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## Ion Rocket to Map Moon with X-Rays172

jralls writes "The Guardian is reporting that a European ion-rocket has taken the last year to reach the moon and is about to enter lunar orbit. Once it slows and gets into a very low orbit, it will probe the surface with x-rays in an effort to solve the long standing puzzle of the moon's origin."
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## Ion Rocket to Map Moon with X-Rays

• #### Visibile from Earth? (Score:3, Interesting)

on Sunday November 07, 2004 @01:07PM (#10746952) Homepage
I wonder if we are able to observe this interplanetary tortoise from earth? If it passes the bright side in full moon, we should have quite a clear view of it since it's going so slowly.

Play iCLOD Virtual City Explorer [iclod.com] and win Half-Life 2
• #### Re:Visibile from Earth? (Score:2)

Why did it take so long to get to the moon?
• #### Re:Visibile from Earth? (Score:5, Informative)

<artturi,karhula&gmail,com> on Sunday November 07, 2004 @01:23PM (#10747065)
Ion rockets can't generate very high accelerations. They can, however, keep going for a long time.
• #### Re:Visibile from Earth? (Score:2, Troll)

If we used some sort of higher powered rocket to generate the velocity, I wonder if ion rockets could hold that velocity for a long time.
• #### Re:Visibile from Earth? (Score:4, Insightful)

on Sunday November 07, 2004 @01:33PM (#10747134) Homepage

If we used some sort of higher powered rocket to generate the velocity, I wonder if ion rockets could hold that velocity for a long time.

Since we are using this space, I wonder what we would need the ion rocket for to hold that velocity. In space, there is not much that could slow you down.

• #### Re:Visibile from Earth? (Score:1, Informative)

by Anonymous Coward
>In space, there is not much that could slow you down.

True. Unless you are somewhat near a large gravity source that the rocket would have to fight against. The Earth for instance.
• #### Re:Visibile from Earth? (Score:2)

I don't think there ever were any problems with holding the velocity. Acceleration, however...
• #### Re:Visibile from Earth? (Score:1)

So the question is, if we used conventional rockets to quickly achieve a high speed, could the ion propulsion continue the excelleration after the rocket burns out?
• #### Re:Visibile from Earth? (Score:4, Interesting)

on Sunday November 07, 2004 @02:20PM (#10747399) Homepage Journal
That is exactly what this thing does...Use a conventional rocket to get away from earth's surface and then continue with ion propulsion to the moon.

Jeroen
• #### Re:Visibile from Earth? (Score:2, Informative)

The general idea of a ionization engine is obviously sustained impulse (as previously stated).

Ionizations engines are typically attatched to probes which have initial combustion engines that give them the thrust required to escape the earth's gravity. Once the probes have escaped gravity, the ion engines allow continual thrust that allow (for extremely long range expeditions) extremely high velocity. It is a competing technology with solar sails - which also allows for huge velocities over long distances
• #### ESA doesn't have a moon capable rocket (Score:3, Interesting)

It's fairly simple. The ESA doesn't have a rocket capable of putting a payload on a lunar path. AFAIK Arianne is really only good for LEO stuff. The only two countries with lunar capable rockets are I believe the Russians and the USA. Of course, the ultimate lunar capable rocket, the Saturn V, is dead, so all we can do is cross our fingers and hope that NASA will come to its senses and bring back the big dumb booster.
• #### Re:Visibile from Earth? (Score:2)

I wonder if we'll be able to see the four elephants too.
• #### Re:Visibile from Earth? (Score:1)

My question is will they be able to see the American flag that *supposedly* resides up there...

this is assuming that they really *did* land on the moon
• #### Re:Visibile from Earth? (Score:3, Informative)

I wonder if we are able to observe this interplanetary tortoise from earth? If it passes the bright side in full moon, we should have quite a clear view of it since it's going so slowly.

I'm curious what make you think it will be going slowly? It will be orbiting the moon at exactly the same speed as any other craft at the same altitude would be orbiting the moon. The type of engine or thrust has nothing at all to do with orbital mechanics.

