Starship Asterisk*

jacklap wrote:What if the monolith in Clarke's 2001: A Space Odyssey wasn't placed on Earth's Moon and Rama didn't leave Sol.
Ok, there's got to be plenty of holes in this picture. I'd like to hear some.

http://en.wikipedia.org/wiki/Phobos_%28moon%29 wrote:
<<In the late 1950s and 1960s, the unusual orbital characteristics of Phobos led to speculations that it might be hollow.

Around 1958, Russian astrophysicist Iosif Samuilovich Shklovsky, studying the secular acceleration of Phobos's orbital motion, suggested a "thin sheet metal" structure for Phobos, a suggestion which led to speculations that Phobos was of artificial origin. Shklovsky based his analysis on estimates of the upper Martian atmosphere's density, and deduced that for the weak braking effect to be able to account for the secular acceleration, Phobos had to be very light — one calculation yielded a hollow iron sphere 16 km across but less than 6 cm thick. In a February 1960 letter to the journal Astronautics, S. Fred Singer, then science advisor to U.S. President Dwight D. Eisenhower, came out in support of Shklovsky's theory, stating:

• [Phobos'] purpose would probably be to sweep up radiation in Mars' atmosphere, so that Martians could safely operate around their planet.
  
  My conclusion there is, and here I back Shklovsky, that if the satellite is indeed spiraling inward as deduced from astronomical observation, then there is little alternative to the hypothesis that it is hollow and therefore martian made. The big 'if' lies in the astronomical observations; they may well be in error. Since they are based on several independent sets of measurements taken decades apart by different observers with different instruments, systematic errors may have influenced them.

Subsequently, however, the existence of the acceleration that had caused the claims was called into doubt, and accurate measurements of the orbit available by 1969 showed that the discrepancy did not exist. Singer's critique was justified when earlier studies were later discovered to have used an overestimated value of 5 cm/yr for the rate of altitude loss, which was later revised to 1.8 cm/yr. The secular acceleration is now attributed to tidal effects, which had not been considered in the earlier studies. The density of Phobos has now been directly measured by spacecraft to be 1.887 g/cm³, which is inconsistent with a hollow shell. In addition, images obtained by the Viking probes in the 1970s clearly showed a natural object, not an artificial one, and the "hollow Phobos" speculations have been relegated to the status of a historical curiosity.

The origin of the Martian moons is still controversial. Phobos and Deimos both have much in common with carbonaceous C-type asteroids, with spectra, albedos and densities very similar to those of C- or D-type asteroids. Based on this similarity, one hypothesis is that both moons may have been captured into Martian orbit from the main asteroid belt. Both moons have very circular orbits which lie almost exactly in Mars's equatorial plane, and hence a capture origin requires a mechanism for circularizing the initially highly eccentric orbit, and adjusting its inclination into the equatorial plane, most likely by a combination of atmospheric drag and tidal forces, although it is not clear that sufficient time is available for this to occur for Deimos. Capture also requires dissipation of energy. The current Mars atmosphere is too thin to capture a Phobos-sized object by atmospheric braking. Geoffrey Landis has pointed out that the capture could have occurred if the original body was a binary asteroid that separated under tidal forces. The main alternative hypothesis is that the moons accreted in the present position. Another hypothesis is that Mars was once surrounded by many Phobos- and Deimos-sized bodies, perhaps ejected into orbit around it by a collision with a large planetesimal.>>

jacklap wrote:A pile of rubble stuck together with plenty of interstitial volume would be a lower density,
but the Martian tidal forces would seemingly break it apart, not to mention the Stickney impactor.

http://en.wikipedia.org/wiki/Phobos_%28moon%29 wrote:
<<Because Phobos's orbital period is shorter than a Martian day, tidal deceleration is decreasing its orbital radius at the rate of about 20 meters per century. In an estimated 11 million years it will either impact the surface of Mars or, more likely, break up into a planetary ring. Given Phobos's irregular shape and assuming that it is a pile of rubble, it has been calculated that Phobos is currently stable with respect to tidal forces. But it is estimated that Phobos will pass the Roche Limit for a rubble pile when its orbital radius drops by a little over 2000 km to about 7100 km. At this distance Phobos will likely begin to break up and form a ring system which will continue to spiral slowly into Mars.>>

http://webservices.esa.int/blog/post/7/1020 wrote:
History , Phobos Fly-By 2010 , Science 23 February, 2010 10:23
Credits: ESA/ DLR/ FU Berlin (G. Neukum)

[youtube]http://www.youtube.com/watch?v=EVekNsgU ... re=related[/youtube]

<<Phobos is doomed. It is gradually spiralling towards Mars and eventually could slam into the planet’s surface, leaving a large crater as its parting gift. Believe it or not, this discovery led to the USA’s President Eisenhower being briefed in 1960 that Phobos could be a space station launched by an advanced Martian civilization.

At the time, calculations showed that the moon’s orbit was decaying at around 5 cm per year. Phobos is in an unusually low orbit around Mars, and so it was thought that this drag could be caused by the upper atmosphere of the planet. Russian astrophysicist Iosif Samuilovich Shklovsky set about calculating whether the atmosphere could indeed be responsible. What he found surprised not only him, but many others too.

For the atmosphere to be responsible, Phobos would have to be hollow, like an Easter Egg. If the moon were solid rock, the atmosphere would have little effect. A hollow moon would be susceptible because it contained so much less mass. But if the moon were hollow, it could not be a natural object. Dr S. Fred Singer, special advisor to President Eisenhower on space developments, briefed the White House on this matter, emphasizing that Phobos could be an ancient abandoned spacecraft.

Writing in the Irish Astronomical Journal in 1964,
Estonian astronomer Ernst Öpik noted that there were in fact three possible reasons for Phobos’s orbit:

1) the observations were in error and Mars was not spiralling inwards.

2) as Shklovsky and Singer suggested – and Öpik agreed that if it were hollow then Phobos was artificial.

3) Mars’s gravity acted across the moon’s irregular shape producing a so-called tidal force, which could rob the moon of energy.

Sadly for the UFO enthusiasts, we now know that the third case is the correct one.
Tidal forces are responsible for the moon spiralling downwards. >>

jacklap wrote:Or maybe the Martian subsurface is full of water and water from Phobos isn't needed.

jacklap wrote:As the saying goes "the big fish eat the little fish". But more seriously, is it possible that Phobos contains a significant amount of water? Water that could be mined (MTU should know about that) and shipped to a Martian colony. Given: Phobos orbits Mars about twice in one Martian day and is in almost a perfect circular orbit around the Martian equator. With our current or near future technology, would Phobos be a practical source of water for a Martian colony, assumming that we muster the guts and determination to go to Mars. Maybe a mass launcher could fling ice cubes (insulated of course) towards the surface. Or maybe the Martian subsurface is full of water and water from Phobos isn't needed. But in time, I suppose, someone will claim that Phobos water has unique theraputic properties and a multibillion-trillion dollar industry is born. But maybe Phobos doesn't have much water and is more hollow than we think

Chris Peterson wrote:

jacklap wrote:Or maybe the Martian subsurface is full of water and water from Phobos isn't needed.

I think that's likely the case. There is probably plenty of water for any sort of colony we're likely to see on Mars anytime in the next century or two- a few dozen people, I'd guess. Not more than a few hundred at most.

wonderboy wrote:If phobos is dropping at a rate of 1.8cm a year would this not increase on a year to year basis as well as phobos speeding up much like a bit of fluff going round and round the funnel of water that goes down a plug hole?