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.

Photograph by Tom Trower, Nasa
Read Caption
A tabletop model of the Kepler space telescope. Launched on March 7, 2009, the groundbreaking instrument looked for planets around other stars.
Photograph by Tom Trower, Nasa

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.

This essay is an entry in our "Dear Spacecraft" series, where we ask writers, scientists, and astronomy enthusiasts to share why they feel personally connected to robotic space explorers.

Dear Kepler,

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.

Exoplanets 101

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.

I am just one Earthling among billions. But 59 Earth-orbits ago, my dad devised a formula that could calculate how many extraterrestrial civilizations are detectable in our galaxy. It was a question he’d been thinking about ever since he was a kid growing up in Depression-era Chicago, wondering whether there were other planets out there, and if any were like Earth.

So, Dad thought it made sense to define the things we’d need to know if we wanted to calculate the probability of finding smart, chatty aliens.

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.

That you provided these insights over just a few years of tending our starry skies is remarkable. And as you were finding new worlds, I was moving into a new world of my own: science journalism.

The first time I reported on you was early 2011, when your team announced roughly 1,200 new planet candidates and a six-world system called Kepler-11. NASA had called a national press conference at the agency’s Ames Research Center, and I—an intern at the San Jose Mercury News—was assigned to report the story. “No offense, but why is the Merc sending an intern to cover this? This is a major story about complicated science," one of NASA’s spokespeople grumbled.

Cue: Panic.

Fresh from defending my Ph.D. in genetics, I had gleaned most of my astronomical knowledge from prints on our walls, nights observing the stars back in elementary school, and an introductory astronomy course in college. I had so many questions. Should I refer to your celestial haul as “exoplanets” or “extrasolar planets”? How precisely could I describe the sizes and orbits of the worlds you’d found? And how the hell did you go planet-hunting at all? Your methods were mystifying to me, like a language I was hearing for the first time.

So I got to work. I nervously scheduled interviews with scientists, talked my way into an early copy of the embargoed research paper, and strategically booked a hotel room so I could beat the Bay Area traffic to Ames. Afterward, I hurried back to the newsroom and dropped everything I knew into a story, while my editors wondered what was taking so long.

It ended up running on A1. Mission accomplished.

Eight years later, I’ve written dozens of stories about you, and now I can more easily explain the whats and hows of your incredible mission. In small patches of sky, you’ve spotted hints of more than 2,600 exoplanets as they traipse across the faces of their distant stars and temporarily block a sliver of starlight, which you register as a brief dip in brightness. Those fleeting smudges offer clues to a planet’s size and orbit, which scientists can use to figure out what faraway worlds must be like. And the worlds you have uncovered—fiery lava planets, puffy mini-Neptunes, some orbiting two stars, some snuggled so close together that each rises in the other’s sky, one maybe dragging a giant moon around—constitute the greatest garden of unearthly delights imaginable.

View Images

An illustration shows what Kepler-42, a star system 130 light-years from Earth, might look like. In 2012, Kepler detected three planets smaller than Earth orbiting this cool, dim star. As it orbits, the innermost planet gets more than 50 times closer to its star than Earth does to the sun.

How wonderful it is to exist in a time of such tantalizing strangeness. How lucky I feel to be sharing your discoveries.

But like all good adventure tales, your story had its share of obstacles. By 2013, you had lost several essential motors that let you hold still as you peered at distant stars; the cosmos would win your staring contest after all. But, though disappointed, your people weren’t deterred. They figured out how to harness the pressure of sunlight itself to keep you stable as you aimed your raptor’s eye at many patches of sky. Reborn as “K2,” you found even more planets, planetary debris in our own neighborhood, and fistfuls of exotic, exploding stars.

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.

It happens to the best of us; we all need a break, especially those as vigilant as you.

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.

Over the years, the view got more and more crowded.

And now, just imagine what today’s children might be wondering about a cosmos so packed with possibilities, thanks to you.

