by Shane L. Larson
July 2015 was a triumphant month in the annals of robotic space exploration — the long held dream of sending a space probe to explore worlds in the outer reaches of our solar system was realized. New Horizons, a robot the size and shape of a baby-grand piano, wrapped in golden mylar, shot past Pluto at 31,000 miles per hour. Semi-sentient and single-minded, New Horizons spent 22 hours on July 14 ignoring its masters on Earth, focusing all its attention on Pluto for the brief moment we call “Encounter Day.” New Horizons had been constructed with this single purpose in mind: to make a nine-and-a-half year voyage across 3 billion miles of the void — a voyage we humans could not make — and record everything it could about Pluto as it blazed by.
For most of the 85 years since Pluto’s discovery, we’ve seen little more of it than a fleck of light, even in our best telescopes. But New Horizons has been steadily crossing the gulf since its launch in 2006, carrying the promise that someday, it would send back pictures to replace the ones in our imaginations.For a long while, the pictures sent back were still only spots of light, Pluto and Charon engaged in a slow and lazy dance around one another. But each day carried our faithful robot 1.2 million kilometers closer, and Pluto grew inexorably larger. For the month or so before Encounter Day, the details visible on Pluto and its attendant moons streamed back to Earth in tiny, tantalizing bits. The spacecraft carries only 16 GB of memory on board — tiny by the standards of the smartphone you have in your pocket, but huge by the standards of the early 2000’s when New Horizons was built. The data link is a paltry 1000 bits per second, about 50 times slower than a dial-up modem (the dominant technology at the time New Horizons was built), and about 1000x slower than the modern high-speed internet you enjoy in your home today.
At those speeds, it takes about 2 hours to download a typical picture you might snap of your coffee or cat with your phone. But these pictures streaming back are from Pluto, 3 billion miles away, and are of things we have never seen before this summer. The past several months have been a veritable circus of emotional highs, punctuated by long waits to find out what secrets Pluto would reveal to us next. Every picture reveals something new, for the first time. This has always been the modus operandi in planetary space exploration.
I was little during the late 1970s, the years when the solar system was being seen up close for the first time. My first real memory of a space probe visiting another planet was of the Viking missions to Mars. On 20 July 1976, 7 years to the day after astronauts first walked on the Moon, Viking 1 became the first spacecraft to ever land on Mars. It touched down on a vast Martian plain that we had named Chryse Planitia — a Lyrical Greek name meaning “the Plains of Gold.”
The landing happened at 7:53pm EDT. At that time, Mars was high in the sky over the United States, east of the Sun and hidden in the blue velvet of daytime. 25 seconds after landing, Viking snapped its first image, a selfie of sorts. It took 4 minutes to transmit the entire image to Earth, but for NASA engineers breathlessly waiting for news from their space age hot rod, the wait was even longer — travelling at the speed of light, it took 19 minutes for the message to cross the gulf of space and reach Earth. The first picture it sent home was of its foot, firmly planted on Martian soil amid a tantalizing scatter of rocks on the surface of an alien world.The next day, Viking sent back the first picture of Mars in glorious living color, and it looks for all the world like a picture from some barren patch of the rocky deserts in the American southwest. Never again would the surface of Mars be unknown. Our imaginations are now forever supplanted by real pictures of the surface of Mars. I don’t remember whether or not these images percolated into the news or not; I’m not cognizant of whether or not I watched the news. But what I do remember is waiting breathlessly for National Geographic to arrive. After each magnificent encounter with another world, an issue would eventually arrive at our house, the cover splashed with images from NASA. The articles within were chock full of images from the missions, everything a young and curious mind with dreams of outer space could desire.
But by the mid-1990’s, a new technology was slowly capturing the public’s attention, and it went hand in hand with the heady future of space exploration: the internet. NASA figured it was going to be big, and they started to figure out how to use it to deliver all the wonders of the Cosmos directly to me and you.
Fast forward to today, and we use the internet for everything. We check the weather. We look for the nearest veterinarian. We get customer reviews of cars. We play games with friends. We read blog posts. We order paper-clips from Amazon.
NASA has become the master of this new technology, delivering images of the Cosmos directly to me and you on our smartphones and computers. Every day, NASA gives us the latest pictures from Hubble: color renderings of delicately twirled galaxies millions of light years away, images of towering columns of stardust making new stars, and pictures of a tiny speck of light at the fringes of the neighborhood around the Sun. But this summer that fleck of light became so much more.
New Horizons, after a 9.5 year journey out from Earth, flew by Pluto for the first time. It is the only spacecraft to ever visit that far away world. It passed within 7800 miles of the surface. At the speeds it was travelling, it sailed across the face of Pluto in just 3 minutes, snapping as many pictures as it could in that brief moment it was close. After it had sailed past Pluto, New Horizons sent a short message home: a simple, “All is well, but I’ve still got work to do!” It then returned to observations, looking back toward Pluto and its family as it receded in the rear view mirror.
The next day, images began to be sifted out of the memory and beamed back to Earth, pixel by pixel. As the images arrived, they revealed a world of wonders and mystery.
Pluto has mountains:11,000 feet high, but apparently made of ice, not rock. How can mountains like that form, and why have they not been slowly eroded into oblivion by impacts and crater formation? Astronomers don’t know yet.
The bright, white heart of Pluto is a vast icy plain called Tombaugh Regio. Largely comprised of nitrogen ice, its vast expanse is divided up into polygonal cells, like irregular tiles on a kitchen floor. Near the fringes, the ice appears to be flowing, like glaciers do on Earth, pushing out into the surrounding valleys and mountains. Why is the ice so vast and smooth? Why are there no craters on it, and what is lifting it up so it can flow near the edges? Astronomers don’t know yet.
Charon, Pluto’s largest moon, is scarred by a rift canyon that is six miles deep and stretches across the entire face of the moon. It is so large that when viewed in profile on the limb of this world, it looks like someone took a cleaver to Charon. Nearby, we have spotted a “Mountain in a Moat” — a mountain sized rock sticking up out of the surface. Apparently its not part of Charon’s crust, but not surrounded by an impact crater either! How did these features form? How long have they been there and how long will they persist? Astronomers don’t know yet.
We’re not worried that we don’t understand these things yet. This is what astronomy is all about — uncovering mysteries, and finding out the explanation for them. Understanding how the Universe works, how things are put together and change over time, tells us about our own small, blue world. Pluto knows part of the story of the beginning of the solar system. Pluto is at the heart of our attempts to understand the nature of planets, and the evolution of the architecture of planetary systems. The knowledge we glean from Pluto will inform the way we think about planets for the next century and beyond.
All of the astronomers you know are still giddy about the information streaming back from New Horizons. It will take more than a year for all the images to get back, and even longer to understand them.
But right now — this moment — is one all of us should savor and enjoy, because as of today, every world in the solar system that has ever been considered a planet has now been visited by spacecraft from Earth.
This includes Pluto, and Ceres. Both were visited by spacecraft from Earth for the first time this year.
All of us witnessed, for the last time, the discovery of new worlds for the first time.
Never again will we see a planet up close for the first time. That sense of astonishment, of unfettered curiosity for a newly seen planet, is now a memory for the ages. It will be replaced by other moments of wonder and discovery, but never again for the surface of an unknown planet. Not in our lifetimes.
We will never again imagine what Pluto might look like. From here on out, you will not be able to open up a webpage and not see real pictures of this far away world.
The next humans to see new planets for the first time, will be those who live to see our species travel to other stars.