# Tag Info

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The answer to the headline question is: No. Most of Saturn's rings are below the Roche limit of about 2.5 Saturn radii. Hence tidal forces will prevent that part of the rings to form a (large) moon. Actually, part of the rings may be caused by loss of material from some of Saturn's moons, as suspected from observations of Enceladus. Accretion of Earth is ...

14

In one sense any point you choose is at "the centre" of the universe and at any point in the universe, at a large scale, the universe looks the same as at any other point. This is not the same as saying the universe is infinite, though (but it could be). The analogy with an explosion is a poor one, as explosions expand into existing space. With the Big Bang ...

14

There are three main formation scenarios for planetary moons. The giant impact hypothesis: The satellite forms as a consecuence of an impact between the planet an a large planetesimal. The Moon is an example, and one of the arguments is that the chemical composition of the Moon matches that of Earth with a significant accuracy suggesting that it is a in ...

11

The currently leading answer is correct to say that moon formation inside the Roche limit is unlikely. However, the disk is evolving due to viscosity between the particles, and as a consequence it "spreads", so that material is able to move to outside the Roche limit. In fact this is a leading possible explanation for the formation of the inner moons of ...

10

Here is my answer to a similar question posted on the physics stack exchange website. Hubble's law (the law that deals with the expansion of the universe) applies to the expansion of space itself, i.e., if two objects stationary to each other that had no force between them were left alone the distance between would increase with time because space itself is ...

10

It’s been a while since I studied this, and meteorites are very much not my field, so I’ll share my current understanding but would welcome corrections from those more informed :-) These meteorites are mostly iron with a small amount of nickel. For a given composition of iron and nickel, there are different crystal structures that can be formed. Of ...

10

The actual density depends on the mineralogy, we don't have a crystalline iron core and silicon crust. You do have a lot of oxygen available, too when you look at the overall elementary abundance. So the abundant materials are Fayalite (${\rm Fe_2SiO_4}$), Olivine (${\rm (Fe,Mg)_2SiO_4}$), Fosterite (${\rm Mg_2SiO_4}$) etc. which make up most of the crust. ...

9

By "visible to the naked eye", I take it you mean "visible from Earth with a small telescope". Saturn's rings are largely water ice, and so they reflect more sunlight back to us. Jupiter's rings, have lower proportions of ice, and lots of smaller dust particles that tend to scatter light forward rather than back to us. The ring systems of Uranus and ...

8

The farther away, the faster the galaxies move away from us. But that's only the overall expansion of the universe. Locally velocities can differ and are to be added to the overall expansion. The Andromeda Galaxy is close enough to Milky Way to be able overcome the overall expansion of space. The Andromeda Galaxy and the Milky Way attract each other by ...

8

If we don't wait for too long, where we don't know for sure, whether protons or atomic nuclei stay stable forever, there won't be just one single element. The most abundant element in the universe will probably stay hydrogen, since it will stay in the intergalactic medium, and thin out by accelerating cosmic expansion. The second-most abundant element will ...

8

The universe doesn't expand away from any centre perse. All the distances are expanding uniformly throughout the universe. This causes such an effect that for each individual observer, it looks as if the entire universe moves away from them. It can be demonstrated using this figure (from google): $A$ represents the universe at one moment, $B$ represents the ...

7

The amount and kind of gases a body can trap depends on the object's surface temperature, and its density & radius (which refers to it's gravity). An object with high gravity and low surface temperature will be able to hold more gases in it's atmosphere. In the case of the Moon, due to its low gravity it could barely trap an atmosphere of Xenon. You ...

7

As Miranda is a rather small object (only 235km diameter) it may simply have not enough mass to make it matter settle into hydrostatic equilibrium under the influence of its gravity, thus it basically retains the irregular shape most asteroids have. This nice arxiv paper discusses the mass limits necessary for a stellar body to settle into a nice round shape:...

6

I don't have enough reputation to comment... I think this might help you understand the formation or binary and more stars systems. This of course is not the only possible method but it might explain the systems with big mass differences. As the initial rotation speed increases (marked in the videos as beta) you will see how the protoplanetary disk breaks ...

5

WHY implies a reason, which is venturing in to the religious realm. The circumstances under which an event such as the Big Bang occurs are guess work at best. Since the Big Bang is a singularity from which time itself started there is no real before the big bang. That's the first problem. The second is that because of the spatial singular nature of the big ...