• #### Re:Visibile from Earth? (Score:2)

It's not going slowly, it's going at the same speed anything else in the same orbit would be at. It's taking a long time to reach lunar orbit because it started out in Earth orbit and needs to accelerate quite a bit. It's using an ion engine, so it'll take longer to achieve a given change in velocity. A conventional rocket would achieve the same change in velocity more quickly, but the end result would be basically the same...except that the conventional rocket would be bigger and heavier, and thus more exp
• #### Where do you think the Moon came from? (Score:3, Funny)

on Sunday November 07, 2004 @01:07PM (#10746953) Homepage Journal

I say the moon came from Uranus, what do you say? Here take a survey [opinionpower.com]!

Survey...

Uranus
Another Galaxy
Mars-sized planet crashed into the earth
Comet
Meteor
Microsoft
Another Dimension
It was a spaceship!
Cowboy Neal
• #### Re:Where do you think the Moon came from? (Score:5, Funny)

on Sunday November 07, 2004 @01:13PM (#10746999)
It was a spaceship!
AKA "Thats no moon"
• #### Re:Where do you think the Moon came from? (Score:2)

AKA "Thats no moon"

ROFTLMAO!!!!!
• #### Re:Where do you think the Moon came from? (Score:2, Interesting)

(Slightly off-topic, but fittingly placed among the Star Wars-related posts.)

Anyway, now that this mode of propulsion is being deployed in (or above) the real world, and the private sector is building spaceships, how long, I wonder, will it be before some rich hobbyist builds a functioning TIE Fighter? All the parts are waiting to be assembled, with the possible exception of the small megawatt-class lasers.

It'd be great; get a bunch of rich Star Wars reenactors together with their lovingly assembled sp

• #### Re:Where do you think the Moon came from? (Score:1)

I voted Microsoft, I imagine the EULA would go something like this:
By viewing or using light relected from the moon you agree to be bound by the terms of this License Agreement. IF YOU DO NOT AGREE TO THE TERMS OF THIS LICENSE AGREEMENT, LEAVE THE PLANET IMMEDIATELY AND/OR KILL YOURSELF.
• #### Re:Where do you think the Moon came from? (Score:2)

Its actually Darth Vader in his death star orbiting above us..
• #### Re:Where do you think the Moon came from? (Score:2)

The death star is in orbit around Saturn [nineplanets.org]
• #### Great title (Score:5, Funny)

on Sunday November 07, 2004 @01:08PM (#10746966) Homepage
I expected the story to read "But when Flash Gordon approaches, will the moon people fight back with their electro-guns? Watch next week to find out!"
• #### Moon mining? (Score:5, Interesting)

<{moc.liamtoh} {ta} {l3gnaerif}> on Sunday November 07, 2004 @01:11PM (#10746986) Homepage
From the article :

"The sun emits X-rays and these are reflected back into space by atoms on the Moon's surface. A magnesium atom will reflect an X-ray in a different way from an iron atom, and Grande's detector can detect these differences.

Flying over the lunar poles, so that it covers the entire Moon as it revolves below, Smart will create strip maps of the surface - and eventually a global map of its composition."

Look like useful data to me if we were in the 'mine the moon' business... maybe in a not so distant future?
• #### Re:Moon mining? (Score:2)

Cool!

Now that GWB is back in office, someone send up a note quick that there is oil and wealth on the moon!

Maybe something useful could come out of his re-election, afterall! ;)
• #### Re:Moon mining? (Score:1)

That won't work! Tell GW that al Qaeda has a secret lunar base deep inside the moon and is using it as a terrorist training camp...
• #### Keep in mind.... (Score:3, Insightful)

that it is not the whole moon. There are areas that light, and x-rays do not reach. Sadly, that is the most inteesting as it may contain ice.
• #### Re:Keep in mind.... (Score:4, Informative)

on Sunday November 07, 2004 @02:46PM (#10747583) Homepage
That is not so. The sun shines (at one time or another) over the whole surface of the Moon, just like it shines over the whole surface of the Earth.
• #### MOD DOWN PARENT (Score:4, Informative)

by Anonymous Coward on Sunday November 07, 2004 @03:21PM (#10747768)
At each pole, there are such deep caverans that sun never reaches it. That includes X-rays and normal sun light. That is why it is possible for ice to be there. And yes, it is considered part of the surface.
• #### Re:Keep in mind.... (Score:1)

There are some craters on the south pole of the moon which never get sunlight inside, which makes them a potentially good spot to collect volatile minerals. See more at Space.com's article on the south pole [space.com].
• #### A year to reach the moon? (Score:2, Insightful)

I keep hearing that Ion propulsion is faster than what we currently use. What's with the incredibly slow travel time?
• #### Re:A year to reach the moon? (Score:5, Informative)

on Sunday November 07, 2004 @01:15PM (#10747009)
The ultimate speed of ion propulsion is higher than that of chemical propulsion.

