). Probably that's where Venus comes in.

deafpolygon• 3 years ago

I guess, Mercury's relationship with the other planets is quite... mercurial.

I'll see myself out.

scrapheap• 3 years ago

So on average Mercury is closer than Venus, but if you're willing to wait then Venus can be closer that Mercury :)

yieldcrv• 3 years ago

interesting how this describes the regional banking crisis

curiousObject• 3 years ago

Venus is not Earth’s closest neighbor

Would it be correct to say that, on average, that statement is false for more than half of each Earth year?

manojlds3• 3 years ago

It's more like 38% of time. Mars is also in picture and it's about 18% of time. Mercury is about 44% of time.

fisian• 3 years ago

It just depends how you measure "closest".

Similarly, Mount Everest is the highest mountain (above MSL), however Mauna Kea is higher if measured by prominance (starting from its base which is under water).

thrdbndndn• 3 years ago

But under what definition of "closet" would it be Venus?

According to CGP Grey's video linked in the comments, not only Mercury has lowest average distance to Earth, it's also spend the most time being the closest planet to Earth, so it already met two definitions I can think of.

jiri• 3 years ago

You can use delta-v, so the closest is the distance rocket use the least fuel/mass. It is a very good measure how easily to get to that destination in space.

scrollaway• 3 years ago

Which orbit is the closest to earths orbit.

jjk1663• 3 years ago

Venus gets closer to Earth than any other planet, which is a perfectly cromulent definition of closest.

ta12433• 3 years ago

When saying Mauna Kea starts at the base, why not claim that with Everest?

Of course in reality neither are the highest mountain, that honour goes to Chimborazo, a good 2.1km higher than Everest (when measured from the Earth's centre)

bee_rider• 3 years ago

I’m pretty sure the tallest mountain in the solar system is Olympus Mons. Unless you measure it from the Earth’s center, in which case I guess it would be something, anything, on Pluto.

2d8a875f-39a2-4• 3 years ago

Very droll. Reminds me that "teaspoon half-life" paper.

fingerlocks• 3 years ago

The title should include On Average, but that makes the article less clickable. I wonder if they’ll update the title when Venus whips by later this year.

amelius• 3 years ago

But is Earth Venus' closest neighbor?

yreg2• 3 years ago

Everyone's closest neighbor is Mercury by this methodology (or Sun if you count it).

quickthrower2• 3 years ago

The paradox is because we use neighbour to mean something else. Imagine 10 RVs doing road trips through SE Asia. Most do extensive tours across multiple countries. One of them stays around a small town the whole time but is on average the closest to any given other van, but never that close to really be called a neighbour but then we call it a “neighbour”

perihelions2• 3 years ago

I think you can replace the whole analysis with a single diagram. You don't actually need to find the closed-form solution in terms of elliptic integrals; the only part we use is whether the integrals have a certain monotonicity property (smaller radius => smaller mean distance). And you can rearrange the "mean distance" integrals in way that the rearranged integrands are pointwise monotonic; and the proof that they're monotonic is an elementary geometric one.

perihelions2• 3 years ago

And here it is, proof in one picture:

https://i.ibb.co/kxjDbWP/a.png

Pure classical geometry (I think?)

The integral over the circle can be rewritten as an integral of a sum of two terms over a semicircle – the term for the local point, plus the term for the mirrored point on the other semicircle. This sum-term is an everywhere-monotonic function of the radius of the circle (in the proof diagram: XA + XB > XC + XD).

(XAQB, XCRD, and XC¹QD¹ are constructed as parallelograms. XC¹RD¹ doesn't mean anything; it's just a construction whose perimeter compares easily against the other two).

beeforpork• 3 years ago

Kinda weird argument. The average actual distance of two planets on some orbits can be expected to be roughly equal to the distance of the farther planet from the sun (because the max. distance is r2+r1 and the min. distance is r2-r1, so this type of 'average distance' is ((r2+r1)+(r2-r1))/2 = r2), of course with some variation because the orbits are not truely uniform nor truely random.

The usual notion of comparing the orbit radii is way more intuitive, I think.

BlackLotus89• 3 years ago

Awesome video of CGP Grey https://www.youtube.com/watch?v=SumDHcnCRuU talking about relative positions of planets

Oh and don't forget the followup https://www.youtube.com/watch?v=LIS0IFmbZaI :)

Edit just saw that someone already commented this ^^

lc9er• 3 years ago

“…the closest, the mostest” is the line I always remember from that video.

