Note: Here is part 2 of the continuing story of "The Planets at 50". This and blogs to follow are related to a set of lectures I gave in June (and am available to do so on again for your group). I spent the month of June in Europe, highlighted by two presentations on the Isle of Man sponsored by the Astronomical Society on the topic of "50 Years of Planetary Exploration: What Have we Learned?" a presentation that can be given again. The Isle was beautiful and our hosts wonderful and I had a great time telling this story to students and citizens. This post is also associated with the similar story set to appear in the next issue of The Planetary Report. The past 50 years have seen great discoveries but also fundamental revolutions in our understanding of how planets and solar systems work. The posts today and over the next few months will tell that story.
TO VENUS: DAWN OF A NEW AGE
The engineers were understandably nervous; they had tried this only 4 weeks earlier. Missiles had an annoying predilection for disintegrating prematurely. The twin of the metallic insect on the Florida launch pad had fallen into the Atlantic when tracking and guidance transcription errors (including a missing hyphen or overline) doomed the flight. Mariner 2 (twin to that ill-fated Mariner 1; in the early days of the Space Age it was prudent to build two in case one was lost) began life as part of NASA's exploration charter but was quickly accelerated in response to the Soviet Union's failed attempt to reach Venus in 1961.
Mariner 2: Launch and Mission
Note how many bits of data were returned . . .
Nearby Venus was high on the list of targets, so similar in size and composition to Earth, yet a profound mystery. We knew it was warmer than Earth but how much so remained uncertain. Despite the high scientific interest and prestige value, Mariner's flight did not, as was also noted at the time, "capture the public's imagination." The low interest may have been due to Venus' mystery shroud of white but more likely because of the lack of a camera on board. The impenetrable clouds meant there were no observable surface features on which to hang a credible anthropomorphic concept like the "canals" that made Mars such a powerful stimulant to the imagination. The clouds thus gave free rein to fantasy, leading to some lurid ideas, captured in paintings, of steaming jungles and large reptiles, bubbling oily wastes, or windblown craggy sand heaps. In 1962 Venus just wasn't Mars. Nonetheless, the flight of Mariner 2 counts as one of the seminal accomplishments of the Space Age, challenging engineers, smashing distance records, and ushering in a new age.
The Venus that never was . . .
Just one vision of a steamy hot Cretaceous style Venus from the late 1950s.
Mariner 2 resembled nothing so much as a 16-foot-wide metallic dragonfly, basically a hexagon box with two solar panel wings, antenna, and instruments. The Atlas bearing Mariner 1 veered off course and was destroyed, but the second Atlas soared nominally (drifting dangerously off-course only briefly) to start Mariner 2 on its 4-month 180 million mile cruise to the cloud-shrouded world on August 27. The cruise had its share of tense moments, from eventual failure of one of the solar panels to a blown fuse, but engineers and scientists began to hope for success as the limping dragonfly swooped in toward the planet on December 14.
A flight spare of the Mariner 1/2 spacecraft currently hanging in the Smithsonian Air and Space Museum. You might not notice this small part of history if you don't look up.
That brightest of sky objects, the Evening and Morning Star familiar to sky watchers, had its first visitor. There was joy in Mudville (also known as the Jet Propulsion Lab in Pasadena) as coherent telemetry was received that day. About 60 Mb of data were returned from the mission. Thats right,60 Mb, but the readings proved Venus to be a hot dry place most unlike Earth, under a dense atmosphere 90 times as heavy as our own and surface temperatures of at least 800°F. It would be 8 years before we had our first picture from the surface and another 22 years before we had a global map and could unravel the history of our nearby twin, all of which would show a fractured volcanic world not unfitting its hadean surface conditions. No place to raise your kids, certainly, let alone establish a human colony.
Venera 4 (1967), first to successfully probe the atmosphere of another world, though its instruments did not survived the descent to the hot crushing atmosphere at the surface of Venus. Venera 7 would do that in 1970.
Beyond the scientific breakthrough in our understanding of another celestial body, Mariner 2 showed simply that a long duration robotic flight into deep space could be done. Long range communications and command and control protocols were proven for the first time. Everything we have since accomplished in our explorations, from Venera 4 to Voyager, from Mariner 4 to Curiosity, begins on December 14, 1962, 50 years ago this autumn.
Part 2b: Maybe Mars . . .
It was now undeniable that Venus was a most inhospitable place, but Mars still beaconed. It had to wait 2 and 1/2 years for the next close approach to Earth and a viable spacecraft. Like Mariner 2, the first Mars Mariner followed several failed Soviet attempts to reach Mars, beginning a long and continuing history of russian frustration at the Red planet. Like Mariner 2, it also succeeded its own twin to Mars (for Mariner 3's protective launch shell failed to open one month before). Mariner 4 began its pass over Mars on July 14, 1965, and this time there was a camera.
