The Evening Star and the Morning Star

Everyone has seen Venus, as a bright, starlike apparition in the evening sky, following the Sun down towards the horizon and setting a few hours later. At various other times of the year, there comes a brief season where an early bird can see Venus rise brilliantly before the Sun, climbing higher until it seems to dim and vanish as the sky brightens after sunrise. When it rises before the Sun, people have long called Venus the Morning Star; half an orbit later, when on the other side of the Sun so that the Sun sets first, Venus is the Evening Star. Before Copernicus promoted the idea that planets orbit the Sun, it was not obvious that these two phenomena were the same body, and early civilisations had distinct names for them. To the Greeks, they were Phosphoros and Hesperos.

For much of the year, Venus sets and rises so near the Sun that we tend not to notice it. During the day, like the true stars at vastly greater distances, Venus is still overhead and just as bright, of course, but it is hard to see because the contrast with the dark sky is lost when the Sun is up. It can be studied during the day if a telescope is used to shut out most of the sunlight, and even with ordinary binoculars if you know where to look. In any observations made over a period of a few months, Venus can be seen to exhibit lunarlike phases (Figure 1.1).

1. You too may be a big hero,

2. once you learn to count backwards to zero.

3. “In German or der English, I know how to count down . . .

4. Und I’m learning Chinese,” says Wernher von Braun.

Lehrer’s song criticizes von Braun’s heroic status in 1960s America despite his fickle national allegiances two decades before; the song aired when his luster in American public opinion was tarnishing (Chapter 3). The Chinese reference is biting, because, several months before, China had exploded her first atomic bomb, the fifth nation to do so, after the United States, Soviet Union, Britain, and France. (Von Braun had little problem counting but admitted before the U.S. House of Representatives having once failed physics and mathematics.) Outer space was the call drawing him down his brilliant if morally ambiguous path, not patriotic inspiration. By age 17 his interest in space flight set the course that determined his career.

Lehrer did not know how ironic his reference to Chinese would become, for two years later, on June 17, 1967, China exploded her first hydrogen bomb, 150 times more powerful than the one Lehrer knew. China took 3 years to transition from fission to fusion weapons, compared to 6 years for the United States, 4 for the Soviet Union, 5 for Britain, 9 for France, and 24 years for India. In October 1966, China launched a nuclear warhead on an intermediate-range missile, detonating it at their Lop Nor test site in Xinjiang (after lofting it over populated Chinese territory).

1. With a holy host of others standing around me

2. Still I’m on the dark side of the moon

3. And it seems like it goes on like this forever

4. You must forgive me

5. If I’m up and gone to Carolina in my mind

People seem forever confused about the Far Side versus dark side of the Moon. Let us be clear – here is an easy mnemonic: the dark side is darker, and the Far Side is farther! They are not the same except once per month, at full Moon. The Moon, like Earth (and other planets), has at any time a side pointed away from the Sun. That is the dark side.

The Moon has another effect in play; the same lunar Near Side always turns to face Earth, with the opposite side – the Far Side – turned away. This matter of physics is common to many worlds. A consequence is that almost half of the Moon’s surface remained hidden to humans until 1959, two years to the day after Sputnik 1’s launch, when the third Soviet lunar probe attempt, Luna 3, photographed the Far Side for the first time (Figure 2.1). Beforehand, that side had been an abyss to human knowledge, more unknown to us than distant reaches of the Universe, and a place where one might peer into space and never see Earth. This sense of isolation James Taylor invokes with the “dark side.”

Choosing the way forward

When Venus Express arrived in April 2006 it became the 25th mission to target Venus successfully. With Japan’s Akatsuki, four spacefaring nations are now engaged in exploring Venus, and the data garnered have painted a vivid and comprehensive picture of what hitherto had been a mysterious, cloud-shrouded world. No seas, swamps or rainforests and no dinosaurs or Treens, but a hot volcanic wasteland with permanent hurricanes and searing acid clouds.

