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Venus is not Earth’s closest neighbor (2019) [pdf]
- curiousObject 3y agoVenus 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?
- manojlds 3y agoIt's more like 38% of time. Mars is also in picture and it's about 18% of time. Mercury is about 44% of time.
- TheSpiceIsLife 3y agoNo
- hpaavola 3y agoCPG Grey, Which Planet is the Closest?: https://www.youtube.com/watch?v=SumDHcnCRuU https://www.youtube.com/watch?v=SumDHcnCRuU
- Blammar 3y agoThe most surprising conclusion is that Mercury is on the average closest to ANYTHING that orbits the sun, including (presumably) long-orbit comets!
- yreg 3y agoIt's totally unintuitive, but makes perfect sense once you know the answer.
- orlp 3y agoThis 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_toad 3y agoThe whirly dirly corollary. talk about cosmic apotheosis.
- m348e912 3y agoDoesn't this also imply that the sun is mostest closest to any planet than any other planet?
- ithkuil 3y agoI 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
- manojlds 3y agoWhy do you complicate it talking of surface vs center of sun. Sun is sun. That's it.
- ithkuil 3y agojust because it made it easier for me to reason about the fact that since the sun has some actual width it's exactly equivalent to a body that would orbit at that distance. If you frame it that way then it's rather obvious that the sun also fits the bill as the "mostest closest body" (albeit not planet)
- hgsgm 3y agoThe center of the sun has the same property, with simpler 0 size orbit.
- ithkuil 3y agoit's not intuitively clear to me whether that is on average closer to the earth or if it's on average exactly as far as something orbiting around that center. Furthermore, since the sun is also orbiting around the shared center of mass of the whole solar system, this displacement albeit very small, is still enough for me to not intuitively understand if it makes the sun's center of mass closer or farther away on average than the closest orbiting body to the sun
- 8note 3y ago"Closest the mostest" makes it feel like less of a gotcha
- pimlottc 3y agoTL;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 3y agobecause other planets use to appear too far sometimes, as it has been shown by whirly-dirly simulation
- nordsieck 3y 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 3y agoThe "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 3y agoI guess an even closer neighbor is the sun.
- dmurray 3y agoNot as close as the moon.
- billpg 3y agoBut 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 3y agoYeah - 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 3y agoIt’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 3y agoOf 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 3y agoI 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 3y 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 3y agoVenus 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 3y agoThis 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 3y agoit 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 3y agoI 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 3y agoI 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 3y agoIf 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_system_delta_v_map.svg https://upload.wikimedia.org/wikipedia/commons/9/93/Solar_sy..., essential information to plan your next interplanetary holiday
- aidenn0 3y agoSo to stretch the analogy to its limits, what if you have someone who lives directly across the freeway from you, and a neighbor whose house is next to the overpass that lets you cross the freeway.
- rini17 3y agoAs light flies yes. But not closest to get stuff there (delta-v). Probably that's where Venus comes in.
- deafpolygon 3y agoI guess, Mercury's relationship with the other planets is quite... mercurial. I'll see myself out.
- scrapheap 3y agoSo on average Mercury is closer than Venus, but if you're willing to wait then Venus can be closer that Mercury :)
- yieldcrv 3y agointeresting how this describes the regional banking crisis
- aaron695 3y ago[dead]
- fisian 3y agoIt 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 3y agoBut 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 3y agoYou 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 3y agoWhich orbit is the closest to earths orbit.
- jjk166 3y agoVenus gets closer to Earth than any other planet, which is a perfectly cromulent definition of closest.
- ta1243 3y agoWhen 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 3y agoI’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 3y agoVery droll. Reminds me that "teaspoon half-life" paper.
- fingerlocks 3y agoThe 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 3y agoBut is Earth Venus' closest neighbor?
- yreg 3y agoEveryone's closest neighbor is Mercury by this methodology (or Sun if you count it).
- quickthrower2 3y agoThe 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”
- perihelions 3y agoI 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.
- perihelions 3y agoAnd here it is, proof in one picture: https://i.ibb.co/kxjDbWP/a.png 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).
- aexol 3y agoGreat discovery ;)
- beeforpork 3y agoKinda 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 3y agoAwesome video of CGP Grey https://www.youtube.com/watch?v=SumDHcnCRuU 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 https://www.youtube.com/watch?v=LIS0IFmbZaI :) Edit just saw that someone already commented this ^^
- lc9er 3y ago“…the closest, the mostest” is the line I always remember from that video.