Symmetry6• 3 years ago

Which planet happens to be the closest to us right now is the metric most congruent to people's notion of closest and is often important for things like time delays in radio communication. By that metric it's currently Mercury, closely followed by Venus[1]. But it will change and keep changing.

In terms of how hard it is to get places you really want a delt-v map[2]. By that metric Venus is the closest at 640 m/s from Earth intercept to Venus intercept.

It's sort of interesting that, over an indefinite period of time, Mercury is closest on average but that doesn't really correspond to our intuitive notion of "closest" nor is it a particularly useful metric for anything that comes to mind. So the whole gotcha here is really pretty silly.

[1]https://www.theplanetstoday.com/

[2]https://i.imgur.com/AAGJvD1.png

MayeulC2• 3 years ago

By that metric Venus is the closest at 640 m/s from Earth intercept to Venus intercept

By the way, I think there is a typo on that delta-v map. I doubt low Venus orbit to Venus is 27km/s, vs 9.4 for the earth, when Venus gravity is just 90% that of Earth.

mnw21cam2• 3 years ago

Depends on whether you take atmospheric drag into account. If you do, then you'll be fighting Venus' thick atmosphere all the way up, and that 27km/s figure could well be accurate.

I don't like it when delta-v maps include atmospheric drag, because the numbers depend on how aerodynamic your rocket is, in contrast to the other manoeuvres where the amount of delta-v doesn't depend on the type of rocket you have at all.

Symmetry6• 3 years ago

The numbers for reaching LEO include typical atmospheric drag losses. That's only a km/s or so on Earth but on Venus with it's very thick atmosphere the losses are much higher.

akolbe• 3 years ago

Basically, the average distance between one planet and another will always be greater than the distance between the respective planet and the sun. (Note that in the table on the last page, all average planet distances for earth are > 1 AU.) Thus whichever planet is closest to the sun will always be the closest on average to any other planet.

Asraelite• 3 years ago

This is true for the Solar System because all our planets have near-circular orbits. Suppose though if you had two planets with highly elliptical orbits and similar arguments of perigee. They will spend most of their time far away from their star but relatively close to one another.

I'm not sure if such an elliptical orbit would be possible while still classifying them as planets and not dwarf planets though.

Mystery-Machine• 3 years ago

Almost true. Good thinking though. There are exceptions to this rule, so it's more of a guidance than the actual rule. For example you could have two planets orbiting the Sun at the relatively similar distance from the Sun and a small distance from each other.

BurningFrog3• 3 years ago

Before morning coffee:

Over an indefinite period of time, I'd expect that all planets are on average placed in the center of the Sun, and equally far away.

Now:

Oh, right. It's not the distance to the average, it's the average of the distance.

madcaptenor• 3 years ago

And the error in your approximation goes up as the orbit gets bigger, which recovers the original result.

dr_dshiv• 3 years ago

Which planetary orbit is closest to Earth’s? That’s what I think people are meaningfully thinking.

ianai• 3 years ago

Venus by that measure.

svachalek• 3 years ago

Yup, that's equivalent to the delta-v definition afaik. (Venus)

ryanmcbride2• 3 years ago

This exact reasoning is why I've always been kind of annoyed by the song Bitch Don't Kill My Vibe by Kendrick Lamar. In the chorus he goes "I can feel your energy from two planets away" and even though I know art doesn't have to conform to scientific reality, poetry and music almost especially, it ALWAYS bugged me from the first time I heard it til today. Like what does 2 planets away even mean? that's a hugely variable distance.

hinkley• 3 years ago

    We're heading for Venus
    And still, we stand tall
    'Cause maybe they've seen us
    And welcome us all, yeah
    With so many lightyears to go
    And things to be found
    I'm sure that we'll all miss her, so

    It’s the final countdown

Someone’s science teacher knows who was too busy writing lyrics in class to learn about outer space…

olddustytrail• 3 years ago

Heh, reminds me of the Simon Singh criticism of Katie Melua's "Nine Million Bicycles".

Which she followed up on https://m.youtube.com/watch?v=21iUUe-W8L4

yazantapuz• 3 years ago

It means that is a huge distance, in human terms. Hugely variable, but huge at the end.

zuminator• 3 years ago

Haha that's an interesting question. I'm figuring that the closest "2 planets away" would be the canonical distance between Earth and Mercury, ie 57 million miles (92 million km).

But it's the other extreme that's more interesting.

Let's say that for a planet to be the "next" planet over at any given time, it has to be the closest one... by direct line measurement, not by orbit. So for Earth, the next planet over could be at any given time Mercury, Venus or Mars. The most isolated Earth can be from all other planets would be when the planet that is closest to us at a given moment is as far away is it can be. That turns out to be Mercury, whose maximal distance is about 138 million miles away (222 million km). There's always going to be a planet that is that distance to us or closer.

