Mars is at opposition.Mars is the fourth known planet in order outward from the Sun, and is in many ways the most Earthlike. Science-fiction writers have used Mars more than any other extraterrestrial place as the setting for civilizations, outposts, and evolution. It is interesting to suppose that the first Martians will come from Earth. Will you live to see the invasion of Mars by Earthlings?
Mars is also known as the Red Planet, although its true color varies from rusty orange to gray to white. Some casual Earthbound observers mistake it for a red-giant star. However, because of its significant apparent diameter, it does not twinkle as does a star. In ancient mythology, Mars was the god of war. The planet has two moons, named Phobos (Greek for “fear”) and Deimos (Greek for “terror” or “panic”).
Mars never passes between Earth and the Sun because the orbit of Mars lies entirely outside that of Earth. Mars occasionally lines up with the Sun when it is exactly opposite the Sun from us. This is called conjunction. There is no need to use the word superior because there is only one kind of Martian conjunction. (With Venus and Mercury, there are two kinds, inferior and superior, as you know from the preceding chapter.)
Mars does not pass through significant phases as do Mercury, Venus, and the Moon. We always see Mars with most of its face lit up by the Sun. However, the brightness of Mars in the sky does vary greatly. It is dimmest when it is at and near conjunction. When it is very close to conjunction, Mars is invisible because its wan glow is washed out by sunlight. Earth travels more rapidly around the Sun than does Mars, so this unfavorable condition never lasts for long. After a conjunction, Mars begins to show itself in the eastern sky before dawn. As time passes and Earth begins to catch up with Mars, we get closer and closer to the Red Planet. As this happens, Mars appears earlier and earlier in the predawn hours, and its brilliance increases. Eventually, Mars reaches a position opposite the Sun so that it rises when the Sun sets, is visible all night long, and sets at sunrise. Then the Red Planet is at opposition, and it rivals Jupiter in brightness. As seen with the unaided eye, Mars at opposition is a more attention-getting sight than any other planet except Venus.
Opposition is the best time to view Mars, but some oppositions are better than others. This is so because the orbit of Mars is far from a perfect circle around the Sun. While Earth’s orbit only varies a percentage point or so either way from perfect circularity, Mars follows a decidedly elliptical path with the Sun at one focus. The best oppositions, in terms of viewing Mars from our planet, occur when three things happen at the same time:
Mars is at opposition.
Mars is at perihelion (closest to the Sun).
Earth is at aphelion (farthest from the Sun).
This can only take place during the northern hemispheric Earth summer, especially during the month of July, because that is when Earth is at aphelion (Fig. 6-1). The ideal state of affairs happens only about once every 15, 16, or 17 years.
Mars’s mean orbital radius is half again that of Earth, or about 228 million kilometers (142 million miles). As a result, Mars has a longer year, in terms of Earth days, than does Earth; in fact, it is 1.88 times the length of an Earth year. The Martian day is about 2.5 percent longer than that of Earth.
When and if we humans set up bases on Mars, we will be perfectly comfortable with our 24-hour time system, although we will have to lengthen the second, minute, and hour by about 2.5 percent. Most of us would not notice such a difference in the face of the other adaptational problems inherent in a relocation to the Red Planet, such as the reduced gravitation, the bitterly cold temperatures, the lack of a breathable atmosphere, the lack of protection from solar ultraviolet radiation, and the infrequent but brutal dust storms.
Figure 6-1. The orbits of Earth and Mars, to scale. The most favorable conditions for viewing Mars occur when Earth is at aphelion and Mars is at perihelion.
The equator of Mars is tilted about 24 degrees relative to the plane of its orbit around the Sun. This is almost identical to Earth’s axial tilt and results in Martian seasons whose extremes are similar (in terms of proportionality) to those on our planet. If you lived at 40 degrees north latitude on Mars, you would see the Sun behave in a manner similar to the way it behaves on Earth as the seasons pass, except, of course, that the seasonal progression would take many more days to go full circle. The summer Sun in the northern hemisphere would rise in the northeast, take a high course across the sky, and set in the northwest, and daylight would last about two-thirds of the solar day. The winter Sun in the northern hemisphere would rise in the southeast, take a low course across the sky, and set in the southwest, and daylight would last only about one-third of the solar day. People living in the Martian southern hemisphere, hailing from such places as Sydney, Cape Town, or Buenos Aires, also would find their seasons familiar, at least in terms of the Sun.
The Red Planet is about 53 percent the diameter of Earth, roughly 6,800 kilometers (4,200 miles). This would put Mars neatly between Earth and the Moon in size if the three orbs could be lined up next to one another (Fig. 6-2). If you were to stand on Mars and look toward the horizon, you would see a strangely foreshortened vista. Similarly, standing on top of one of the highest mountains, you would be able to perceive the curvature of the planet.
