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Old 08-28-2012, 09:30 PM
 
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The Kepler space telescope has located two planets orbiting a pair of stars. Planets orbiting binary stars are called circumbinary planets. Kepler has detected 4 systems with circumbinary planets, but this find is noteable in that it's the first time binary stars have been spotted with more than a single planet.

One of the planets is in the habitable zone from the binary stars. It's thought to be a gas planet, a little larger than Uranus, making a complete orbit in 303.2 days, and is probably not suitable for life as we know it. The other planet is too close to the stars and orbits them in 49.5 days. The planets are 3 and 4.6 times the diameter of Earth. The stars sip around each other in 7.5 days. The largest of the two stars is similar to our sun.

It's thought that most stars like our sun are binary systems. The new system raises the bar that more binary systems with multiple planets are likely to be found.

Two alien planets found with twin suns - Technology & science - Space - Space.com - NBCNews.com


A short image gallery here:
'Tatooine' Solar System: 2 Alien Planets with Twin Suns (Gallery) | Space.com







NASA's Kepler Mission Discovers Multiple Planets Orbiting Twin Suns - YouTube
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Old 08-31-2012, 01:28 AM
 
Location: Wasilla, Alaska
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Very kewl!

There are two kinds of binary systems, a tight binary (like Kepler-47), and a loose binary (like Alpha Centauri A & B). Tight binaries can only have one solar system, but loose binaries can have two solar systems. Life, assuming there is any, would be considerable different on tight binaries than on loose binaries.

If we were standing on a habitable planet orbiting the Kepler-47 system, every 7.5 days when the small sun is closest to the planet, would be the hottest day that "week" on the planet, and just 3.75 days later would be the coldest day of the "week." It would also be interesting to see how a tight binary would effect the tides, as well as the orbits of the planets. If the smaller star orbiting the primary star is giving little gravitational tugs on the planets with each of its orbits, then the planets would be moving slightly further away from the barycenter of both stars with each orbit.

The luminosity and spectrum of the light would also be different each day, depending on the orbit of its companion star. I wonder how that would effect photosynthesis. It would be very cool if the plants changed color on a daily basis.

It would certainly offer a very picturesque sunrise and sunset, or should that be "sunsrise" and "sunsset?"
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Old 08-31-2012, 12:46 PM
 
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Originally Posted by Glitch View Post
Very kewl!

There are two kinds of binary systems, a tight binary (like Kepler-47), and a loose binary (like Alpha Centauri A & B). Tight binaries can only have one solar system, but loose binaries can have two solar systems. Life, assuming there is any, would be considerable different on tight binaries than on loose binaries.

If we were standing on a habitable planet orbiting the Kepler-47 system, every 7.5 days when the small sun is closest to the planet, would be the hottest day that "week" on the planet, and just 3.75 days later would be the coldest day of the "week." It would also be interesting to see how a tight binary would effect the tides, as well as the orbits of the planets. If the smaller star orbiting the primary star is giving little gravitational tugs on the planets with each of its orbits, then the planets would be moving slightly further away from the barycenter of both stars with each orbit.
Good points Glitch. The orbits of the planets in such a system is pretty much what I was referring to in another thread (can't remember which) with respect to feeezing and scorching temperature variations. On the larger (gas) planet in the habitable zone, such variations would be expected to result in extremely wild and active weather conditions. The inner planet (not in the habitable zone) could be a large rocky planet, but more similar in some ways to Mercury.

From the illustrations of the planetary orbits in the Kepler-47 system, it looks like the orbits are pretty lop-sided. If these illustrations are a fair representation, I would think the tidal forces would be pretty extreme between the closest approach and the farthest from the stars, perhaps causing the planets to stretch like a ball of silly putty, heating up the interior and causing a lot of volcanic activity, kind of like the moon Io. Of course, it really depends on the distance from the stars.