So imagine that Mars happens to be 137 million miles from us while Mercury and Venus are both at least 138 million miles away. That would make Mars the "next" planet over. Then the "next" planet over from Mars could be either Venus or Mercury. If we're assuming Mars is as isolated as possible than the next closest planet besides Earth would be Mercury which at its furtherst could be at most 198 million miles away (319 million km). Thus, ignoring trigonometry which would put a constraint on the Mercury-Mars leg of the triangle, two planets away from us could be at most 336 million miles (540 million km) away.

So between 57 and 336 million miles is your answer.

hulahoof• 3 years ago

I always assumed this line uses the traditional order of planets from the sun and referenced the common trope that "Men are from Mars, Women from Venus".

adql2• 3 years ago

In terms of how hard it is to get places you really want a delt-v map[2]. By that metric Venus is the closest at 640 m/s from Earth intercept to Venus intercept.

Well, that's also a minimum that changes over time. It might be closest at a particular moment but still not "on average"

distortionfield• 3 years ago

Did you read to the end? The point of the paper is not the gotcha about which planet is really closest. Their point is that their PCM method allows you to quickly estimate distances between groups of planetary bodies in a novel way. They aren't trying to be "gotcha" about it, they're introducing a new model for estimating solar distances.

nuncanada• 3 years ago

Yup silly.. And people consider the closest mostly in the sense of the closest distance between orbits not distance between planets...

eyelidlessness• 3 years ago

I don’t understand. Two objects are on average closest, but that’s unintuitive because another object is closer based on some astronomical measurement which isn’t distance, which is more intuitive how?

aexol• 3 years ago

Great discovery ;)

plank• 3 years ago

Yes, play of words. And with a choosen weight function.

If, e.g., the weight function would not be ‘sum over all distances in a given timeframe with the same weight’ but for instance ‘… with weight 1/(distance^2), the results would be different (mercury would not win for each planet).

I guess if someone asks, ‘which neighbour’ is closest, I would say the neighbour living literally next door, even though on workdays our distance is much larger (as we work in different cities) then that other neighbour three blocks down who works in the same city as myself.

belter• 3 years ago

Technically, Earth also does not rotate around the Sun, instead around the center of mass of the Solar system...

https://spaceplace.nasa.gov/barycenter/en/

https://space.stackexchange.com/questions/9365/do-the-planet...

ta12433• 3 years ago

The barycentre of the solar system moves, sometimes it's well inside the Sun, sometimes it's just outside. I wonder what the average position is...

However the Earth-Sun barycentre is always inside the Sun.

Ekaros• 3 years ago

Which planet on average have shortest travelable route? That is not one going through huge hot blocking object.

ta12433• 3 years ago

Shortest measured how?

As a photon flies? Mercury.

In terms of energy required to get there? Venus.

In fact Mercury is the furthest planet in terms of energy required -- it's easier to get to Neptune than Mercury.

In time to get there assuming minimum energy and no gravity assists from other planets? Venus I think, but maybe Mars.

short_sells_poo• 3 years ago

I suppose another very loosely defined notion of closeness is the degree of human habitability, in which sense Mars might be closest. Both Venus and Mercury are incredibly hostile environments, although one could argue for floating cities on Venus and a thin habitable zone at the poles of Mercury.

I understand of course that anywhere "not on Earth" is incredibly hostile to Human life, at least what we can see with present day technology. For truly habitable planets, we might have to consider other star systems and even then there's no guarantee we'll find one.

I don't know to what degree is the abundance of oxygen as a loose element a sign of life, but I'd expect it to be bound to minerals anywhere without significant plant-like life. Perhaps finding another habitable planet is the same task as finding life on another planet?

vikingerik2• 3 years ago

And why is Mercury so hard to get there in terms of energy required? It's because its orbital velocity is so fast and you need to match that. (You can get there without matching the orbital velocity, but that won't be useful, you're either doing a non-capturable flyby or a very hard impact.)

Mercury's orbital velocity is 48 km/s. Earth's is 30. An object at infinity would be zero. Kinetic energy is proportional to velocity squared. Square those numbers and you see the energy differential between Earth's orbit and Mercury's is greater than going from Earth to infinity.

jasonlotito• 3 years ago

The difference between closest planet on average versus closest orbit.

jtbayly• 3 years ago

Of course Mercury is the closest to everybody else on average. That's why they made him the messenger God!

passwordoops• 3 years ago

Reminds me of this classic SMBC about the fastest animal

https://www.smbc-comics.com/?id=3457

ttfkam2• 3 years ago

I find it amusing seeing so many otherwise intelligent people so upset about a fact that contradicts their intuition. It's like when you tell people that if you throw a baseball from the International Space Station toward the Earth, the ball will end up in front of you and behind you at various points in the orbit.