But the mass being expelled at high speeds (the ions) is so low, that accelleration is VERY slow. So it takes a long time to get up to speed, but the maximum speed you can theoretically reach is much greater than that of chemical rockets.
• #### Re:A year to reach the moon? (Score:5, Informative)

on Sunday November 07, 2004 @01:33PM (#10747131) Homepage
Actually, the maximum speed that you could theoretically reach is the same in both cases: c

The difference is that it will take a chemical rocket much more propellant to get there, because it is far less efficient in its use of propellant mass (i.e. it has a lower specific impulse).

• #### Re:A year to reach the moon? (Score:2)

I thought nithing with a mass could be accelerated to c since it would take an infinite ammount of energy to accelerate it to c since the mass of the object grows the more it reaches c.
• #### Re:A year to reach the moon? (Score:1)

You are correct, as an object approaches the speed of light, the object's mass increases, requiring exponential quantities of fuel as the object approaches c.
• #### Basic rocket physics makes it a bit clearer (Score:5, Informative)

on Sunday November 07, 2004 @05:25PM (#10748697) Homepage

Look up any reasonable book on mechanics and you will find a formula for the final velocity of rockets that have a empty mass M, mass of fuel m, and have an exhaust velocity v. The final velocity of the vehicle is ...

V = v . ln( (M + m)/M )

In other words ion rockets will beat chemical rockets because they eject their exhaust at a reasonable fraction of c, whereas chemical rockets have exhaust velocities more like velocities we see on earth (e.g. bullets). So chemical rockets need lots of mass, but that's ok because they throw out lots of mass. Trouble getting to space is expensive ... each kilo of fuel you put in orbit better be wisely used ... so in space ion rockets make sense (apart from the fact you can't use them on Earth anyway ... wouldn't be able to lift off even).

Hope this makes things a bit clearer.

• #### Re:A year to reach the moon? (Score:3, Funny)

I think they should have used Twin Ion Engines [wikipedia.org] to get a little better acceleration...
• #### Re:A year to reach the moon? (Score:5, Informative)

on Sunday November 07, 2004 @03:40PM (#10747897)
> The ultimate speed of ion propulsion is higher than that of
> chemical propulsion.

Depending of course on the fixed mass of the spacecraft, vs it's propellant mass, of course. You get more momentum change from given amount of propellant, but if you only had a teaspoon full of propellant, or the spacecraft was exceptionally massive, you wouldn't get more velocity.

> But the mass being expelled at high speeds (the ions) is so
> low, that accelleration is VERY slow. So it takes a long
> time to get up to speed, but the maximum speed you can
> theoretically reach is much greater than that of chemical
> rockets.

To expand, the measure of efficiency of a rocket engine is the specific impulse or ISP. It's how much momentum change you get per unit of propellant mass, and the usual unit is seconds (lb-sec/lb). The highest actually-achievable ISP from a chemical rocket is somewhere in the 475 seconds. The Saturn 5 first stage was more like about 350, and monopropellant thrusters used for many satellite propulsion systems is more like 150-180! That means that if you want to change the velocity a lot, you need a whole lot of propellant.

I'm not sure which engine this particular program uses, but the ISP of the typical Xenon ion thruster is something like 1800. So you have to carry fantastically less propellant for a given velocity change, meaning it can weight less at liftoff, meaning you can use a weaker/cheaper booster.

The downside is that you don't get something for nothing. It takes, not surprisingly, a whole lot of electrical power to make it go. So you put in 4000-5000 watts of power, and it only generates .04 lb of thrust - .64 of an ounce, pushing a spacecraft weighing thousands of pounds on the ground. So the acceleration is very small, meaning takes a long time to get going. The other downside is that the Xenon ions, although chemically pretty neutral, shoot out at such high speeds that anything that gets in the exhaust gets eaten away. This may or may not be an issue depending on there you put it relative to the rest of the spacecraft.

