“Marchenko,” Amy said. “I have to apologize to you. I couldn’t simply let you on board. I was secretly hoping you would find a way in spite of my refusal. But if I had officially permitted it, the return to Earth would have been blocked for us. I hope you understand. And you too, Francesca.”
Marchenko did not answer. All of them looked at the pilot. Francesca nodded, but did not say anything. To her, the order to leave Marchenko behind must have felt like a personal betrayal, and she will have to get over it, Martin suspected.
They heard a beep. “Mission Control,” the voice of Watson said. Martin was startled. Did they find out? he wondered.
“Transmitting file,” Watson said, and started the video message.
“I am glad you made it through this detour I presented to you,” Devendra said. “The whole team here sends condolences for the loss of Dmitri Marchenko. We are really going to miss him.
"I have attached a file with the updated course data for your return trip. In addition, there is a message especially for Martin. It is about the signal, I should add. Capcom, over.”
All of them were looking at him. About the signal... What did Devendra mean by this? Did Mission Control uncover something, after all?
In his cabin, he sat on his bed, took a deep breath, and called up the message. On the screen he saw an older, bald man who looked somehow familiar to him.
“Martin,” the man said in only slightly accented German. “My name is Robert Millikan. I work at the Green Bank Observatory and I am the reason you were first sent to Titan and then back to Enceladus. I am sorry I got the crew into danger—particularly you. I am glad NASA gave me the opportunity to send you a personal message. I do not expect anything else from you, don’t worry. I would be happy, though, if we could meet for a cup of coffee after you have returned to Earth.”
Author's Note
Great to see you here! This means you survived your adventure on icy Titan. I really hope you enjoyed the experience. Titan is my favorite celestial object—no, it's actually in third place on my list, Earth being #1 and Mars #2. I must confess I'm addicted to traveling, and Earth, at least right now, is my only option. I will be in Vietnam when this book first comes out in the English language. Of course I’ll be eagerly following the book launch from there.
My travel addiction is surely rooted in my past. I grew up in Eastern Germany on the wrong side of the Wall, where all trips outside the Eastern Bloc were verboten. Instead, I traveled in my books. Authors such as Arthur C. Clarke, Ray Bradbury, Jules Verne, Stanislav Lem and—I bet you don't know this man—Klaus Frühauf, took me to places nobody had yet been. Science fiction was already a worldwide phenomenon when I was growing up in the 1970s and ’80s, and there were no walls in the books. I never dreamed my own books would someday be published in such faraway places as the United States, Australia, Canada, Great Britain, and India. This is a true marvel!
But back to Titan. I’m intrigued by this moon because it is so similar to Earth. It has rain, lakes, and clouds, but I must confess it’s a bit colder. Mars, which I hope humanity will reach in my lifetime, is boring compared to Titan. I hereby invite you to keep reading as I take you on a guided tour of Titan.
As you might have suspected, the International Life Search Expedition won’t get home quite yet. On their way back to Earth lies Jupiter’s inhospitable volcanic moon Io—and ruthless forces on Earth are pursuing their own interests, to the peril of ILSE’s crew. Please join me as their odyssey continues in my next book, The Io Encounter. You can find it here:
hard-sf.com/links/344027
If you register at hard-sf.com/subscribe I will keep you informed about new Sci-Fi novels being published. You will then receive a free PDF version of The Guided Tour of Titan with color illustrations.
If you somehow missed the first book of the series, it’s not too late to find out more about these characters and their mission. You can purchase The Enceladus Mission, the prequel to The Titan Probe, for $3.99 on Amazon:
hard-sf.com/links/344018
Brandon Q. Morris
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Web: www.hard-sf.com
E-Mail: [email protected]
Translator: Frank Dietz, Ph.D. Editor: Pamela Bruce, B.S.
Final editing: Marcia Kwiecinski, A.A.S., and Stephen Kwiecinski, B.S.
Technical Advisors: Michael Paluszek (President, Princeton Satellite Systems), Dr. Ludwig Hellmann
Cover Design: BJ Coverbookdesigns.com
Brandon Q. Morris is a registered trademark of the author.
