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Offline turnipsock

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« on: 30/12/2007 20:30:07 »
Olympus Mons, the highest mountian in the solar system is measured at 27km. It's on Mars which doesn't have a sea level, so what do they use as a reference for this measuerment?


 

Offline neilep

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« Reply #1 on: 30/12/2007 22:16:21 »
This is a great question...I don't suppose they can impose a false sea level so in this case I would imagine that just take the exact measurement from the base.....or...as I suspect the average height of the surface !

...but what do I know...I'm just a sheep !!
 

Offline rosalind dna

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« Reply #2 on: 30/12/2007 22:20:48 »
Olympus Mons, the highest mountian in the solar system is measured at 27km. It's on Mars which doesn't have a sea level, so what do they use as a reference for this measuerment?

Turnipsock is these of the highest mountains in the solar systems right that is
the nine planets in our solar system. Mars also being the Greek god of war too.
http://www.nineplanets.org/mars.html 
http://en.wikipedia.org/wiki/Olympus_Mons
http://volcano.und.edu/vwdocs/planet_volcano/mars/Shields/olympus_mons.html


This is a great question...I don't suppose they can impose a false sea level so in this case I would imagine that just take the exact measurement from the base.....or...as I suspect the average height of the surface !

...but what do I know...I'm just a sheep !!
good one
 

Offline turnipsock

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« Reply #3 on: 31/12/2007 00:18:32 »
I think there may only be eight planets in the solar system now, we lost one a while ago.
 

Offline rosalind dna

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« Reply #4 on: 31/12/2007 12:19:01 »
Yes and it was Pluto but that was what Google said. But it was replaced
another planet with a rather unpronounceable name something like Sneda, I think.

http://en.wikipedia.org/wiki/Pluto

The most recently found planet so this may make it 10 planets, but Turnipsock
or someone will correct me. fine.

http://en.wikipedia.org/wiki/90377_Sedna
http://news.bbc.co.uk/1/hi/sci/tech/7082257.stm

 

Offline turnipsock

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« Reply #5 on: 01/01/2008 21:32:37 »
This is a great question...I don't suppose they can impose a false sea level so in this case I would imagine that just take the exact measurement from the base.....or...as I suspect the average height of the surface !

...but what do I know...I'm just a sheep !!

It looks like it is the average height of the surface, if Wikipedia is to be trusted.

It seems a bit unfair using this reference to mearsure something on Mars and then using something different on Earth.

If we were to removed the water from the earth, what would be the average height of our surface? I guess that since the earth is mostly underwater, the average height would be below sea level.
 

Offline chris

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« Reply #6 on: 04/01/2008 09:37:58 »
True, but the deepest parts of the ocean on Earth are 5 miles or so, which would still mean that Everest falls far short of Olympus Mons!

Interestingly, the huge weight of Olympus Mons has deformed the curst of Mars. The planet is turning (like the Earth), and to remain stable it has shifted its rotation and the crust has distorted, so that the volcano now sits on the planet's equator.

This was discovered in the last 12 months by looking at what looks like a giant shoreline on the surface of Mars.   The problem was, the shoreline seemed to rise and fall by kilometres over its length - and that's a high tide even on a good day!

Here's an excerpt from the interview I did with Taylor Perron, who published these findings in Nature last year:


"There is every reason to think that Mars was once a much wetter place than it is today including what looks like an extensive coastline thousands of miles long on the northern hemisphere. The only problem is that the shoreline changes in height in some areas by several kilometres making people think that perhaps we have been fooled and it is not the vestiges of a Martian Mediterranean after all, but now Harvard's Taylor Perron thinks that there is another explanation, which is that the surface of Mars has been deformed by the planet altering its axis of rotation and the direction of this change has been dictated by Olympus Mons, Mars's massive volcano, which wants to sit on the planet's equator and if you calculate how the planet would have altered its spin axis in sympathy with Olympus Mons, those changes directly map onto the features of the ancient shoreline suggesting that Mars really was once a very wet place. Nature 447, 840843

Taylor Perron: We have been trying to reconcile some observations about the early history of Mars and specifically observations that have to do with the amount and distribution of water on early Mars. Few different observations suggest that there may have been oceans at one time in the ancient Martian past. The northern hemisphere of Mars contains a very large topographic basin and this basin has a very smooth flow much like Earth's ocean covered by sediment that has been redistributed over a very large area. In addition, there are some very large channels that were carved by huge floods that end right at the margin of this basin and so the water that carved those channels would have flowed into and at least partially filled the basin and then finally from images in the 1980s that appeared to be coastal land forms and these can be traced continuously for thousands of kilometres right around the margins of this northern basin.