Brett
• #### Re:A year to reach the moon? (Score:3, Funny)

by Anonymous Coward
They are using euro ions, which require extended committee meetings and discussions before determining the appropriate direction in which to apply their force.
• #### Re:A year to reach the moon? (Score:2)

What you heard is that the specific impulse is way larger than with chemical, meaning that the exhaust velocity is very high. That means that you have a very efficient means of propulsion, with each particle of exhaust producing more thrust/particle than chemical rockets do. The exhaust being a tenuous gas however, the actual THRUST is very low (and the thrust/weight ratio even more so). Because it works in the vacuum of space and can run for years on end, the eventual velocity that this low thrust can impa
• #### Re:A year to reach the moon? (Score:2)

shouldnt this have had a fairly substantial speed to start? Ie, the space torch orbits about 29,000 Km/hr which is about the minimum for low earth orbit.
• #### This is insane! (Score:2, Funny)

by Anonymous Coward
Anyone still using film up there is going to be pissed when their exposures are ruined.
• #### It's from Wisconsin. (Score:4, Funny)

on Sunday November 07, 2004 @01:16PM (#10747017)
Everyone learns that the moon is made of cheese in the cartoons. I bet they'll say it's from Wisconsin.
• #### New tourist slogan (Score:4, Funny)

<macrom75@hotmail.com> on Sunday November 07, 2004 @01:22PM (#10747052) Homepage
"Come to the moon and smell our dairy air!"

Doesn't quite have the same ring...
• #### Choose your cheeze (Score:1, Funny)

Finally we can have proofs that the moon is made out of cheese..

I do hope it's cheddar..
• #### Possible Resolution to US moon landing hoax theory (Score:5, Funny)

<jpgarner@gmail.com> on Sunday November 07, 2004 @01:20PM (#10747034) Journal
Will these guys be able to snag some good shots of the trash we left on the moon? Exluding the flag of course, which can't be trash cuz its on a stick.
• #### Re:Possible Resolution to US moon landing hoax the (Score:1)

if you know what the trash looks like on x-ray, then you could try searching for it... I think they are more interested in the rocks below the trash tho, so the camera's are probably designed to see that and not the surface (with the trash).
• #### A Space Odyssey (Score:2, Funny)

Isn't that the way the monolith will be found?
• #### Re:A Space Odyssey (Score:1)

That's 3 years too late. Our civilisation is doomed.
• #### Re:A Space Odyssey (Score:2)

The first monolith was found in the crater Tycho, because of its strong magnetic field. Hence Tycho Magnetic Anomoly (TMA).

• #### wow (Score:5, Funny)

on Sunday November 07, 2004 @01:25PM (#10747077)
sobering thought that that headline sounds exactly like something you might hear in a pulp sci-fi movie from the 50's...
• #### Re: wow (Score:2, Funny)

> sobering thought that that headline sounds exactly like something you might hear in a pulp sci-fi movie from the 50's...

Science has finally caught up with fiction!

• #### From the article -- galactic bowling physics? (Score:5, Insightful)

on Sunday November 07, 2004 @01:41PM (#10747179)
Smart's map should provide that data and show if scientists are right in believing that the Moon coalesced from a vast ring of debris generated when an ancient planet the size of Mars destroyed itself after crashing into Earth. Understanding the origins of the Moon will therefore give insights into the nature of our planet.

Doesn't this mean earth should have some huge dent in it, and not be so round? Look at the sizes of Mars and Earth [nasa.gov]. Are you surprised earth is still here after a crash of that magnitude? I am. Maybe earth was a lot bigger before a Mars-like planet destroyed itself crashing into earth, but then I go back to my question about the roundness of the earth.

Maybe someone more knowledgeable wants to talk about that. The article doesn't go into any great detail on that, which causes a lot of questions to be raised.

• #### Re:From the article -- galactic bowling physics? (Score:1, Informative)

by Anonymous Coward
The eart wasn't a solid mass 4 billion years ago. It was molten.
• #### Re:From the article -- galactic bowling physics? (Score:4, Informative)

on Sunday November 07, 2004 @01:59PM (#10747271)
Thanks. Your information enabled me to do some googling.

For anybody who is interested, here's a theory [uc.edu] (bottom of the page): "one theory says the moon formed when a big, molten chunk of crust was knocked/blown off from the rest of the planet". And much more info [google.ca] about it.

• #### Re:From the article -- galactic bowling physics? (Score:4, Informative)

on Sunday November 07, 2004 @02:20PM (#10747403)
The earth wasn't a solid mass 4 billion years ago.

