Phobos and Deimos Once a Single Moon?

blamanj writes "Phobos (fear) and Diemos (panic), the twin moons of Mars have caused astronomers grief for years, as conventional hypotheses about the moons either violate physical laws or have difficulty accounting for their observed orbits. Now a new hypothesis conjectures that they were once a single moon, that broke apart in an ancient catastrophe."

Comments

FUD

[limekiller4]

Great. Now we just need to find moons Metus (fear), Ambiguitas (uncertainty) and Dubium (doubt) and convince Gates to purchase them...

Re:FUD

[Anonymous Coward]

Metus, Ambiguitas, and Dubium are latin; whereas Phobos and Deimos are Greek... If my math is correct, of course.

Re:FUD

[Antisthenes]

They are, and it goes without saying that Greek is the superior tongue. ;-) Uncertainty would be amphisbetesis, "dispute, controversy" (those e's are eta's, by the way, not epsilon's) and doubt would be apistia, "unbelief, distrust".

S.C. Woodhouse, English-Greek Dictionary
Henry George Liddell, Robert Scott, A Greek-English Lexicon

Those 3

[Rhinobird]

Haven't those three long since crashed into the Earth?

Doom?

[sirmikester]

Maybe the catastrophe was related to the demon's gate that was forming... and was later reopened in the Doom games... think about it.

Re:Doom?

[Channard]

Gotcha. Loading one into my experimental matter transporter right now.. hey, anyone here a strange growling noise?

Re:Doom?

[Channard]

Hear, I mean (sp).

"Destination: Deimos"

[WTFmonkey]

Awesome! It's about time we set up a base somewhere we don't have to wait for months to get results from launches. But is that any cheaper than maintaining the supply chain to a base (food, air, parts)? Logistics, anyone?

Re:"Destination: Deimos"

[kfx]

Logistics are no problem! The UAC is in the process of building a matter transporter system, and we've got marines to make sure nothing goes wrong!

S. Fred Singer INFO

[MonkeyBoyo]

I don't know how "new" this theory is. Here is some info on S. Fred Singer.

Doubtful

[CheshireCatCO]

Right, there's a lot here that makes me dubious of the claim. First off, I should point out that I've worked on the capture problem for Mars's moons. (The results haven't been published, although the did land a grant.)

First off, why is synchronous orbit a hint as to their breakup? There's no reason that synchronous orbit is preferred, either as a capture point or as a point for breakup. In fact, synchronous orbit is an unstable equilibrium: a slight perturbation drives everything away from it. (Which is why Phobos is heading inward and Deimos outward.)

Also, he needs to explain why a larger moon orbited there happily (without perturbation!) for billions of years before breaking apart. In the very least, we're witnessing Mars's moons at a very unusal time, and such coincidence make me (and most astronomers) nervous.

Also, Phobos has drifted inward since any such breakup. Why isn't it breaking up more? Unless there's some internal strength (in which case, why did it break up then?), it should.

To be honest, I sort of question his background for this. Besides the fact that he's not an astronomer, he wants to put a base on Deimos? The surface gravity on those moons is virtually non-existant. (For Deimos, being smaller, it's under 1 cm/sec^2, I believe.) No one could even walk around properly. (Although, if he hollowed it out and made a colony ship out of it, we could launch it to Tau Ceti... But it might encounter some hostile, three-eyed aliens.*)

I'd be happy to hear him explain his idea to a group of dynamicists. Hell, I'll volunteer. But I'm very skeptical for now.

(* Kudos to anyone who catches *that* reference.)

Re:Doubtful

[Tablizer]

Which is why Phobos is heading inward and Deimos outward.

I am curious as to why they are drifting. Anybody have the scoop?

Re:Doubtful

[CheshireCatCO]

Glad you asked!

