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

Chapter 15 focuses on Mars, the closest planet to Earth that humans might be able to visit. As of writing, there had been only two successful US missions to Mars: Mariner 9 in 1971 and Vikings 1 and 2 in 1976. These missions, Soviet missions, and some Mars meteorites found on Earth have taught us that Mars might have held water (and its moons, Phobos and Deimos, still do). The Viking missions conducted multiple experiments on the surface looking for evidence of life: examining exchanges of gases between Mars’s soil and atmosphere, introducing organic materials to see whether something would eat or oxidize it, and introducing radioactive carbon dioxide to look for interactivity. The results were inconclusive. Mars is likely lifeless, but it still might hold the secrets of how life emerged.

The most recent high-profile mission to Mars, the Mars Observer, launched in 1992, failed just before it was to insert itself into Martian orbit. It was the culmination of a decade of work, the first US mission to Mars in 17 years, and was designed to collaborate with future Russian programs. Likely caused by a ruptured fuel tank, it was NASA’s first post-launch failure in 26 years. Sagan reflects on the success rate of missions, noting that they have failed about one-third of the time. Because planetary exploration continues to require cutting-edge technology, this failure rate is likely to continue. For this reason, Sagan makes a case for robot spacecraft over human missions and calls for unmanned missions to return to sending two probes at once. Often when one of the spacecrafts fails, the second one succeeds. This was the case for Mariner 4 after Mariner 3 failed. Mariner 9 outlasted Mariner 8. But only one Mars Observer was launched because NASA used the space shuttle instead of a Titan rocket.

Sagan indicates that future Mars missions, if they happen, will be collaborative across multiple space programs. The undertaking is too costly for one nation to take on. In 1987, Mikhail Gorbachev proposed a Soviet-United States joint mission to Mars that was turned down by the Reagan administration due to concerns about the exchange of technology. But by the early 1990s, Russia, the US, Japan, and the European Space Agency regularly worked together. Sagan then digresses to imagine, in the second person, what future Mars exploration might look like. He pictures robots on Mars controlled in real-time by humans on Earth, and virtual reality, where data collected on Mars is used to build virtual spaces that anyone can explore. He makes the case that robotics and machine intelligence have much to offer while sending humans to Mars cannot be justified by science alone.

Sagan then laments the lack of foresight in NASA’s development of technology. The Mars Observer was more expensive than it needed to be because NASA wanted to justify its investment in the space shuttle. The plans for developing an international space station are not being leveraged for its most obvious use: long-duration space flight. Multistage chemical rockets remain the primary method of propulsion at the time of writing only because NASA has already invested in their development. Sagan believes NASA would serve to better invest in other propulsion methods which would pay off in the future: single-stage rockets, airplane-assist launches, ion, nuclear, or electronic propulsion systems, and solar sails. The chapter ends with another gesture to the far future, again in the second person, when Martian and deeper planet exploration seems normal.

Chapter 16 debates the value of missions to Mars and other planetary research missions. The momentum afforded by Apollo wore off during the 1980s, and the results of the robot missions grew less inspiring as people’s priorities shifted. Space programs are confronting their legacies and deciding how to best continue what they started. President George H. W. Bush, on the twentieth anniversary of Apollo 11 (July 20, 1989), announced a plan to land humans on Mars by 2019. But the program was dead on arrival. The political purpose, with the ending of the Cold War, had lost its importance.

Sagan runs through the pros and cons of a mission to Mars. The biggest reason not to support such a mission is that there are social and infrastructure concerns on Earth that need to be dealt with. Another is that there has been little economic benefit to space exploration. There are comparatively fewer financial justifications for planetary visits than there were for explorers of Earth; there are fossil fuels to mine and drill, but that kind of investment would take generations to pay off. Even the “spinoff” innovations have been largely exaggerated; instant food, digital imaging, and cordless technologies were accelerated by Apollo, but pacemakers, Velcro, and other technologies have been misattributed. Using the “spinoff” justification only shows that the programs cannot justify themselves; there are more efficient ways of investing in applied sciences than going to Mars.

Sagan reiterates his argument that space exploration has social utility: a more cosmic perspective that alerts humans to urgent dangers to Earth, a reason for increased international cooperation, and inspiration for children to pursue STEM fields and higher education. He notes that approval ratings of NASA’s accomplishments have risen over time and that most US citizens at the time of writing are in favor of going to Mars. He argues that the more the media exposes the public to scientific ideas, inspired by space missions, the more human intellectual curiosity and optimism will improve: “The more science in the media […] the healthier, I believe, the society is” (228).