The smaller size of Mars, combined with a density somewhat lower than that of Earth, produces a less intense gravitational field than the one we know. Your weight on Mars would be 37 percent of your weight on Earth. If you weigh 160 pounds here, you would weigh 59 pounds there. You would be able to throw a baseball much farther on Mars than you can on Earth. While golf-loving astronauts might not be able to drive a ball as far on Mars as they did on the Moon, they would do better than they can on Earth. A golf course on Mars would have to be much larger than one on Earth, and to make things more interesting, there would be no shortage of boulders and sand traps.
Figure 6-2. Mars is a bit more than half the diameter of Earth.
There is evidence that the crust of Mars is thicker than that of Earth. There is also evidence that the Martian mantle historically has been less active than that of Earth.
The surface area of a sphere is proportional to the square of the diameter, whereas the volume is proportional to the cube of the diameter. Mars, being approximately half the diameter of Earth, has one-quarter the surface area but only one-eighth the volume. This means that the surface-area-to-volume ratio of Mars is twice as great as that of Earth, causing Mars to cool off faster after its formation along with the rest of the Solar System. All these factors have combined to create a world where the crust does not move very much.
On Earth, crustal plates float around over the mantle, so volcanoes move gradually away from the hot spots underneath. On Mars, however, little or no such movement has occurred, so some volcanoes have built themselves up to enormous proportions. The crowning glory of the Martian volcanoes is Olympus Mons (Mount Olympus), which is 24 kilometers (15 miles) tall and measures 600 kilometers (370 miles) in diameter at its base.
Mars is pitted in some places with impact craters. In fact, when Mariner 4 took the first close-up photographs of Mars in 1965, coming within 9,800 kilometers (6,100 miles) of the surface, craters seemed to dominate the landscape. This led astronomers to believe that Mars might be as desolate as our own Moon. It was up to later missions to demonstrate otherwise. An entire planet cannot be characterized by looking at only one spot. Suppose an alien civilization were to send a probe past Earth and happened to obtain photographs of only the Sahara Desert?
The southern hemisphere of Mars consists of highlands, and this is where most of the impact craters are found. The northern hemisphere, in contrast, is several kilometers lower in elevation and appears flooded over by the lava from volcanic eruptions. Various parts of the surface have a dusky gray, almost green appearance. This greenish cast was seen by the first people who looked at Mars through “spy glasses.” The dark regions, along with illusory straight dark lines that seemed to lead from them toward the polar ice caps, led some respected scientists to believe that Mars must be home to an intelligent civilization.
Numerous probes followed Mariner 4, and with each new set of photographs and data, the hope for finding life on Mars diminished. Many scientists believe there is an abundance of water locked up on Mars in the form of permafrost beneath the surface. Some water ice also appears in the polar caps. In addition to water ice, during the polar winters there is frozen carbon dioxide (dry ice) in the polar caps, particularly the southern cap, which endures a longer winter.
Dried-up riverbeds are the most interesting features seen on the surface of Mars. After careful analysis, most geologists have agreed that these marks could only have been made by running water. One theory is that Mars was at one time covered to some extent by a shallow sea or perhaps by large glaciers that melted during a series of volcanic eruptions.
Mars has oxygen, but almost all of it is bound up with elements in the surface and with carbon in the atmosphere. The result is a rusty world, with an atmosphere consisting almost entirely of carbon dioxide (CO2). The barometric pressure at the surface of Mars is less than 1 percent of the pressure on Earth. Were it not for the fact that CO2 is a heavy gas, the atmosphere of Mars would be even thinner than this.
Despite the thin air on Mars, weather occurs, and it can be extreme. Winds aloft can reach speeds of around 400 kilometers per hour (250 miles per hour); near the surface, they commonly rise to 120 kilometers per hour (75 miles per hour). It would be a mistake to say that such winds are of “hurricane force” because the thin air on Mars produces far less wind pressure for a given wind speed than the air on Earth. However, dust particles from the surface are picked up and travel right along with the wind, blowing high up into the atmosphere, where they at times shroud the planet completely. During these massive dust storms, which can be accompanied by lightning, the surface features of the planet practically disappear. As seen from the surface, such a storm would produce a dark red sky, obscuring the sun and casting an evil gloom over the landscape.
One of these planetwide dust storms was indirectly responsible for the discovery of the four largest Martian volcanoes. These include Olympus Mons (already mentioned as the largest mountain on the planet), Ascraeus Mons, Pavonis Mons, and Arsia Mons. As the storm abated, the dust gradually settled. The peaks of the volcanoes were seen first; more and more of them appeared as the Martian sky regained its characteristic clarity.
High clouds, similar to cirrostratus and cirrus clouds on Earth, are sometimes observed on Mars. In addition, Olympus Mons is occasionally shrouded in a thin veil of cloud, in much the same way as high mountains are cloud-covered on Earth. These Martian clouds are far less substantial than their Earthly counterparts, and scientists doubt that they produce much, if any, precipitation. However, they do produce a sort of fog at the top of Olympus Mons. Standing inside the caldera of this monstrous mountain on a foggy morning, you might for a moment imagine yourself in the Namib Desert on the southwestern African coast.