Let's start with moons outside of synchronous orbit. These moons raise a tidal bulge on their planet. (The one on Earth is most apparent in the oceans. Or, rather, at their edges. But there's a bulge in the rock, too.) Now, the planet is spinning and it isn't a perfect fluid. So it will tend to carry the bulge forward with it, before the bulge can move back to under the moon where it wants to be. A balance is struck between these two competing forces where the bulge rides somewhere ahead of the moon.

The moon, then, feels a tug forward in its orbit. This tends to give it angular momentum, so that it drifts outward. (Angular momentum increases as you go out from the central object.) The planet, meanwhile, is being pulled backward so that its spin slows down. (As it must, to conserve angular momentum in the system.) This is why Earth's day in lengthening and why the Moon has drifted about 60 Earth radii from where it formed over the past 4.5 billion years.

What happens of the moon is *inside* synchronous orbit? The opposite happens: the moon moves ahead of the bulge and gets pulled back. So it drifts in.

I'll leave it as an exercise to the reader to work out what retrograde (backward orbiting) moons do. Triton is an example, by the way.

Re:Doubtful

[WolfWithoutAClause]

Besides the fact that he's not an astronomer, he wants to put a base on Deimos?

No, he's right, or in orbit around it. It makes a lot of sense. There's probably ice on Deimos and/or Phobos. If so, that's rocket fuel; the space equivalent of oil. And Deimos is ideally placed for this- it's high up above Mars (but not so far that you can't go down), and close in delta-v terms to the Earth, ideal for sending fuel back to Earth orbit to fuel Mars and Lunar missions. It's also a great source for rock for use for radiation shielding in LEO. And don't imagine for a moment that a Deimos base precludes a Mars base- it enables a Mars base.

The surface gravity on those moons is virtually non-existant. (For Deimos, being smaller, it's under 1 cm/sec^2, I believe.) No one could even walk around properly.

Yeah right, real important, no walking.

Re:Doubtful

[CheshireCatCO]

Walking is generally important, unless you want the astronouts to stay seated all the time. If there were in zero-g, they could float. But there's enough gravity to make that annoying, but not nearly enough to walk. Also, they'd still need to do daily exercises to keep their bones and muscles from atrophying.

You're making a pretty large leap from "probably water" to "send fuel back to Earth". There probably isn't that much water to start with, given that these guys are a few kilometers across.

It's not a good idea. You're better off parking a space station in orbit on its own. It'll be easier to handle, more flexible and you don't lose any advantages.

Re:Doubtful

[Alsee]

Good explanation, thanx. That's sort of been itching at me but I never asked/checked why it works in that direction.

an exercise to the reader to work out what retrograde (backward orbiting) moons do

The bulge would lag even more and the moon would spiral in even faster no matter where it is.

I don't happen to be an expert on Triton, but I would therefore conclude that it is a young moon and started with a much larger orbit.

-

Re:Doubtful

[CheshireCatCO]

Exactly on the first point.

Not sure of the timescale on the second point. All of this depends on not just the planet's spin and mass, but also on the mass of the moon (bigger is actually better, as I recall), the moon's distance and the tidal reponse of the planet. Since Neptune's upper layers are pretty fluid, I'm guessing that they don't dissipate much and so Triton doesn't move as fast as the Moon. But I'd need to check up on that. (Earth-Moon face a lot of evolution, more now than is typical, because of ocean bulges trying to squeeze through narrow straights. (Gibralter, Magellen, etc.)

Re:Doubtful

[WolfWithoutAClause]

If there were in zero-g, they could float. But there's enough gravity to make that annoying, but not nearly enough to walk.

Garbage. If the gravity is 1cm/s^2, then that is 1/1,000g. It takes about 14 seconds to fall down from a height of 1m and when you hit the deck, it's like you've fallen 1mm. That's zero-g in my book. No you can't walk- but you don't need to.

Also, they'd still need to do daily exercises to keep their bones and muscles from atrophying.

Yup. It would be possible to send a centrifuge there; but it isn't known whether there is enough gravity on Mars to stop atrophy anyway.

