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Our Moon Could Become a Planet
anthemaniac writes "Earth's moon is drifting away from us more than an inch every year. In a few billion years, if the system survives, the moon would be reclassified as a planet under the new IAU definition. You gotta wonder if the astronomers who dreamed this definition up had thought of that."
I know a lot of the other comments about this are just saying that our system probably won't be around or that of course it won't be a moon because it's not in orbit, but what I think is more interesting is about the definition of a planet which they seem intent on creating...
Pluto may oir may not be a planet, but who cares? Don't change the definition because it doesn't change anything and it alters what we have traditionally though of it as and causes confusion with no real benifit. As to the three new planets which might come about because of this I think we should treat them with scepticism, I'm not completely against change if there will be an imporvement to understanding but I feel these things are not really in the spirit of being "planets" (I know that sounds crazy but you probably know what I mean...)
*''I can't believe it's not a hyperlink.''
So is this established fact now? I thought the that was far from proven, and even a quite debated theory.
But maybe the impact hypothesis has gained traction in the science community since I heard of this?
Beware: In C++, your friends can see your privates!
As far as the moon pulling away, it's not going to complicate anything, for a host of reason already pointed out:
- the sun will by then become a red giant and (possibly) engulf the earth and the moon;
- just what will live on earth by then, and will they care (about the moon not being the moon, I mean);
- if the moon leaves earth orbit, well it's not earth's satellite anymore, right? So what's the issue then about it being a planet.
About the whole IAU thing, the point is that there currently is *no* definition of what a planet is, apart from "something we call a planet". Planets were designated as such by tradition. It's always tricky to find a definition that matches a more or less arbitrary "accepted meaning".
Let me give it a go:
- define planetoid as a body who's mass is large enough to make it round(-ish - d'oh!) - their hydrostatic definition - and doesn't ignite; you can add arbitrary size/mass requirements if you feel like it.
- define planet as a center of mass orbiting a star and orbited by at least one planetoid.
- the biggest (by size or mass, your pick) planetoid of is designated the same as the planet, the others are designated satellites.
The problem is they're saying if a "moon" is orbiting a barycenter that's not inside another planet, then it's not orbiting that planet and becomes a planet itself. For this reason, they argue Charon is a planet, rather than a moon.
The problem is that barycenter of Jupiter's orbit around the Sun is also outside the Sun. Therefore, by the same logic, Jupiter wouldn't be a planet.
Bruce
The energy to lift the Moon's orbit comes from the rotational energy of the Earth, which is limited. As the Moon gets higher the Earth rotates slower. There may not be enough energy to lift the Moon high enough to qualifty.
To be fair, it was a reasonable interpretation of your post to think you were saying "it won't be a moon because it will escape and go FLYING INTO SPACE!!1" instead of the intended point "if it no longer fits a definition, it isn't what's defined. This is news?". 'course, the AC was more than a bit condescending about it.
The fact that we have tendency to kill other members of our own species through hatred is a major cause for wars and national conflicts (WWII is a good example). This tendency could easily augment into a large-scale nuclear war which could leave the Earth uninhabitable for all species, killing 100% of the population.
The problem here is our definition of "Planet" is fairly ambigious to start with. Just as "baby" can mean a tiny human between 0 and 2 years old or your girlfriend.
crazy dynamite monkey
la lunra. If you're going to simply use the word "moon" from another language, why pick Spanish? You might as well use something more logical.
Maybe you should RTFA. The SPACE.com story is talking about in a few billion years, when the barycentre of the Earth-Moon system has moved above the surface of the earth. That would make the Earth and the Moon double planets. In a few billion years. The IAU FAQ you quoted was more concerned about right now.
We'll be a Type III Civilization and we will be able to push the moon back into orbit.
What was your username again? -BOFH
Why can't something be both a planet and a moon? As far as I understand it, the new IAU definition of a planet is something that's in orbit around a star, is not a star, and is large enough for gravity to make it roughly spherical. A moon is something that's in orbit around a planet. So you could argue that our Moon is already a planet (it's in orbit around the Sun as well as the Earth). The same would apply to many other large moons in the solar system.