The Guided Tour of Titan
Introduction
Titan is the largest moon of the ringed planet Saturn, and the second largest one in the solar system, after only Ganymede, one of Jupiter’s moons. If Titan orbited the sun, as Earth and Mars do, it would doubtlessly be considered a planet, since it is somewhat larger than Mercury, the planet closest to the sun, although Mercury is considerably heavier. And nobody has tried to deny Mercury the status of a planet.
What most fascinates us is Titan's similarity to Earth. Titan has everything our home planet possesses—oceans, lakes, rivers, a dense atmosphere with weather phenomena like rain and storms, seasons, deserts with dunes—yet this moon is also as different from Earth as a celestial body could be. What other similarities and what differences are there? What do we know about one of the most exotic places in the solar system, and where does our knowledge meet its limits? Is it realistic to think there might be a life form like the ILSE crew encountered on Titan? Would any life form be expected there? Join me on an exciting journey! I can promise you interesting insights and views.
Orbit and Shape
Titan has a mean diameter of 5,150 kilometers. Mercury, the planet closest to the sun, is a bit smaller, measuring 4,880 kilometers. On the other hand, Titan does not consist entirely of rock as Mercury does, and therefore Titan—at about 134 metric tons—has only about a third of its mass. This is still a very high number, so a comparison with Earth’s moon might help: Titan has a little less than 1/44 the mass of Earth, and 1.8 times the mass of our moon.
For a long time Titan was believed to be the largest moon in the solar system. This was due to its atmosphere, which reaches high up and makes this moon look bigger than it really is.
The gravitational acceleration on its surface is 1.35 meters per second squared. Humans would only have one-seventh of their terrestrial weight. This value is a bit lower than on Luna—Earth’s moon—which is smaller than Titan.
The comparison between Titan and Earth’s moon is a bit misleading, since Titan is part of a completely different system. It belongs to Saturn, which is surrounded by its rings and at least 62 moons, including Enceladus. You can find Enceladus’s biography at the end of my novel Enceladus. Titan contains more than 95 percent of the total mass of Saturn’s moons. It is a veritable giant, at least compared to its siblings. It was therefore quite justified for the British astronomer John Herschel to name it after a race of deities in Greek mythology, the Titans. Their leader was Cronus, called Saturn by the Romans, and the gas giant Saturn with almost 100 times the mass of Earth (the clear number 2 in the solar system) does indeed lead Titan—and its siblings—around like each is on a leash, using its enormous gravitational pull.
Titan is clever enough to keep a safe distance from its planet. On average it is 1.2 million kilometers away from it, while our moon orbits Earth at a distance of about 380 thousand kilometers. This means the orbit of Titan is quite a bit outside the known rings of Saturn. For comparison, the distance from Earth to Mars is approximately 55 million kilometers at their closest convergence.
Even though Titan is considerably farther away from Saturn than the Moon is from Earth, it needs just a little more than half the time for an orbit, just under 16 days versus 27.3 days for our moon. It also moves considerably faster, reaching an orbital velocity of 5.57 kilometers per second. Per second! It is not easy to catch up to Titan without a running start. In comparison, Earth’s moon moves at
the sedate speed of 1.02 kilometers per second. The plane in which Titan orbits its planet is slightly, very slightly (only one-third of one degree) tilted against the plane of the rings. If you could be there, like the crew of ILSE, you would only see the rings of Saturn as a line. Besides, it would be hard to detect them from the surface through the dense atmosphere. The orbit itself is almost circular, though not quite—the point closest to Saturn and the one farthest from it differ by 41,000 kilometers, about 3 percent of the mean distance.
During the aforementioned 16 days, Titan rotates exactly once around its axis. This is called a captured rotation, which leads to this moon always turning the same side towards its planet. Earth’s moon does the same thing. Seen from the surface of Titan, Saturn therefore is always at the same location in the sky. The spot where Saturn is directly overhead is used to start the count of meridians. On Earth, on the other hand, the prime meridian has been assigned to Greenwich near London. Titan's rotational velocity at its equator is about 12 meters per second, compared to Earth’s 463 meters per second.