Sagan also recognizes that a human mission to Mars is a long way away. He recommends several things that space programs can do first: develop more international cooperation in space exploration; use the space station to plan and test long-duration space trips, including psychological effects; send probes to orbit the sun; improve the state of robotics and machine intelligence; figure out how to use Martian materials for fuel; invent new methods of propulsion; and explore near-Earth asteroids. Each of these avenues is cheaper than Mars missions. Sagan also argues that solving some social problems on Earth will lead to a mission to Mars: “the most important step we can take toward Mars is to make significant progress on Earth” (230).

Chapters 17 and 18 address collisions between objects in space and what humans should be doing about asteroid and comet threats to Earth. This chapter opens with a discussion of planetary rings, from Galileo’s discovery of Jupiter having “handles” to the recent Voyager discoveries of rings on Neptune and Uranus. Our Moon was likely created when an object the size of Mars collided with Earth 4.5 billion years ago. The debris either blasted into space, reformed into Earth, or became the Moon.

There are many rogue “worldlets” (objects smaller than planets) in orbit around the Sun that range from the size of dust particles to hundreds of kilometers across. Most are found in an asteroid belt between Mars and Jupiter. These worldlets are likely prevented from forming a new planet due to their proximity to Jupiter’s gravity. There are other asteroids whose orbits pass near Earth. At the time of writing, there are about 200 cataloged “near-Earth” asteroids and millions more unidentified. They are mostly small, a few kilometers or smaller, with names such as Icarus, Cerberus, and Quetzalcoatl. Some are rocky and full of metal (and might be worth mining). Some have their own moons. We continue to record the various worldlets in the solar system for Earth’s safety and because some might be worth visiting. Sagan singles out Nereus, a near-Earth asteroid that is about a kilometer across. He argues that visiting Nereus would make more sense than a mission to Mars.

Compared to asteroids, comets are made of more dust and ice than rock. Their paths are thus less susceptible to gravity. Between July 16-22, 1994, the comet Shoemaker-Levy 9 broke up in Jupiter’s gravitational field and its pieces collided with the planet. Watching the comet fragments hit Jupiter was a global event. It was also a chance for scientists to learn more about planetary collisions and a reminder that something like it can one day happen to Earth. When a comet passes Earth, pieces hit the atmosphere and look like shooting stars, but as Sagan reminds us, “there is a continuum that connects these shimmering visitors to our night skies with the destruction of worlds” (240). Scientists estimate 20% of near-Earth asteroids will eventually hit Earth, and that there are over 2,000 near-Earth asteroids that are larger than a kilometer and thus capable of doing catastrophic damage.

This chapter begins with a parable about solutions to problems that create new problems. The city of Camarina in Sicily, which drained a marsh to protect itself from diseases, then left itself open to be invaded by the Syracusans. Sagan considers this concept as he discusses what we should do about the threat of worldlets hitting Earth.

Sagan references the “cretaceous-tertiary collision,” which wiped out the dinosaurs, and suggests that even a less energetic collision could cause humanity’s extinction. An asteroid the size of the “cretaceous-tertiary collision” asteroid (over 10 km across) occurs approximately every 100 million years, but an asteroid over 2 km across, large enough to cause global catastrophe, occurs every million years. An asteroid 200 meters across, which can cause nuclear winter, occurs every 10,000 years, and every few hundred years an object about 70 meters across causes an impact the size of a nuclear weapon.

After the Shoemaker-Levy 9 impact on Jupiter, Congress began a study in coordination with space agencies around the world to catalog the rest of the near-Earth asteroids and other possible Earth-approaching objects. At the time of Sagan’s writing, the only plausible methods for stopping asteroids and comets en route to Earth are blowing them up with nuclear weapons or diverting their path with a nearby nuclear explosion. However, like the marsh of Camarina, these methods have their own concerns: new trajectories or debris might cause new collisions, the force of the explosion might change other trajectories, and the use of nuclear weapons will always be high risk if there is potential for a “madman” to rise to power. This last one, Sagan believes, would be mitigated by multinational cooperation and safeguards.

Humans will either be destroyed by a future asteroid or comet collision, destroyed by their own technology, or saved by the responsible use of that technology. Sagan is in favor of a slow study approach. Send more robot probes into the solar system and learn more before deciding. But he also notes that while most things in the book have an open timeline, dangers like global warming and asteroid or comet collision force people to act soon. For this reason, Sagan urges that humans continue pursuing space exploration—both to learn more about these worldlets and to begin diversifying humanity’s future on different planets. In the long run, Earth will need to become unified politically and learn how to move nearby worlds around. All intelligent beings in the universe, Sagan writes, must eventually choose “spaceflight or extinction” (266).