I think Asimov said something like this in one of his thousand books. His argument was that, unique among (known) moons, Luna's orbit is always curved towards the sun, making it more of a coplanet than a proper moon. But I can't remember which book it was, unfortunately.
--
I don't want to rule the world... I just want to be in charge of mayonnaise.
If the moon going further away from the Earth causes the barycenter of Earth to drift outside its surface, then the Earth will be orbiting a point outside itself, with its orbit becoming greater the farther the barycenter drifts, until it peaks at one point. This is similar to Pluto constantly orbiting a point outside itself, as illustrated in this NASA chart hosted by Wikipedia. I think that when a moon begins to have that effect, it should be classified as a planet.
Currently, the Earth's barycenter is three-fourths of the way to its surface, causing it to sort of wobble, rather than fully orbit an invisible point. This is like an analogy: This is like a Chippendale stripper doing a pelvic thrust, rather than running around in a circle.
Earth's orbit around the sun currently makes the sun wobble in a barely perceptible fashion. Jupiter's orbit around the sun, however, causes the sun to orbit a point about 7% above its surface. I think that there should be a new class of planets for the purposes of describing a planet that makes a star orbit itself in this manner.
Clearly, all brown dwarfs orbiting a star would also have a similar or greater effect. The best way to describe it, in my opinion, would be by merely affixing "co-orbital" to describe a planet altering the sun's orbit in this fashion, or a brown dwarf orbiting a star doing this.
If this causes a planet to be "co-orbital" for only part of its orbit, or a natural satellite to be a planet for part of its orbit, in some eccentric situations, that's fine with me. There's one other issue with the new definition that makes me uncertain, though. EL61 is a "minor planet" that has a very oblong shape caused by its own orbit around the sun. If it were in a slower, closer orbit, its own gravity would almost certainly be enough to warp it into a nearly spherical shape. Should EL61 be considered a planet, despite its problem?
I think you're confusing the term "humans" with "human civilization as we are familiar with it."
The odds of current civilization lasting another thousand years may be low, for the reasons you cite. The odds, however, of us successfully wiping out so much of the population that humans are no longer a viable species within the next thousand years are, in my opinion, fantastically low. We breed too fast, we're spread over 30% of the planet's total area, and we're highly adaptable to changing conditions.
Frankly, I fully expect some descendant species of humans to be living here pretty much right up until the planet is inside the sun.
Reality has a conservative bias: it conserves mass, energy, momentum...
From http://www.psych.utoronto.ca/~peterson/primate/ch
So, no, humans aren't even exceptional in the capacity for murder.
Fanatically anti-fanatical
What's the estimated surface tempurature of this reloaced Earth? How big would the sun look from there?
The Moon cannot escape the Earth's gravitational field (unless there is a very large external perturbation). As the Moon slows it will orbit increasingly farther out, UNTIL it is traveling too slowly to maintain any orbit, at which point it will spiral in until broken up by tidal forces. Earth will get rings (and more than a few major impacts). If the Moon were traveling at escape velocity, it would already have departed. Since it isn't, it can't (on its own).
There may be a bit of a race condition between the Moon's orbital mechanics and the Sun's progression along the "Main Sequence", which will put it into a "red giant" phase where the extended "surface" may be near, or beyond, Earth's orbit. At that point, both parts of our Earth-Moon system will experience significant drag and spiral into the Sun's core.
Moving away at its current speed, it would have taken 10bn years to move from the Roche limit to its current position. (In rough figures: 4*(10^8)m / (0.04m/year) = 10^10years)
But the moon is drifting away due to tidal effects. So it would have been drifting faster in the past. Taking that into account, the MAXIMUM possible time the Moon could have been orbiting earth is less than 1.5bn years.
So how come many scientists think the Earth-Moon system is 4.5bn years old? Maybe they just haven't done the math.