Reminds me of the quote: The universe is under no obligation to make sense to you.

macspoofing2• 3 years ago

I find it amusing seeing so many otherwise intelligent people so upset about a fact that contradicts their intuition.

It's not quite that. It's a semantic issue. Colloquially, people think of "the closest planet" as a planet having an orbit closest to that of earth's, whereas the article proposes a different definition of 'average distance' between the planetary bodies. Both definitions are correct, but I argue that the former definition is actually better as it conveys more information about the structure of the solar system, and is more intuitive.

ttfkam2• 3 years ago

As I said, amusing.

ryandrake• 3 years ago

I find it amusing seeing so many otherwise intelligent people so upset about a fact that contradicts their intuition.

Find a smart person who's never heard of the Monty Hall Problem[1] and tell them the answer without an explanation. They'll want to fist fight you over it. Even after you prove it with math, some won't believe you.

1: https://en.wikipedia.org/wiki/Monty_Hall_problem

renewiltord2• 3 years ago

It's like how people don't realize that the sum of 1 and 1 is 0. Many smart people will disagree but it is nonetheless a fact.

macspoofing2• 3 years ago

It's like how people don't realize that the sum of 1 and 1 is 0. Many smart people will disagree but it is nonetheless a fact.

No, it isn't a fact. This assertion is a common internet troll trick that relies on misusing the "product property of square roots" [i.e. sqrt(xy) = sqrt(x)sqrt(y)], with the "trick" being that the "product property" is only applicable for x,y >= 0 and x,y ∈ ℝ, and therefore cannot be used to "prove" 1+1=0.

Why purposely mislead people who may take you at your word?

arp242• 3 years ago

That Mercury is closer than Venus on average is very intuitive: it just never gets very far away from us due to its orbit being so close to the sun. Makes perfect intuitive sense to me.

But this is not a math or intuition problem, it's about ambiguity on what exactly is meant with "closer" – you can have multiple definitions of that: "closest at this particular point in time", "closest at any point in time", "closest on average". None of these are more correct than any other.

friend_and_foe• 3 years ago

If you look at the chart at the end of the article, Mercury is every planet's nearest neighbor by their methodology.

All they're finding is "on average each planet is closer to the sun than any other planet" which isn't saying anything.

magneticnorth• 3 years ago

I appreciated having this pointed out to me - it's fairly clear once the point is made, but I'd never really thought about it. Of course most of the time other planets are over on the other side of the sun and very far away, but it's easy to just picture the school-style orbital map where everything is in a line together and closest approach = closest, period.

I dunno, I thought it was neat! A slight paradigm shift in how I think about the solar system.

RheingoldRiver• 3 years ago

SAME! I was waiting for this comment. To me this is result is wonderful! It's like, the physical world behaving in an intuitive, mathematical way once you realize it. I loved reading this.

I love it.

anton-107• 3 years ago

and is there no such pair of planets that revolve around the Sun while staying on the same "side" of the Sun?

dabluecaboose• 3 years ago

The way orbits work, orbital velocity is tied to distance. So unless the planets were in the same orbit, one is going to be going faster than the other (the closer one in a radial velocity sense is moving faster, and the further one in a tangential velocity)

jalk• 3 years ago

Oh, this perhaps explains why my horoscope is wrong a lot of the time

dav_Oz• 3 years ago

Distance: a straight line (i.e. shortest line in Euclidean geometry) between two points - is a one dimensional object/projection. On Earth crust where we evolved as 1 m long objects immersed in 1 atm of mostly nitrogen at around 290 K and at a constant pull at 1 g on a spinning ball at 11.5 µHz ... you get the idea ... a very straightforward concept.

Applying it to dust and gas particles (massive enough for gravity to shape it into a spinning sphere) in a vacuum falling towards (on a stable enough orbit) a gas ball with 99.8% of the total mass in the system, itself in hydrostatic equilibrium with its own gravity pull through nuclear fusion of hydrogen into helium ... Well, we are not used to that kind of motion i.e. geometry on astronomical scales. But once you see what dictates the (near) stable motions of all those tiny particles the solution is simple: in the solar system the sun is nearest to all objects in the system, on average. Whatever is nearest to the Sun is the closest on average to all other elliptical moving objects. From Neptune's perspective Mercury is barely moving and oscillating so fast as to standing still. So, in the case of planets the underlying geometry is moving along (stable) elliptical (i.e. closed path) orbits (approx. Newtonian mechanics), applying our "straight" lines for "distance" is amiss here and can lead to confusion. I personally like to see it more - inspired through e.g. Kepler's imagination[0] - as a geometrical-dynamic system (Kepler orbits) more akin to music.