It's still not a solid mass now.
• #### Re:From the article -- galactic bowling physics? (Score:1, Interesting)

by Anonymous Coward
Any planet (or asteroid, or whatever) above a certain mass will become spherical under its own gravity. I don't have the numbers at hand, but it is surprisingly low, if I recall correctly it would have to be roughly 30 miles wide to have enough mass.
• #### Re:From the article -- galactic bowling physics? (Score:1)

I saw something on the Science Channel about this, and the illustration they had involved the two planets hitting each other and swirling around a bit. Since the earth is mostly moltent rock, I think during the collision, a lot of that came in to fill it in. Plus this was a long long time ago, so the Earth could have covered it up by now. Not the best explaination I know, I can't say I understand it all myself.
• #### Re:From the article -- galactic bowling physics? (Score:2)

Don't forget that the Earth was molten at the time, and even if it wasn't, look at what is left of the Yuccatan crater due to the forces of erosion. Wind and water are very, very powerful forces.
• #### Re:From the article -- galactic bowling physics? (Score:3, Informative)

by Anonymous Coward
There was once a theory that the Pacific Ocean was the hole left when the moon was pulled out of the Earth, but...

There is a reason why small objects, like asteroids, are often irregular in shape, while large objects, like planets, tend to be nearly spherical. All parts of an object are attracted to each other by gravity, this tends to pull the object into a spherical shape. Above a certain size (which depends on the materials involved) the object is not strong enough to maintain its shape and collapses
• #### Biq == Round (Score:5, Insightful)

<slashdotbin@hotmail.com> on Sunday November 07, 2004 @02:21PM (#10747404) Homepage Journal
Beyond a certain size, gravity pulls things into a spherical shape. The immense pressure makes the insides molten and irregular structures eventually sink down in. Mars has Mons Olympus, the tallest volcano in the solar system, this is because Mars is smaller and has less gravity than Earth. The larger the planet the more regular it has to be. Asteroids can be highly irregular because they haven't the size and gravity to collapse them into spheres.

The mountains on Earth may appear huge to us insects on the surface, but from a distance the earth appears as smooth as a billiard ball.

Ironically this event was so big, that unlike latter smaller hits, all evidence in the way of dents will be gone as the entire globe virtually liquefied and coalesced again. Though I wouldn't rule out some exotic mass distributions that might lend evidence of it.

• #### Re:From the article -- galactic bowling physics? (Score:5, Interesting)

on Sunday November 07, 2004 @03:46PM (#10747935)
Take a look at the moon. Those dark spots are the sites of enormous ancient impacts. They may have been holes briefly, but they then filled up with lakes of lava. As far as the Earth goes, the impact was so devastating that the outer layers of the Earth had to reform by falling back down.

The following contains some links to mostly non-technical explanations of planetary roundness. I'd like to point out that part of this explanation [sciam.com], by "Derek Sears, professor of cosmochemistry at the University of Arkansas and editor of the journal Meteoritics and Planetary Science," is wrong. He says "Planets are round because their gravitational field acts as though it originates from the center of the body and pulls everything toward it." But this is a circular argument (pardon the pun). Generally a non-spherically symmetric distribution of matter doesn't have a gravitational field that acts as if it originates from the center of the body (the "center" being the center of mass). Spherically symmetric mass distributions do have this special property, so what Sears really implied is that planets that are already round will have gravitational fields that point towards the object's center of mass. This does absolutely nothing to address cases of objects that deviate from perfect roundness, i.e. all celestial bodies. This explanation [astronomycafe.net] by Dr. Sten Odenwald suffers from the same argument, and there's even a hint of it here [nasa.gov]. Nonetheless, these explanations are approximately true, and require bizarre shapes to break them.

For example, imagine a homogenous, perfectly shaped doughnut (a torus with a circular cross section). At the center of the doughnut hole we'd feel no gravitational field at all (a perfectly balanced tug-of-war). But deviate from the exact center just a tiny amount, and the closer side of the doughnut becomes more attractive than the other. One suddenly experiences a gravitational field that points away from the center of mass.

• #### Re:From the article -- galactic bowling physics? (Score:2)

For example, imagine a homogenous, perfectly shaped doughnut (a torus with a circular cross section). At the center of the doughnut hole we'd feel no gravitational field at all (a perfectly balanced tug-of-war). But deviate from the exact center just a tiny amount, and the closer side of the doughnut becomes more attractive than the other. One suddenly experiences a gravitational field that points away from the center of mass.

