The Interstellar Age (29 page)

Finally, after the successful August 1989 flyby of Neptune and the completion of the playback of all the imaging data taken during approach, flyby, and departure, Sagan and others once again raised the issue of trying for the solar-system portrait. While
Voyager 2
had been diverted southward after gracefully arcing over the north pole of Neptune, it was still relatively close to the ecliptic.
Voyager 1
, now more than 30 degrees above the plane of the solar system and still climbing, had the superior view. In late 1989 the idea was pitched again, but once again it was put off while additional calibrations were performed on the cameras to make sure that the Neptune images, especially, could be properly analyzed. It seemed a prudent precaution, and so Sagan and the other advocates waited some more.

The possibility came to a head after the Neptune flyby, though, when it was revealed that because of impending budget cuts to the
Voyager
program, many of the technicians who were responsible for the commanding of the cameras and the pointing of the spacecraft were to be laid off or transferred to other jobs almost immediately.
These people’s skills would be needed to plan, acquire, and process the portrait—which had to happen soon if it were going to happen at all. An internal debate began within NASA over whether the cash-strapped
Voyager
project could afford to spend time and effort on what some people apparently regarded as a superfluous stunt. In the minds of some of the leaders of the planetary exploration program at JPL and NASA headquarters at the time, not only was there no science value in these images, the attempt would be yet another distraction as the project was winding down its staffing and preparing for the long interstellar phase of the mission.

This kind of attitude was far from uncommon in the leadership of NASA at the time. So-called education and public outreach activities like Sagan’s solar-system portrait were not regarded as worthy of inclusion on planetary-exploration mission budgets. The attitude was pervasive across much of science in the ’70s and ’80s and was part of the reason that Carl Sagan had been denied membership in the National Academy of Sciences. Much of his work was regarded by his peers, especially members of the Academy, as “soft” science—communications and education-related or even (as I can imagine in the minds of some of his more jealous peers) grandstanding.

Times have changed. NASA and National Science Foundation proposals for funding the research programs of individual scientists now
must
demonstrate how we will communicate and disseminate our results to the general public, and in what specific ways our work has general relevance and importance to our society.

Fortunately, after the Neptune encounter, top NASA officials such as Associate Administrator for Science Len Fisk and Administrator Richard Truly shared Carl Sagan’s vision of the historic,
aesthetic value of the solar-system family portrait. Ed Stone was also a strong supporter of the idea. He recalls a dinner at Caltech organized by Sagan and The Planetary Society just before the
Voyager
Neptune flyby in 1989, during which he, Sagan, Fisk, and
Voyager
Project Manager Norm Haynes talked about what it would take to make “the picture of the century” happen. By this point in time it was essentially a budgetary issue, as
Voyager
’s funding was set to ramp down steeply right after Neptune. Happily, Fisk and Truly interceded to make sure the people and resources were made available for this one last
Voyager
mosaic, which was taken on February 14, Valentine’s Day, 1990.

Voyager
imaging team liaison Candy Hansen was involved in the planning of the mosaic, and she recalls that even after the NASA HQ directive, there was lingering disdain from some of the project leadership. “Some of the science management was doing the equivalent of holding their noses,” she recounted to me, “and so at our sequence kickoff meeting they made me—essentially acting as a sequence engineer—make the presentation, rather than the usual process of asking a science team lead. But that was my chance to take the podium and sermonize about what a fabulous opportunity this was and how profound the images would be—hah!” Ed’s and Candy’s support and Carl Sagan’s enthusiasm made a difference, and with the blessing of NASA’s top brass, they made it happen.

