9

Setup:

We are in a alternate timeline where there is a Counter-Earth that always stays perfectly on the exact opposite side of the Sun from our Earth. It has about the same size and mass as our planet, but is lifeless. It doesn't have a moon.

Everything that happened on our planet historically goes down the same way, i.e. the effective point of departure from our timeline is the discovery of Counter-Earth.

Question:

Roughly in what year would scholars first start suspecting Counter-Earth exists? When would its existence be proven? What tools would be used to do so?

Mark
  • 17,827
  • 1
  • 44
  • 85
NoUsernameSelected
  • 99
  • 2
  • 1
    Not quite a duplicate, but a number of questions have covered counter-Earths and the discovery thereof: https://worldbuilding.stackexchange.com/questions/8651/what-are-the-possibilities-of-a-dwarf-planet-orbiting-opposite-earths-orbit https://worldbuilding.stackexchange.com/questions/40225/how-technological-advanced-a-civilization-would-need-to-be-to-prove-the-existanc https://worldbuilding.stackexchange.com/questions/21479/making-a-counter-earth https://worldbuilding.stackexchange.com/questions/102685/could-two-planets-follow-the-same-orbit-and-never-see-each-other – Mark Mar 11 '18 at 08:16
  • It's probably worth reading about the Stability of the Solar System and that page summarizes some studies made into just how small a starting difference can result in huge differences over geological time scales. – StephenG - Help Ukraine Mar 11 '18 at 08:23
  • Probably when we actually get people in space or when we start sending probes nearer the sun. – skout Mar 11 '18 at 14:09
  • 2
    I am not sure you are asking the right question. Really, doesn't it amount to 'When was it discovered by our world that there was NOT another planet at the far Lagrange point L3? Such a planet has been hypothesized throughout Human history, at least since the concept of our solar system developed. We did not prove it's existence, but we did prove its non-existence. At this point, what if we had proven the opposite? – Justin Thyme Mar 11 '18 at 14:13
  • "We are in a alternate timeline where there is a Counter-Earth that always stays perfectly on the exact opposite side of the Sun from our Earth" -- not going to work. Even discounting how could it have formed, or avoided going the way of the lost planet Theia, the configuration is not stable even if you remove all other planets. With the Solar System otherwise the way it is? No way. You need large quantities of magic, or Kardashev-II planetary-sized ACS (which is the same thing, as per Clarke's Law). – LSerni Mar 11 '18 at 14:15
  • This could work, provided you are willing to re-work the entire solar system. Some handwaving at the time of the solar system creation, and a re-arrangement of the planets. What would change in our narrative would be some romantic notions of the sky. Astrology, for instance. Same thing, only different wording. – Justin Thyme Mar 11 '18 at 14:27
  • For those posting that it is not possible, we are continually finding planetary systems that are 'impossible' based on what we understood. Really, planetary systems have proven time and time again that they really don't care two hoots about our 'theories' of what is and is not possible. – Justin Thyme Mar 11 '18 at 14:32
  • @JustinThyme, you can (with some difficulty) have a system with two "Earths". Unlikely as it may seem, you could perhaps even have a system with a Moon at least partly made of cheese (or carbon compounds very like cheese, anyway). What you can't have is our Solar System with a counter-Earth, or the Earth's Moon made of cheese, because that would not "just" introduce factors outside our theories: it would actively contradict centuries of observations. – LSerni Mar 11 '18 at 14:49
  • @LSerni, you're missing a point about this site. Our job is to answer the OP's question, not deny his question because we know the factual oribtal mechanics won't work. That's his problem to deal with. We get a lot of qustions on this site where people try to not answer the question because they don't want to deal with the "fiction" in "science fiction." – JBH Mar 11 '18 at 15:49
  • 1
    @JBH, I may have expressed myself imprecisely. As things stand the planet is impossible. The OP must change something (or introduce something). I have suggested magic and alien ACS. The how the planet is there will perforce influence how it's discovered, and therefore when (that is why I've upvoted James K's answer and yours, but not RonJohn's). I do know that "my job is to answer the OP's question"... I was merely stating why I felt I was unable to do my job. – LSerni Mar 11 '18 at 16:51