Chris Smith: So, this is like a sort of Mars seaside?

Taylor Perron: That is right, exactly. Now, all of these things were taken as pretty strong evidence that there was at one time an ocean on the surface of Mars, but the monkey wrench was thrown into the works by some measurements collected by the Mars globe surveyor launched in the late 1990s that made a global topographic map of Mars and it was recognized that elevations along these shorelines rise and fall by kilometres and shorelines formed at sea level and elevations of course are measured relative to sea level. So, the elevations along the shore line should be constant.

Chris Smith: And there is no way this could be a feature which has been introduced after the shore line was made, for instance by surface movement or tectonics or something?

Taylor Perron: Well, that is exactly what we are proposing actually is that originally these shore lines even though they are not flat now, may have been flat, i.e., created at sea level at some time in the past and then subsequently deformed by very large scale processes.

Chris Smith: Now, what is the evidence that that has happened?

Taylor Perron: Well, it is known that sea-level variations can result on Earth from changes in the location of Earth's rotational axis and so, by extension you might expect the same thing that happened on Mars.

Chris Smith: Can you actually measure this process happening so you can wind the clock back on Mars and actually workout how this would have happened and why would it have happened?

Taylor Perron: What we can do is predict what the change in sea level would have been for a given reorientation of the planet and then take the deformation that is currently observed in the shore lines and infer what the change in the rotation pole of Mars would have to have been to give you that deformation.

Chris Smith: And can you compare it with anything else on the surface to give you an absolute sort of gold standard measure of what that rotation was doing in order to confirm your measurements?

Taylor Perron: Well, there is one other thing that we can use in exactly that way to test this inference of the pole paths and that has to do with a very large volcanic feature on one side of Mars called the Tharsis rise. The Tharsis rise includes Olympus Mons, which a lot of people have heard mention of this is the largest mountain in the Solar System. In elevation, it is about three times the height of Mount Everest and this is important because a planet is rotationally more stable when its mass is furthest from its rotation axis, which is the equator.

Chris Smith: And is that what you see?

Taylor Perron: Well, that is what we currently see with relation to Tharsis, which is centred almost exactly on the equator and just as a large mass like that will tend to move towards the equator, once it gets there, it is going to want to stay there and so, if the rotation pole on Mars changes it is going to have to change in such a way to keep Tharsis on the equator and that means that there is only one path that the rotation pole could follow and that is a circle that is 90 degrees away from Tharsis. And it turns out that the path of the rotation pole that is required to match the deformation that is presently observed in the shore line follows almost exactly this path that is predicted from the location of Tharsis.
 

Offline InfraDead

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« Reply #7 on: 07/01/2008 16:27:50 »
I think there may only be eight planets in the solar system now, we lost one a while ago.

Yeah, Pluto is now considered a dwarf planet because it hasn't cleared it's orbit of debris, which a proper planet must have done.
 

Offline chris

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« Reply #8 on: 07/01/2008 19:17:51 »
Oh, that's interesting - have you got a reference for the "definition" of a planet these days please infradead?

Chris
 

Offline InfraDead

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« Reply #9 on: 07/01/2008 20:56:21 »
Oh, that's interesting - have you got a reference for the "definition" of a planet these days please infradead?

Chris

I actually read this in the space section of Guinness world records 08. But I looked into it further and found out:
"A planet, as defined by the International Astronomical Union (IAU), is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals".
So it must be rounded by it's own gravity, but must not cause thermonuclear fusion, and must have cleared it's orbit of debris or "planetesimals". And the last part is what Pluto has failed on.