Even twenty-five years later the resulting mosaic is mesmerizing. Starting out at Neptune and working its way inward in case the cameras got damaged,
Voyager
was commanded to snap photos of one planet after another. When the camera was pointed toward the sun to try to photograph the inner planets Mercury through Mars—all bunched up close to the blinding glare of our parent star—there
was some saturation of the images, but the camera was not fried. “In order to minimize the glare from the sun while trying to image the inner planets,” Randii Wessen told me, “
Voyager 1
was commanded in such a way that its high-gain antenna blocked some of the glare for the cameras—like a person at the beach, placing their hand in front of their face to block the sun.” It was Candy Hansen’s job to look through the images as they came in, to make sure that everything had gone OK with the observation. Just like Rich Terrile, by this point in the mission, she knew in great detail what stars look like in
Voyager
images, and she also knew every little artifact and blemish of the
Voyager
cameras by heart. So even though the photos were mostly empty black space, she was still able to quickly zoom in and isolate the stars and the blemishes from . . . something else. “Found Neptune—check. Saturn—check. No Mars—as expected, the crescent view would be too dim,” she recollects, remembering her first views of the solar-system portrait images. “I finally got to the photo that was pointed at the Earth. At first I couldn’t find it—there was a lot of scattered light in the image—but then I spotted it, in a ray of that scattered light.” It turned out that one swath of yellowish scattered sunlight had passed right through
Voyager
’s photo of the Earth.

Our world was “
a pale blue dot . . . a mote of dust suspended in a sunbeam,” Carl Sagan poetically intoned. “As I am sitting here recalling that experience,” Candy wrote to me, “there are chills going down my spine, just like that day when I saw our little planet from a vantage point so far away.”

Once again the citizens of Planet Earth, then numbering about 5 billion, bore witness to the next great paradigm-shifting change in perspective. This time it was not just off-world, not from just beyond
our backyard, but a vista from
out there
, looking down from near the edge of the sun’s realm to behold the entire solar system. As was his way, Sagan challenged and inspired us to internalize this new perspective, and to use it to guide our paths forward. “
It has been said that astronomy is a humbling and character-building experience,” he wrote. “There is perhaps no better demonstration of the folly of human conceits than this distant image of our tiny world. To me, it underscores our responsibility to deal more kindly with one another, and to preserve and cherish the pale blue dot, the only home we’ve ever known.”

The powerful message and literal imagery of
Voyager
’s
Pale Blue Dot
photo led to a string of
selfies by subsequent planetary exploration missions. Many of the people who have gone on to become leaders in NASA’s robotic planetary exploration missions were either trained by, worked with, or became disciples of Carl Sagan, and as such they are the kind of people who understand the enormous symbolic, inspirational, and educational value of photographing our home world from space. Some of my favorite planetary selfies include hypnotizing movies of the Earth spinning gracefully on its axis while the
Galileo
and
MESSENGER
spacecraft made their gravity-assist flybys of our planet on their way to Jupiter and Mercury, respectively; a glorious HD movie of a full Earth rising over the horizon of the moon from the Japanese
Kaguya
lunar orbiter; and absolutely stunning photos of our distant, faint planet nestled against the rings of Saturn, taken while the
Cassini
orbiter was passing through Saturn’s shadow.

For the most recent one of these spectacular
Cassini
photos, NASA and the
Cassini
imaging team asked people to go outside at a particular time of day (or night) on July 19, 2013, look up, and smile
and wave as the
Cassini
camera, from nearly a billion miles away, took an image of the (now) 7 billion of us all crammed into a single pixel.
Cassini
imaging team leader Carolyn Porco, who worked with Sagan on the
Voyager
imaging team, wrote on her Facebook page, “
After much work, the mosaic that marks that moment the inhabitants of Earth looked up and smiled at the sheer joy of being alive is finally here. In its combination of beauty and meaning, it is perhaps the most unusual image ever taken in the history of the space program.”