There probably isn't that much water to start with, given that these guys are a few kilometers across.

Both hydrogen and oxygen are very abundant in the universe; and H2O seems to be common too. Do you have any idea how much mass a 'few kilometer' body contains? Clearly not. Consider a 1 km cube. 1000m by 1000m by 1000m of which say 1% is ice. If the body has a density only twice that of water, then that is 2 billion tonnes. We only need a few thousand tonnes a year at most for the foreseeable future; and there would be millions of tonnes of ice in just a 1km cube- Phobos and Deimos are much, much bigger than that; and the density of these bodies indicates are that they are made of much more ice than that.

You're better off parking a space station in orbit on its own.

Yes, probably true, although anchoring it or orbiting it around Deimos is probably indicated.

Re:Doubtful

[CheshireCatCO]

You also have to land the base onto the moon, and then secure it down. Do you know how hard it is to land in that kind of gravity? Really? It took a lot of careful effort to manuver NEAR/Shoemaker around Eros. And they didn't have to contend with a nearby Mars.

"Do you have any idea how much mass a 'few kilometer' body contains? Clearly not."

One might have assumed that, in order to calculate the surface gravity, I actually used that number. But that would ruin your attempt to take a swipe at me, wouldn't it? So go ahead and give logic a miss.

The rock is NOT 1% water. I can almost promise you that. It's an asteroid. Asteroids formed inside the "frost-line" in the protoplanetary disk. There would little or no water adhered to the rocky material in this region. Hell, EARTH isn't even 1% water, and we've had quite a bit delivered to us from the outer solar system via cometary impacts. (Deimos would have had far fewer of those and wouldn't easily hold on to any water on its surface anyway. You might think about what surface gravity/escape velocity has to do with that.) So you're making up a number, one that is unreasonably large. Which is jind of funny, because a little reflection tells you that if the water WERE mixed in through the entire volume, as you claim, you'd have to mine it out. Again, you're in microgravity here. That's hard, no matter what you think you learned from "Armeggedon".

And, no, the densities do NOT tell you that they're made of ice. Who told you this? (Or are you making this up as you go?) They're densities are low because they are probably fairly porous. In order words, you're planning to mine empty space. We have plenty of that already, thanks for inquiring.

"Yes, probably true, although anchoring it or orbiting it around Deimos is probably indicated."

See above. You need to think this through to consult someone who actually knows about this stuff. Orbiting a small rock is hard as hell, espcially with Mars right there playing with your orbit all the time. On the other hand, how do you plan to anchor to Deimos? (I repeat, once again, "see low surface gravity") It's a not a very dense rock, so driving in an anchor (how would you do that, anyway?) would be tricky since it'd be anchored in lose dirt for the most part.

Look. Take an astronomy class. Talk to someone about this. Please. Your information is clearly inaccurate.

Re:Doubtful

[WolfWithoutAClause]

Do you know how hard it is to land in that kind of gravity?

Yes. It's trivial.

It took a lot of careful effort to manuver NEAR/Shoemaker around Eros.

I wasn't born yesterday. That was because the speed of light made it really difficult to remote control the vehicle at that distance. Stick a man onboard and it's really, really easy.

Asteroids formed inside the "frost-line" in the protoplanetary disk.

True, kinda. But so did the Earth. The frost-line doesn't form until the protoplanetary disk gets blown away when the Sun lit up. The Earth lost most of its water because the Earth got very hot due to volcanic activity after forming, not because of its distance from the Sun. A smaller body wouldn't suffer then same fate (although the surface ice sublimes away within the radius of the asteroid belt.)

And, no, the densities do NOT tell you that they're made of ice. Who told you this?

See this (among many, many other places): Deimos and more particularly check out Phobos

(Or are you making this up as you go?) They're densities are low because they are probably fairly porous.

Really? Where did you get porosity from?

It's a not a very dense rock, so driving in an anchor (how would you do that, anyway?)

