May 25, 2020

Titan Unveiled by Ralph Lorenz & Jacqueline Mitton

Perhaps no world in the Solar System is as enigmatic as Titan. Until the last decade or so, what was known about this distant moon of Saturn could barely fill out a postcard, let alone a book. Titan Unveiled published by Princeton University Press is the first book solely dedicated to the moon, centering mostly on the phenomenally successful Cassini-Huygens mission to the ringed planet.

At a radius of 2,575 km, Titan is larger than several planets (and Plutoids!) and would be easily considered a planet in its own right if it directly orbited the sun. Along with Neptune’s giant moon, Triton, it is also one of the only moons in our solar system with an appreciable atmosphere, and is just now coming to be seen as a dynamic place were the environment is in flux. It’s also refreshing to see a tome covering robotic space exploration, which sometimes gets a short shrift in favor of the sexier, manned missions. Don’t get us wrong; we’d love to see manned missions to Saturn in our lifetime; (anyone remember the original screenplay and novel for 2001?) But it was Huygens that sent us our first postcard from this distant world. The author, Ralph Lorenz, expertly intersperses the text with notes from his own log. A planetary scientist at the John Hopkins University of Applied Physics laboratory, many of his tales as a scientist at the University of Arizona’s Lunar and Planetary lab in Tucson brought back memories for me, as an amateur astronomer in the same town until a recent move to northern Maine. Tucson is a veritable Mecca for astronomers; where else is it considered “nothing special” to have David Levy as your next door neighbor?

The Huygens mission itself was headed by the European Space Agency (ESA) and piggybacked on Cassini orbiter, which would serve to relay data back to Earth as it flew by Titan in the critical few hours of decent. The mission was daring and a huge gamble; when launched, no one knew for sure if Huygens would land on a hard icy plain or splash down in a rolling methane sea. When Voyager 1 flew past Titan in 1980 it revealed a world shrouded in haze. Cassini was better armed, with atmosphere penetrating radar, used to map Titan on its many passes. Launched in a dazzling night shot in late 1997, the probe took six years and four planetary flybys to reach Saturn. Interestingly, the author was present at the launch but makes no mention of the demonstrators protesting the plutonium power plant; unfortunately, in the outer solar system, the sun is too dim to use solar cells as a source of power. In the words of the late Carl Sagan, “space exploration may be the best use of nuclear power that I know of…”

The mission was not without its tribulations; on a test run of the relay system while the probe passed the Earth, it was revealed that a problem existed between the synchronization due to the Doppler shift between Cassini and Huygens. An alteration in its planned insertion orbit reduced the differential to 6km/s, slow enough for the synchronizer to work properly. The data retrieval  was also backed up by ground receivers at Green Bank and Park radio observatories, which proved crucial when Channel A data was lost. To assure redundancy, Huygens was wired with two separate computers, each with a separate radio channel; A & B. Programs such as the Doppler Wind Experiment were devastated. And of course, the Huygens probe had to power up and function on its own after years of travel through the cold, radiation riddled vacuum of space. The author also notes that the Cassini mission itself spanned a huge time change in technology; when conceived in the early 1990′s, the World Wide Web barely existed! The download speed itself as the probe transmits data is much slower than a prehistoric dial up connection; the storage drive on Cassini has about 2GB of space, about half what’s on my Ipod nano. Ah well, my nano is not radiation hardened (Yet). Speaking of which, an ultimately cool video was made of Huygens decent. So cool, I keep it on my Ipod to show folks!

The author’s own experiment was a surface penetrometer, a probe on the underside of Huygens that measured the impact of the probe to test the consistency of what it landed in. In the end, the probe landed not on solid rock or choppy seas, but a marshy slush somewhere in between. A two word email to his wife announced to the world what Huygens had landed in: “crème brûlée!”

There was no guarantee that the probe would return data during its brief few hours of life on the surface. Temperatures are in the 94K= -179C range; liquid methane take the place of liquid water in the Titan hydrological cycle. The imager on Huygens was fixed; there wasn’t even a guarantee that the decent chute wouldn’t obscure it after landing!  Ultimately, the probe revealed an image of a methane ice strewn field, our first look at a bizarre landscape and the most distant surface image of an alien world.

But the odyssey doesn’t stop there.   Cassini is still orbiting Saturn, returning some awesome science. Farther afield, plans are in the making to send a dedicated orbiter with a glider or automated “blimp” to Titan in the next decade. If anything, this first glimpses offered by Huygens beg further exploration. Read Titan Unveiled, then marvel at the explorations of the mysterious moon to come!


  1. [...] blimps and submersibles on Europa, Titan, and Enceladus will all operate well out of the Sun’s domain [...]

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