stolfi@jumbo.dec.com (Jorge Stolfi) (01/24/89)
Jonathan Leech writes: > > We have more samples of asteroidal material than lunar material > and closeup photos of Martian moons ... spectroscopic and > radar observations ... Not exactly. Yes, we have lots of meteorites, but we only *think* they are bits asteroids---we do not know for sure. We DO know that they are at best a very skewed sample. For one thing, rocky meteorites are much harder to recognize than metallic ones, and hence they are highly under-represented in our collections. There are probably lots of meteorites (and perhaps asteroids) made of loose dust or of volatile materials, but those never reach the ground; and yet those would be the most interesting ones. We also don't know whether the Martian moons are captured asteroids; this is only a conjecture, plausible but with no hard evidence to support it. Even if they are asteroids, we have no idea as to how typical they are of the whole lot. (In fact, there probably isn't such a thing as a "typical" asteroid). Spectroscopic and radar observations of solid objects can only give broad hints as to the average composition---say, "metallic" vs "rock". Also, radar can't see deeper than a few inches, and spectroscopy can't see deeper than a few mm. > Landing 6 times on the moon does not make it a 'known quantity' > by any stretch of the imagination. Come on. We know a *lot* more about the moon than about any other body outside the Earth. Certainly there are many unanswered questions about the moon, but they are nothing compared to our abysmal ignorance about the rest of the solar system. (Quick, how many open questions about the moon can you think of? How many of those could be resolved by returning there?) I submit that more than 90% of the scientific value of the Apollo program came from the first moon landing, and specifically from the soil samples it brought back. It is always nice to have more data, but the last few Apollo landings added very little to the knowledge we got from the first few. It would have been foolish to continue spending the limited money available on additional Apollos instead of on things like Viking and Voyager. Jorge Stolfi stolfi@src.dec.com, ...!decwrl!stolfi ``Strange, this lunacy,'' he said to Barbicane after the delegation left, ``and it's a type of madness that often hits the best minds. One of our most famous scientists, Arago, told me that many perfectly sane and respectable people will experience great excitement and behave incredibly whenever the moon posesses them. '' --Verne, _From the Earth to the Moon_ (1865) ------------------------------------------------------------------------ DISCLAIMER: The above opinions are not the sort of stuff my employer, my teachers, my friends, or my mother would like to be associated with.
tneff@well.UUCP (Tom Neff) (01/25/89)
In article <13531@jumbo.dec.com> stolfi@src.dec.com (Jorge Stolfi) writes: > ... I submit that more than 90% of the scientific value of the Apollo >program came from the first moon landing, and specifically from the >soil samples it brought back. > >It is always nice to have more data, but the last few Apollo landings >added very little to the knowledge we got from the first few. Most of Jorge's article (not quoted) was reasonable but this is a calumny. Apollos 16 and 17 were the really big science missions. The quantity and sophistication of the experiments and activities was an order of magnitude better than on the first few missions. I can list the specifics if folks are interested. >It would have been foolish to continue spending the limited money >available on additional Apollos instead of on things like Viking and >Voyager. Not at all the same proposition; not hard to agree with either. -- Tom Neff tneff@well.UUCP or tneff@dasys1.UUCP
alastair@geovision.uucp (Alastair Mayer) (01/27/89)
In article <13531@jumbo.dec.com> stolfi@src.dec.com (Jorge Stolfi) writes: >Jonathan Leech writes: >> >> We have more samples of asteroidal material than lunar material >> and closeup photos of Martian moons ... spectroscopic and >> radar observations ... > >Not exactly. Yes, we have lots of meteorites, but we only *think* they >are bits asteroids---we do not know for sure. We DO know that they are Actually, we are pretty sure - reflection spectra of various meteorites have been mached very well to some specific asteroids - Vesta, for example. Also, for three meteorites whose falls have been recorded photographically well enough to determine their (previous) orbits, it has been determined that the orbits originated in the asteroid belt. Not all meteorites have been so associated with asteroids, though - some have been identified as almost certainly coming from the Moon, and two or three others are very probably of Martian origin. >at best a very skewed sample. For one thing, rocky meteorites are much >harder to recognize than metallic ones, and hence they are highly >under-represented in our