As a ten year old, I would take daily breaks from a long summer of yard baseball and building trails through the woods to go to the public library and that of a local college, hoping to spot the latest Voyager image of Neptune and Triton, its planet-sized moon. I would scour every newspaper, magazine, CD-ROM – anything that came in, hoping to see a slightly sharper view of these mysterious worlds.
Of course many days ended in disappointment. When that happened, or when I had some extra time after seeing the latest from Neptune, I would seek out what else I could find. Via NASA publications, books, and especially back issues of periodicals, I was able to relive a whole history that I had missed. I rode around the far side of the moon with Luna 3. I saw our view of Mars evolve from Christian Huygens first spotting of dark markings and polar caps to our first glimpse of Martian craters from Mariner 4 (incidentally, 50 years to the day before the New Horizons Pluto flyby). I got to ride along with Mariner 6 and 7 as they zoomed in on Mars and Mariner 9 as it watched dust clouds abate and the surface reveal itself on a global scale
|I would set out book and compare how worlds looked as different spacecraft approached.|
Mariner-10 brought us the cloud covers of Venus and the cratered surface of Mercury, and the Venera and Viking landers took us to the surfaces of Venus and Mars. The Pioneers gave us glimpses that were enough to tell us that the Jovian and Saturnian systems were far more complex and interesting than we thought from our earthbound view, but while they were very good at studying other things such as magnetic fields, they were small spacecraft designed to pave the way for the follow on, Voyager.
While the previous missions revealed a world (or, in the case of Mariner 10, two worlds but separated by years), the Voyagers visited planets with planet-sized moons as well as a retinue of smaller companions. From the volcanoes of Io to Titan’s thick atmosphere, from Europa the billiard ball with a hint of a global ocean to Miranda with its jigsaw puzzle surface, each encounter was a grand tour of a mini solar system.
August 25 - encounter day - finally came and I was glued to the coverage on PBS. Neptune and its great dark spot created a lot of buzz, and Triton looked like, well, a cantaloupe (at least in places). I didn’t get to watch all the coverage – my mother made me go to bed, telling me I’d thank her for it someday (still hasn’t happened). I remember after much arguing, responding, “OK, but I’ll be there next time.”
Next time. There was much to do about Voyager 2 reaching the edge of the solar system, exploring its most distant planet and its moons. That was technically true at the time – from 1979 to 1989, Pluto was inside Neptune’s orbit. But the proclamation that we had completed the initial reconnaissance of the solar system felt hollow, because there was one major world that hadn’t received a visit – Pluto. But the Voyagers, speeding out of the solar system, could not help us anymore.
It would take great effort by people such as Principle Investigator Alan Stern, to finally get humanity on its way to filling this gap with the launch of New Horizons in 2006, 17 years after Voyager visited Neptune. In the intervening years, three things changed our view of Pluto. From ground based and Hubble Space Telescope observations, we produced our first crude maps, revealing Pluto to be one of the most high contrast objects in the solar system. This indicated that it isn’t simply a carbon-copy of Triton, which is thought to be a captured satellite and is similar in size and mass to Pluto.
Second, the Kuiper Belt of distant worlds beyond Neptune, predicted a half a century earlier, became real to us, transforming Pluto from an oddball to the largest of these outer worlds that we can only faintly see from earth. Pluto remains the largest, and is the only one to have a moon so big that it could be a planet in its own right (technically, Pluto and Charon form a double planet). Two more small moons were found, a number which has since risen to four.
The Plutonian system is the last menagerie of worlds on the scale reminiscent of the ones surrounding the giant planets that we have yet to visit, albeit without the giant planet. It is the only unexplored household name in the solar system. It is the only remaining world that humanity had in mind when it reached out into the solar system with the Mariners, Lunas, and Pioneers.
The experience of seeing the new images as they come down and the reactions of scientists in real time has been a priceless experience – much different from scrounging around at the local library – oh, and Mom, told you I’d be here. There are plenty of small worlds left to explore and our studies of even much-visited Mars are far from complete – this is the end of the beginning, by no means the actual end, if one even exists. But will be no single unexplored target that stands tall above the others. There will be no great region of the solar system taunting us. The initial reconnaissance will be complete. Some people have gotten to live the whole journey - 66 years since Luna 3. The rest of us have joined it in progress. July 14, 2015 will be the last opportunity to live it as it happens. It is truly a special time to be alive.