Mariner Mars 1964, Mariners 3 and 4 to Mars: imaging plans? Options

[Guest_BruceMoomaw_*]

While we're on the subject of lost opportunities: I heard in spring 1967 that NASA was seriously considering launching a sixth Lunar Orbiter made out of the program's leftover spare parts (though it was thought unlikely even then), and remember thinking how nice it would be if they'd fly it with a copy of the gamma-ray spectrometer from the failed 1962 Rangers. In 1977 I learned, to my astonishment, that they had planned to do just that. (Otherwise it would have been similar to Orbiter 5, but would have photographed the Moon's far side in as good detail as Orbiter 4 had done for the near side.)

Well, they ended up leaning against flying this (it would have flown in Nov. 1967) even if Orbiter 5 had failed, and its success totally kiboshed Orbiter 6. I find myself wondering, though, just how much of Lunar Prospector's data might have been gotten three decades earlier if they had flown this -- or put the GRS on Orbiter 5. (I doubt the GRS could have detected the hydrogen at the poles, but I don't know it for sure.)

[edstrick]

Bruce Moomaw: ".... But they did come fairly close to adding an Earth-occultation photometer that could have told us what the cloud-top altitude was, which makes me wonder whether it might have clued us in to the clouds being sulfuric acid -- which instead wasn't discovered until 1973....."

I doubt it would have helped much. We actually "knew" what the cloud top altitude was from the visible/(and IR?) spectra of CO2, assuming the atmosphere was CO2 dominated, and not mostly nitrogen. And UV data indicated little Rayleigh scattering gas above the cloudtops, so there wasn't a huge over-abundance of Nitrogen.

What we didn't know was the "altitude" o fhte suface below the cloud tops!.... where the bottom was.

The expectation was that we'd eventually learn the cloud composition from infrared spectra, but that was "underinformative" and we weren't experienced enough to find a match to the so-so at best quality data we had. Somehow, people never included sulfuric acid in lists of candidates matched against cloud data so there never was a good match. A review article from the early 70's showed a distinct sense of frustration at the lack of progress and lack of signs of how to make progress in solving the problem.

It took polarimetery data from earthbased observations to suddenly break the logjam. It showed with astonishing precision that the cloud particles were non-absorbing spherical droplets, about 2 micrometers in size with a narrow size distribution, and last but overwhelmingly most importantly ... a refractive index of 1.44 +- 0.01 (If I remember right).

This totally blew away any candidates and yielded 90% sulfuric acid droplets as the only even close match.. and it wasn't close.. suddenly everything fit and made sense.

[Guest_BruceMoomaw_*]

They certainly came breathtakingly close before then -- hydrochloric acid was one of the favorite theories.

[edstrick]

I'd have to dig in my "stacks" to find the review article that tried to evaluate a good number of candidates for Venus' Clouds against the observational data and failed. Hydrochloric was one of them, and flunked on a number of grounds, I think the main one being the observed abundance above the clouds was far to low for the clouds observed temperature. They'd have to have been much colder to have the observed HCL vapor levels.

Sulfuric Acid just didn't seem to be on anybody's list so the multiple choice answere was: D.) None of the above. It might have emerged as a leading candidate if it had been included in the list.

Based on Venera and Vega descent composition data, and argued-about Pioneer Venus cloud particle spectrometer results, there are other composition particles in the clouds, but we know almost nothing about them, and the information is distinctly contradictory. Venera 13/14 and/or Vega 1/2 collected aerosol on a filter and then x-ray fluorescence'd them for element abundances, and got (besides sulfur), I think, Iron and Phosphourus. Iron Chloride was a proposed cloud component in the early 70's, I think. Sulfur crystals are one candidate for larger particles, but I don't know the current status on that as a candidate.

Polarimetry has almost always been a technique in search of problems to solve in Planetary Science. Unfortunately, it's far less revealing of particle properties when measuring scattered light from solid, non-spherical particles, whether they're martian dust and ice hazes, Jovian etc ammonia and other hazes, or Titanian tholin smog. It does help study atmosphere structure, the size/abundance of aerosols with altitude, and the crude physical properties of the aerosol particles, but it's only had the one "mega-success" of nailing the main Venus cloud composition.

[ljk4-1]

Any truth that Mariner 4's flight path was aimed at a region of the
planet where a number of "known" canals were?

[Phil Stooke]

Not really. Any long strip of images like that would cross a few canals. The targeting was all just about the trajectory design and a desire to see light and dark areas.

Phil

[Guest_BruceMoomaw_*]

At that time they had very little confidence in their ability to aim the Mars Mariners within more than a few thousand km of ANY target -- and sure enough, Mariner 4 ended up flying by Mars at 1200 km higher altitude than had been intended in the midcourse maneuver. Just photographing Mars would be adequate.

[edstrick]

For the canal freaks, the flyby trajectory and viewing was rather disappointing, as the image strip generally crossed what were generally mapped as minor, low-contrast canals.