Also, our solar system has at least three dwarf planets, Pluto, Ceres and Eris.
« Last Edit: 07/01/2008 20:58:05 by InfraDead »
 

Offline chris

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« Reply #10 on: 07/01/2008 21:05:55 »
Thanks, that's really useful - you've taught me something tonight!

Chris
 

Offline InfraDead

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« Reply #11 on: 07/01/2008 21:12:27 »
Thanks, that's really useful - you've taught me something tonight!

Chris

Cool, consider it repayment for teaching me loads of new stuff every week on your show.
« Last Edit: 07/01/2008 21:26:39 by InfraDead »
 

Offline rosalind dna

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« Reply #12 on: 07/01/2008 21:36:59 »
Yes, I agree and I learn so much on this site daily.
 

Offline turnipsock

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« Reply #13 on: 08/01/2008 03:14:38 »
yes but, no but, isn't our moon rounded by it's own gravity?
 

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« Reply #14 on: 08/01/2008 10:16:33 »
Any size of object in space will naturally end up round if it can 'flow'.  If it is too rigid, it won't.
From the definition you have quoted, I guess this means that it is big enough to make this happen on its own then we call it a planet.
There are a lot of tidal forces on a 'moon' due to its parent planet. these can cause a small body to flex and to settle to a round shape although it might not if it was out on its own in space.
Some of the closer satellites of the larger planets are full of volcanic activity because of the frictional forces from these tidal effects. This constant 'stirring up'  and melting gives them a very flat  surface and destroys the craters that you would normally expect to find (unlike on the Moon, where the tidal effects are smaller).
 

Offline chris

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« Reply #15 on: 09/01/2008 23:11:48 »
Not all moons are round!

Last summer (2007) scientists published the most thorough analysis yet of the moon Hyperion, which orbits Saturn. It's a bizarrely shaped object that turns out to be mostly empty space. Here's a radio interview I did with Carolyn Porco about the discovery...

Chris Smith: Ask someone to name the most exciting planet in the solar system, and apart from Earth they'll inevitably say Saturn. Most people are transfixed by the ring system, but also tucked away in orbit are some of the most intriguing moons that we know about, including one called Hyperion which resembles a giant piece of sponge. In fact, sponge is quite appropriate because 40% of it is empty space. But how did it get like that? Well, two papers in this week's edition of the Nature podcast have made use of the Cassini spacecraft which arrived at Saturn in 2004 to take a closer look. Here's Carolyn Porco.

Carolyn Porco: Hyperion is a smallish moon, it's 270 kilometres across, a very irregularly shaped moon. In fact it's the largest irregularly shaped moon in the solar system, and it was surprising even before we got there with Cassini because it's a tumbling moon, it doesn't spin nice and uniformly like all the other bodies, it tumbles through space. So that was one clue that it was a strange moon. And then when we got there with Cassini, one fly-by was very close and we got beautiful views of the surface, and the surface is certainly the most unusual looking surface in the solar system.

Chris Smith: Why is that?

Carolyn Porco: If you were to look at Hyperion you would think that it was a cosmic sponge, like it was something that someone had grabbed out of the ocean, a very large ocean. It is pockmarked with craters and they're very close together and they're very deep-looking. The craters are very fresh and well-preserved looking. So it doesn't look like the normal cratered surface we see in the solar system where generally the craters are somewhat eroded and subdued and there's ejecta that covers the surfaces of the craters, and it tends to make things soft-looking. On Hyperion, things do not look soft-looking.

Chris Smith: Do you know why?

Carolyn Porco: We think now we do know why. We were able to fly by Hyperion and measure the slight change in the velocity in Cassini and that tells us how massive the body is. Of course from the images we know how big it is and we can measure its volume. If we put that together with the size of the body, that tells us its density. So on Hyperion we now know its density; and its density is surprisingly low.

Chris Smith: So it really is like a sponge.

Carolyn Porco: Well, you sort of could think of it that way. Actually, the way we think of it is that its density is very low, it's about a half a gram per centimetre cubed, that's about half the density of water.