Cheers,

Nadia

A whole new world:

planets beyond our

solar system

On October 30, 2018, NASA declared that

the Kepler spacecraft has run out of fuel,

marking the end of an era. Of the 3,924

confirmed exoplanets, Kepler discovered

more than two-thirds of them, including

many of the 55 known “Goldilocks worlds,”

where it's neither too hot nor too cold

for life as we know it. In April, NASA

launched Kepler's successor: the

Transiting Exoplanet Survey Satellite.

star

HOT ORBITAL zone

Warm ORBITAL zone

COLD ORBITAL zone

TOO COLD

Here planets

orbit far from

their suns, so

any surface

water remains

frozen.

Mars

JUST RIGHT

Water present

on a planet orbiting

here can remain

liquid, given the

right atmospheric

pressure.

Earth

TOO HOT

Venus

On planets

orbiting close to

their respective

suns, surface

water evaporates

into space.

Mercury

0.1

10

1,000 EARTH

MASSES

LIFE IN A BOX

Planets in the box have the right atmospheric

pressure and temperature to maintain liquid

water on their surfaces. In our solar system,

only Earth and Mars are in the box. The cold

gas giants, however, are literally off the chart.

NASA detected and confirmed more than 2,650

planets with the Kepler and K2 missions (lighter

color). Most are hot super-Earths or Neptune-

size worlds between one and six Earth radii.

Most confirmed exoplanets are much larger and

hotter than Earth, characteristics that make them

relatively easy to detect. This logarithmic scale

allows for an easier comparison of the exoplanets.

DANIELA SANTAMARINA AND MICHAEL GRESHKO, NG

STAFF. SOURCE: ABEL MÉNDEZ, PLANETARY HABITABILITY

LABORATORY, UNIVERSITY OF PUERTO RICO AT ARECIBO

Graphic updated from 2014 interactive:

https://www.nationalgeographic.com/astrobiology/

goldilocks-worlds

Note: Exoplanet mass estimated from mass-radius

relationship when not available.

A whole new world:

planets beyond our solar system

star

On October 30, 2018, NASA declared that the Kepler spacecraft has run out of fuel, marking the end

of an era. Of the 3,924 confirmed exoplanets, Kepler discovered more than two-thirds of them,

including many of the 55 known “Goldilocks worlds,” where it's neither too hot nor too cold for life as

we know it. In April, NASA launched Kepler's successor: the Transiting Exoplanet Survey Satellite.

HOT ORBITAL zone

Warm ORBITAL zone

COLD ORBITAL zone

TOO HOT

JUST RIGHT

TOO COLD

Water present on a planet orbiting

here can remain liquid, given the right

atmospheric pressure.

On planets orbiting close to their

respective suns, surface water

evaporates into space.

Here planets orbit far from their

suns, so any surface water

remains frozen.

Mercury

0.1

LIFE IN A BOX

Mars

NASA detected and confirmed more than 2,650

planets with the Kepler and K2 missions (lighter

color). Most are hot super-Earths or Neptune-

size worlds between one and six Earth radii.

Planets in the box have the right

atmospheric pressure and the right

temperature to keep surface water in

a liquid state. In our solar system, Earth

and Mars are in the box. Mercury and

Venus are outside. The cold gas giants

are literally off the chart.

Venus

1

EARTH

MASS

Earth

10

100

1,000

Most confirmed exoplanets are

much larger and hotter than Earth,

characteristics that make them

relatively easy to detect.

This logarithmic scale allows for an

easier comparison of the exoplanets.

10,000

EARTH

MASSES

WARMER

EXOPLANET TEMPERATURE

COOLER

DANIELA SANTAMARINA AND MICHAEL GRESHKO, NG STAFF.

SOURCE: ABEL MÉNDEZ, PLANETARY HABITABILITY LABORATORY, UNIVERSITY OF PUERTO RICO AT ARECIBO

Graphic updated from 2014 interactive: https://www.nationalgeographic.com/astrobiology/goldilocks-worlds

Note: Exoplanet mass estimated from mass-radius relationship when not available.