The real question is in defining a "habitable zone". The idea is a range that would allow water to generally remain is a liquid form. If the orbit of the planet is somewhat eccentric, and taking into account the alignment of both stars with the planet, then IF the planet were a rocky planet with water, water could liquify at the closest point, then freeze hard at the furthest point. And complicating it even more, as you say, is when both stars are aligned with the planet (which would be frequent) making it very toasty at the closest point.

Neither of the two planets have been directly observed, but have been determined by the change in brightness of the stars as the planets cross in front of each. Kepler-47 is about 4900 light years away.

The planets are known as Kepler 47 b and Kepler 47 c. As mentioned, if any life could exist on such planets, it probably would be very different than life as we know it. However, it's pretty doubtful either of these planets could host any life at all, life as we know it. Still, the discovery does open up the possibility for planetary systems of other binary stars. If the conditions were right, it's possible life could get a foothold and thrive in a binary system. How complex such life could become is hard to say though.

The nature of the Kepler-47 system - Charlotte Mathematical Science | Examiner.com
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Old 08-31-2012, 01:41 PM
 
Location: Seattle, Washington
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Originally Posted by Glitch View Post
Very kewl!

There are two kinds of binary systems, a tight binary (like Kepler-47), and a loose binary (like Alpha Centauri A & B). Tight binaries can only have one solar system, but loose binaries can have two solar systems. Life, assuming there is any, would be considerable different on tight binaries than on loose binaries.

If we were standing on a habitable planet orbiting the Kepler-47 system, every 7.5 days when the small sun is closest to the planet, would be the hottest day that "week" on the planet, and just 3.75 days later would be the coldest day of the "week." It would also be interesting to see how a tight binary would effect the tides, as well as the orbits of the planets. If the smaller star orbiting the primary star is giving little gravitational tugs on the planets with each of its orbits, then the planets would be moving slightly further away from the barycenter of both stars with each orbit.

The luminosity and spectrum of the light would also be different each day, depending on the orbit of its companion star. I wonder how that would effect photosynthesis. It would be very cool if the plants changed color on a daily basis.

It would certainly offer a very picturesque sunrise and sunset, or should that be "sunsrise" and "sunsset?"
Awesome post Glitch. My imagination is having fun with this one, trying to imagine the experience of living on or even just visiting such a planet.
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Old 08-31-2012, 08:52 PM
 
Location: Wasilla, Alaska
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The planets are known as Kepler 47 b and Kepler 47 c. As mentioned, if any life could exist on such planets, it probably would be very different than life as we know it. However, it's pretty doubtful either of these planets could host any life at all, life as we know it. Still, the discovery does open up the possibility for planetary systems of other binary stars. If the conditions were right, it's possible life could get a foothold and thrive in a binary system. How complex such life could become is hard to say though.
You are overlooking one thing. If Kepler-47c is a planet like Uranus or Neptune, and it is in the habitable zone, then that would make any moons that surround Kepler-47c also in the habitable zone. Neptune has the largest moon in our solar system - Triton. I think it is reasonable to assume that there are probably rocky type moons orbiting Kepler-47c.
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Old 08-31-2012, 11:24 PM
 
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You are overlooking one thing. If Kepler-47c is a planet like Uranus or Neptune, and it is in the habitable zone, then that would make any moons that surround Kepler-47c also in the habitable zone. Neptune has the largest moon in our solar system - Triton. I think it is reasonable to assume that there are probably rocky type moons orbiting Kepler-47c.
We have no way of knowing if Kepler-47c has any moons or if it does, what size they may be. Although it has been suggested that the planet may be a gas planet, it isn't known. It may be reasonable, but it's just speculative right now. Neither of the planets have actually been seen. They've been determined to exist based on the change of brilliance as they pass in front of the stars. It's possible to determine the atmospheric composition of the planets, maybe moons as well, but we're not at that point yet. Maybe the James Webb space telescope will be able to provide a better look at some of these things.