Explosives, blow a tubular hole and screw in a crampon. You don't need much strength anyway. Deimos is tidally locked, so using a tether out towards L1 or L2 is pretty simple. Alternatively, just using a free floating station at Deimos' general orbital radius works pretty well too.

Re:Doubtful

[CheshireCatCO]

OK, this is my last post on this, because it's become clear that you really don't know the details.

First, the speed of light lag was only part of the landing on/orbit around Eros problem. I know, I've spoken with many of the mission scientists. And, no, it isn't trivial. You can't dismiss it that easily.

In the case of Deimos, is a postive SOB. You'll have to orbit within around 11 km of the average surface if you go retrograde, 5 if you go prograde. Given that you're orbiting a moon that is only 6 km in radius, that's pretty tight. (You get this from looking at the Hill radius for Deimos and Mars. It's a very small Hill sphere.) The fact that it is irregularly shaped makes you job that much harder.

Second, you don't know what the frost line is. The frost line is in place IN THE PROTOSOLAR NEBULA. It is there BEFORE THE NEBULA DISSIPATES. That's why we get icy bodies beyond 5 AU and little water inside that distance. Please, for the love of all that is good in the world, look some of this up?

And Earth did NOT lose its water from volcanic activity. Volcanoes can't give water enough heat to escape the Earth. I don't know *where* you heard that little gem, but you need to go back and smack that person. And small bodies have it WORSE. Their escape speed is much lower, so a little thermal energy makes you escape. Look at Mercury and the Moon. (If you're astute, you'll note that neither has any significant amount of water. Possibly theres a bit in the permanently shadowed craters near the poles, but that's the only place you'll find any.)

Next, SEDS needs to update their site. (Notice the date on the webpage? 5 years ago. A lot has happened with asteroid studies since then. And I have caught plenty of mistakes on the Nine Planets site in the past, so please don't take it as gospel. The best thing to do is to talk to someone who works in this field.) We've found that many asteroids have low densities, apparently because they are filled with a lot of vacuum. They very in how much this is the case, but we're pretty sure that low densities is a hallmark not of water (as in the outer solar system), but rather high porosity. Some asteroids show signs of being little more than loose rubble piles.

Where am I getting this from? Journals, talking to the other planetary scientists, etc. I hate to harp on this, but it's relevent: I am a planetary scientist myself.

And finally, as for screwing something in (to gravel?), how are you going to screw it in, pray tell? You need to push down to make it go in. In that gravity, you have no useful weight. No weight, no pushing in.

Look, you gain exactly jack for putting a base on a dinky rock like Deimos, and the trouble involved is nowhere near worth it. You might as well go with a station, where you have control over the orbital distance, you don't have to muck about with the difficulty of putting the base on the moon or the annoyances of the small, but omnipresent, gravity.

Re:Doubtful

[WolfWithoutAClause]

First, the speed of light lag was only part of the landing on/orbit around Eros problem. I know, I've spoken with many of the mission scientists. And, no, it isn't trivial. You can't dismiss it that easily.

Yes, you very much can. When the vehicle has enormously more thrust than its weight it becomes just a control issue, and people are very good at control. I'm not belittling the Eros team in any way- it's just that the problem they solved is not the same issue as landing on Deimos or even Eros with a man in the loop. You don't have to orbit at all.

Volcanoes can't give water enough heat to escape the Earth.

That's only partly true. There are interactions with solar wind and magnetospheres and partial pressures and so on. The Sun's solar wind is quite capable of blowing away water vapour.

Look at Mercury and the Moon.

Oh please! Mercury is right next to the Sun and neither body has any significant atmosphere. Water vapour is just gone from these surfaces.

The best thing to do is to talk to someone who works in this field.

No. The only thing that matters is what is actually there. The only way to find out is to travel there and find out.

No weight, no pushing in.

Newton would be shocked to hear you say that.