In the introduction I mentioned Titan having seasons. These are caused by its orbit around the sun. Together with its planet Saturn, Titan orbits our central star in about 30 years. On Earth, as you might remember from your school classes, seasons are caused by the tilt of our planet’s axis relative to its orbit. The same applies—even to a slightly higher degree—to Saturn and the orbital plane of all its rings and moons. This also causes seasons on Titan, which last a quarter of each Saturnian year corresponding to 30 Earth years, i.e. about 7.5 years. In 2010, the last summer ended in the southern hemisphere. 37.5 years later, in 2047, it will be autumn in the southern hemisphere, where the ILSE astronauts land.
While Titan has at least 61 siblings, it orbits Saturn in relative solitude, as the others seem to keep their distance due to Titan's large size. The next moon closer to Saturn is Rhea (695,000 kilometers orbital distance), and farther out is Hyperion, the odd-looking moon that resembles a sponge, at a distance of 242,000 kilometers.
The Atmosphere
When Voyager 1 managed to take the first close-up pictures of Titan in 1980, scientists were quite disappointed. They had hoped for views of the surface, but the NASA probe could not provide the desired views due to the dense atmosphere. The gas layer is thick and never opens up. Imagine this on Earth—no nice blue sky, only thick, gray clouds 24 hours a day.
It is quite exceptional for Titan to have an atmosphere. And the astronomers were ultimately glad about it. There is no other moon where this is the case, in quite the same way. Astronomers had suspected this for a long time, but it was only with Voyager 1 that they gained truly usable insights. These have been refined by now, but not overturned.
In many ways, the gas layer around Titan exceeds the one around Earth. Titan's gas layer reaches higher (1,200 kilometers instead of 100 kilometers), it weighs 1.19 times as much, and it generates a surface pressure which is 50 percent higher—meaning 1.5 bar. If one takes the lower gravity into account, this means every square meter of ground on Titan has ten times as much gas above it as on Earth, and its density is five times higher than on our planet. This offers the practical advantage of allowing humans in winged suits to fly under their own power on Titan, as their lift would be higher and their weight lower.
The Various Layers
What would we see while descending to the surface of Titan in a lander module? First we would cross the ionosphere at an altitude of about 1,200 kilometers. The ionosphere consists of two layers of charged particles. These reflect radio waves quite well.
At an altitude of 450 to 500 kilometers comes the mesosphere, the first layer of haze, consisting of methane molecules condensing up here due to the cold. Most of the air molecules are nitrogen, at 98.4 percent of the total, but methane (CH3) is chemically more interesting. At a great altitude the energy of the solar wind breaks up the methane into free radicals which combine with other molecules, sometimes forming very complex compounds. Researchers have discovered ethane, diacetylene, methacetylene, acetylene, propane, cyanoacetylene, hydrogen cyanide, and many others. The astrophysicist Carl Sagan coined the term ‘tholins’ for these reaction products, which does not refer to their composition, but rather to the way they are created.
However, these relatively heavy compounds do not manage to stay in the thin layers but instead drift downward. At an altitude of 100 to 200 kilometers they create an optically opaque layer of orange-colored haze, the tholin layer, which thwarted the attempts of Voyager 1.
Below an altitude of 40 kilometers the atmosphere gets slowly clearer. It is assumed the tholins rain down to the surface from there. Sagan already suspected these complex molecules might contribute to creating predecessors of life on the surface.
Below the tholin layer the air contains a relatively high amount of methane, up to four percent. Depending upon the season, methane and ethane clouds can form (the latter have been verified near the North Pole) that send rain down onto the surface. Storm clouds, like cumulus clouds on Earth, are possible here, and can cause heavy precipitation from an altitude of 15 kilometers.
Where does the Atmosphere come from?
Currently, the origin of the Titan atmosphere remains a mystery. The two large and rather similar Jupiter moons—Ganymede and Callisto—do not possess a significant gas layer, so Titan must have been 'lucky' at some point in its evolution. In the first 50 million years after the moon came into being, the energy of the sunlight should have eliminated any traces of methane, which tells us this gas is being generated on a continuous basis. This moon appears to gain some advantage from orbiting so far away from the sun. This decreases its exposure to the solar wind, and it has managed to hold onto its atmosphere better than the planet Mars did.
