What If The Moon Were Replaced By Other Planets? | Hacker News Reader

What If The Moon Were Replaced By Other Planets?

boredpanda.com

84 pointsdhruvbhatia37 comments

What if the earth had rings like Saturn:

http://io9.com/if-earth-had-a-ring-like-saturn-508750253

The author describes how bright they would be at night and what they would look like at different locations on the planet.

Wow, now I will never be able to look the same way at our boring, ringless sky.

Or give up on those boring planet things and just live on the ring itself:

http://en.wikipedia.org/wiki/Orbital_%28The_Culture%29

[NB I prefer Culture Orbitals to Niven Rings - largely due to everything else being in the Culture would imply.]

Plus, I think that if you strip away all the Culture magic-tech, their orbitals are still more plausible than Niven's Unobtanium-Brand scrith.

This video has been floating around for awhile and based on the same premise Jupiter completely obliterates the sky. I don't know which version is correct though, the video or this series of images. Just a point of comparison.

http://www.youtube.com/watch?v=DNlLnaJiGY8

Edit in reply to the below, I was just about to add that same comment... that it may be a field of view thing. This additional video seems to support to that.

http://www.youtube.com/watch?feature=fvwp&v=usYC_Z36rHw&NR=1

Start the video in a dark room with fullscreen. Awesome experience.

From the notes in youtube: "I created this video in After Effects, and because of certain technical considerations had to keep the field of view at 62 degrees"

I think you'll see that the choice of field of view makes all the difference.

Something to ponder as well. The center of the Moon is 300000km away and Jupiter is 70000km in radius! So Jupiter would bridge almost one quarter of the distance towards us.

True, but is the distance he's using in these photos the distance from center to center or edge to edge. That also poses the question of what exactly is the edge...

We all die! :-) Okay, it's cool looking. But nothing will live up to the two stars in Star Wars. :-) Though, I don't know the feasibility of the science on that one.

There are systems with twin stars.

But how stable would a planet's orbit be in a two-star system?

http://en.wikipedia.org/wiki/Twin_star_system#Planets says »Simulations have shown that the presence of a binary companion can actually improve the rate of planet formation within stable orbital zones«

two star systems are more common than a single star system in the universe.

https://news.ycombinator.com/item?id=5938999

Our neighborhood has a triple-star system!

That's a triple-planet system. Presumably millerm's asking about stable-orbit, habitable-zone planets in a multiple-star system, like Kepler 47: http://news.nationalgeographic.com/news/2012/08/120829-new-p...

Nope, the system mentioned here [1] is a triple-star system. Read the first line [2].

[1]:https://news.ycombinator.com/item?id=5938999 [2]:http://en.wikipedia.org/wiki/Gliese_667

Thank you for the correction; apologies for my error.

Someone should photoshop these up relative to the initial moon photo so that the earth is illuminated to whichever amount is correct by the reflective properties of the visiting planet. It would be cool if they accounted for hue as well. The Jupiter one would be quite bright and reddish, et cetera.

Possibly one of the most interesting things this shows is just how big space is. Even though Saturn and it's rings are nearly 30x bigger than the earth, it would still be over 200,000km from the surface of the earth in this case.

That's where the math gets fuzzy. If the earth is about 10000 kilometers in diameter (yes I am well aware I'm rounding to one sig fig, and in this case it's OK) then saturn + rings being 30 times bigger (in diameter I assume?) would be 300,000km, so being a mere 200,000km away does that mean from the center in which case we'd be part of the ring system (whoops) or a further 200 megameters past the biggest part of the rings in which case I'd call it 500,000 km away not 200,000 km.

How fast would we have to orbit if Jupiter were that close?

EDIT: Is Io closer to Jupiter than the moon is to Earth (I believe I answered this myself, I think the we would be closer in this picture by ~100,000km)? What would be the tidal effects of the depicted picture? Would we be tidally locked? I assume volcanic activity and earthquakes would at least increase and I imagine be catastrophic (if it would hypothetically replace the moon with all orbital mechanics updated to sustain a stable orbit).

