Pale Blue Dot: A Vision of the Human Future in Space

The eleventh chapter continues the topic of non-Earth atmospheres by discussing Venus. Like earlier chapters, Sagan first introduces Venus as it would have appeared to the first humans: the brightest star in the night sky and the closest planet to Earth. Even with the naked eye, it has a yellowish color. It has been our sister world, and it has almost the same mass, size, and density as Earth. Astronomers identified that Venus was covered in sulfuric acid clouds as soon as they had telescopes to see it. However, in the 1960s, nobody had seen the surface of the planet.

Sagan then introduces the Mariner 1 and Mariner 2 missions. Launched in 1962, Mariner 2 made many of the important first readings of Venus. It was the first successful planetary probe and thus “the ship that ushered in the age of planetary exploration” (147). After an aside in which Sagan explains that he had tried to convince NASA to include cameras on the Mariner spacecraft—and makes an argument for photography as a scientific tool—he admits that cameras would not have been able to see past the cloud layer because Venus is always overcast. Even using infrared, as Sagan and a team tried at the University of Texas in 1970, they still couldn’t penetrate the clouds of Venus. It was the Galileo spacecraft that first was able to get imaging of Venus’s great mountain ranges (using a more powerful range of infrared imaging). Then the Pioneer 12, the Soviet Venera 15, and the Magellan inserted radar telescopes into orbit around Venus.

One of the earliest breakthroughs in the study of Venus occurred in 1956. Radio telescopes discovered that Venus was emitting radio waves commensurate with a surface temperature of over 300 degrees Celsius, which was much hotter than its clouds. The extreme heat was possibly a misreading caused by highly charged particles in the clouds, a hypothetical and very intense Venusian magnetic field. However, Sagan hypothesized (correctly) that the heat was real and the result of a greenhouse effect. Only in 1967 was it confirmed that the surface of Venus was even hotter than expected, over 400 degrees Celsius. That year, the Soviet Venera 4 mission dropped a probe into Venus’s clouds, and Mariner 5 flew by Venus, both confirming the hot surface. The hope that our nearest planet might be hospitable to human visitors was dashed.

The twelfth chapter moves from the atmosphere to the surface of planets. The chapter opens with a description of volcanos in the second person, inviting readers to a volcano’s rim to appreciate its primordial power. Sagan runs through several significant eruptions in human history: the Santorini volcano in 1623 BC that originated the Atlantis myth, the destruction of Pompeii by Mount Vesuvius in the first century, the “year without summer” in 1815-1816 after the eruption of Mount Tambora in Indonesia, and the deadly recent eruptions of Mount Pelee (1902) and Nevado del Ruiz (1985). Volcanos have the power to destroy cities, poison the air, cool the climate, and thin the ozone layer.

The chapter then describes what a volcano is scientifically: a hole in the surface of a planet where molten rock beneath the surface can escape. Every planet has a different internal temperature based on radioactive elements and the residual energy of its formation. Most planets go through periods of intense geological activity as they are being formed or reformed. In most cases, we can only see evidence of their aftermath. When humans only had telescopes to examine the Moon, some people believed the craters might have once been volcanos, but we now know, after studying samples of moon craters, that they are almost all impact craters. The Moon’s volcanic life ended billions of years ago. In 1971, NASA’s Mariner 9 arrived in orbit around Mars. After a sandstorm passed, it identified four giant volcanos. One of them, Olympus Mons, is the largest volcano in the solar system, three times taller than Mount Everest and 100 times bigger than Earth’s largest volcano, Mauna Loa in Hawaii. Olympus Mons and many of the volcanos on Mars are relatively young, suggesting that Mars might have once had a denser atmosphere.

In 1990-1993, the Magellan mission discovered that Venus is covered in volcanic activity. There is more diversity of volcanic formations on Venus than anywhere else. Most notable are rivers of lava longer than the longest rivers on earth, something scientists at the time of Sagan’s writing could not explain. In the last 500 million years, Venus’s surface has cooled down.

In 1979, when Voyager 1 passed Jupiter’s moon Io, the entire moon was covered in volcanos, many active at the same time. One, called Mount Pele, was active as Voyager 1 passed but had stopped by the time Voyager 2 passed, four months later. Io is unique because the molten rock differs in chemical makeup for many of the volcanos, leading to differently colored lava: sulfuric yellows, for instance. Unlike the Moon or Mars, Io’s surface is still changing. Exploring volcanic activity on Io would help us to better understand the volcanos on Earth.

Chapter 13 again starts in the second person. This time “you” are at home watching Apollo 11 on television. Sagan notes that the Apollo program was the result of difficult, routine work, but also declares that its effect on the viewer far surpassed its technical feat: “you could glimpse that we humans had entered the realm of myth and legend” (164). To clarify, Sagan turns back to early humankind. He talks about the many meanings of the Moon in human history and how it has affected our language from “lunatic” to “menstruation.” He explains that, for many centuries, “the Moon was a metaphor for the unattainable” (165) but that, after 1969, “the Moon is no longer unattainable” (166). Everyone watching the Moon landing on TV shared a moment when the Moon changed from a symbol to a place.

Sagan posits a question: “What was Apollo really about?” (166). Humans went back to the Moon several times but never again after 1972. In fact, at the time of Sagan’s writing, no humans left orbit since 1972. Sagan wonders aloud what happened to human space travel. When John F. Kennedy announced, in 1961, that Americans would land on the Moon, no American had achieved orbit. Young Sagan, watching that speech as a newly minted PhD, found the mission described by President Kennedy—to send humans to the Moon and back—to be strange. It was more gesture than science.

The decision to go to the Moon was political and military. The Soviet Union had achieved more in space than the United States, and President Kennedy wanted to take the lead in the space race. Furthermore, much of the technology used for space exploration could be adapted to war. Sagan writes that reaching the Moon implied “demonstrating rocket potency” (168). The Apollo missions led to scientific discovery, but political and military considerations drove the program. The final mission to the Moon, Apollo 17, was the first with a scientist onboard.

Whatever the motives, the Apollo program was a success. Beyond the fact that astronauts returned with valuable samples, the dream of planetary exploration had a new symbol. Without the momentum provided by Apollo, it is unlikely that there would be any more Mariner missions, any Vikings, Pioneers, Voyagers, Galileo, Magellan, or Cassini. Apollo captured the imagination of the world. It inspired optimism about technology and enthusiasm for the future. Sagan’s final thought is that humanity needs something like it again.