There were, and still are, plenty of puzzles to solve concerning the nature of the surface and interior, and the behaviour of the thick atmosphere. More missions must follow. But what, how and when? The scientists, engineers, managers and politicians who will answer these questions and write the next chapter in Venus exploration cannot consider Venus as a solitary objective. The agencies face huge internal and external competition for resources, and must target the highest priorities if they are to satisfy their own scientific communities, not to mention their government paymasters. Often this means leaving lower priority destinations unprobed for long periods, as has already happened with Venus during the years from 1994, when Magellan shut down, to 2006, when Venus Express commenced operations. So what happens next at Venus depends not only on goals and priorities for that planet, but on where the excitement lies elsewhere in the Solar System and beyond, and where Venus fits in with the rest of the international planetary programme.

Earth-based spectroscopic studies of Venus flourished for a while as planetary astronomers exploited the newly discovered infrared windows. In particular, when these were combined with the data from the earlier space missions, a more complete picture of the atmospheric environment on Venus began to appear.

The success of the telescopic observers served to emphasise the strong argument for taking the powerful technique of spectral imaging in the ‘windows’ to Venus on the close and versatile platform offered by a spacecraft. As we have seen, none of the Mariner or Venera spacecraft had this capability, and we Pioneer Venus investigators naïvely failed to make and exploit a major discovery by not using its near-infrared capability on the nightside to detect the emission from the deep atmosphere.

By 1989, NASA was preparing the Galileo Jupiter orbiter spacecraft for launch. Galileo was to reach Jupiter by means of close flybys of Venus and Earth, and would reach Venus in February 1990 (Figure 7.1). As it happened, the Jupiter orbiter carried an instrument perfectly suited for observing Venus, the Near Infrared Mapping Spectrometer (NIMS). Those of us on the Galileo team who were also interested in Venus science quickly calculated that NIMS could achieve a spatial resolution on Earth’s neighbour that was far better than the Earth-based near-infrared images. Also, it had a spectral range that overed all of the known and predicted windows.

With these words, Armstrong concluded the competition that had gripped the world for years between the two most powerful nations – the United States and the Soviet Union – on Earth and now the Moon. Six and a half hours earlier, he and Edwin “Buzz” Aldrin set their 8-ton spacecraft carefully onto the lunar surface with fewer than 45 seconds of fuel left, fulfilling a promise made eight years before by their martyred president. Stepping onto the Moon, they reached the apex of a perilous journey that in several days would fulfill the president’s second promise – to return them safely to Earth. Their success engaged the work of hundreds of thousands of people and the attentions of billions of people. It was a cosmic and geopolitical culmination that, with the following lunar landings, bears on any future human exploration of space, as we will see.

Armstrong had much on his mind, but his terseness also reflected his characteristic lack of self-absorption. [BOX 2.1] He was selected in part for his steely, split-second ability to make the right choice concerning balky, expensive, and complex flying machines. He had made the right choices in combat, as a test pilot, in Earth’s orbit, in training for lunar landing, and in the landing that day at Tranquility Base, or else he would not have lived to step onto the Moon. He was not easily distracted from the mission. [BOX 2.2]

Venus is well known to everyone as the brightest star in the evening or morning sky. Of course, this brilliant stellar object is not actually a star, but a planet, the closest to Earth and, it turns out, the one that most resembles our own world in size and composition. It should therefore be the easiest to explore by astronomers observing fromthe Earth with telescopes, and indeed there is a history of Venus observations that extends back to the earliest recorded times. However, as observations got better with the invention and improvement of the telescope, the result was often frustration because so little detail could be seen on our bright neighbour. Instead it was found that the surface is shrouded, apparently at all times and at all places, by thick layers of nearly featureless cloud. It was not until the first spacecraft arrived, just half a century ago, that the true character of Venus began to be revealed.

This book presents an account of the exploration of Venus, from the earliest days to the latest research using planetary space missions. It also ventures some visions of the distant future when Venus is explored by humans, and might once again have an Earthlike climate (if indeed it once did in the past, as many scientists believe). The space projects and other types of investigation are covered in some detail, especially their scientific objectives and accomplishments.

