Adding planets to the solar system?

A question that has been gnawing at my brain for a while now: Suppose a new planet was artificially added to the habitable zone of our solar system, either between Earth and Mars or between Venus and Earth. This planet would be terrestrial with a size/mass in the Mars-Earth range.

Ignoring the logistic of this, I'm wondering if this could theoretically be done without causing major disruptions to the system. I know just enough about orbital mechanics to be aware that all the planets interact with each others through gravity, so I figure some noticeable changes are unavoidable, but that's where my understanding ends.

If the new planet is exactly between Venus and Earth, it would be about 30.5 million kilometers from either one at it's closest point of orbit. If placed between Mars and Earth, the minimum distance would be 27 million km. (Though Mars has quite a bit more orbital eccentricity than Earth and Venus.) For reference, Venus and Mercury are the two planets closest to each other in this solar system, being separated by a bit over 50 million km.

So, um, is 30-something million km too close? From what I can tell it's certainly possible for planets to be even closer, but will the new planet inevitably mess with its neighbors? I suppose you can keep it from affecting Earth too much by setting its orbital speed so that it always maintains a fixed distance from us, but that still leaves the other neighbor planet to consider. Basically, I don't want to have any collisions or Mars catapulted out of its orbit or Venus sent spiraling into the sun or whatever.

I just don't know enough about this subject to tell what would happen. Astrodynamics is really complicated and I'm a simple man who mostly writes about magic people hitting each other with swords.

 

I'm thinking (without having any real knowledge about the subject) that the planets ended up exactly where they are (orbitally) because of some balancing act that forces them to those positions. It seems like if one were added it would throw that balance way off and might cause catasptrophic effects, especially on the nearest neighbors. Possibly either they would (over a period of centuries or eons) all shift their orbits to achieve a new balance, or possibly just destruction. Or maybe just some really wicked high tides and low tides. That's about all I can think of for now.

And I really didn't say anything you haven't already covered.

 

I'd post in a physics forum, maybe r/physics. I think there is also a hard science fiction subreddit too but that doesn't mean the answers there will be accurate.

My guess is that the effects wouldn't even be noticeable on Earth, other than a new 'wandering' star.

I'm just basing it on the (possibly flawed) logic that if there would be an effect of a planet of this mass and distance added to the system, we would also experience effects when Mars is in retrograde, etc. and the distance gets greater or smaller between our planets, but I've never seen any, except maybe some annoying social media posts about how everything is going to get worse because astrology.

 

I have a program called Universe Sandbox where you can create physic simulations using planets and stars and stuff. I'm not sure how accurate it is, but anyways, I put another Mars between Earth and Mars and honestly there wasn't that much of an effect. A 24 hour day turned into a 23.9 hour day. The global temperature fell about a degree, but other than that it was still stable. I kept adding planets which didn't do much so I went ahead and added six Saturns between Venus and Earth and Earth fell into an ice age. Take of that what you will.

 

That would have a huge effect if that's accurate though (a 23.9 hour day and a one degree drop in temperature). I'm assuming you mean Fahrenheit, which would still be significant.

Edit: mainly referring to modern technology and time related systems, which affects a lot. Pre-historic mankind might not notice.

 

It was Celsius; slightly bigger shift.

 

This would catastrophic very rapidly. The planets are stable the way they are because they are in resonance with each other. This keeps the otherwise chaotic behavior of multi body physics in check.

Adding any major mass to the mix would destroy that resonance and throw the system into chaos. Planets would start drifting in their orbits.

I’m doing the forces in my head, but I’m fairly certain Venus would stall and head towards the Sun, and the Earth would speed up and be thrown into a higher orbit. We’d freeze within a few decades and in few centuries I’d imagine the oceans would freeze over completely. If Venus headed towards the sun, It’d likely get close to Mercury, which would fling it back out, likely pushing your new planet and Earth into even higher orbits where they’d start interacting with Jupiter and then everything would go into chaos.

Putting something into orbit is minimally adding to the mass of the system, but most importantly it dramatically changes the potential energy of the solar system and the gravitational interactions will cause that new energy to spread out between the planets.

 

Sure, that's very likely if it was done randomly. What I'm wondering is whether or not you can get it reasonably stable if you do it very deliberately, with insanely advanced technology and tons of complicated math and stuff. An ideal scenario, basically.

Ah yes, Reddit. That's... some kind of website, right?

Well, the planets have always been there, is the thing. Whatever influence they have is part of the system and any instabilities worked themselves out early on. For example, the moon is thought to have formed because the proto-Earth smacked into a trojan planet (Theia) whose orbit wasn't stable enough. Also, we may have had more planets early on but Jupiter migrated away from the sun which could have flung them out of the system.

At this point we don't really notice how the planets interact because it's all normal to us. However, some 19th century astronomers noticed that something was affecting the orbit of Uranus, which led to the discovery of Neptune. So, we actually found a planet simply because the behavior of another planet indicated it should exist.

I know of it, and it's supposedly pretty accurate. I should probably look into acquiring it so I can run simulations like this myself.

There are other factors as well, like the albedo (how much light the planet reflects) and what type of atmosphere it has.