The fierce orange glow of Mars in the night sky was difficult to ignore. Its skies after all were clear and the white "icy" polar caps, rust-colored surface and the ethereal ever changing dusky "linear" markings fueled rich if poorly informed speculations. Even so, the largest telescopes of the time, including the 200-inch Palomar, could not make out geologic features. This was well before adaptive optics and space telescopes. Nonetheless, it was possible that Mars was near enough to the Sun and Earth-like enough (including its curiously Earth-like 24.6-hour long day) to be or have once been warm and perhaps wet enough to support life. This question was a source of intense speculation in the early 20th century and science fiction flourished on it, leading to Orson Well's "War of the Worlds" broadcast of 1938. Although Mars was looking a little less friendly in 1964 as we began to tease out more data, we were not prepared for what we did find. Yet the question of life there, both ancient and recent, remains unresolved to this day.
The best of Mariner 4 (first Mars image, left; best resolved image, right).
Effective resolution is 3 to 5 km.
A grand total of 635 kB worth of data were returned by Mariner 4, required more than week to transmit to Earth, such was the maturity of the instrumentation and deep space telecommunications in 1965. Other instruments confirmed that the atmosphere was extremely thin, that Mars lacked a magnetic field, and cosmic rays bombarded the surface. For many the Mariner 4 imaging results were key. These were the first images of another world from deep space. And they were discouraging. The 22 grainy 6-bit images seemed to show only craters, when they showed anything at all. Gone were canals and green "vegetation" and all the other fantasies of the first half of the 20th century. Mars now seemed dry, hostile and barren. Interesting conclusions to draw from modest images of less than 2% of a planet.
Mariner 6 and 7 arrived in July-August 1969 just a week or so after the Apollo 11 lunar landing. Together they increased mapping coverage to ~20% of the surface, but in a classic case of restricted perception imaging was planned without any understanding of the planets markings and missed all the interesting features that would make Mars interesting! Most of what it showed only seemed to reinforce the dried-out Moon-like perception from Mariner 4, but also showed some odd surface "chaos" textures, the importance of which would not be understood until 1972. Again, no canals . . .
The first man-made object to orbit another planet (narrowly beating Mars 2), Mariner 9 arrived in November 1971 at Mars to map the entire planet in preparation for the Viking landers planned for later that decade. This mission marks my first real interests in planetary missions, and I still have the newspaper clippings beginning with the failure of Mariner 8. The Mariner 9 mission was hastily redesigned to complete both the global mapping and high-reolution - surface-changes tasks of the two birds.
As the global dust storm that greeted the Soviet and American spacecraft abated, a remarkably complex planet of giant volcanoes and chasms, and, most provocatively, dry river valleys emerged. Mariner 9 revealed a complex planet that had been geologically active and very wet indeed. Mars was surprisingly Earth-like after all, or at least had been. Hopes were rekindled.
It takes an Orbiter. To really get at a planet and unravel it, it helps to stay awhile and map it in its full glory, as this Mariner 9 mosaic of channeled areas on Mars demonstrates. Cassini is paying so many dividends at Saturn for that very reason.
Hopes were rekindled for the Viking landers, whose dramatic landings in 1976 produced only ambiguous results for biology but dramatically showed us a planet that had been very wet in its distant geological past. There would be an 17 year gap between Viking's end and the next successful arrival, Mars Global Surveyor and Pathfinder/Sojourner in 1997. These were followed by a more spacecraft, producing global maps and amazing vistas more astounding than any artist could imagine.
Pollack? or Mars? If you guessed Mars you are correct. Sometimes the Universe is just plain beautiful, but if you must know, these are layers a few meters thick near the polar region of Mars.
Terrabytes of data returned from a slew of instruments bring us to today where we have meter-scale mapping from orbit, rovers traversing kilometers, layers of gypsum and other water bearing minerals. Mars is now the most comprehensively mapped celestial body outside our own. Despite this, the basic question of life on other worlds remains unanswered but the discoveries at Mars and in the Outer Solar System would radically alter our understanding of its probability.
With the successful landing of the MERs and Curiosity on Mars, we see the beginning of real surface exploration of other worlds. We also saw something perhaps unexpected. Ordinary citizens came along for the ride. Millions watched on the WWW, but thousands came out into the street to watch live in Times Square, New York and dozens of places world wide as the vehicle landed. True, much of that night and the fascination of the wheeled vehicle zipping around the alien landscape was the technological thrill ride of it all. But it also speaks well of our nation and says that intelligence is not quite dead yet, and that we in this nation do support space exploration We do want to know what is out there. With the vast volumes of data yet unexamined (we have much work to do) we may yet begin to understand what happened there while life began here.
Voyager - A Solar System Wide Open
50 Years - What We've Learned (Parts 1-3)