I agree with what you suggested, that every 7.5 days when the small sun is closest to the planet, would be the hottest day that "week" on the planet, and just 3.75 days later would be the coldest day of the "week." But I would also take it a step farther to say temperatures would vary even more depending on the orbits, especially Kepler-47c since it's described as being in the habitable zone. If its orbit is as eccentric as had been illustrated, which is what it looks like to me, temperature would be pretty extreme, even for any moons.

I have to admit that I was actually thinking of moons similar to ours, dry and barren. My bad. I hadn't considered ice-covered moons with possible liquid oceans below the ice layer. We don't know that for sure either about our own solar system, although there are some tantalizing hints, not only of liquid water, but maybe life as well. It's too early to jump to conclusions. We simply don't yet know. We need to better explore those icy moons to know for sure. Any way you look at it though, Kepler-47c is bound to be a very interesting planet with its own surprises. Even if there are moons around Kepler-47c, it's not going to change the orbit of the planet or its moon(s). There are many unknowns. How close or far are the moons from the planet? How large or small are they? How eccentric or not are their orbits? Would they have an atmosphere?

I'm still inclined to think that if there is any life on either the planet (even though it may be a gas planet) or its moons, it would probably be very different than life as we know it.
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Old 09-01-2012, 10:58 AM
 
Location: Wasilla, Alaska
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We have no way of knowing if Kepler-47c has any moons or if it does, what size they may be. Although it has been suggested that the planet may be a gas planet, it isn't known. It may be reasonable, but it's just speculative right now. Neither of the planets have actually been seen. They've been determined to exist based on the change of brilliance as they pass in front of the stars. It's possible to determine the atmospheric composition of the planets, maybe moons as well, but we're not at that point yet. Maybe the James Webb space telescope will be able to provide a better look at some of these things.
Very true, it is all speculation at this point. However, if there are planets then it is a good bet that there also moons. Our solar system has 174 moons, counting the six moons around small dwarf planets. Of the 168 moons around regular planets, only three orbit rocky type planets. The remaining 165 moons are around the gas and ice giants. So it is not much of a stretch to imagine moons around other planets of similar size.

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I agree with what you suggested, that every 7.5 days when the small sun is closest to the planet, would be the hottest day that "week" on the planet, and just 3.75 days later would be the coldest day of the "week." But I would also take it a step farther to say temperatures would vary even more depending on the orbits, especially Kepler-47c since it's described as being in the habitable zone. If its orbit is as eccentric as had been illustrated, which is what it looks like to me, temperature would be pretty extreme, even for any moons.

I have to admit that I was actually thinking of moons similar to ours, dry and barren. My bad. I hadn't considered ice-covered moons with possible liquid oceans below the ice layer. We don't know that for sure either about our own solar system, although there are some tantalizing hints, not only of liquid water, but maybe life as well. It's too early to jump to conclusions. We simply don't yet know. We need to better explore those icy moons to know for sure. Any way you look at it though, Kepler-47c is bound to be a very interesting planet with its own surprises. Even if there are moons around Kepler-47c, it's not going to change the orbit of the planet or its moon(s). There are many unknowns. How close or far are the moons from the planet? How large or small are they? How eccentric or not are their orbits? Would they have an atmosphere?

I'm still inclined to think that if there is any life on either the planet (even though it may be a gas planet) or its moons, it would probably be very different than life as we know it.
The overwhelming majority of moons in our solar system are dry and barren without an atmosphere. The largest moon in our solar system is Triton, which does have an atmosphere, but its atmosphere is 70,000 times less dense than Earth's atmosphere. Which means that it is highly doubtful that any moon around Kepler-47c, assuming there are any, would have sufficient atmospheric pressure to allow for liquid water on its surface.