Suzuzu used Mars for this, which barely has any atmosphere due to lacking a magnetic field. Putting Earth or Venus in the same orbit would have different results.

 

I still have no idea what the short or long term effects would be, and encourage you to do more research. Maybe it would be minimal and mankind would adjust. Maybe it would be catastrophic in centuries (a short period of time, obviously, on a cosmological scale).

I had never heard of the Hill Sphere but that may be a factor but the Earth's Hill Sphere is less than one million miles, but when talking about long term consequences, even forces outside that may have consequences but I think you have some artistic license there.

As has been mentioned, it's really a 'Three Body Problem'. Maybe you should make that a major plot point in your book and how that drives civilization to do amazing things. Oh wait...

 

Instead of a new planet, how about some kind of moon in orbit around Jupiter? I mean, it wouldn't receive enough sunlight, but Jupiter radiates more heat than it receives. Capturing such a planet would almost certainly expel all of the Galillean moons from Jupiter's orbit, which could cause problems of its own, of course, unless they were expelled from the Solar System.

I'm envisaging some kind of forest moon, inhabited by a race of primitive race of bear-people.

 

I think adding two planets would just muck things up more.

Isn't that also how Pluto was discovered? And I know astrologers believe that orbital variations suggest the existence of another planet (or "planetoid") out there that they call Transpluto (or Trans Pluto). Thought so:

https://www.history.com/this-day-in-history/pluto-discovered

I had never heard of that Universe Sandbox program but it sounds like the best way to approach trying to figure out the effects of adding a planet.

 

I'm pretty sure that many people would care quite a lot, actually. (Specifically, astronomy and science nerds.) Like, pointing out when science fiction gets something wrong is basically its own genre on Youtube.

Don't you think Jupiter has enough moons as it is?

Seriously, though, I just a bit infatuated with the idea of someone or something putting a habitable planet in the Goldilocks zone close to Earth. Kinda like we were handed an alien planet to practice exploring without having to leave the solar system, or it was offered as a backup Earth or something.

"Yub nub."

Yeah, there has been several hypothetical planets. Same guy who discovered Neptune also figured there should be a planet very close to the sun past Mercura, which was called Vulcan. People spent decades trying to spot it until it was concluded it doesn't exist. Turns out the physics involved were more complicated than people realized which threw off the calculations.

It's actually kinda popular among certain let's players on Youtube. Though, most just seem to use it to destroy the Earth in various ways. I saw this one video where a guy tried merging all the moons into a single body, and it basically resulted in a Mars-sized planet completely covered in water. I thought that was pretty neat.

 

There already is a potential candidate - Venus, if the atmosphere can be thinned and the slow rotation issue solved. The first one could be dealt with if (thinking out loud) a comet crashed into the planet with microbial life that converted the carbon dioxide into something else, or sequestered it into the planet's crust.

 

I think it needs a bit more than just sequestering the CO2:

Wikipedia: https://en.wikipedia.org/wiki/Venus

That's toasty even compared to Phoenix in summer.

 

The seasons and temperate zones are also influenced by the axial tilt of the planet.

If I was adding another earthlike planet I would be tempted to put it exactly opposite earth in the same orbit at the same orbital speed.

 

The 1969 film 'Doppelganger' has this exact premise. Don't think there ever was a book though.

 

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

 

That sounds like the theoretical planet I've heard of called Nemesis (probably what Naomasa just posted about).

 

No, Nemesis is something different:
https://en.wikipedia.org/wiki/Nemesis_(hypothetical_star)

(my wiki-fu is strong)

 

Wow, you know what? I had heard about it from a friend, and he seemed to think Nemesis was a planet. I suspect he mixed up Nemesis and the counter-earth planet (he does tend to mix things up a lot, or just doesn't explain them well). This is the same guy who used to come over every week or so and tell me about a new asteroid or comet that's supposed to wipe out the Earth. Each time I'd remind him of all his previous extinction warnings that never panned out, and he'd just say "Yeah, well, this time it's real man!" And then I'd say "You said that last time, and the time before that... " He's also constantly saying "Dude! They found Atlantis!!" Oh, and he keeps hearing things out in the woods, and when I ask him what he thinks it was his response is usually "I don't know, but it was big!" It always implies Bigfoot. At one point I'd ask him "How big? Big like a deer? Big like an elephant?" And he'd say something like "A little bigger than a man, and it was walking on two feet." I don't know how you could know that from hearing a sound in the woods at night.

I should know better than to pass on anything he said as factual information.

 

If Nemesis were a brown dwarf then technically it would almost be a gas planet, much bigger than Jupiter.

I thought Nemesis was another Earth clone conspiracy theory or story and even googled 'Nemesis' when I was trying to find the film 'Doppelganger'.

There's also the conspiracy theory/pseudoscience on Niburu or Planet X. But I think those revolve (no pun intended) around a planet just outside our near Solar System that is currently not visible.

 

He used to tell me about that too. In fact I suspect he was talking about several of them and just didn't make clear distinctions.

 

Suppose to new planet was added at a Lagrange point. Would that change the analysis?