From Mercury to Venus Help

Attaining Orbit

In space there are no days and nights, except those that are produced artificially by the environmental systems on board the ship. In the living quarters of the Valiant there are no windows; the spinning of the gravity wheel would give you vertigo if you had windows to gaze from. However, there are pictures on the walls that change on a 24-hour cycle: landscapes with illumination that mimics the spectrum of the Sun on Earth’s surface. Your room has scenes of the rural Midwest. It is winter there right now, and the ship’s computer has determined that there has been plenty of snow in the last couple of weeks.

With realistic views out the “windows,” plenty of videos, music albums, a big library of books (the real, bound paper kind), an increasing workout schedule, good food, and a friendly crew, time goes fast. You wake up one morning and notice that all your “window” scenes have been reprogrammed to show the clouds of Venus swirling beneath the ship, whitish yellow, and a ruddy horizon that quickly fades away to black higher up.

“We are in an equatorial orbit,” explains the first officer over breakfast. “Our descent and flight will be along the equator, where the clouds race around the planet in four Earth days. You might notice, if you’re astute, that our orbit is retrograde.”

Venus spins contrary to all the other planets, that is, from east to west. The clouds, too, move in that direction. But what does the first officer mean by “flight”?

Shuttle Or Airplane?

The first officer will not attempt to land on Venus. “Landing craft have been devised that can survive conditions at the surface,” says the first officer, “but they are prohibitively expensive. We could never venture outside. All we could do would be sit around and peer out through thick, reinforced little portholes, like those in an undersea vessel.”

You will fly just beneath the clouds, in a hybrid shuttle/aircraft contraption reminiscent of the X-15 high-altitude craft used by the United States in the middle of the twentieth century. The upper-level winds rush along in the Venusian atmosphere at 400 kilometers (250 miles) per hour. “Venus has a huge, continuous, retrograde jet stream,” says the first officer, “and we are going to ride it once around the planet at an airspeed of 800 kilometers (500 miles) per hour.”

You do some quick calculating. Venus is about 40,000 kilometers in circumference; you will be moving at 800 + 400, or 1,200, kilometers per hour with respect to the surface. You decide to use your wrist calculator. “Calculator,” you say, “divide 40,000 kilometers by 1,200 kilometers per hour.” The little thing speaks up in its synthesized voice: “Solution: 33 hours and 20 minutes.”

You look quizzically at the first officer, who has now been joined by the captain who will wish you a happy trip.

“Don’t worry,” says the captain. “The planetary atmospheric reconnaissance vehicle (PARV) has a bathroom, a refrigerator, and a stove. Just like home.”

“There will be gravity for most of the trip,” says the first officer. During the ride beneath the clouds of Venus, during which you hope to get a good view of the surface on the sunlit side and some spectacular lightning shows on the nighttime side, you will be riding in an aircraft in a gravitational field almost of exactly the same strength as that at the surface of Earth.

“There are plenty of airsick bags,” says the first officer. “Venus can be a stormy place. I hope you didn’t eat too much for breakfast.”

A Wild Ride

The descent to the cloud tops goes smoothly, and the yellowish white barrier rises up to meet the shuttle just as you cross the twilight line into darkness. The rumble of the rocket engines fades as the first officer allows atmospheric drag to slow the aircraft down. “We won’t come through the bottom of the cloud layer until halfway through the night,” says the first officer as he sips on a glass of lemonade. “We are letting the atmosphere do all the work of slowing us down. The jet engines will start after we get under the clouds.”

The view out the windows turns from cream-colored to yellow, then orange, then rusty, then brown, and finally black. You imagine that you can hear the hiss of the sulfuric acid droplets as they eat away at the exterior of the craft, but you know this cannot actually be taking place because of the protective coatings that keep heat, radiation, and corrosion from affecting the shell of the vessel. Just as the windows have completely blacked over, you feel the first jolt.

For the next 8 hours you lie flat on your back, your seat all the way down to horizontal, strapped in tight, and try to sleep. You don’t get airsick, but you worry that something will go wrong, the craft will shake apart, and you will be sent tumbling down into hell. Then finally the violent ride becomes smooth, and you hear the whooshing sound of the jet engines, which are now propelling the craft beneath the clouds of Venus at midnight.

All around the ship, lightning flashes: yellow, blue-white, brilliant white. With each flash, you can see the ceiling of cloud deck above. You cannot yet see the planet’s surface.

“We’re 40 kilometers (25 miles) above the landscape down there,” says the first officer. “You’ll be able to see it as soon as we come back into daylight. That will be in about 8 hours.”

“How high are we going to fly?” you ask.