Despite Ambrose Bierce’s sardonic treatment, the real Professor Simon Newcomb did not think much of possible lunarians. Newcomb was Bierce’s elder contemporary, a foremost American astronomer (founding president of the American Astronomical Society) and noted author on lunar motion. In 1870 he visited Europe and found a theory running rampant allowing for possibly habitable conditions on the Far Side of the Moon. He effectively crushed it.

In 1824 Franz von Paula Gruithuisen published observations of what he saw as buildings, streets, and other structures of a massive city in jumbled terrain north of crater Schröter (Figure 11.1). Despite his campaign to show other scientists these structures, few were convinced. Gruithuisen wrote more about the Moon; he is credited with first realizing that lunar craters formed largely via impacts with other objects orbiting the Sun, more than a century before Eugene Shoemaker showed it.

The main achievement of the Mariner flybys and the Venera landings that took place between 1963 and 1983 was to show us the general nature of the Venus atmosphere and surface for the first time. Like all good experiments, they posed almost as many new questions as they answered. They therefore stoked controversy when it came to the interpretation of what clearly are very complicated, time-dependent phenomena, such as global circulation and weather in the atmosphere, and erosion and volcanism on the surface.

Spacecraft that fly quickly past the planet, and probes that descend rapidly through the atmosphere to die soon after on the surface, are the simplest missions to implement and are great for an initial exploration. However, to really understand what is going on, on a complex world, better coverage in space and time is needed than is obtained by a few scans across the planet or one vertical profile in the atmosphere. The second phase of Venus exploration would therefore require coordinated measurements from planet-circling orbiters for mapping and monitoring of the global atmosphere and surface, and of the near-space environment filled with neutral and charged particles and magnetic and electric fields. Ideally, these would be complemented by large numbers of simultaneous probes at different longitudes and times of day and night.

In the mid-1980s, Venus exploration by spacecraft received a big boost from what seemed at the time a rather unlikely source: Earth-based telescopes in observatories on mountaintops. This was unexpected because the key discoveries that could be made from 50 million miles away, with our atmosphere in the way, were thought by most of us to be essentially in the past. Close-in polar orbiters, entry probes and landers ruled almost everyone’s thoughts – those who thought about Venus at all – as the twentieth century moved towards a close. The ground-based observers were, in any case, more preoccupied with distant galaxies and cosmology, and nowadays are generally reluctant to devote expensive telescope time to poking around in what they see as their own backyard. Also, of course, there was the usual endless rivalry for funds between planetary and deep-space astrophysicists, and between space scientists and traditional astronomers, to be taken into account.

The breakthrough happened in Australia. Astronomers at the Anglo-Australian telescope in New South Wales had developed a new near-infrared imaging spectrometer optimised for imaging extended objects such as star formation clusters and the nearby planets of the Solar System. Venus was prominent in the sky, with a bright crescent showing and most of the disc dark, when the observers turned the big 3.9-metre aperture telescope in its direction in June 1983. Examining the data, they were surprised to find that the nightside was not in fact dark everywhere in the near infrared spectrum, but instead ghostly bright features were present at a few wavelengths just longer than visible light (Figure 6.1).

1. “The moon is backing away from us

2. an inch and a half each year. That means

3. if you’re like me and were born

4. around fifty years ago the moon

5. was a full six feet closer to the earth.

6. What’s a person supposed to do?

7. I feel the gray cloud of consternation

8. travel across my face. I begin thinking

9. about the moon-lit past, how if you go back

10. far enough you can imagine the breathtaking

11. hugeness of the moon, prehistoric

12. solar eclipses when the moon covered the sun

13. so completely there was no corona, only

14. a darkness we had no word for”

15. – Dorianne Laux, 2004, “Facts About the Moon”

Mythology in most traditional cultures tells of the Moon’s birth. It seems appropriate that, of all creation’s elements, the Moon was born from the Hindu primal entity’s mind. Of all scientific accounts of creation of major extraterrestrial Solar System bodies, the Moon’s has most generated debate, and still does. Foremost physicists attacked the problem, and it has orbited basic scientific questions such as Earth’s age and how the Sun and stars generate energy. The effect of the Moon’s birth on Earth was so profound and unbelievably violent that it took time to accept it. Before Apollo, understanding the Moon’s birth was largely a mental exercise, starved for data, while stellar or galactic astrophysics progressed via remote telescopic and spectroscopic observations. Now we ask how much our understanding of the Moon’s origin is complete and correct.

