by neufer » Sun Mar 28, 2010 3:35 pm
Chris Peterson wrote:wonderboy wrote:BMAONE23 wrote:Olympus Mons is also almost directly opposite the Hellas Impact site see the Global Relief Map
So are you saying it may be a possibility? I dunno if it would be possible, but a 15 mile high volcanoe has a chance of doing something like that doesn't it?
If it were a stratovolcano, I'd think it a lot more likely. But Olympus Mons is a shield volcano, like those found in Hawaii. Such volcanoes are associated with slow, gentle flows of very liquid lava, not with explosive eruptions. Also, it is hard to understand how two bodies ejected from a latitude of 18° would end up in circular, low inclination orbits. Finally, you'd expect the moons to be basaltic in composition, which they don't appear to be.
I think some sort of capture hypothesis makes better sense.
1) If Olympus Mons was first formed by the concentrated stress from Hellas Impact on the opposite side then certainly
at that time it could have spewed out non basaltic matter (as might the splash back at Hellas itself).
2) Any capture model would still have to explain the circular, low inclination orbits.
Certainly the circular, low inclination orbits are due, in part, to the same tidal forces which are draining energy & angular momentum from the moons today.. since, if for no other reason, both the 124,000-year obliquity cycle and the 171,000-year precession are constantly changing where the Martian equator is situated:
http://www.spacedaily.com/news/mars-water-science-00d.html wrote:
<<Mars' "obliquity" -- the tilt of its spin axis -- is known to slowly increase and decrease between about 15 degrees and 35 degrees over a 124,000-year cycle (unlike Earth's tilt, which slowly rocks through a range of only 4 degrees thanks to the stabilizing tuggings of our large Moon). Indeed, recent studies suggest that occasionally -- at intervals of a few tens of millions of years -- Mars' obliquity may swing from 0 degrees all the way up to 60 degrees. At present -- by sheer chance -- Mars is about halfway through one of its obliquity cycles, at a tilt of about 25 degrees.>>
http://en.wikipedia.org/wiki/Astronomy_on_Mars wrote:
<<As on Earth, the effect of precession causes the north and south celestial poles to move in a very large circle, but on Mars the cycle is 171,000 Earth years rather than 26,000 years as on Earth.>>
[quote="Chris Peterson"][quote="wonderboy"][quote="BMAONE23"]Olympus Mons is also almost directly opposite the Hellas Impact site see the Global Relief Map[/quote]
So are you saying it may be a possibility? I dunno if it would be possible, but a 15 mile high volcanoe has a chance of doing something like that doesn't it?[/quote]
If it were a stratovolcano, I'd think it a lot more likely. But Olympus Mons is a shield volcano, like those found in Hawaii. Such volcanoes are associated with slow, gentle flows of very liquid lava, not with explosive eruptions. Also, it is hard to understand how two bodies ejected from a latitude of 18° would end up in circular, low inclination orbits. Finally, you'd expect the moons to be basaltic in composition, which they don't appear to be.
I think some sort of capture hypothesis makes better sense.[/quote]
1) If Olympus Mons was first formed by the concentrated stress from Hellas Impact on the opposite side then certainly [b]at that time[/b] it could have spewed out non basaltic matter (as might the splash back at Hellas itself).
2) Any capture model would still have to explain the circular, low inclination orbits.
Certainly the circular, low inclination orbits are due, in part, to the same tidal forces which are draining energy & angular momentum from the moons today.. since, if for no other reason, both the 124,000-year obliquity cycle and the 171,000-year precession are constantly changing where the Martian equator is situated:
[quote=" http://www.spacedaily.com/news/mars-water-science-00d.html"]
<<Mars' "obliquity" -- the tilt of its spin axis -- is known to slowly increase and decrease between about 15 degrees and 35 degrees over a 124,000-year cycle (unlike Earth's tilt, which slowly rocks through a range of only 4 degrees thanks to the stabilizing tuggings of our large Moon). Indeed, recent studies suggest that occasionally -- at intervals of a few tens of millions of years -- Mars' obliquity may swing from 0 degrees all the way up to 60 degrees. At present -- by sheer chance -- Mars is about halfway through one of its obliquity cycles, at a tilt of about 25 degrees.>>[/quote]
[quote=" http://en.wikipedia.org/wiki/Astronomy_on_Mars"]
<<As on Earth, the effect of precession causes the north and south celestial poles to move in a very large circle, but on Mars the cycle is 171,000 Earth years rather than 26,000 years as on Earth.>>[/quote]