[0]https://en.m.wikipedia.org/wiki/Harmonices_Mundi

ecocentrik• 3 years ago

Is the point of this paper that astronomers should be more careful with their descriptive terminology and avoid using words like neighbor and neighborhood that describe static relationship when those relationships don't apply? If so, that's probably a lesson we can apply more universally.

sbussard2• 3 years ago

This is academic click bait. No astronomer is shocked by these conclusions. It is a waste of time.

hgsgm5• 3 years ago

Not everyone is an astronomer.

Not everything needs to be "shocking".

sbussard2• 3 years ago

It is still trivial

fnovd• 3 years ago

This is only true when it is meaningless.

Let's say my friend was born on January 2, 1900, and I was born on January 1, 1900. Who has the closer birthday to someone born on January 1, 2000?

If you say it's me, well guess what, you're wrong! My birthday is 1 day farther away, just count the days.

If you say it's my friend, well guess what, you're wrong! January 1 == January 1. It's the same birthday, obviously.

Incidentally this is why I think LLMs are a lot more impressive than many here give them credit for. Language is ambiguous and being able to create something novel & coherent using an algorithm is an amazing achievement. Embedded in our use of words is a lot of information that is often incongruent with the understood meaning of the word, as this example shows. Apparently humanity itself has two divergent "hallucinations" of what the word "closest" means in this context. We really can't blame the AI for imitating us when that's what we ask it to do.

TheSpiceIsLife• 3 years ago

throwaway5752• 3 years ago

In the commonly understood way, orbitally, Venus definitely is Earth's closest neighbor.

I appreciate pedantry as much as the next person, and it's an interesting article, but this article article and the approach outlined would not aid survival to an interplanetary colonist. They could enjoy being technically correct in the short remainder of their life, while being carbonized. And to follow up pedants, I am well aware of surface conditions on Venus.

vba616• 3 years ago

Skimming the comments, I didn't see anyone specifically making the simple observation that the minimum distance corresponds to intuition.

Is arbitrarily choosing the average distance for the concept of "closeness" being pedantic, or just obtuse?

shmerl• 3 years ago

Supposedly Mercury is closest to every other planet at some point. But since distances change all the time, there is no constant "closest".

jjk1663• 3 years ago

We speak a language made for medieval peasants to talk behind their lords' backs, it's hardly surprising that our vocabulary leads to ambiguity when talking about orbital mechanics.

NovemberWhiskey• 3 years ago

I suspect that if you're defining "closest neighbor" using anything other than a delta-v budget, you are probably doing it wrong.

mikeInAlaska• 3 years ago

Mercury by average. I've wondered in the past it we could land people on Mercury... at the right distance from the sunset terminator where the surroundings had cooled to, say 21 degrees C, (70F). With a 1408 (Earth) hour day, the landing party could stay for quite a while before needing to relocate again towards the terminator, or leave.

cratermoon• 3 years ago

The PCM treats the orbits of two objects as circular, concentric, and coplanar.

Keeping the coplanar assumption, in common with previous estimates, may be a problem. Mercury happens to have an orbital inclination of 7°, second only to Pluto's at 1x7°. Mercury also orbits in an ellipse with an eccentricity of 0.21. Again, this is second only to Pluto, with an orbital eccentricity of 0.25.

I'd like to see a model that takes into account inclination and eccentricity. For the most accurate model, the concentric assumption also fails. Strictly speaking, none of the planets orbit the sun. Rather, the sun and the planet both orbit the barycenter of the sun-planet system, and that will be different for each planet. While the difference is negligible for most planets, for Jupiter the barycenter is quite a distance from the center of the sun: at 1.07 times the diameter of the sun. That's just shy of 100,000km above the surface of the sun.

ilyt• 3 years ago

That's like saying "Jeff isn't my closest neighbour because he goes to work every morning, while John WFH, so on average John is closer"

Technically correct but not exactly first thing you think about.

rdlw• 3 years ago

To force the analogy into a slightly more accurate mold, it's more like if John actually moved away every morning and moved back every afternoon.

Venus is not Earth’s closest neighbor (2019) [pdf]

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