# Tag Info

40

You really need a full-blown stellar evolution model to answer this precisely and I'm not sure anyone would ever have done this with an oxygen-dominated star. To zeroth order the answer will be the similar to a metal-rich star - i.e. about 0.075 times the mass of the Sun. Any less than this and the brown dwarf (for that is what we call a star that never ...

30

This NASA page says this photo was taken on April 28 2006. Using Celestia, I managed to find the picture from Cassini that best lines up with the photo. It doesn't match up precisely, but that's to be expected as the calculated orbital elements of all these moons (and cassini) in the software won't necessarily match up to reality precisely. Below is the ...

24

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 ...

23

Pan, Daphnis, and various other moonlets, I would argue, are inside the rings. If you explicitly discount the Encke gap (which Pan orbits in) and the Keeler gap (which Daphnis orbits in) as being part of the ring system, Daphnis would be your answer, as it is a ~8 km object in a 42 km gap. (for comparison, Pan is a ~35 km object in a 325 km gap) Really, ...

22

Titan "lakes": Published Open Access in Science: Radar Evidence for Liquid Surfaces on Titan Campbell, D. B., Black, G. J., Carter, L. M., and Ostro, S. J., Science 302, 5644, pp. 431-434, 17 Oct 2003 DOI: 10.1126/science.1088969 This was a really elegant experiment! A continuous, unmodulated, circularly polarized 13 cm wave was broadcast from Arecibo ...

20

Rings are made up of tiny (and not so tiny) pieces of rock and ice that are in some way the bits "left over" from the formation of the planet. The theory involves the Roche limit - and is that particles that are already within this limit can't accrete into a larger body because of the tidal forces involved. Another theory is that they are formed when a moon ...

16

Elements of answer: It is not an easy question, as we lack of data to constrain strongly the density and mass of Saturn's rings. However, a first clue of their density is their optical depth (that is a measure of the transparency of a medium). The densest rings are the one of the main ring system (rings A, Cassini Division, B and C) plus ring F; they are ...

16

One second of googling reveals the whole archive: http://esamultimedia.esa.int/docs/titanraw/index.htm (note you can click onto the strips to inspect them!) The archive depicts the whole decent of the Huygens lander onto Titan, with the first picture being on the ground, and some of them seem to be taken from higher up altitudes, pages 17-27 you can see the ...

14

First of all, at that distance seeing the Moon and seeing the Earth amounts to the same thing. At its closest, Saturn is around 3000 times as far from Earth as the Moon is, so viewed from Saturn, the Moon is never more than about a minute of arc away from the Earth. If you can see Earth from the North Pole of Saturn, you can see the Moon, also. (Though it ...

13

The JPL Solar System Simulator doesn't show Epimetheus but does show Titan behind the Encke gap at 2006-04-28 08:12 UTC. The simulated surface texture is probably composed of VIMS images in infrared wavelengths where Titan's atmosphere is relatively transparent. On the real Titan, haze scatters visible light so strongly that the surface is indistinct and ...

12

This is a big one, so I'll split it into parts based on the questions you asked: 1) Earth has roughly a distance of 1 AU to the sun, Saturn between 9 and 10. Sun's gravity would therefore have a much stronger influence on these rings. Would it already be enough to distort the rings (e.g. even leading to the sun "stealing" parts of it) or would the rings ...

12

To answer this, one really has to understand how the geometric and bond albedos are defined. Let's start with the bond albedo since its simpler. Bond Albedo The Bond Albedo is just the fraction of energy hitting a surface that gets reflected. To simplify the process, let's say I shoot 100 photons of all the same energy at Enceladus. Of those 100 photons ...

12

Yes, if you observe Earth and the Moon at a favorable time. Near a Saturn summer solstice, e.g. between 2012 and 2022, Earth appears well above the horizon from Saturn's north pole. If the planet body is out of the way, so are the rings. The other observability issue is Earth's elongation from the Sun. This reaches a maximum of about 6$^\circ$ at intervals ...

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 ...

11

Hours to days. The orbital period is proportional to the 3/2 power of the orbital radius, and the orbital period of the moon Methone (and thus of the particles in its associated ring arc) is very close to 24 hours. Working from the orbital radii given in this table, I get: D ring: ~5 hours C ring: ~6-7 hours B ring: ~8-10 hours A ring: ~12-14 hours F ring:...

