Happy Anniversary, Voyager I

This September marks a special sort of birthday. It’s the 40th anniversary of the launching of Voyager 1.

Voyager 1 is a probe built by NASA, launched on September 5, 1977 to study the outer Solar System. Its primary mission was to study Jupiter, Saturn, and their various moons. Having accomplished this, the probe is now winding down its secondary mission, which is to study the distant regions beyond the planets before it loses power and becomes destined to drift through the galaxy as a mute, lonely messenger until the end of time.

It may seem odd to celebrate the anniversary of a machine, but think of what this amazing invention has accomplished. Currently, Voyager 1 is over twelve billion miles away from Earth. No man- made object has ever gone so far. In fact, Voyager is the only man-made object to make it to interstellar space.

Across all that vast expanse of time and space is an equally long list of achievements. In 1979, it made a close approach by Jupiter, sending back some of the most spectacular images of the planet. Thanks to Voyager, scientists discovered the existence of active volcanoes on Io, one of Jupiter’s moons. This was a major discovery, as previously, the only known volcanoes were on Earth. From there, Voyager photographed Saturn and its moons before proceeding through the heliosphere, a bubble-like region created by solar wind. All that time, Voyager continued to record and transmit data back to Earth, helping scientists learn much about the outer limits of our Solar System.

But this letter isn’t really about Voyager. It’s about Earth.

Rewind back to February 14th, 1990. Having completed its primary mission, Carl Sagan, the famous astronomer and author, asked NASA to turn the probe’s camera around to take one last photograph of Earth and the other planets. Between February 1 and June 6, Voyager took sixty still images. Each image contained about 640,000 individual pixels, and as the probe was so far away, it took about 51⁄2 hours for each pixel to reach Earth.

The most famous of these photographs was of our home planet—now just a pale blue dot amidst the infinite blackness of space.

If you’ve ever seen this photo, you know what a stirring, thought-provoking image it is. Imagine our world, filled with life, oceans, mountains, deserts, forests and cities, reduced to nothing more than a speck. It serves to illustrate just how small we really are compared to the unceasing vastness of the Universe. But it also serves another, more powerful purpose.

These days, we know that the Milky Way galaxy isn’t empty. It’s bursting with stars, cosmic rays, solar wind, clouds of dust, asteroids, comets, and even other planets. But it contains no other life, none that we’ve found. The closest planet potentially capable of supporting life is so far distant, it would take millions—millions!—of years to get there. That’s longer than our species has even been alive.

Until further notice, we are alone.

Our pale blue dot is just one of billions in the night sky, but it is unique. We are on an island amidst a dark, silent ocean. An oasis inside the barrenness of space. A single, precious garden surrounded totally by desert.

What the pale blue dot photo really shows is that our planet is significant. It’s all we have. It shelters us, sustains us, provides for us, entertains us. If there is another world richer and more beautiful than ours, we’ve yet to find it.

Here’s how Carl Sagan put it:

The Earth is the only world known, so far, to harbor life. There is nowhere else, at least in the near future, to which our species could migrate. Visit, yes. Settle, not yet. Like it or not, for the moment, the Earth is where we make our stand. It has been said that astronomy is a humbling and character-building experience. 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.

- Carl Sagan, Pale Blue Dot: A Vision of the Human Future in Space (Ballantine Books, 1994)

So why should we celebrate Voyager’s birthday? Not just because it’s a record-setting pioneer, the first interstellar traveler we know of. Not just because of the contributions it has made to science. Not just because it will probably still be traveling the cosmos even after the Earth itself is long gone.

We celebrate it because this little probe is the ultimate example of both our ingenuity and our fragility. Because it’s a postcard from us, the people of the pale blue dot, to the rest of the galaxy.

So, happy birthday, Voyager! You’ve had a great forty years. Here’s to the eternity left to go.