4 Answers4

8

As soon as we started closely observing the sky.

https://en.wikipedia.org/wiki/Counter-Earth#Scientific_analysis

The gravitational forces of the other planets on a Counter-Earth would make its orbit unstable. Venus has 82% of the mass of Earth and would come within 0.3 AU of the location of a Counter-Earth every 20 months, providing considerable gravitational pull that over the years would move its orbit into sight of observers on Earth.

EDIT: adding @a4android's excellent comment clarifying my answer

What RonJohn is saying is that a Counter-Earth won't remain perfectly on the opposite side of the Sun. This will have happened, possibly, billion of years ago. The Counter-Earth would keep being seen as a star almost as bright as Venus & close to the Sun quite often. The ancients would know it was a planet.

RonJohn
  • 17,593
  • 2
  • 39
  • 80
  • What RonJohn is saying is that a Counter-Earth won't remain perfectly on the opposite side of the Sun. This will have happened, possibly, billion of years ago. The Counter-Earth would keep being seen as a star almost as bright as Venus & close to the Sun quite often. The ancients would know it was a planet. – a4android Mar 11 '18 at 11:28
  • There is nothing in the OP question that indicates the solar system has to mimic our own, except for the location of this alternate earth. There is nothing in the question that demands that Venus exists. In fact, Venus could BE this other planet, perhaps, with just a bit of handwaving in the formation of our solar system. – Justin Thyme Mar 11 '18 at 14:23
  • For the effects of Venus instability (or actually any gravitational instability whatever the cause), see e.g. http://farside.ph.utexas.edu/teaching/336k/Newtonhtml/node126.html . The point we're interested in is L-3. – LSerni Mar 11 '18 at 14:59
  • This is the right answer, but it doesn't really answer the OP's question. In what year did we start "closely observing the sky?" Personally, methinks it would have been at the time of Kepler and Galileo, mid-life would have been the year 1600, but it could have been as early as Copernicus, 1500. – JBH Mar 11 '18 at 15:36
  • If "everything that happened on our planet historically goes down the same way", then there must be a Venus: after all, every astrological / astronomical culture on Earth has recorded observations of this planet! – elemtilas Mar 11 '18 at 15:37
  • @JBH humans started "closely observing the sky" at least as far before Stonehenge that enough knowledge was accumulated to see the need for an astronomical calendar. – RonJohn Mar 11 '18 at 15:39
  • @JustinThyme, it's a safe assumption that if, as the OP states, history only diverges from the time of the discovery of the counter-earth, that everything else in the solar system as discoverable before that moment must be identical. Venus was one of the earliest identified celestial bodies. – JBH Mar 11 '18 at 15:40
  • @JBH in actuality, we've been observing (as opposed to "casually looking at") the heavens soon after the beginnings of agriculture. – RonJohn Mar 11 '18 at 15:42
  • RonJohn, you're right, but it wouldn't be enough to discover the counter-earth. That would require orbital mathematics and the ability to analyze orbital perturbations. Therefore, stonehenge is far too early to discover the counter-earth, which would have only been a minor effect accomodated by the creators of stonehenge. I believe the B.C.s are impossible. – JBH Mar 11 '18 at 15:42
  • Now that I really think this through, the issue of orbital math is the key to identifying the divergence. The ancients would never have seen the counter-earth as it fictionally is always on the other side of the sun. It would not be discovered by direct observation, but only through the process of explaining why the observable planets behave as they do. That puts us back to the 1500-1600 time frame. – JBH Mar 11 '18 at 15:45