Chris Smith: And this density that you're seeing is like that because it's such a porous structure?

Carolyn Porco: Well, they go hand-in-hand; it's porous because it's under-dense, or it's under-dense because it's porous. The question is why are either of those circumstances holding for Hyperion when the bodies around it have higher densities? So that's a puzzle. But in any case, the result of its low density is that when a crater is made, when an impacter comes and ploughs into the surface of Hyperion, because the body is so under-massive for its size, the ejecta...most of it escapes and it does not come back down on the surface to either fill in smaller craters or make the larger craters look smoother. So we think that's why Hyperion has a sponge-like appearance.

Chris Smith: Any other interesting changes that you see on the surface of the moon when you take these very careful pictures that you've got in your paper?

Carolyn Porco: Oh yes, we see another thing that is just so striking. The craters have dark materials on the floors of them, and what is interesting is that the visual and infrared mapping spectrometers and the other spectrometers on Cassini have measured the composition of that.

Chris Smith: Let's bring in Dale Cruickshank who is author of a second paper in Nature this week. Dale, you've used some of those instruments and you've got an analysis of what the surface composition of Hyperion is. What did you find?

Dale Cruickshank: That's right, Chris. As Carolyn noted, the Cassini spacecraft carries a wonderful compliment of very, very capable instruments, and basically what we find is the surface of Hyperion is made of dirty water ice. Normal fresh fallen snow or fresh ice exposures have a very high reflectivity, yet Hyperion does not, and so the conclusion we reach from that is that the ice is not fresh and pure but dirty. We can even speculate now as to what some of that dirty material is. As Carolyn notes, this dark dirty stuff appears to be concentrated or ponded in the bottom of some but not all of these craters.

With the mapping spectrometers aboard Cassini we've been able to focus in on those concentrations of the dark stuff and find that it indeed is well matched by complex organic material that we can synthesise in the lab and also that we can extract from certain kinds of meteorites and as well that we find in interstellar dust and also appears in comets. So what we're finding is a common thread, in my view, that organic material of the kind dusting the surface of Hyperion and concentrating in the bottoms of the craters may be this same organic stuff that we find widespread not only in the solar system but throughout our galaxy and other galaxies as well.

Chris Smith: Do you think that Hyperion is unique or do you think that we're very likely to see the same thing cropping up elsewhere in the solar system and beyond?

Dale Cruickshank: You know, almost everything that we visit in the solar system is unique, and I wouldn't be surprised if Hyperion remains that way, even as we explore other bodies. But let me go on to one other really important finding that in fact may be a key to some of Hyperion strange characteristics, and that is we find carbon dioxide ice, CO2
ice, all over the surface of Hyperion. So we're exploring that in detail, but the information we get from the VIMS instrument that is this mapping spectrometer on the Cassini spacecraft is that the carbon dioxide ice is attached to some other molecule, almost certainly H2O, and the details of that, which remain to be puzzled out, make Hyperion unique so far in the solar system.

Chris Smith: So I guess we'll just have to watch this space for more fertile findings from Dale. But Carolyn, that must add quite a bit to effectively what your imaging first flushed out.

Carolyn Porco: Oh yes, it does. In fact it draws a connection between Hyperion and the other bodies like Iapetus and then there's Phoebe and so on in the Saturnian system. And that's precisely what we want to know when we go to a place like Saturn with a spacecraft like Cassini is just what does the whole planetary system tell us about not only how that particular planetary system came to be but how the whole planet formation process works, and perhaps the interchange of materials among the bodies, and what do their physical characteristics and the trends in them with distance from the primary body mean. So as I'm listening to Dale my head is spinning with questions that I would love to ask him, and I know we'll probably be doing this around tables at future Cassini meetings.

Chris Smith: Carolyn Porco from the Space Science Institute in Boulder Colorado, and Dale Cruickshank who is at the NASA Ames Research Centre. They've got two papers in Nature this week looking at the structure of Saturn's moon Hyperion, the only moon in the solar system, as far as we know, that's 40% empty space.

 

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