Setting aside the Sun and the Moon, Venus is the brightest and the prettiest object in the sky. It is the closest planet, and the most Earthlike in size and structure. It has a thick atmosphere, and a serious case of greenhouse warming that resembles in many details the process threatening to cause serious global change on Earth. The surface has mountains, rivers and seabeds, but no water. The atmosphere contains familiar gases, nitrogen, carbon dioxide, water vapour.

As humankind gets more and more technically proficient, we explore Venus in greater detail and we learn much about our origins and the history of the Solar System that we inhabit. We will fly to Venus in person eventually, first to fly around the planet and return, then to orbit, and then to float in the Earthlike conditions near the cloud tops. Wemay even descend to the surface, in bathysphere-type craft with some advanced system of thermal control and a strong hull. Finally, we may become so godlike that we restore Venus to its earlier, more Earthlike state and move in there. There is nowhere else that seriously offers that possibility, not even Mars, until we reach the stars and their planets.

Let us begin with a thought experiment. Had Venus and Earth been swapped at birth – that is, at the time when they had accumulated virtually all of their present mass but before their atmospheres were fully evolved – what would the inner Solar System look like today? In this thought experiment, Venus is now at Earth’s distance from the Sun, and Earth 30 per cent closer than it was. Venus still rotates slowly and has any bulk compositional differences it acquired by forming at the closer position to the centre of the protosolar cloud, or as a result of any random processes that actually happened when planetesimals were combining to form the planets.

Currently, theories of the formation of the Solar System would have the gases in the protosolar cloud dissipate into space, and the atmospheres of Earth and Venus form later, mostly from gases that exhaled from their interiors. This would not have changed in their new positions, and in any case we believe at present that the gases that were supplied to the atmospheres of both planets were roughly the same. The motions of the planetesimals within the accretion zone jumbled the condensed and trapped volatiles that would later form the atmospheres of each planet. If Earth and Venus were truly identical in composition at the outset then presumably the result of swopping orbits over 4 billion years ago would be to produce much the same result as we have today.

The first European mission to Venus had its origins in a Russian mission to Mars.

In 1996, a huge payload lifted off from Baikonur Cosmodrome, bound for the red planet, consisting of an orbiter, two ‘surface stations’ destined for a soft landing, and two penetrators which would impact the surface at high speed in order to burrow to a considerable depth and make measurements of the subsurface material. On board the orbiter was a number of scientific experiments built by European, mainly French, scientists who were collaborating with their Russian colleagues to explore the surface and atmosphere of Mars.

The launch on 14 November 1996 went well at first, but then everything was lost. The third stage of the booster was supposed to burn twice, once to achieve a temporary orbit around Earth and then again to align the trajectory towards Mars. The second burn failed and the scientific payload, over 6 tons of it, plummeted back to Earth.

The political situation in the eastern bloc was, by then, such that there was no prospect of rebuilding the mission and trying again. Instead, the Europeans looked into a project of their own which would use a smaller satellite to carry duplicates of the instruments they had built for the Russian mission. This could get to Mars in 2003; Mars Express was born.

The Moon, planets, and stars beckon as vast expanses of territory and potential experience and understanding beyond us. To experience it, you need to reach out. It is unlike anything you have done, and not what you evolved to do. It is true wilderness, not with predators (that we know of), but many perils. Mainly, it is oblivious. First, you must escape the clutch of the mother planet that bore you. Whether humans choose to surmount this challenge says as much about humanness as outer space. Do we choose to go? The good news is that we may have more than one chance to ascend this height. The bad news is that this may cause us to procrastinate. What is the imperative? Do we have so much time?