collections. There are probably lots of >meteorites (and perhaps asteroids) made of loose dust or of volatile The technical term for such bodies is "comets" :-) >materials, but those never reach the ground; and yet those would be the >most interesting ones. > >We also don't know whether the Martian moons are captured asteroids; >this is only a conjecture, plausible but with no hard evidence to >support it. Even if they are asteroids, we have no idea as to how >typical they are of the whole lot. (In fact, there probably isn't such >a thing as a "typical" asteroid). > >Spectroscopic and radar observations of solid objects can only give >broad hints as to the average composition---say, "metallic" vs "rock". Actually, by comparing spectra with meteorites, and analysing the meteorites, we can get a very good guess at the average composition of a given asteroid. >Also, radar can't see deeper than a few inches, and spectroscopy can't see >deeper than a few mm. > >> Landing 6 times on the moon does not make it a 'known quantity' >> by any stretch of the imagination. > >Come on. We know a *lot* more about the moon than about any other body >outside the Earth. Certainly there are many unanswered questions about >the moon, but they are nothing compared to our abysmal ignorance about >the rest of the solar system. > >(Quick, how many open questions about the moon can you think of? >How many of those could be resolved by returning there?) A lot. See below. >I submit that more than 90% of the scientific value of the Apollo >program came from the first moon landing, and specifically from the >soil samples it brought back. 90% of the scientific value from a few bags of dirt? What about the scientfic packages left by Apollo shots *after* 11? (The primary mission of Apollo 11 was just "land and get back" - after that they could afford to spend some time on science). Or the traverses done in the lunar rover (Apollo 15-17)? >It is always nice to have more data, but the last few Apollo landings >added very little to the knowledge we got from the first few. Not true. For example, "dark halo" craters were thought to be of volcanic origin up to Apollo 16, which showed them to be impact craters which dug up ancient mare basalts that had been covered by white plains due to the Orientale impact event. >It would have been foolish to continue spending the limited money >available on additional Apollos instead of on things like Viking and >Voyager. > > Jorge Stolfi > stolfi@src.dec.com, ...!decwrl!stolfi To return to the question of what open questions there remain about the moon, let me mention a few points raised by Dr. Ray Hawke of U. of Hawaii in a paper he presented at the International Space Development Conference in Denver last May ("Geological Studies Supported by a Lunar Base") - impact cratering: there are some questions best resolved by field studies and major traverses, eg. mode of ejecta emplacement, distribution of impact melt as a function of size, depth and origin of ejecta units, nature of crater modification processes, origin of crater rays. - vulcanism: about 2/3 of the types of mare basalt on Moon have *NOT* been sampled (types det'd by remote sensing), we have no samples of lunar mantle, no information on ancient vulcanism, need to investigate some possible still active sites (Alphonsus?) and settle debate on Kreuger crater (which may be a volcanic caldera) - cometary impacts on lunar surface - several craters (eg Reiner gamma on Western Procellarum) show both magnetic and albedo anomalies, they may be comet impacts, in which case there may be associated hydrated material. (This would be *very* significant to space colonization/industrialization if so!) Finally, studying the moon in more detail provides a much better baseline or control against which to compare studies of other bodies. To quote Dr. Hawke (from the tape of his talk): "I don't think you're going to understand fundamental planetary processes by studying Ganymede or Mercury. You've gotta understand them on the Moon first. You're not gonna go to a very complex place like Mars or Ganymede to understand impact cratering if you can't understand it on the Moon. The situation is much more complicated you got volatile-rich materials in the subsurface of Mars, and atmosphere; the situation is all screwed up. You gotta go to the simple example of a place where material has not been eroded, degraded; where there's no nasty atmosphere to screw things up or blow dust on the deposits. The Moon is a baseline." Of course this was wrt Moon vs other planets, not asteroids, but the point holds. You're not going to understand really high-energy impact events from studying asteroids -- they tend to get consumed by such processes :-) -- "The problem is not that spaceflight is expensive, | Alastair J.W. Mayer therefore only the government can do it, but that | alastair@geovision.UUCP only the government is doing spaceflight, therefore | al@BIX it is expensive." |