I think the radiation Jupiter puts out would kill us before the Earthquakes got a chance to.

Perhaps, but I am more interested in the physical affects to the Earth.

That Jupiter one scared the crap out of me. Having watched Melancholia just recently might have helped as well: http://www.imdb.com/title/tt1527186/

Glad I'm not the only one who found the images a little freaky, for some reason I can't quite place!

When I see things like this, I always wonder how the gravitational force of these planets being so close to Earth would effect life on Earth.

Serious tides. In practice, no Earth!

Moon produces a 1m high tide in the ocean (I recollect from years ago). Moon is 1/80 of Earth mass, Jupiter is 300+ Earth masses, so 24000x as high a gravitational pull....

Well, more than tides, it would produce probably-unsurvivable levels of volcanism.

The Roche limit of Jupiter is apparently 242,000 km (I think I'm using the right one, at scale Earth has no tensile strength), and the closest the Moon ever comes is 363,104, putting us barely outside of it, but Earth is still getting pretty roiled.

Oh, and to be clear, when I say "unsurvivable", I mean for life in general. Certainly we're not looking at anything like modern multicelluar life, we're looking at what we today call "extremophiles", if we're lucky. This puts us 60,000km closer to Jupiter than Io, and also the Jupiter system is quite full of radiation. I don't know if Earth's magnetic field could shield us, and I also don't know what Jupiter's tides would do to it.

Interesting note: A World out of Time by Larry Niven ends up with Earth in Jupiter orbit. However, it was orbiting much further out. The Jovian system isn't necessarily intrinsically hostile, it's just this puts Earth way too close to it.

I'm completely talking out of my ass, but I think Jupiter would also block out the sun. But even with that, Earth would still be a VERY hot place, right? All that pressure from Jupiter must create some heat (along with the increased volcanic activity), I'm guessing. Also, am I wrong to think that Jupiter has got to look bigger than that?

Macabre as it is, it's really fun to think about this stuff.

Not to mention the radiation

http://www.sciencedaily.com/releases/2001/03/010329075139.ht...

Orbits "nearby" both gravity wells are unstable. Knowing that geostationary orbits are stable enough in the earth-moon system for commercial purposes, I think low earth orbit weather satellites would remain stable in a "small" change like Earth-Mercury. Someone with a lot more spare time on their hands will have to figure out at what point geostationary comsat orbits become unusably unstable. I have a gut feeling, not having run the numbers, that a Earth-Jupiter system might not even have stable low earth orbits for weather satellites, much less high orbit geosync for comsats.

If for example, Mars, eliminated stable enough comsat orbits, you could put transponders on the surface of Mars for Earth use. And vice versa, I guess.

I would imagine this would greatly complicate the design and operation of a usable space tether / elevator. With obvious exceptions like absolutely perfect tidal locking would mean its pretty easy to string a lightly tensioned rope from one planet to the other.

At some point I imagine even "launch loop" technology would get messed up gravitationally. Building a computer stabilized ultra small scale launch loop (like maybe 50 feet?) has always been an "in my infinite spare time" experiment idea. They're very stable under ideal conditions, the hard/fun part is all in the spinup/spindown and in perturbations and active oscillation dampening. You want a launch LOOP aka circle, not a launch LISSAJOUS.

There's more to life than just spacecraft, of course. But it is a kinda interesting topic.

Ripped off from:

http://www.dailymail.co.uk/sciencetech/article-2345679/Photo...

I just need to point out that the moon is not a planet, so the title should read "What If The Moon Were Replaced By Planets?", or something like that

...but the Earth was somehow still lit by the regular old moon?

Seriously, how did they manage to take one look at their handiwork without realizing this obvious flaw?

I believe the distance is not taken into account on this visualization. The same distance would simply make planets collide.

Who you callin' a moon, little rock ball!

I wonder how much the planets will look different when they are brought in place of moon specially mercury and neptune.

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