The temperature on Mars never rises above the freezing point as we know it on Earth. At night in the winter, Mars would make Antarctica seem inviting by comparison. As if this were not bad enough, the Sun blasts the surface with ultraviolet radiation because the air is not thick enough to shield against it. Some high-speed solar particles also might reach the surface following solar flares.
If there is any sort of life remaining on Mars, it must be a primitive sort of bacteria or virus or some hardy “germ” similar to the toughest organisms on Earth. Even these life forms would not be found on the surface but underground.
After the invention and deployment of the first telescopes in the seventeenth century, some observers of Mars claimed to see straight lines connecting the dark areas near the equator with the polar caps. Percival Lowell, one of the most noted astronomers of all time, theorized late in the nineteenth century that these canals logically would have been constructed by a civilization intent on surviving a planet whose climate was becoming ever-more hostile. Numerous canals, as they were called, were mapped by some observers. These were optical illusions; the orbiter probes showed no such canals (although the dried-up river beds they did see were every bit as interesting and were no illusion).
No sign of life has ever been found on Mars. There is no indication that intelligent life has ever set foot (or appendage of any other sort) on its surface.
Science-fiction writers have taken advantage of the fact that Mars, while not a hospitable place by Earthly standards, at least presents an environment where life might survive with the proper equipment. Thus H. G. Wells’ novel The War of the Worlds, published around the year 1900, created a cult of people who believed in the existence of native Martians. Ironically, it was our own Earthly disease bacteria that prevented us, in this horrifying tale, from being annihilated by the gigantic, slimy aliens whose ships came streaking down like meteorites and who stalked our planet in armored contraptions resembling nothing humanity had ever seen before.
Mars has been suggested as a possible colony for pioneers from Earth. Perhaps the water ice in the permafrost can be released, plants can be introduced to provide oxygen for the atmosphere, and other large-scale operations can be launched in an attempt to make Mars into an Earthlike place. However, the obstacles to such a project are formidable indeed. The low surface gravity, the lack of a substantial magnetic field to protect against the solar wind, and the possibility that the undertaking could create some horrible, incurable new disease strains must all be taken into consideration. Arguably, it will be far easier to control the population explosion on our own planet so that it never becomes necessary to colonize Mars.
Despite all the naysayers, we Earth dwellers undoubtedly will try to go to Mars. Why? Because it is there, and we have the technology to get there. Who knows? Maybe we will find primitive life there. Maybe Mars bases will be built. Maybe people will learn to think of the Red Planet as their home, being born, educated, and employed there. We will then, by all rights, be entitled to call ourselves colonizers of space! However, it will take a special sort of human being to endure the rigors of a life spent on Mars.
Imagine that you go on a mind journey and, for a few moments, become one of those privileged few who get to walk around on Mars, taking precautions, of course, to ensure that you do not suffer the fate of H. G. Wells’ fictitious Martians and perish from some unknown disease for which your body has no defense.
As you accelerate away from Venus, the primary problem will be one of fuel. It will be necessary to accelerate considerably to hurl the vessel out to the orbit of Mars. Here you encounter one of the bugaboos of long-distance space travel. The more you accelerate, the more fuel you need at the outset, and the more fuel you tank up with, the harder it becomes to accelerate in the first place. Fortunately, there is a way around this problem on the way from Venus to Mars. You can refuel by making a rendezvous with one of the space stations in orbit around Earth (Fig. 6-3).
Figure 6-3. On the way from Venus to Mars, an interplanetary vessel can refuel at an Earth-orbiting space station.
The trip from Venus to Earth is uneventful, and you enter an equatorial orbit high above the surface.
“We’ll be staying here for a couple of days,” says the first officer. The ship needs to be checked over, and the Venus craft will be taken off our hands. We’ll use the Mercury lander to set down on Mars, but we also need to get the MUV.”
“What is the MUV?” you ask.
“That’s short for ‘Mars utility vehicle.’”
“I should have known.”
“The MUV is a like the SUVs (sport utility vehicles) that were popular when cars used to burn fossil fuels to get around. Of course, this vehicle, like most modern Earth surface transport vehicles, is powered by compressed hydrogen. The only difference is that the MUV needs to take along its oxygen, too,” says the first officer.
“Can’t the oxygen be extracted from carbon dioxide in the Martian atmosphere?” you ask.
“If that were possible,” says the first officer, “there would be hundreds of robotic MUVs roving Mars right now. It might someday be possible to get oxygen from subsurface water ice on Mars by melting it and electrolyzing it using solar energy, but that is not a convenient way to obtain oxygen for a moving vehicle run by a combustion engine.”