Neither of the two planets around Kepler-47 A & B are anything like the planets we have in our solar system. Both appear to be closer to brown dwarfs than planets. Kepler-47b is only one quarter the size of Jupiter, but is 2.7 times denser, giving it a gravity of 95 G. Kepler-47c is bigger at just under half the size of Jupiter, but with an even higher density (17 times), giving it a gravity of 255 G. The density of both these planets would give them very strong magnetic fields.

The eccentricity of Kepler-47c's orbit, if depicted correctly, is not severe enough to remove it from the habitable zone, but, it does appear to be more severe than Earth's eccentricity. Which would lead to some pretty extreme seasons.

Considering the extremely high density of Kepler-47c, I like to entertain the idea that one or more of its moons may be extremely large, possibly even capable of supporting microbial life with a dense atmosphere. The tidal forces on any of Kepler-47c's moons would be huge, squeezing and stretching its moons far more than Jupiter squeezes and stretches its own moons.
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Old 09-01-2012, 01:49 PM
 
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Very true, it is all speculation at this point. However, if there are planets then it is a good bet that there also moons. Our solar system has 174 moons, counting the six moons around small dwarf planets. Of the 168 moons around regular planets, only three orbit rocky type planets. The remaining 165 moons are around the gas and ice giants. So it is not much of a stretch to imagine moons around other planets of similar size.
Although we do have numerous moons in our solar system, the majority of them tend to be pretty small. If that might indicate being somewhat typical of other solar systems, then most of their moons will also be rather small in size, although no doubt a few perhaps large enough for some kind of atmosphere. There's no guarantee that there must be moons, or sizable ones, orbiting other planets. For example, in our own solar system, both Venus and Mars reside at the fringe of the habitable zone, but Venus has no moons and the pair orbiting Mars are too small for an atmosphere, and are probably captured asteroids. Earth is the only planet in the habitable zone with a sizable moon, and it has virtually no atmosphere.


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Originally Posted by Glitch View Post
The overwhelming majority of moons in our solar system are dry and barren without an atmosphere. The largest moon in our solar system is Triton, which does have an atmosphere, but its atmosphere is 70,000 times less dense than Earth's atmosphere. Which means that it is highly doubtful that any moon around Kepler-47c, assuming there are any, would have sufficient atmospheric pressure to allow for liquid water on its surface.
Titon is also a sizable moon with an actve atmosphere. There has been some speculation that it might have some extremophile life forms. It's possible, but I'm doubtful. If there is, I'd say it would be very different from life as we know it, and would probably exist way below the surface. I agree that any moon around Kepler-47c is unlikely to have any liquid water on the surface, although it's possible they could have water ice in deep polar craters (depending on the rotation of the moon) or below the surface.

There has been some thought that Titan might have a liquid ocean a hundred kilometers below the surface, sort of sandwiched between the surface crust and the core.
Saturn Moon Titan May Hide Buried Ocean | Space.com


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Originally Posted by Glitch View Post
Neither of the two planets around Kepler-47 A & B are anything like the planets we have in our solar system. Both appear to be closer to brown dwarfs than planets. Kepler-47b is only one quarter the size of Jupiter, but is 2.7 times denser, giving it a gravity of 95 G. Kepler-47c is bigger at just under half the size of Jupiter, but with an even higher density (17 times), giving it a gravity of 255 G. The density of both these planets would give them very strong magnetic fields.
I haven't heard of anything about what the suspected composition of Kepler-47b, although 47c is suspected to be a gas planet. Thanks for the info.


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Originally Posted by Glitch View Post
The eccentricity of Kepler-47c's orbit, if depicted correctly, is not severe enough to remove it from the habitable zone, but, it does appear to be more severe than Earth's eccentricity. Which would lead to some pretty extreme seasons.
Agreed, seasonal weather conditions on Kepler 47c would be pretty extreme.