5

There are elongated craters from grazing impacts, and these can sometimes get rather odd shapes like Schiller on the Moon and Orcus Patera on Mars (the later is a bit contested, it might have formed from something other than an impact). Double impact craters is another possibility. Some craters occur simultaneously (more direct picture). Splitting impactors ...

5

The "mass gap" is an observed deficit in the number of compact objects with mass between 2.5 and 5 solar masses. The "mass gap" is/was not understood. Such objects may be rare because they are difficult to detect or because something about the supernova process leads to a bifurcation between the most massive neutron stars and the least ...

4

What is in the center of the universe? This question over at Physics.SE: "Did the Big Bang happen at a point?", which has an answer with over 300 UpVotes, explains: "The simple answer is that no, the Big Bang did not happen at a point. Instead it happened everywhere in the universe at the same time. Consequences of this include: The ...

4

To answer your second question first: Yes, antimatter does exist in the same space as matter. In fact, the universe creates antimatter (and an equal amount of matter) every day as a matter of course in events like lightning strikes and supernovae, and even in certain nuclear decays. Humans create it in particle accelerators for research and for commercial/...

4

Definitely a UFO - Unidentified Flying Object, not necessarily aliens :-). A few possibilities I can think of (would be nice to know how fast the objects were going, and whether or not they disappeared), arranged by most plausible to least plausible: Birds If it was just after sunset, or just before sun rise, birds could have been flying up far above, ...

4

"Galactic bars develop when stellar orbits in a spiral galaxy become unstable and deviate from a circular path. The tiny elongations in the stars’ orbits grow and get locked into place, forming a bar. The bar becomes even more pronounced as it collects more and more stars in elliptical orbits. Eventually, a high fraction of the stars in the galaxy’s inner ...

4

The UV luminosity of a galaxy can be calculated, given a stellar population. This population, in turn, can be calculated given an initial mass function (IMF), i.e. the distribution function of stellar masses. In this case, the UV luminosity should be linearly proportional to the star formation rate (SFR), sometimes written $\Psi$. The UV is primarily emitted ...

4

It seems strange to me that a galaxy, which I imagine as a structure with some level of cylindrical symmetry, goes on to develop an elongated bar structure in its central region. The general idea is that galaxies with thin, kinematically "cold" (= stars or gas clouds in close-to-circular orbits) disks are generically unstable to non-axisymmetric ...

4

First things first, but in this case, second things first. When an asteroid or moon, passes the Roche Limit, it breaks apart and forms rings around the primary body. This is a widely believed misconception of the Roche limit. The Roche limit pertains to objects that are held together by gravitation only. Once chemical bonds come into play the Roche limit ...

3

The favored theory is a giant impact, at the end of the final stage of planetary formation (Canup, 2005). A "giant impact" is a collision with an object of a comparable size of the planet. That is also the most probable scenario for lunar formation (Canup, 2004).

3

The amorphous geometry of the Universe is currently being studied, and the large scale distribution of the galaxies is similar to a sponge. The measure in the middle of the image represents 1.5 billion light years. light travels in every direction, and at the time of the big bang, there was no light to travel anywhere, and early in the theory of the big bang,...

3

Earth and moon are thought to be formed by the collision of two planets. So we have at least these two protoplants. The cores probably ended mainly in the core of Earth; that's inferred by the much higher mean density of Earth in relation to Moon. Iron-nickel meteorites strongly indicate at least one pre-existing planet large enough to form an iron-nickel ...

3

I will edit this with the appropriate equations and timeframes in a few hours when I get back to my office. For now I will address the foundations of your questions with some basics. 1: The radius of the frost line is determined by the star itself (edit: More precisely the nebula that the star forms from.), more in-depth answer will come with edit. 2: The ...

3

There is a certain sense in which the moon does have an atmosphere. Even Mercury has an atmosphere in this sense. Though the sense is mostly in a "technically there are particles floating around the solid surface", but at densities which would make for very good vacuums on earth. The more practical/intuitive definition of atmosphere excludes such meager ...

3

It's because of the Sun. It might be good if I give a quick overview on star formation before I get to the meat of the issue. Here's star formation in a few simple steps: Giant Molecular Cloud forms. A large region of gas and dust, essentially a dense version of the interstellar medium, coalesces into an interstellar cloud. GMCs can be tens or hundreds of ...

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