The first officer has just been informed, by means of his digital communicator, that there is a problem with the Valiant, your main ship. Apparently, the life-support systems need some further work before you can embark on the journey to Mars.
“What is the problem?” you ask.
The first officer explains how the life-support system works. “It makes use of the Sun’s ultraviolet radiation to manufacture oxygen by a sort of super-plant photosynthesis. Specially bred plants, a result of genetic engineering research, recycle the carbon dioxide from our breath and produce oxygen from it. The result is, ideally, a self-sustaining system that could, if it were possible to overcome other problems, work long enough for humans to go all the way to Saturn and back. (Beyond Saturn, solar radiation is not intense enough for the system to work.) The problem at the moment appears to be that the plants have come down with some sort of ailment,” he says.
“What does this mean?” you ask.
“Replacement photoplants,” says the first officer. “And a few new decorative plants as well.”
“You mean all those potted plants in the residential areas are real?” you ask.
“Of course they’re real,” says the first officer. “You didn’t think they’re plastic, did you? They serve at least two important functions. They assist with the oxygenation of the air, and they help make the ship look less institutional.”
The trip to Mars will take several months; this delay only adds to the tedium of interplanetary travel.
“Is there time enough for me to go down and visit my family for a while?” you ask.
“Yes,” says the first officer. “But not enough money. The new space shuttles are smaller, faster, more efficient, and less expensive to operate than the gigantic rocket-boosted ships of the late twentieth and early twenty-first centuries, but they aren’t free, and this mission was difficult to get approved. Taking civilians such as yourself into space has always been unpopular with certain people in the establishment.”
You will watch more videos, read more books, and work out with ever-increasing devotion. The exercise is vital, and not just for staying in physical shape. An attitude problem can take hold of space travelers if they don’t get enough exercise. The captain had explained it once, when she was in one of her rare talkative moods.
“It’s called, logically enough, ‘space-travelers’ depression,’” she said. “It is like the old problem they used to call ‘cabin fever,’ except worse. Fortunately, there is a simple cure. It involves careful attention to nutrition, plenty of visible light at the same wavelengths as those from the Sun, and a great deal of aerobic exercise.”
So you take your vitamins. You make sure you eat the right foods, in the right amounts, and on the right schedule. You drink plenty of water. And you increase your workouts to twice a day, for an hour and a half each session. The last thing you need is to get depressed 50 million kilometers (30 million miles) from your home planet.
By the time the ship nears the Red Planet, you are more video-literate, audio-literate, and aerobically fit than ever before in your life. “Most civilians,” the first officer explains, “are mistaken for California natives when they return to Earth from one of these journeys.”
“They are thin, they are fit, and they know every character in every movie produced during the last 100 years.”
The orbit around Mars, just as the trip from Earth to Mars, will be exactly in the Earth’s ecliptic plane (not that of Mars). There’s a good reason for this: fuel economy. Altering the plane of travel, even minutely, is a fuel-guzzling business. Because of this efficiency, the round trip between Earth and Mars requires less fuel than did the journey from Earth to Mercury, then to Venus, and then back to Earth.
Some astronomers think Phobos and Deimos are ex-asteroids that ventured too close to the planet and were captured by its gravitation, although there is reason to believe that one or both of them congealed from ejected material as the result of large asteroids or small protoplanets striking Mars long ago. Both moons are tiny compared with their parent planet, and both moons require large telescopes to be seen by Earthbound observers.
“We’ll be passing Deimos and then looking at Phobos from a distance as part of this tour,” says the first officer. “Deimos is the smaller of the two. It orbits the planet in about 30 Earth hours. There has been some talk of putting several large communications satellites on Deimos so that it can serve as a repeater for maintaining contact among exploration crews.”
“Landing on Deimos would be a problem, wouldn’t it, because of the low gravity?” you ask.
“Deimos is too small to have any gravitation to speak of, at least from a practical point of view. It is a chunk of rock only about 13 kilometers (8 miles) in diameter. Anyone who wants to rendezvous with Deimos will have to dock with it instead. One suggested scheme has been to harpoon it. A small rocket would be fired at Deimos, would crash-land there, and then burrow into the surface. However, no one has been able to figure out how to make sure the harpoon wouldn’t get pulled out and send construction workers scattering into Mars orbit. The escape velocity is less than 6 meters (about 10 feet) per second.”
“Aren’t regular communications satellites good enough?”
“Generally speaking, yes. But there would be room for gigantic storage batteries on a piece of rock like Deimos or Phobos, and these could serve several satellites. They could be charged with massive solar panels,” says the first officer.
“There’s something,” you say, pointing to an irregular object, half lit by the Sun, the other half eerily glowing with Mars-shine. Deimos is only about 20,000 kilometers (12,500 miles) above the Martian surface, and the Red Planet looms large.