Re:Doubtful

[Alsee]

I just tried google and a couple of sources say something like the following:

Triton could not have condensed from the primordial Solar Nebula in this configuration; it must have formed elsewhere (perhaps in the Kuiper Belt?) and later been captured by Neptune

So at least in some sense it is "young" in that it didn't start there, it was later captured. I haven't seen any further discussion of the age, but I didn't look very hard.

-

Re:Doubtful

[CheshireCatCO]

Yeah, you get that from the fact that it orbits retrograde and its orbit is fairly inclined relative to Neptune's equator. That said, damn if we know how to capture such a huge chuck of ice and rock as Triton. Although it seems easier to do when the planet is very young and has a more extended atmosphere.

Lol

[Anonymous Coward]

Am i the oney one how thourght the wording of this funny

Origin of the two moons presents a longstanding puzzle to which one researcher proposed the new solution at the, 6th International Conference on Mars, held here last week.

Still There?

[Markus Registrada]

What, is that moon still there? Sometimes it seems like things just go around and around the drain forever.

Seriously, it's funny how astronomers always think that nobody will touch these rocks that are just sitting there in handy orbits. It's the same with Cruithne, the asteroid that co-orbits earth. They always say it will join Earth again in 600 years (or whenever), and it never seems to cross their minds that we might have found something more useful to do with it by then.

Deimos will probably be more useful, though, than Phobos, as a counterweight to attach to the end of the big elevator down to the surface. We might have to move Phobos out of the way -- making the elevator shimmy this way and that so that Phobos just misses colliding each time past is asking for trouble.

Re:Still There?

[AlanGreenSpandex]

it's funny how astronomers always think that nobody will touch these rocks that are just sitting there in handy orbits.

Well you see, they spent so much time tweaking their model that (by this point) they don't even want to contemplate having to predict events caused by human intervention.
=-)

Thats no moon...

[andersen]

Thats no moon... Its a space station.

Re:Non-Linear Dynamics

[quinkin]

I agree that that is the situation in a classical two body system.

Unfortunately, classical physics cannot calculate a three-body system (it can be approximated quite closely by using iterative two-body calculations and restricted three-body techniques etc.).

The Earth/Moon orbit, is not periodic but is in fact quasi-periodic (so it has an near periodic cycle - or time to return "near" to origin).

I'll leave calculation of the three body integral as a readers exercise (bad physicist joke).

Q.

Why call it a catastrophe?

[TripleA]

Ok, I don't KNOW, but I am quite certain no animals, bugs, fishes or whatever where harmed when the moon became moons. So why was it a catastrophe?

Kepler's Third Law

[Martin Spamer]

First off, why is synchronous orbit a hint as to their breakup? There's no reason that synchronous orbit is preferred, either as a capture point or as a point for breakup. I dont think the article suggest it is, in fact I suggest that since
In fact, synchronous orbit is an unstable equilibrium: a slight perturbation drives everything away from it. (Which is why Phobos is heading inward and Deimos outward.)

I think this is what he is suggesting, a synchronous orbit is not prefered because it is unstable. On a large moon that instability leads to break up. Consider the differental effect of Kepler's Third Law on the inner and surface of the moon. Mass within transfer obit radius is drawn towards the gravity well and the mass outside the transfer obit radius would be thrown away. The larger the object the more the stress this would cause. The central question seems to be is this stress enough to overcome the moons structural stability, and this is a question for materials scientiest not astronomers.

Re:Kepler's Third Law

[CheshireCatCO]

Perhaps he is suggesting that, but it's wrong. Angular momentum is transfer to the moon as a body force, not diffrentially. The moon can simultaneously run ahead of the bulge and behind it. In fact, at synchronous orbit, it does neither. It's perfectly aligned. Which is why the Earth-Moon system is heading for that right now. (It won't be stable for Earth, but that's because we feel the effects of the Sun pretty strongly, too. Pluto-Charon are already there, and are fairly happy. But they're really far from the Sun and tides vary as one over distance cubed.)

