• Abstract and Figures
• Public Full-text

ＩＳＳＮ ０９１７－７３８８ COMMUNICATIONS IN CMO Since 1986 MARS No.406 25 January 2013 OBSERVATIONS No.32 PublishedbytheInternational Society of the Mars Observers Night Thoughts of a Classical Mars Observer—Part II By William SHEEHAN he late Gérard de Vaucouleurs (1918‐ This is not to say that in the pre‐sputnik T1995) best remembered today as a galax‐ era all Martian studies were reliable and ies astronomer at the University of Texas at well‐considered; far from it. The signal to Austin but a leading Mars observer in his noise ratio has always been low. But the day, wrote an interesting, if opinionated, ar‐ confusion has been compounded and the ticle in 1965 entitled “The Slow Progress of input rate so multiplied that a quiet, Martian Studies.”1 On the eve of Mariner 4 sober assessment of our current knowl‐ (1964), de Vaucouleurs cast a long and often edge of Mars is very difficult. Noise is scathing glance back at the history of Martian increasing faster than signal! I would es‐ studies since the turn of the (20th) century, timate that while the volume of publica‐ and noted that the “growth rate” in pub‐ tions about Mars during the past decade lished papers was only about 6 percent per [since the perihelic opposition of 1956] year, with bulges following the perihelic wasovertwicethetotalfortheprevious oppositions (1909, 1924, and 1956; in 1939, half‐century our reliable knowledge of the effect was blunted, owing to the outbreak theplanethasnotincreasedpropor‐ of World War II). He added that many of the tionately. papers that appeared in the post‐Sputnik era, under the stimulus of the so‐called “space Among the controversies that de race,” were hasty, and that “results or in‐ Vaucouleurs referred to were the supposed terpretations were offered (usually with secular acceleration of the satellites of the much fanfare) that had to be withdrawn planet which led the Russian astronomer (more quietly) afterward.” He added (p. Shklovskii (1916‐1985) to infer that they were 181): hollow, and hence might be artificial; W. M. Ser3-0419 CMO No. 406 Ser3-0420 Sinton’s misidentification (1956) of new ab‐ utes;asimilarobservation,atTithonius sorption bands in low‐resolution infrared Lacus, was reported by Tsuneo Saheki (1916‐ spectra of the surface of Mars that were in‐ 1996) on December 8, 1951; a sudden bright‐ ferredtobeevidencefortheexistenceof ening was observed by Saheki at Edom chlorophyll but proved to be telluric in origin Promontorium on July 1, 1954, and so on.) and produced by the heavy water molecule The French astronomer writes scathingly, ev‐ HDO; ideas that de Vaucouleurs regarded as idently referring to Saheki’s 1951 observation premature about the nature of Martian sur‐ (p. 187): face materials, for instance, observations of their polarizing properties which were found Some purported observations of bright to match a fine‐grained limonite. His argu‐ flashes on Mars, sometimes quoted as ment against the latter identification is worth evidence for volcanic activity (not to citing (p. 188): mention hydrogen bomb explosions or optical signals from the natives!) are Limonite is a sedimentary rock on Earth; probably illusory or spurious. I have in‐ if Mars has never had much water, how vestigated in detail one such “observa‐ could sandy sediments cover three‐ tion” and found that at the given time quarters of the planet’s surface? In fact the face of Mars depicted in the report another proposed identification based on was not turned toward the Earth. Also infrared reflectivity invokes the igneous the amount of detail shown on the draw‐ rock felsite and recent spectrophotometric ing was utterly beyond the capability of observations are reported to match felsite the telescope used (of any telescope, in better than limonite…. fact, since Mars was a mere 5‐seconds of arc in diameter). A letter of inquiry to the He was no fan of Dean McLaughlin’s theo‐ observer elicited no clarification. ry (1954) that the dark albedo markings con‐ sisted of windblown dust blown from active Having worked himself into a lather of Martian volcanoes located at the sharp tips of outrage about amateur observations of some of them, and was singularly unim‐ flashes or flares on Mars, he takes a further pressed with the “purported observations of stab at the “continued flood of amateur bright flashes” which had been taken as evi‐ drawings showing a Martian surface covered dence of volcanic theory. (The most famous with a canal network straight out of Percival of these reports were made by Japanese Lowell’s books,” and continues: “It is unfor‐ astronomers. For instance, on June 4, 1937 tunate that most of the aerospace industry Shizuo Mayeda (1914‐1952, or named other‐ pictorial publicity (and even a recent Air