- plank 3y agoYes, 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.
- Symmetry 3y agoWhich 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/ https://www.theplanetstoday.com/ [2]https://i.imgur.com/AAGJvD1.png https://i.imgur.com/AAGJvD1.png
- MayeulC 3y 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.
- mnw21cam 3y agoDepends 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.
- TeMPOraL 3y agoHere is the OG source of those numbers: https://old.reddit.com/r/space/comments/1ktjfi/deltav_map_of_the_solar_system/ https://old.reddit.com/r/space/comments/1ktjfi/deltav_map_of.... Skimming the thread, they made "assumptions" for cases like taking off from bodies with atmosphere. Here is more on how they came up with the number for Venus, including some actual math: https://old.reddit.com/r/space/comments/1ktjfi/deltav_map_of_the_solar_system/cbsq64k/ https://old.reddit.com/r/space/comments/1ktjfi/deltav_map_of.... The OG image mentions that there are assumptions being made. The image linked by GP is a derivative work, improving on and crediting the work of /u/CuriousMetaphor, however it omits some of the caveats in the legend.
- belter 3y agoTechnically, 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://spaceplace.nasa.gov/barycenter/en/ https://space.stackexchange.com/questions/9365/do-the-planets-really-orbit-the-sun https://space.stackexchange.com/questions/9365/do-the-planet...
- ta1243 3y agoThe 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 3y agoWhich planet on average have shortest travelable route? That is not one going through huge hot blocking object.
- ta1243 3y agoShortest 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 3y agoI 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?
- vikingerik 3y agoAnd 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 3y agoThe difference between closest planet on average versus closest orbit.
- given 3y ago[flagged]
- jtbayly 3y agoOf course Mercury is the closest to everybody else on average. That's why they made him the messenger God!
- passwordoops 3y agoReminds me of this classic SMBC about the fastest animal https://www.smbc-comics.com/?id=3457 https://www.smbc-comics.com/?id=3457
- ttfkam 3y agoI 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.
- macspoofing 3y 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.
- ttfkam 3y agoAs I said, amusing.
- George83728 3y agoSince you invoked the "universe making sense", I'll explain this using an example created by man: "The Space Shuttle Orbiter reentered the atmosphere at approximately Mach 25, making it the fastest aircraft ever flown." The Mach 25 reentry is an empirically verifiable fact. But reasonable people can object to the above assertion on grounds that have nothing to do with that verifiable fact; what exactly constitutes an aircraft and what is the proper way to compare the speeds of aircraft? A reasonable person can assert that speed comparisons between aircraft must be made in level flight, making the shuttle orbiter ineligible for such a record. Some may also object to the characterization of the shuttle orbiter as an aircraft, or the implicit exclusion of other reentry vehicles which were even faster. The universe does not have any objectively correct definition of aircraft, or any objectively correct way to compare aircraft speeds. These are wholly subjective. It has nothing to do with people "wanting the universe to make sense." Similarly, the universe does not hand us any objectively correct meaning of a planet's "neighbor". Nobody in this thread has disputed any objective empirical facts. The disagreement is solely around the subjective meaning of the ill defined term "neighbor". The disagreement is over pure semantics, not science.
- friend_and_foe 3y agoIf 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.
- anton-107 3y agoand is there no such pair of planets that revolve around the Sun while staying on the same "side" of the Sun?
- dabluecaboose 3y agoThe 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)
- magneticnorth 3y agoI 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 3y agoSAME! 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.
- jalk 3y agoOh, this perhaps explains why my horoscope is wrong a lot of the time
- dav_Oz 3y agoDistance: 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 https://en.m.wikipedia.org/wiki/Harmonices_Mundi
- ecocentrik 3y agoIs 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.
- deleted 3y ago[deleted]
- _9hey 3y agoThis is academic click bait. No astronomer is shocked by these conclusions. It is a waste of time.
- fnovd 3y agoThis 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.
- deleted 3y ago[deleted]
- throwaway5752 3y agoIn 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 3y agoSkimming 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 3y agoSupposedly Mercury is closest to every other planet at some point. But since distances change all the time, there is no constant "closest".
- deleted 3y ago[deleted]
- jjk166 3y agoWe 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 3y agoI suspect that if you're defining "closest neighbor" using anything other than a delta-v budget, you are probably doing it wrong.
- mikeInAlaska 3y agoMercury 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 3y 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 3y agoThat'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 3y agoTo 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.