Bring it on

[Cackmobile]

$30 billion is nothing. Cut the military budget by that much. They get something like $350 billion. Or the shuttles. That would be sweet as.

Wrong title sir

[Anonymous Coward]

You forgot the R between the two O's.

Re:Non-Linear Dynamics

[CheshireCatCO]

Er, what's your point? The moons are behaving as predicted by the theory, just like ours is. There's obviously some error in it, but there always is. (There's error in our orbital calculations for the Earth, another thing we can't actually integrate exactly. Do you not believe that we know pretty well where Earth will be in a month?)

Re:The Reasons

[pyr0]

"Where is the science in declaring that archaeopteryx is the descendent of dinosaurs and ancestor of birds?"

Umm...let's think about this....maybe because the skeletal structure (that's a concrete observation by the way, no speculation) shares characteristics with both?

Anyway, the creation vs. evolution argument from a philosophical standpoint doesn't interest me either, because nobody wins. This is how most of my arguments go: I list several pieces of data that detail why the earth is 4.6 billion years old, or point out reasons why man has to be descended from a primate ancestor, blah blah blah, etc....and then my opponent just throws faith up in my face typically. You can't argue against that, so I try not to now.

I like to argue A) against people who try to exploit things that are not related (like your argument about the moon) or B) who use "pieces" of actual valid scientific data while ignoring the rest of it as "evidence" for creation. It just doesn't work.

Point A: That's like saying, "the rock I randomly placed on my window-sill happens to cast a shadow *exactly* on a sticker on my computer at 4pm on December 2nd, which is the reason I tripped and hurt myself last June."

Point B: Trying to tell everyone (this is just an example...I know it's completely unrelated to your post, but I'm just trying to tell you I'm not blindly ripping creationists just because I want to but because I have knowledge of certain things) Rb/Sr radiometric dating doesn't work because in some cases you get isochron lines that gives dates *way* older than a rock really is...while what they're really ignoring is the part that if when you form the rock you mix magmas of two different isotopic compositions, you start out with a rock that has a positive isochron slope thus accounting for the discrepancy(chapter 9 in Faure, 1986).

Anyway, I'm just rambling and burning karma points now, so I'll quit.

Re:Offtopic? -- here's why

[js7a]

I am metamoderating the parent comment's "Offtopic" moderation right now as "fair."

I was raised Baptist, taught "creation science," and I still have a stack of books by Josh McDowell somewhere. I just took a look at trueorigins.org, icr.org, and andswersingenesis.com. Nothing new there. I know the arguments. They are lies, designed to keep preachers and their churches in positions of authority and power.

Since college I have been a Quaker (Religious Society of Friends.) We have no problem with the possibility of God's motive force guiding and shaping natural selection. But we see the evidence of evolution in the world around us and we know that since God does not reveal himself to us as an ordinary occurance, that He expects us to use our head in relation to the fossil record, nuclaic cell biology, etc. We are not so stupid as to presume that Genesis is any more than an allegorical myth.

How presumptious is it of you to suggest that the omnipotent God is so weak that He could not have designed the very thought occuring in your head this moment when he set the universe in motion billions of years ago? Only your conformist herd mentality and desparate attempt to cling to the idea of an afterlife keep your nose in the Holy Babble, and result in your adherance to creationism. I feel sorry for your inability to believe in a God without buying in to the popular myths of your cultural ancestors over the millenia. You have more intelligence than that, and God wants you to make use of it, as a thinking human being capable of integrating the evidence you obtain from the scientific method and peer review, not as a superstitious sheep.

You asked.

Re:Offtopic? -- here's why

[js7a]

Okay, well, it had nothing to do with the moons of Mars.

That in itsself should be enough for the parent comment, but I want you to understand why "creation science" is thought of so poorly even by theists.

God gave you a brain. Use it. Please don't presume that God is so stupid that He could not have designed live via evolution a billion years ago.