“That is Deimos,” says the first officer. “It orbits Mars in a nearly perfect circle. That casts some doubt on the theory that Deimos is an asteroid that was thrown out of its original solar orbit by the gravitation of Jupiter. But that is a popular theory.”
“How much extra fuel did it cost us to see this piece of rock?” you ask.
“Not much,” says the first officer. “But it would cost too much to go right up to Phobos, the inner moon; we will have to be content to look at it through our telescopic cameras. Come with me.”
The first officer leads you into a dimly lit room with a huge screen on one wall. There is something strange about that screen; it is obviously there, but you can’t ascertain how far away it is. “Is that a holographic projection system?” you ask.
“Yes,” says the first officer. “And the first projection we’ll see is an animated rendition of Mars, Phobos, and Deimos (Fig. 6-4). The piece of rock you just saw is the smaller, higher, and slower of Mars’ two moons. Phobos orbits much closer to the planet. This illustration is to scale. Note that Phobos revolves around Mars much faster than Deimos. In fact, Phobos is inside what is called the synchronous-orbital radius. Phobos revolves around Mars faster than the planet rotates on its own axis. This means that an observer on Mars will see Phobos move across the sky from west to east.”
“It almost looks like an artificial satellite in this picture.”
“Phobos eventually will suffer the fate of most artificial satellites. It likely will spiral into Mars and crash. This will produce a significant impact. Phobos is not huge, but I wouldn’t want to be on Mars when it hits. The gravitation of Mars may break Phobos up before it can crash, and then Mars will have a ring system.”
Figure 6-4. Mars, Deimos, and Phobos, and the orbits of the two moons, drawn to scale and viewed from high above the Martian north pole.
The next image is of a dark, stonelike object that seems to be falling out from underneath a curved, inverted Martian horizon. “That is Phobos rising right now,” says the first officer. “Actually we are looking back at it. We are still at a higher altitude than Phobos and have slowed down in preparation for Mars orbit. Phobos is catching up to us. We will be passing its orbital level while it is safely on the opposite side of Mars.”
“It looks like a lump of coal,” you say.
“Phobos is made of material called carbonacious chondrite, similar to that of many meteoroids and asteroids,” says the first officer. “Its albedo is only 0.06. This means that it reflects only 6 percent of the light that strikes it.”
“How large is Phobos?”
“Slightly bigger than Deimos, about 20 kilometers (12.5 miles) in diameter, but elongated.”
“Right now it looks like a hand grenade with the top part taken off so that there’s a hole in the top,” you say.
“Wait a while and it’ll change,” says the first officer. He’s right; a short while later it looks almost spherical.
“Is the hole an impact crater?” you ask.
“Yes. It is called Stickney,” says the first officer. “If Phobos was originally an asteroid, it struck a lot of other asteroids before it attained orbit around Mars. The impact that made Stickney might be the one that knocked Phobos out of the asteroid belt, if, that is, Phobos was indeed an asteroid at one time. I am not sure that this is true.”
“This might sound like a stupid question,” you say, “but—”
“There are no stupid questions.”
“Okay. You showed me an image of Deimos and Phobos in orbit a while ago.”
The image reappears on the holographic screen.
“All right,” you continue. “The orbits of both Phobos and Deimos look like perfect circles.”
“The orbit of Deimos is essentially a perfect circle. Phobos has an elliptical orbit, but the eccentricity is small, so the orbit is almost a perfect circle too,” says the first officer.
“Can we look at the orbits as seen from the plane of Mars’ equator?” you ask.
“Certainly,” says the first officer. He smiles. “We’ll look at the situation from just outside the equatorial plane so that we can get a little perspective.” The view changes. The moons now appear to be orbiting Mars as seen from slightly above their orbital plane. As you suspected, they both orbit almost exactly above the equator of Mars (Fig. 6-5).
“If those moons were originally asteroids and were captured by the gravitation of Mars, why are their orbits both so nearly circular, and why are they both so nearly in the plane of Mars’s equator? That’s quite a coincidence, isn’t it?”
“That,” says the first officer, “is not a stupid question. In fact, it may answer the riddle of how these moons came into existence. I believe that both of these moons formed as the result of one or two major impacts in Mars’s distant past, just as the Earth’s moon is believed, by many astronomers, to have formed. It would have taken only a modest-sized object to blast that much material into orbit.”
“But both moons are made of asteroid-like stuff,” you say.
“Yes,” says the first officer. “I think that one or two large asteroids—much bigger than either Phobos or Deimos—crashed into Mars. This melted the big asteroid, and most of it was absorbed by Mars. However, some of this asteroid was cast into Mars orbit, along with some ‘molten Mars,’ and from that stuff, the moons formed. This is my theory,” says the first officer.
Figure 6-5. Mars and the orbits of its two moons, drawn to scale and viewed from nearly in the equatorial plane.
We may never know exactly how these moons were created.