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Originally Posted by Glitch View Post
Considering the extremely high density of Kepler-47c, I like to entertain the idea that one or more of its moons may be extremely large, possibly even capable of supporting microbial life with a dense atmosphere. The tidal forces on any of Kepler-47c's moons would be huge, squeezing and stretching its moons far more than Jupiter squeezes and stretches its own moons.
We'd all like to think there might be the possibility of microbial life somewhere, perhaps on a moon of 47c. I think it would depend on how close or far such a moon might be from the planet, assuming it has sizable moons. If the moons are too close, it wouldn't necessarily rule out the possibility of life, but if tidal forces are too great, it would suggest that the moon may eventually break up and be pulled into the planet making the prospects for such life relatively short lived. Although, if there are numerous additional moons orbiting the planet, it's possible for a moon to be kept in check by gravitational interactions from other moons, at least for a while. The scenario of such a moon affected by tidal forces, as you described, would probably be similar to Io with constant volcanic activity continually changing the surface landscape of the moon. That might not be too condusive for the prospects of life.
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Old 09-01-2012, 09:04 PM
 
Location: Wasilla, Alaska
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Originally Posted by NightBazaar View Post
Although we do have numerous moons in our solar system, the majority of them tend to be pretty small. If that might indicate being somewhat typical of other solar systems, then most of their moons will also be rather small in size, although no doubt a few perhaps large enough for some kind of atmosphere. There's no guarantee that there must be moons, or sizable ones, orbiting other planets. For example, in our own solar system, both Venus and Mars reside at the fringe of the habitable zone, but Venus has no moons and the pair orbiting Mars are too small for an atmosphere, and are probably captured asteroids. Earth is the only planet in the habitable zone with a sizable moon, and it has virtually no atmosphere.

Titon is also a sizable moon with an actve atmosphere. There has been some speculation that it might have some extremophile life forms. It's possible, but I'm doubtful. If there is, I'd say it would be very different from life as we know it, and would probably exist way below the surface. I agree that any moon around Kepler-47c is unlikely to have any liquid water on the surface, although it's possible they could have water ice in deep polar craters (depending on the rotation of the moon) or below the surface.

There has been some thought that Titan might have a liquid ocean a hundred kilometers below the surface, sort of sandwiched between the surface crust and the core.
Saturn Moon Titan May Hide Buried Ocean | Space.com

I haven't heard of anything about what the suspected composition of Kepler-47b, although 47c is suspected to be a gas planet. Thanks for the info.
Kepler-47b has an estimated upper mass limit of 2.7 Jupiter masses and an estimated radius of 0.265 Jupiter radii, giving it an estimated upper density limit of 190 g/cm^3, which is consistent with the density of a brown dwarf, but an object of this size is too small to be a brown dwarf. These values give Kepler-47b a upper surface gravity limit of 950 m/s^2, so a person who weighs 200 pounds on Earth could weigh as much as 19,000 pounds on Kepler-47b. Kepler-47b is 0.2956±0.0047 AU away from its stars, and completes an orbit of Kepler-47 once every 49.514±0.040 Earth days. The black-body temperature of Kepler-47b is 450 K or 177°C, which is consistent with moderate heat inside an oven. Extreme pressure from gravity and the planet's atmosphere may make liquid water possible despite the high temperature, which would boil liquid water at atmospheric pressure on Earth. However, the extreme gravity (95 G) is likely to crush most forms of life.

Kepler-47c has an estimated upper mass limit of 17 Jupiter masses and an estimated radius of 0.410 Jupiter radii, giving it an estimated upper density limit of 330 g/cm^3, which is consistent with the density of a brown dwarf. This makes sense because the International Astronomical Union considers an object with a mass above the limiting mass for thermonuclear fusion of deuterium (currently calculated to be 13 Jupiter masses for objects of solar metallicity) to be a brown dwarf, whereas an object under that mass (and orbiting a star or stellar remnant) is considered to be a planet. These values give Kepler-47c a upper surface gravity limit of 2500 m/s^2, so a person who weighs 200 pounds on Earth could weigh as much as 51,000 pounds on Kepler-47c. Kepler-47c is 0.989±0.016 AU away from its stars, and completes an orbit of Kepler-47 once every 303.158±0.072 Earth days. The black-body temperature of Kepler-47b is 247 K or -26°C, which is similar to Earth's black-body temperature of 255 K or -18°C. Extreme pressure from gravity and the planet's atmosphere should make liquid water impossible, however, forcing it into a high-pressure phase of ice. The real temperature is likely to be significantly higher due to the deuterium fusion that occurs in objects of this size.