11

It did not detect methane lakes. It found that Titan was shiny (in radar terms): that is, the reflections were from a smooth surface rather than a rough one, and at the same time not very intense. As a result (quoting the 2003 New Scientist article Radar reveals Titan's methane lakes linked in one of the comments to your question), “some researchers ...

10

It appears (and I am no expert) that Saturn's ring evolution is governed mainly by "viscous spreading" - collisions between ring particles; and also by interactions with Saturn's moons (resonances); and bombardment with meteoritic material. There appears to be no consensus on how old the ring system is. Most theories of their formation have this taking ...

9

What's going on with the distortion of the rings on the upper half when they (presumably) cross in front of Saturn? The brownish areas you see on Saturn are ring light, analogous to seeing the Earth by moonlight. Saturn's rings light up Saturn's night sky, particularly just after sunrise and just before sunset. The two dark bands across the face of Saturn ...

9

I'll give this one a shot. Correction is welcome. Upper atmosphere temperature. It's not just elements that give a planet color, but the temperature of elements. When we examine what a planet looks like, we're basically talking about reflected sunlight from the planet's surface or atmosphere. With Earth, its atmosphere is transparent enough that its ...

9

That the rotation period of the bulk mass of a planet is estimated through something with the magnetic field is true. But let me maybe elaborate a bit in-depth on that. No planetary magnetic field is a dipole. Earth has strong magnetic anomalies over the Atlantic, there may be ionic disturbances by moons like Io, or your magnetic field is just really crazy,...

9

The vast majority of the particles in Saturn's rings are small, on the order of $\sim10^{-1}$ m or lower. The columnar number density, according to data from Voyager 1 and Earth-based observations, can be approximated as a function of particle radius by a power law for all particle radii $a$ in meters such that $0<a<1$, as can be seen on this log-log ...

9

For these kind of questions, you might want to use Stellarium, a free open source planetarium. You can specify the location of the observer on many celestial bodies, including Saturn. Any time between 2011 and 2023 With this tool, you can see that the moon will be in the northern saturnian sky non-stop between 2011 and 2023. You can also see that the moon ...

8

Salem is at 42.5° north. At the equator, the position of the sun varies by 23.5 degrees on either side of the vertical over the course of each year, due to earth's 23.5° axial tilt with respect to the ecliptic. Saturn, however is not on the ecliptic. It departs by about 2.5° over the course of its 29.45 year, 9.5 AU orbit. So once every 29.5 years Saturn's ...

8

The various moons are on orbits that are mostly a lot more than 1km apart from other moons. The orbits are stable, so the moons just keep going round Saturn on the same orbit. The moons are far enough apart that they have negligible gravitational influence on other moons. So the moons never get close to each other and don't collide. There are moons, like ...

8

Consider the dimensionless parameter $k$ for some planet, given by $$k \equiv \frac{\Omega^2 a^3}{G M}$$ where $\Omega$ is the planet's equatorial sidereal rotation rate, $a$ is the planet's equatorial radius, $G$ is the universal gravitational constant, and $M$ is the planet's mass. The values for this dimensionless parameter are 0.003461 for the Earth, ...

7

This puzzle is something called the Mimas paradox. The two bodies are nearly twins, but Mimas is substantially less active than Enceladus. There are currently several proposed solutions: Mimas cooled quickly, before it entered its resonance with Tethys (which contributes to tidal heating, just as Dione does for Enceladus). A "hot start" from rapid ...

7

Large binoculars are already enough. If you have some at home, try them. At our recent public outreach event, we had a 20x magnification on them. You need a relatively heavy mount though, or at least have an attachable weight to a tripod. This is needed in order to damp shaking of your mount, which can severely impact the viewing experience. It would be ...

6

First, Azimov was writing (Edge 1982, and Earth 1986) before the first extra solar planets were tentatively detected (1989), or definitely detected 1991 or 1992. So what he wrote could not be based on any real data on extra solar planets, and must have been an educated guess. However both books were written after the discovery of Charon, so he may have been ...

6

As you can see, Saturn is eclipsing the sun in this image. This eclipsing causes the white outlining of the planet in this photo. The bottom ring is indeed passing on the other side of Saturn which would explain why it is not visible in this image. However, the ring passing in front of Saturn is being cast in the shadow of the planet. The light cast on the ...

6

You will not be able to see Saturn's rings directly with a 15x70 telescope, but you will be able to notice that Saturn appears elliptical, not round. This is due to the shape of the rings around the planet, but you will not be able to resolve the hole between the rings and the planet (much less the Cassini gap). Just as an impractical suggestion in the ...

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