“We have leveled off now,” says the first officer. “This is as low as we dare go. If we went a little lower, the atmosphere would slow us down too much. Then we would lose altitude, and the drag would increase further, slowing us down still more, and we would plunge to the surface and crash.”

“That is not what I want to hear,” you say.

“Don’t worry,” says the first officer. “I am well trained.”

The Landscape Of Hades

Finally, you fall asleep. As you awaken, it is starting to grow light outside. This is a morning like none you have seen before. Above you are orange clouds, and beneath you stretches a rolling, sullen, reddish plateau advertising the fact that life cannot exist there. You know that the air pressure at the surface of Venus is as great as the pressure 1,000 meters (3,300 feet) beneath the surface of the sea, deeper than SCUBA divers ever venture. A Venus lander would have to endure pressure like a submarine, be able to fly like an airplane, take off like a rocket, and all the while endure temperatures that rise higher than the hottest day in the Caloris Basin of Mercury.

On the windows you see what looks like rain. But this is no ordinary rain; it is sulfuric acid virga , liquid that precipitates from the noxious clouds and evaporates long before it can reach the ground.

Highlands loom. “That’s the continent called Aphrodite ,” says the first officer. “Of course, it is not a continent in the same sense as those on our home planet because there is no ocean on Venus. We just call it a continent because it is one of two large regions of high land. The other is near the pole and is known as Ishtar .”

Suddenly you see a bright orange glow and then what looks like a dull flash coming from a ragged, mountainous area.

“As you can see, that is an active volcano. We are lucky to be here while it’s putting on a show. The volcanoes on Venus are something like those on the Big Island of Hawaii, with one important difference. As far as we know, the crust of Venus does not move over the volcanic hot spots the way the crust of Earth does, or if there is movement, it is much slower. The chain of the Hawaiian Islands was formed as Earth’s crust moved over a hot spot welling up from Earth’s mantle (Fig. 5-7 A ). On Venus, however, a single hot spot gets a chance to produce a volcano for a longer time (Fig. 5-7 B ).

Figure 5-7 A. On Earth, the crust drifts over a hot spot, as in this rendition of the Hawaiian Island chain.

Figure 5-7 B . On Venus, volcanoes tend to stay put over hot spots for a longer time than on Earth.

Back To The Main Ship

No sooner have you passed over the volcano, which is too far below to be cause for concern, than the first officer orders you to strap down again. “It’s time to begin our ascent,” he says. “This ought to be a smoother ride than the one on the way down; we will be using rockets all the way.” All the food and drink must be put away; seat backs and tray tables are returned to their upright and locked positions. Then the thunder of the rocket engines drowns out all other sound, and the force of acceleration pushes you back into your seat, harder and harder, with force you have not felt since you blasted off from the space center at the beginning of this voyage.

“You know,” says the first officer, “if Earth had formed a few million kilometers closer to the Sun, it would have turned out like this place. There would have been a little more carbon dioxide (CO ₂ ) in the atmosphere. That would have retained a little more solar heat, which would have increased the CO ₂ level. The result would have been a vicious circle like the one that took place here on Venus. Carbon dioxide makes up almost all the atmosphere of Venus below its clouds. As you know, CO ₂ is called a greenhouse gas because it tends to trap heat. The principle is much the same as that which keeps a greenhouse warm in winter. Short-wave infrared and visible-light rays penetrate the glass or the CO ₂ and heat up the surface. The surface, in turn, radiates long-wave infrared, but the glass or the CO ₂ is opaque to that, so instead of being reradiated into space, the long-wave infrared is absorbed and turned into heat. If this had happened on Earth, the oceans would have boiled away, the oxygen would all have been bound up with carbon, and our planet would be almost as hot and every bit as dry as this place. Of course, we would not care. We would not exist.”

“I’ve heard some people say that a runaway greenhouse disaster could occur on Earth if humans keep generating CO ₂ and cutting down forests without replenishing them,” you say. “But I don’t know what to believe. Is that really true? How critical is the balance? Are we on the verge of tipping it the wrong way?”

“No one knows exactly,” says the first officer. “There’s only one way we will ever find out for sure whether or not the danger is real, and that is for the worst to happen. I would rather not learn the truth that way. Would you?”

The landscape below melts away into a ruddy blur, the cloud ceiling seems to rush down on the craft and swallow it up, and then, having seen enough for one day, you pull down the window blind, close your eyes, and try to imagine yourself strolling through a grassy field or along a windy beach on Earth, a place that you are now beginning to realize is special indeed.

Practice problems of this concept can be found at: Mercury and Venus Practice Problems