Do you have a link to a proof of this? I know that this is not the case for a

• #### Re:From the article -- galactic bowling physics? (Score:2)

At the moment, this [mathpages.com] is all I can find.
• #### Re: From the article -- galactic bowling physics? (Score:2)

I don't know the deep maths (didn't do anything like that in my maths degree...) but one issue occurs to me: are objects with very different gravitational fields stable? If a roughly spherical shape is deformed (plastic flow due to gravity, impact, fragmentation, accretion, whatever), then its gravitational field will maintain a roughly spherical shape; but is that true of toroidal objects, for example?

I wouldn't be surprised if the majority of shapes with radically non-spherical gravitational fields are

• #### Re:From the article -- galactic bowling physics? (Score:2)

It was Lister playing Planet Pool. "Played for and got!"
• #### Re:From the article -- galactic bowling physics? (Score:2)

Well, maybe that explains why we have continents which do not cover all of Earth's surface? (Reminder: The sea floor is a different material than the continents!)
• #### It's George Bush's Moon Mandate. (Score:2, Funny)

Free X-rays for all Moon residents. Take that Canada!
• #### Re:It's George Bush's Moon Mandate. (Score:1, Informative)

by Anonymous Coward
This is an EUROPEAN spacecraft.
• #### Just remember... (Score:3, Funny)

on Sunday November 07, 2004 @02:05PM (#10747306)
....what happened when they probed Mars with X-rays! Watchout! (is Gary Sinise piloting?)
• #### Opposed by GNAW&NPS (Score:1)

Scientists believe nuclear-powered ion-drives are their only real hope of exploring deep space, and vigorously support their development. Not surprisingly, anti-nuclear protesters, like the Global Network Against Weapons and Nuclear Power in Space, have pledged opposition.
Too much time on Slashdot. Any group that starts GNA... automaticly activates my mental filters. (No great loss in the case of Huggers In Space.)
• #### Scientists Discover Moon Core Made of Cheese (Score:1, Redundant)

News at eleven.
• #### from 'dept' topic (Score:2, Interesting)

Posted by CmdrTaco on 01:06 AM -- Monday November 08 2004
from the dept.

I've always read the 'from the so and so and whatever dept' cuz it's humourously funny and cynic at the same time.

This time, it's just plain ol' from the dept. I just wonder, whether it is an oversight or CmdrTaco really does not have anything witty to say about it? :-P

I know, I know it is off-topic, mod me down then.. I probably deserve it.

• #### The ion drive is the real story (Score:5, Interesting)

on Sunday November 07, 2004 @04:42PM (#10748317) Homepage
Ion drive technology allows you to explore space in ways that chemical rockets simply can't.

Quoting from the article,
"We have shown that even a small ion engine like Smart's can get us across space. Now we are planning to build space telescopes and robot probes to planets such as Mercury, using bigger and more powerful ion engines. These will take years off space-travel times. Instead of decades-long missions, we will take only a couple of years to cross space for future projects."

But,
"Ion engines need electricity and only solar panels can provide enough at present. So ion engine missions will be restricted to planets and moons near the Sun."

So the solution to deep space exploration is nuclear-powered ion-drives and NASA is working on it.
• #### Re:The ion drive is the real story (Score:2)

Specifically, the proposed Jupiter Icy Moons Orbiter [nasa.gov] mission. Browse the site if you're interested, lots of info there, and linked from there.
• #### Accreted Rings (Score:2)

Can any astrogeologists explain why the assumption is that the Moon is a result of debris from a two-planet crash as opposed to regular accretion of debris the way moons were formed on the other planets? Billions of years ago, each planet was a gradually coalescing disc, and the jovian planets still have evidence of this in their rings. The closer planets instead have moons - I assume because the Sun's gravity is stronger at our closer distance from the Sun, and caused the rings of the closer planets to agg
• #### Re:Accreted Rings (Score:3, Insightful)

It's really freaking big. Mercury and Venus don't have any moons, and the moons of Mars appear to be captured asteroids...relatively tiny rocks not big enough to form themselves into spheres. The Earth-Moon system is nearly a double planet. Of the inner planets, Earth is the only one with a decent moon...and it's a monster compared to the planet.

In any case, the planets you see now are just the ones that stayed in the system. Material didn't just cleanly accrete directly into the existing bodies. Most of t

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