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Originally Posted by NightBazaar View Post
We'd all like to think there might be the possibility of microbial life somewhere, perhaps on a moon of 47c. I think it would depend on how close or far such a moon might be from the planet, assuming it has sizable moons. If the moons are too close, it wouldn't necessarily rule out the possibility of life, but if tidal forces are too great, it would suggest that the moon may eventually break up and be pulled into the planet making the prospects for such life relatively short lived. Although, if there are numerous additional moons orbiting the planet, it's possible for a moon to be kept in check by gravitational interactions from other moons, at least for a while. The scenario of such a moon affected by tidal forces, as you described, would probably be similar to Io with constant volcanic activity continually changing the surface landscape of the moon. That might not be too condusive for the prospects of life.
Both Kepler-47a & b would also have extensive magnetic fields, certainly much greater than Jupiter's. If moons were too close (like Io is to Jupiter) then they would be getting cooked.
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Old 09-01-2012, 10:31 PM
 
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Kepler-47b has an estimated upper mass limit of 2.7 Jupiter masses and an estimated radius of 0.265 Jupiter radii, giving it an estimated upper density limit of 190 g/cm^3, which is consistent with the density of a brown dwarf, but an object of this size is too small to be a brown dwarf. These values give Kepler-47b a upper surface gravity limit of 950 m/s^2, so a person who weighs 200 pounds on Earth could weigh as much as 19,000 pounds on Kepler-47b. Kepler-47b is 0.2956±0.0047 AU away from its stars, and completes an orbit of Kepler-47 once every 49.514±0.040 Earth days. The black-body temperature of Kepler-47b is 450 K or 177°C, which is consistent with moderate heat inside an oven. Extreme pressure from gravity and the planet's atmosphere may make liquid water possible despite the high temperature, which would boil liquid water at atmospheric pressure on Earth. However, the extreme gravity (95 G) is likely to crush most forms of life.
Great info, thanks! Do you have a link for that? I'd like to Bookmark it.


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Both Kepler-47a & b would also have extensive magnetic fields, certainly much greater than Jupiter's. If moons were too close (like Io is to Jupiter) then they would be getting cooked.
Well, yes, in the end it would cook. The thing about Io is that it experiences Tidal Heating in part (a large part) because of the pull of Jupiter's gravity. But it's also tugged from the other side by the gravitational pull of Europa. Io is closest to Jupiter and Europa is second. Both Jupiter and Europa sort of keep Io in its orbit, but not without causing significant effects to Io. The result is that Io ends up being tidally stretched like a piece of taffy, the effect of which causes extreme friction inside Io, which in turn causes Io's interior to heat up and eject material in the form of volcanoes. So, yes, it would heat up from Tidal Heating, but I think it would probably fragment before actually entering Jupiter.

I would think if there was a reduction in the orbits of both Io and Europa, Io would probably begin to break up. Once the chunks drift close enough to Jupiter and fall into the atmosphere, they'd definitely heat up and cook the remains. A similar example of celestial bodies is Shoemaker-Levy which began breaking up from a very close pass near Jupiter in 1992 on its way toward the sun. That breakup was clearly the result of Jupiter's gravity. It appears the fragments exploded after entering Jupiter's upper cloud layer in 1993

Tidal Heating Tutorial

Tides and Volcanoes on Io: Tidal Forces Cause Volcanic activity on Jupiter's Moon Io | Suite101.com

Comet Shoemaker-Levy 9
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