The Mars lander, the Eagle, awaits. You’re not eager to get inside its cramped cabin and endure weightlessness, even for a short while. The artificial-gravity wheel on the Valiant has been slowing down gradually since you left Venus, where the gravitational pull is nearly equal to that of Earth. The shock of weightlessness nevertheless will be unpleasant; you have never tolerated it well.
Your first question, naturally enough, is “Where will we land?”
The first officer responds, “The best places, in my experience, are the calderas (craters) of old Martian volcanoes. While some of the volcanoes on Mars might still erupt from time to time, none are active at the moment. If a volcanic eruption were imminent, there would be signs, just as there are on Earth.”
“What kinds of signs?” you wonder.
“We have seismometers in all the landing-site calderas,” says the first officer. “The one we will be visiting today is called Pavonis Mons. This means “Peacock Mountain.” It lies almost exactly on the Martian equator. It happens to be only a few days past the Martian vernal equinox, so the Sun will rise directly in the east, follow a course right up to the zenith, and then set in the west, 12 Mars hours later.”
“A Mars hour is . . .”
“About 62 Earth minutes,” says the first officer. “We have decided to divide the Mars day up into 24 hours according to the Sun, just as is done on Earth. You won’t notice any difference between Mars time and Earth time. We have special wristwatches with quartz oscillators aligned so that they function according to Mars time. Here.” He hands you a watch. You strap it on over your pressure suit.
The descent proceeds smoothly enough. A huge crater yawns beneath the Eagle. “I don’t like this,” you say. You have visions of an impromptu Vesuvius or Krakatoa eruption replay, with the Eagle as part of the volcano’s ejecta. “No need to worry,” says the first officer. “If there is any sign of trouble, which is less likely than getting hit by a bolt of lightning on Earth, we’ll be out of here. We have rehearsed all kinds of emergency evacuation scenarios.”
It is almost sunset as the Eagle touches down. At the last moment before touchdown, the Sun vanishes beneath the rim of the crater. The sky above is pink where the Sun was, magenta all around, fading to deep purple and finally to black at the zenith. You think that you see a tiny white dot moving down toward the eastern horizon. “Is that Phobos?” you ask.
“No,” the first officer says, “That is our main ship.”
The outside temperature is –40°C, which happens also to be –40°F, at sunset. The thermometer plummets fast. It will drop down to –90°C, or –130°F, in the predawn hours.
“That’s colder than it ever gets in Antarctica,” you say.
“And the thin air, if you could stand outside and not die from the lack of pressure, would make it seem even colder than that.”
“I can’t imagine –130°F, no matter what the pressure,” you say.
“Think of the worst possible arctic blizzard, with the temperature far below zero and the wind roaring like a hurricane. Then imagine getting into a swim suit and going outside and just standing there.”
“I get the idea.”
“At the poles during the Martian winter, it can get quite a lot colder even than that,” says the first officer.
“It is beyond my comprehension.”
“Now we need to get some sleep,” says the first officer.
“In this cramped little vessel?” you ask.
“Well, not out there on the Martian desert sand. If you want to stay awake all night, go ahead, but don’t keep me up.” He nods his head and begins to doze off. All you can do is peer out the window and try to see if you recognize any constellations. You think you see Orion, tilted nearly on its side, hovering low in the eastern sky.
Then you, too, fall asleep. You wake up to sunshine on your face after what seemed like only a few seconds.
“The dreamless sleep of space explorers,” says the first officer. “And now we will perform the little test for which we came.”
The Mars utility vehicle (MUV) reminds you of pictures you saw of the very first Moon rovers in the Apollo missions of the mid-twentieth century. And in fact, the two are quite similar.
“What’s that?” you ask as the first officer unfolds a huge, gossamer-thin, butterfly-like sheet of material.
“A kite,” he says.
“A kite! How will that fly here?”
“It is a windy day, or hadn’t you noticed?”
You get into the MUV with the first officer. Then you feel a tug on your pressure suit and hear a whisper against the side of your helmet. “That’s a little bit of breeze.”
“A 20-meter-per-second breeze,” says the first officer. “Or, in old-fashioned terms, a good 45-mile-an-hour gale. Look over that way.” He points toward the southern rim of the caldera. Then you see plumes of pink dust rushing along from east to west.
“Is this wind enough to fly that kite?” you ask.
“More than enough,” says the first officer. “We’ll get away from the Eagle and then try to communicate with some other explorers that happen to be on the far side of the planet right now. This kite will support an antenna. A long-wire antenna, just like the first radio experimenters used around the year 1900 to see if they could send their signals across the Earth’s Atlantic Ocean.”
“Why can’t we do this experiment from the Eagle? I feel nervous out here with nothing but a pressure suit for protection.”
“That feeling is normal,” says the first officer. “All astronauts, or nearly all, get the same feeling when they go on their first roves away from a space vehicle. It’s like free diving in the middle of a big lake or in the ocean. That’s not the same thing as paddling around in a swimming tank.”