  • @JBH as a4android mentioned, the drift would have happened billions of years ago. Thus, our astronomical ancestors would not have called it "Counter-Earth"; they'd have just said it was "yet another planet". Only in the Keplerian era would astronomers have deduced that it was, in fact, a Counter-Earth in the same orbit as Earth. – RonJohn Mar 11 '18 at 15:46
  • That denies the OP's requirements. As I just explained to @LSerni, avoiding the question because it doesn't meet factual analysis turns this site into physics.SE. The "fiction" in "science fiction" is the requirements the OP posted. Given that his factually impossible situation is fictionally possible, when would we have figured this out? – JBH Mar 11 '18 at 15:51
  • @JBH OP needs to edit the question to "when would we have realized that this 'other planet' was really a Counter-Earth?" – RonJohn Mar 11 '18 at 15:54
  • @JBH, The specific facts would have changed in the narrative, but it does not necessarily mean the narrative itself would change. Weather or not the tenth planet exists, it would not change anything about the historical narrative of earth to this point. Weather or not Venus exists changes nothing about our history, until we set out to explore it. So what if astrology changes slightly? If astrology itself still exists, what is different about the overall narrative? It is that change in the narrative itself which makes it 'alternative history', not the minor details of the narrative.. – Justin Thyme Mar 11 '18 at 17:30
  • The issue of Venus' discovery becomes 'So what? Perhaps Mars was the first planet discovered? Is there anything that would have changed in human history had that have been the case? Would any discovery, any war, any nation, be changed? Would any person have been, or not been, born? Would the industrial revolution never have happened? The French revolution? Does the existence or non-existence of Venus change anything about the human narrative? – Justin Thyme Mar 11 '18 at 17:40
  • That is what 'alternative history' addresses. The drastic change in the overall narrative. Not he piddling little details. – Justin Thyme Mar 11 '18 at 17:43
  • @JBH, wow, so we'd know about a counter earth for approximately 500 years and not be able to go there. What about communication with them though (assuming it had native inhbitants of course)? – Len Mar 11 '18 at 23:07
  • @Len, until you can push something into space, how can you communicate? The problem is line-of-sight and radio transmissions. This big, honkin' signal disrupter called the Sun is in the way. That means you need to bounce the signal around a ring of satelites. JamesK's answer is the practical answer, you really can't do anything about the counter-planet until you develop satelite tech and you can't reach them until you get to people-to-mars tech (half our orbit is a very long distance). – JBH Mar 12 '18 at 16:06
  • @JBH, right, but communication (if there was any to be had) would have been possible for at least the last few decades, since we do have satellites now and have even sent probes to other bodies in our solar system. We may not be able to reach them just yet, but we'd know if there were inhabitants and would have made contact by now (2018). – Len Mar 12 '18 at 17:19
  • @Len, per Jamesk's answer, we reached the ability to do that in the 1960s. The Viking mars probes were 1975ish, so that could reasonably be the first pictures sent back from counter-earth with communication tech developing slightly faster to acommodate the skip around the sun. – JBH Mar 12 '18 at 18:45
6