wise Haruhisa Mayeda), using an 8‐inch re‐ Force chart) should perpetuate this bad opti‐ flector, saw an intense point of light sudden‐ cal illusion.” ly appear near Sithonius Lacus; it scintillated like a star and disappeared after five min‐ Of course, these comments were made on 25 January 2013 Ser3-0421 theeveofthespacecraftreconnaissanceof daytime several hours after the Mars spectra the red planet, when at last the signal to were obtained, and it turned out that on the noise ratio began to improve significantly day he had done this the air was consider‐ (and Mariner 4 itself showed a crater‐pocked ably drier than on the nights when the Mars surface and no canals, finally demolishing spectra were taken (the same problem of once and for all the Percival Lowell‐inspired comparing spectra under identical atmos‐ dream of intelligent canal‐builders on Mars). pheric conditions had hampered attempted Even more striking were the revelations of detections of water vapor in the atmosphere Mariner 9 (1971), which provided the first of Mars going back to the days of William high‐resolution views of the entire surface of Huggins and Jules Janssen). However, Dean Mars from orbit and revealed those grandi‐ McLaughlin’s views about windblown dust ose features which then seemed so strange accounting for the caret‐shaped endpoints of and unexpected: Olympus Mons and the the maria and the general streakiness of the Tharsis shield volcanoes, Valles Marineris, Martian surface markings have proved to be the dry riverbeds. (I hasten to add that the prescient, and there are volcanoes (though initial dour impression of a dead and not active) on Mars on a scale that de cratered Mars like the Moon after the Mari‐ Vaucouleurs did not envisage. The expecta‐ ner 4 and even the Mariner 6 and 7 flybys tions of classical observers concerning the proved to be even more wide of the mark nature of the surface materials also proved to than the pre‐Mariner interpretation of the be well‐informed. The planet is swathed in planet; which proves that improved signal to an “ocean” of iron‐oxide dust, and limonite, noise without a large enough sample size can the reddish rust‐brown material prominent in be even more misleading than low signal to deserts in the Southwestern U.S. that inspired noise with a large sample size. The classical the visions of observers such as Lowell, gives observers at least had the advantage of being the planet its reddish hue; plagioclase feld‐ able to survey the whole Martian world at a spars are found in low‐albedo regions, while glance—or at least the hemisphere of it that there are also areas rich in hematite and oli‐ happened to be in view during a given ob‐ vine. So the classical astronomers had much servations—as opposed to the narrow strips of it right. Some of these materials are associ‐ of Mars shown by the flyby Mariners.) ated with sedimentation on the Earth. We Over forty years after Mariner 9, we can now know, of course, that Mars has indeed look back to de Vaucouleurs’ essay with a had not only volcanoes but significant modicum of amusement. It seems to me that amounts of water in the past. Indeed, the the classical astronomers he takes to task classical Mars—minus the canals—with a didn’t do so badly after all. The hollow Mar‐ much thicker atmosphere, water‐carved fea‐ tian satellites have fallen by the wayside, ob‐ tures on the surface, and active volca‐ viously, and Sinton’s observations were an noes—does, in fact, correspond with the real innocent mistake—necessarily, he had had to Mars—but not the Mars of today; the Mars of obtain his comparison solar spectrum in the the first billion or so years of its career after CMO No. 406 Ser3-0422 its formation. who was an unusually compulsive observer —most astronomers saw little point in study‐ Lowell and other observers saw a ghost ing Mars far from opposition. of that bygone planet, and were haunted by As in the past spectra of two bodies ob‐ it. But in the ghost they recognized the fea‐ tained under similar conditions—such as the tures of a real world. They clearly enough Moon and Mars‐‐were used in the search for realized that Mars was a planet that was in‐ water vapor in the atmosphere of one relative volved in an evolutionary process, that it has to the other (with the obvious pitfalls that experienced its own version of “climate Sinton’s sad case illustrated), a comparison of change,” and the general trend—toward de‐ the classical meteorological record of Mars, sertification—that Lowell wrote about is which began in 1877 with Trouvelot’s obser‐ broadly true. Though Mars is now a desert vations, with that of the Earth, where reason‐ more harsh than any on the Earth, it once ably good temperature records go back to had water enough.

Load more

  15

Copy Link