What finally nuked the canalist's hopes were the global Mars Rotation Sequences from Mariners 6 and 7 on approach.

[Bob Shaw]

For the canal freaks, the flyby trajectory and viewing was rather disappointing, as the image strip generally crossed what were generally mapped as minor, low-contrast canals.

What finally nuked the canalist's hopes were the global Mars Rotation Sequences from Mariners 6 and 7 on approach.

Imagine if the random-ish targetting of Mariner IV had picked up on any of the dried up river channels - or if we'd recognised what we were seeing on those Mariner 1969 far encounter sequences (Valles Marineris is there, if you look not very hard at all!). Or if just *one* Soviet image had scooped the US with a picture of a dried-up-something, or a volcano, or...

Still, we got there in the end (and even Mars Observer has now, in effect, flown again!).

Bob Shaw

[Guest_BruceMoomaw_*]

Oh, yes. I well remember the shock when the dust cleared and all those things started getting gradually unveiled before Mariner 9. Still, I doubt that their earlier discovery would have done much to change the schedule of launches -- the one aspect of that schedule that wasn't rational was the launch of the 1969 flyby Mariners instead of jumping directly to 1971-type orbiters, and that was a consequence of the fact that the Mariner Mars program kept getting expanded incrementally as the Voyager Mars program gradually fell apart. (I even learned recently that in 1968 they seriously considered cancelling the second 1969 Mariner flyby so that they could save money by rebuilding the craft into one of the 1971 Mariner orbiters, as they rebuilt the 1969 spare flyby craft into the other 1971 orbiter.)

[Guest_PhilCo126_*]

Talking about Mariner IX... Phil (Stooke) I've contacted You about the Martian Moons article
Thanks again for Your help...
Philip

[Bob Shaw]

Oh, yes. I well remember the shock when the dust cleared and all those things started getting gradually unveiled before Mariner 9. Still, I doubt that their earlier discovery would have done much to change the schedule of launches -- the one aspect of that schedule that wasn't rational was the launch of the 1969 flyby Mariners instead of jumping directly to 1971-type orbiters, and that was a consequence of the fact that the Mariner Mars program kept getting expanded incrementally as the Voyager Mars program gradually fell apart. (I even learned recently that in 1968 they seriously considered cancelling the second 1969 Mariner flyby so that they could save money by rebuilding the craft into one of the 1971 Mariner orbiters, as they rebuilt the 1969 spare flyby craft into the other 1971 orbiter.)

Bruce:

As things turned out, yes - but if Mars had been seen as more like Earth than merely a big Moon then we might have seen quite a different turn of events. Stephen Baxter had fun with some of these possibilities in his novel 'Voyage'.

Bob Shaw

[Michael Capobian...]

Bruce:

As things turned out, yes - but if Mars had been seen as more like Earth than merely a big Moon then we might have seen quite a different turn of events. Stephen Baxter had fun with some of these possibilities in his novel 'Voyage'.

Bob Shaw

I wrote a story with William Barton that appeared in Amazing a few years back called "Thematic Torus in Search of a Cusp." It's also alternate history starting with Mariner IV finding large structures on Mars. For us as kids Mariner IV was a watershed event, and I didn't really get interested in planetary exploration again until Voyager.

Michael

[Guest_BruceMoomaw_*]

It was for me, too. Although I was already interested in science, it was the news in a Sept. 1964 issue of "My Weekly Reader" that there were two Mariners scheduled to go to Mars (which I hadn't known, although I already knew about the Rangers and the 1962 Mariners) that turned my tentative interest in Solar System exploration into a flat-out obsession.

By the way, Harry Turtledove -- who specializes in alternate history (he's just finishing up Vol. 10 of his grisly history of the world if the South had won the Civil War) -- wrote a novel called "A World of Difference" back around 1990 on how things would have turned out if everything had been just as it actually is except that Mars was Earth-sized and therefore capable of holding a CO2 atmosphere dense enough to keep it habitable despite its distance from the Sun, and the last photo from Viking 1 had shown an indignant native advancing on it with a club. Plausibly but depressingly, the US and the Soviets would immediately have started trying to convert the Martians to their particular ideologies. (Since such a planet would have been dazzlingly bright white rather than red, it would have been called "Minerva".)

P.S.: I admire the hell out of Barton's considerably grimmer and more likely alternate history story "Age of Aquarius", on what the Sixties would have been like if the Cuban Missile Crisis had turned out just a wee bit differently.

[Michael Capobian...]

P.S.: I admire the hell out of Barton's considerably grimmer and more likely alternate history story "Age of Aquarius", on what the Sixties would have been like if the Cuban Missile Crisis had turned out just a wee bit differently.

I do too, and I'm a character in it. It's a shame it hasn't been reprinted. Did you catch his alternate lunar program story "Harvest Moon" in Asimov's last year?

Michael