Given your requirements that the counter-earth orbit entirely opposite the Earth and ignoring the factual difficulties involved with this orbital alignment, when would we have discovered (aka, "proved") that the counter-earth must exist?

Answer: sometime between the years 1500 and 1600, the years of Copernicus, Galileo, and Kepler.

That's when we developed the mathematics of orbital mechanics well enough that we could determine what was causing the orbital perturbations in the other planets.

Before this time, people would have created everything from messy stories to very complex astrolabes in the effort to rationalize the planetary movements they were seeing. They would have been whomping complex and would demonstrate time and time again that something wasn't properly understood.

Once orbital mathematics moved from infancy to reasonable maturity, one of those great astronomers would have published a treatise exclaiming, "there must be a planetary body directly opposite from ours!" And that's when history would diverge.

JBH
  • 122,212
  • 23
  • 211
  • 522
  • These orbital mechanic calculations would have lead us to believe there was another planet at L3, but they are not proof. Consider that our current orbital mechanics indicate a planet in a very elliptical orbit beyond Pluto's orbit, but it is only a THEORY until it is actually OBSERVED.Planet 10? Another Earth-Size World May Lurk in the Outer Solar System – Justin Thyme Mar 11 '18 at 17:09
  • But I do agree that it's existence would have been first hypothesized in the period you indicated. Now, it begs the follow-up question be asked, "What difference would that knowledge have made, and when would it start to make a difference?" Would it matter, until we could actually GET to it? It would, perhaps, be a better (easier?) objective than Mars, as it is in the same orbit. That would put the date around the beginning of the first Sci-Fi space novels - say 1860 or so - before the narrative changed. – Justin Thyme Mar 11 '18 at 17:21
  • @JustinThyme, your follow-up question is entirely correct. While the point of divergence may have been the 1500-1600s, the amount of divergence wouldn't be substantial (perhaps not even significant) until we had the ability to care. In that regard, JamesK's answer may be the better as the world's space programs would and could launch satelites to prove the planet, which would be a measurable divergence. It would have advanced long-distance satelite recon considerably because it was close enough to be achievable and would hold the potential of life. – JBH Mar 11 '18 at 18:44
  • It would also be really, really neat for a stereoscopic view of the universe. But it would need repeater satellites. – Justin Thyme Mar 11 '18 at 19:55
5

In a system of universal gravity obeying an inverse square law, such a planet will not exist, as is discussed in other questions. As such we must suppose that gravity behaves differently in this universe. In particular I will assume that there are no gravitational consequences of this planet. It causes no perturbations of Venus, and is in a stable "orbit" of the sun.

It could not be detected by Earth bound observers. I would be hidden by the sun for anyone on Earth. It could not be detected by its reflected light off Venus (too dim)

It would only be found by space probe, probably one of the Mariner series, or the Russian Venus probes in the 1960s. As they take an image of the stars, for navigation purposes the extra bright object would be very clear and very surprising.

James K
  • 11,546
  • 28
  • 56
3

As others have noted, the gravitational pull of other planets, notably Venus, would prevent this planet from always remaining exactly on the opposite side of the sun. I haven't done the calculations, so I'm not sure if it would deviate ENOUGH to actually be visible from our Earth.

But regardless, I suppose, for the sake of the question let's assume not. Counter-Earth is always behind the Sun or so close to the Sun that it is invisible.

Once people discovered gravity and starting figuring out orbital mechanics, they would figure out that there must be another planet of this mass and in this orbit. Neptune was discovered this was in 1846, and it's effects are much smaller and more difficult to observe than Counter-Earth's would be. So absolute latest is early 1800s. I would have said earliest is when Newton formulated theory of gravity, 1687. (I'm not sure on what basis others have said 1500s. Maybe they're making different assumptions or maybe they know something about the history of astronomy that I don't.) But I'd say that -- going by the assumption that it is never visible from Earth and we can only deduce its existence from gravitational effects -- it would have been discovered sometime in the 1700s.

As to what difference it makes to history ... hard to say. How would Earth history be different if Mars or Venus did not exist? This depends a lot on how "fragile" you think history is. Think of all those time travel stories. If someone went back in time and changed one little thing, would the effects quickly peter out, lost in the rounding errors, and history proceeds as before? Or would that one small change create larger and larger ripples until history was totally different?

In this case, if someone said, "Hey, I've proven that there is this Counter-Earth on the other side of the Sun", would people basically say, "Wow, how interesting", and go on with their lives as before? Or would it lead one person to spend a night standing on a hill staring at the sky, and while he's standing there he catches cold and dies, and he was the person who would have made some crucial scientific discovery, and so, etc. Or, would someone wonder how life on Counter-Earth might be the same or different from life on Earth, and this leads him to philosophize about why history happens the way it does, and he proposes some ground-breaking new theory that changes how we look at the world, etc.

You say this world is lifeless, so there would be no issue of people communicating with the (non-existent) inhabitants. So aside from the philosophical implications, and possible "butterfly effect" sort of incidental implications, there would be no direct effect until space travel was developed to the point where people could travel there.

Jay
  • 14,988
  • 2
  • 27
  • 50