“But why do we have to be all the way out here in the middle of nowhere just to test a radio?” you ask.
“There would be too much radio noise near the Eagle. Electromagnetic interference. All the Eagle’s computers and instruments generate electromagnetic noise. This is a sensitive little radio. It operates at a very low frequency, just 2 kHz, where the waves travel in contact with the surface of the planet,” says the first officer. “Here. You drive the MUV.”
“Two kilohertz! That’s audible sound!”
“It would be if we connected a speaker to the transmitter output rather than an antenna,” says the first officer.
You drive the MUV along toward the great plumes of pink. It’s like riding in a golf cart, except faster and with a slower but more exaggerated rolling motion. Red Martian rocks and boulders litter the floor of the caldera, stretching away in all directions as far as you can see. After about 20 minutes, the first officer says, “We stop here.”
He unreels the antenna line, a thin aluminum wire, and the delta-wing kite sails upward. “Don’t try this at home,” says the first officer.
“Why not?”
“Static electricity can build up, even on a clear day, and reach dangerous levels. I’ve got a couple of scars to show you exactly what it can do.”
“Can’t the same thing happen here?” you ask.
“Yes,” says the first officer. “But our pressure suits are metal-coated to protect against the solar wind and the ultraviolet. That also will discharge any . . . “
At that moment a spark jumps from the kite line to the first officer’s sleeve and from his ankle to the ground. You can’t hear it because of your protective headgear and because the Martian atmosphere is so thin, but you can imagine the “Pop!” it would make back home on Earth.
“Why must you use such low frequencies?”
“Higher frequencies require an ionosphere, or else artificial satellites, to propagate over the horizon. However, very low frequency (VLF) radio waves do not, at least not on a planet that can conduct electricity to any significant extent,” says the first officer. “Mars, according to our data, should conduct well enough to allow VLF waves to travel all the way around the planet.” He pulls out a sheet of paper from the pocket of his pressure suit and hands it to you. “Please see Fig. 6-6.”
Figure 6-6. Low-frequency radio waves might allow over-the-horizon communications between exploration parties on planets that have no ionosphere, such as Mars.
“Interesting,” you say. “Primitive but interesting.”
“This MUV rolls on wheels, and they are more primitive than this antenna.”
“That’s a good point,” you say.
“That’s high enough,” says the first officer. The kite is now a tiny triangle against the sky, almost straight overhead. “Two and a half kilometers up.”
The radio tests are conducted. The radio itself is a small, battery-powered box with an old-fashioned telegraph key. The first officer taps on the key, then listens, then taps some more, then listens some more.
“Well?” you ask.
“Negative,” he says.”
“Is it supposed to work?”
“In theory, yes, if we have enough transmitter power and a long enough antenna.”
“Has anyone ever done this before?” you ask.
“Not successfully,” says the first officer. “Not from such a vast distance.”
“Why can’t you use communications satellites? Why this old-fashioned stuff?”
“We can use satellites once they are up and working. This is only an experiment. If we can ever get this type of communications system to work, explorers to the moons of the outer planets and someday to worlds beyond our Solar System might use it for communication before any satellites are launched.”
The first officer spends the next 2 hours verifying that the people on the opposite side of the planet actually have been testing their radio, then testing some more, and even trying a couple of different frequencies. All the results are negative.
The Sun is near the zenith in a sky that has become a uniform pinkish orange when the first officer says, “Time to pack up and head on back to the Eagle. We’ll be taking off early. There’s no time to lose.”
“What’s the hurry?” you ask.
“Do you see all the dust in the sky?”
“Yes. Isn’t that normal?”
“No. We have reports from the Valiant, as well as from general observation stations, that a planetwide dust storm might be brewing. We must get off the surface soon, before the winds aloft get so strong that we can’t get back to the Valiant at all,” says the first officer.
“I was just starting to feel safe down here,” you say.
“My friend, we are on the planet Mars. We are millions of kilometers from Earth and within real-time communications range of only a few other human beings in the entire Universe. The pressure outside your suit is so low that you wouldn’t stay conscious for 3 minutes without it. The temperature right now is –40°C, which happens also to be –40°F. However, the wind chill is much colder. It is hard to say whether you would die of suffocation or exposure if your pressure suit failed. There are several weak links in the chain that is keeping us alive. We must be certain that not a single one of those links is allowed to break. A full-Mars storm can last for months. By the end of it, links would not only be missing, but the whole chain would be gone.”
“So this means . . .”
“It means a total change of plan. I am going to make sure we get off of this planet as soon as possible. Premature termination of mission,” says the first officer.
You ask, “Didn’t you know about the impending storm before you decided to bring us down here?”
“No. There were no signs of a storm when we left the Valiant. At least, none that we yet have the ability to detect. This storm developed suddenly.”
“It’s as if a hurricane formed out of a clear blue sky in a single day,” you say. “I’ve never heard of such a thing.”