There are many more spacecraft self-portraits of our home world—it seems like we can’t stop wanting to look at ourselves from new perspectives. My favorite is one that I played a role in helping to take (I guess selfies are like that). I count myself among Carl Sagan’s disciples, having been influenced at an early age by his
Cosmos
TV show, his books and magazine articles, and by the immense good fortune of getting to be a colleague of his for a short time at Cornell University. When I had the chance to help lead a robotic planetary-imaging investigation of my own as the lead scientist for the Pancam color stereo cameras on the Mars exploration rovers
Spirit
and
Opportunity
, I was looking for chances to take photographs that would capture some of the same aesthetic, artistic, and
inspirational appeal as the
Pale Blue Dot
. Happily, my friend and rover team leader Steve Squyres, another Sagan disciple, was a kindred spirit.

One such chance came in March 2004. Both
Spirit
and
Opportunity
are solar-powered, meaning that the power available to drive or take pictures is often dictated by the amount of dust in the atmosphere or by whether the solar panels are dusty or clean. Rover team colleagues Mark Lemmon, Mike Wolff, and I were all originally trained as astronomers, and so we’d been looking for ways to take
some astronomical photographs—that is, of stars or other celestial objects, with the rover cameras. About 63 Martian days or “sols” into
Spirit
’s mission in Gusev Crater, we found ourselves with an abundance of solar power, and thus able to power the rover and camera heaters that would let us take images in the extra-frigid twilight hours before sunrise or after sunset. We knew that Earth was a “morning star” as viewed from Mars at that time (just like Venus and Mercury are sometimes visible as “stars” during twilight from Earth), and we had the power—could we spot ourselves in the Martian sky? Twilight is bright because of all the high-altitude dust in Mars’s atmosphere, so we weren’t sure if we would be able to see the Earth against the five a.m. predawn sky.
But the next day when the images were beamed back—voilà, there we were! We’d taken the first photo of our home world from the surface of another planet.

We one-upped our feat by taking the first Earthrise
movie
from the surface of another planet in late 2005, using the cameras on the
Opportunity
rover to snap the Earth and Jupiter rising gracefully in the predawn sky above the dunes of Meridiani Planum. We’d worked up valid scientific justifications for taking all these Earthrise photos—for example, the need to measure the thickness of dust or water ice clouds/fog in the early-morning Mars atmosphere. But in the end, for me, it was just the sheer thrill of being able to look up, to glance back—like the
Voyagers
—to take a historic and introspective photo from a rare perspective, and to ponder what it means to explore a world where
we
are the aliens, experiencing it vicariously through the eyes of a
robot.

9

The Edge of Interstellar Space

W
HERE DOES THE
solar system end? When I was in grade school, there were nine planets, and once you got out to Pluto, that was it. For science fair one year I spray-painted the inside of a box black, speckled it with white paint for stars, tipped it on its side, taped a drawing of the sun on one end, poked nine holes in the top, and hung cutouts of the planets from pieces of yarn. Solar system in a box! Scientists back then didn’t know a whole lot more.

The
Voyagers
and other robotic missions since have revealed the incredible diversity of worlds within our solar system, including what are essentially mini solar systems around Jupiter and Saturn. Some moons, like Ganymede and Titan, are larger than the planet Mercury. Those moons, plus Europa and Enceladus and others, may harbor subsurface oceans. Earth is not the most volcanically active
place in the solar system—Io is. Some large asteroids, such as Vesta and Ceres, appear to have had geologic histories as active as any planet’s. And—among the most surprising discoveries—the solar system does not end at Pluto. Starting in 1992, astronomers have been discovering more and more relatively large, Pluto-sized planetary bodies lurking in the Kuiper Belt beyond Neptune. Almost 1,300 KBOs are now known, and the census is far from complete. The largest one yet found is called Eris, and it’s a planetary body almost 1,500 miles wide (larger than Pluto, and about one-quarter of the mass of the Earth) with a moon of its own, called Dysnomia. Eris orbits, on average, almost twice as far from the sun as Pluto—the solar system doubled in size again when Eris was discovered in 2005. Astronomers estimate that there could be 100,000 or more KBOs larger than a hundred miles or so across, and perhaps hundreds of millions of them that are more comet-sized, only a few miles across.