Dear Kepler: How you wrung worlds from the cosmos and changed my life
- Ten years after the telescope's launch, a journalist reflects on how it shaped her personally even as it revolutionized how we see the universe.
Ten years ago, you soared into space and slipped beyond Earth's gravitational grasp, leaving a wake of fire in Florida's nighttime sky. Twinkling above you were the stars you would mine for alien worlds. Below you spun a world on the verge of a scientific revolution.
You, Kepler, are one of the most transformative spacecraft humans have ever made. But you're gone now, and though we've both known for a few years that the end of your star-studded journey was drawing near, it still feels wrong.
For much of your time aloft, you seemed invincible: a planet-hunting probe that bravely competed in the cosmos’s most challenging staring contest, in which your unblinking eye caught the flickering light from hundreds of thousands of stars. In doing so, you not only revealed that our galaxy is stuffed with planets—you helped me connect with who I am.
One variable in this “Drake equation” is the fraction of stars that have planets; another is the average number of habitable worlds in a given stellar system. When my dad wrote it nearly six decades ago, no one had any idea what the values of those two variables were. After all, until the 1990s, we hadn’t even spotted a single planet orbiting a star other than our sun.
Thanks to you, we now mostly know those crucial values. On average, at least one world circles each star in the sky, and roughly one-fifth of stars probably host a rocky, Earth-size planet in an orbit where the temperature is right for liquid water to trickle, pool, and wash over its surface. As well, some scientists think there’s an average of one habitable world per planetary system—perhaps even more, if you consider moons and other solid objects as being life-friendly. And why not? In our neighborhood, icy moons are among the best places to look for life beyond Earth!
These numbers are revolutionary. They’re telling us that if life emerges on other planets as it did here, then there are literally billions of surfaces for life-forms to fasten themselves onto and make their own. Countless Earths are hiding in our galaxy’s starfields, gravitationally tethered to stars both like and very unlike our sun. And if evolving life is sculpted by its environments, as it was here, then many of those distant worlds might not only host life as we know it—but also life as we don’t know it.
And then, your fuel started running low. Your team on Earth fought their hardest to keep you going—to wring as much data as they could from your sputtering gaze—but eventually, they instructed you to rest, 388 years to the day after the death of Johannes Kepler, the astronomer whose name you bear.
Now, fittingly, among all the worlds you’ve spotted, you will keep closest to the planet that loves you best. We both will loop around the sun together for billions of years, until our home star eventually balloons into a red giant and devours us both—an exquisite flash, perhaps, in an alien astronomer’s telescope.
But know that even now, your legacy is grand and decisive. When I first showed my dad an image of your field of view—populated by all the alien planets you’d found by 2011—he responded with a sharp inhale. “So many planets….” he said, astounded.
And now, just imagine what today’s children might be wondering about a cosmos so packed with possibilities, thanks to you.