The initial composition of the moon might have played an important role. It probably consists of only 50 percent rock, plus water ice and ammonia (NH3). The latter could be the source of the nitrogen in the atmosphere. During all these millions of years, Titan has been shedding a large part of its atmosphere—there is enough left, in part because there was so much of it to begin with, and in part because gas is continually provided from its interior.
Ganymede and Callisto lack such sources, since they came into being farther inside the solar system, where higher temperatures allow less ammonia to accumulate.
The Surface
After the Cassini probe sent down the Huygens lander in 2005, we saw quite well what things look like on Titan—at least during summer in the southern latitudes. If you ever go there yourself, you should prepare for the cold. The average temperature on the surface is minus 179 degrees. There are no major temperature differences between the poles and the equator, three degrees at most. This is due to the sun never shining directly on the surface. Some of its energy is absorbed by the haze layer and then distributed across the entire moon, and some is reflected back into space. This leads to a negative greenhouse effect, which means the surface would be warmer if the haze layer allowed more sunlight to shine through.
So you’d better be dressed warmly when you leave your spaceship. And don’t forget your flashlight as well—on Titan it is always twilight. I would recommend landing on the side facing Saturn. While you won’t be able to see the planet (or the sun), Saturn's reflected light illuminates the scenery a bit better, so you don’t have to travel around in absolute darkness.
Here is another insider tip. Definitely bring along a night vision device, as the cloud layer is relatively transparent in the infrared spectrum, and you might want to see the sun again.
By the way, the sky appears to be the same color as Titan looks from afar, a dirty orangish brown. You will only get to see clouds seasonally. These are methane clouds; either ice clouds at high altitude (30-50 kilometers) or mountainous-looking storm clouds similar to those you know from terrestrial thunderstorms. They cause precipitation—ice-cold methane rain you had better avoid, because it is so cold it would definitely overtax the heating system of your spa
cesuit. If you risk it, or if you find a safe refuge with a window, you would see giant raindrops, as big as hailstones, less drop-shaped and more round, floating down with impressive slowness. A lot of liquid can rain down in a short time. Hopefully you did not land in a depression! Once the clouds move away, you should try to catch a glimpse of the rainbow, which consists of reddish stripes.
Thunderstorms such as I described in the novel are also possible, though they don’t happen very often. The thunderclaps reach an observer more slowly than on Earth, as the speed of sound is only 215 meters per second (instead of 340 m/s). On the other hand, they sound much more bass-heavy, and generally resonate across greater distances. So if you hear booming sounds during your walk, a thunderstorm might be coming—better try to find shelter quickly. By the way, in the novel, the value Francesca calculated for the speed of sound during her hike was a bit too low, because she did not correctly remember the effect of the temperature on the compression coefficient of nitrogen (I don’t either, but I get help from an online calculator, see bit.ly/2mQUG2k).
Usually it is not too windy near the ground. Scientists predict soft breezes of less than a meter per second (on Earth this would be ‘light wind’) blowing westward. But in spring and fall there can be more violent movements of air reaching down to the ground, and these winds formed the dunes on Titan. You could not call this a ‘storm,’ as it is only a moderate wind blowing eastward at up to ten meters per second.
Nothing is the Way it Seems
Speaking of the ground, if you landed near the equator, as the Huygens probe did, your first step would lead you across sand. Sand? Just take a sample with you into a warm room. You will soon realize not everything that appears to be sand is in fact silica, like the sand on Earth. The fine grains of the Titan desert consist of water ice with additional organic compounds that rained down from the tholin haze. However, the sand was created in a way similar to terrestrial sand—by erosion. Like the entire surface of this moon, the mountains on Titan consist of ice, which at these temperatures is as hard as granite. They erode just like granite due to rain and creeks digging a bed into them. In the large deserts the grains of sands clump together into dunes shaped by the wind. They can reach heights of up to 300 meters. They are not as soft as sand dunes on Earth, and over time they may solidify.
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