“You speak of Earth,” says the first officer. “This is Mars.”
You ride the MUV back to the Eagle. Mars, which smiled in the morning, scowls now. The horizon has become brown as the Eagle rises from the surface. The winds begin to buffet the craft.
“Don’t crash,” you say.
“Don’t worry,” says the first officer. “I am well trained.”
Within seconds the Eagle has cleared the dust, which for now is confined to the first 200 or 300 meters above the floor of the caldera. The crater rim and the slopes of Pavonis Mons are in the clear, but the crater floor is an obscure mass, as if bathed in smog. “If the storm becomes intense enough, these dust clouds will be kicked up high into the atmosphere, possibly covering the entire mountain below us. In the extreme, the dust might obliterate all surface features, ascending several kilometers into the sky,” says the first officer.
“You say you cannot forecast the severity of the storm?” you ask.
“Weather forecasting on Mars is an inexact science, to say the least,” says the first officer. “Have you ever heard of the butterfly effect?”
“Yes, that’s the principle that deals with large, long-term consequences arising from small causes.”
“If the butterfly takes off from Olympus Mons, the storm will cover the southern hemisphere. If the butterfly takes off from Pavonis Mons, the storm will cover the northern hemisphere. However, if the butterfly takes off from the Huygens Crater, the storm will envelop the entire planet.”
“You are joking, of course,” you say.
“Of course,” says the first officer. “But the principle is clear, isn’t it?”
“Yes, but there is one flaw in that theory.”
“There are no butterflies on Mars.”
“I know what you mean anyway.”
“The butterfly effect is the reason we have no way of knowing for certain how extensive this particular storm will be. Martian weather, it seems, is more sensitive than Earth weather.”
“Maybe the whole Martian ecosystem, such as it is, is more sensitive than that of the Earth,” you say.
“We don’t know until we test it. There are people back home who want to try to change the climate of Mars. Make a new world out of it. Try to get plants, or at least some sort of lichens, to grow. Maybe even try mold spores, bacteria, viruses. Anything. Anything that might change this planet into a world that humans can exploit,” says the first officer.
“Do you think humanity will ever make a livable planet out of Mars?”
“I don’t know.”
“That’s not a scientific answer,” you say.
“I prefer to let certain mysteries remain mysteries,” says the first officer. “I don’t think we humans are ready to make a planet of our own.”
“Time will tell,” you say.
“Time always tells,” says the first officer.
QuizRefer to the text if necessary. A good score is 8 correct. Answers are in the back of the book.
1. If the Martian day were divided into 24 hours of equal length, then one Mars hour would be approximately how long?
(a) A little shorter than an Earth hour
(b) Exactly the same as an Earth hour
(c) A little longer than an Earth hour
(d) Variable, depending on the time of year
2. The mean orbital radius of Mars is
(a) about two-thirds that of Earth.
(b) about the same as that of Earth.
(c) about 1.5 times that of Earth.
(d) about twice that of Earth.
3. Suppose that an object has a weight of 50 pounds on Mars. On Earth it would weigh approximately
(a) 18 pounds.
(b) 37 pounds.
(c) 74 pounds.
(d) 135 pounds.
4. Phobos appears to traverse the Martian sky from west to east because
(a) Phobos’ orbital period is less than Mars’ rotational period.
(b) Phobos’ orbital period is greater than Mars’ rotational period.
(c) Phobos’ orbit is retrograde.
(d) That’s not true! Phobos traverses the Martian sky from east to west.
5. In terms of size, Mars is
(a) larger than the Moon but smaller than Mercury.
(b) larger than Mercury but smaller than Earth.
(c) larger than Venus but smaller than Earth.
(d) larger than Earth.
6. With respect to its orbit around the Sun, the equatorial plane of Mars is
(a) on a level.
(b) tilted about 24 degrees.
(c) tilted about 45 degrees.
(d) tilted about 90 degrees.
7. The smaller of the two Martian moons is called
(a) Deimos.
(b) Phobos.
(c) Olympus Mons.
(d) Pavonis Mons.
8. Suppose that you stand at the Martian equator when the planet’s north pole is at its maximum tilt away from the Sun (that is, the Sun’s declination is the most negative). The Sun will rise
(a) directly in the east.
(b) somewhat south of east.
(c) somewhat north of east.
(d) in the west.
9. Volcanoes can build up to larger size on Mars than they can on Earth because
(a) the Martian crust does not float around in plates on the mantle the way Earth’s crust does.
(b) Mars has a more intense gravitational field than does Earth.
(c) the atmosphere of Mars is thinner than that of Earth.
(d) This statement is not true! Volcanoes on Mars never get as big as the volcanoes on Earth.
10. Mars appears as a crescent through a small telescope as viewed from Earth
(a) when it is near inferior conjunction.
(b) when it is near superior conjunction.
(c) when it is near opposition.
(d) at no time.
