On Tuesday, we’ll visit Pluto

I was one of two kids at my school who entered the first grade already knowing how to read. When the teachers realized this, they excused me from reading class and allowed me to spend that hour in the library. Before long, I discovered one of its greatest treasures: a thin pictorial volume about the solar system.

Each double page presented a spectacular vista of an entirely different world, far beyond anything I could have imagined.

The first pages showed the planet Mercury, its cracked, barren landscape baking under an enormous sun. On Venus, a hat-shaped lander sat among strange-colored rocks, the air thick as soup. Mars was shown with a blue sky and a thin layer of lichens on some of its rocks. There was a dramatic view through the top of the clouds on Saturn to the rings arching across the sky. And so on, up to Pluto, where the late-afternoon sun, a very bright star in a black sky, cast bluish light across an empty valley.

Others may have seen the book as a science text or an art book. I read it as a travel guide. These were places — well, with one caveat. Every illustration in that book was the product of an artist’s imagination, based on very sparse (and often erroneous) information. No one really knew what any of these places, least of all Pluto, looked like close up. How I hoped we might someday get there and find out!

I memorized the short descriptions on each page and told everyone I could about them: my parents, my teachers, any friends who would listen. My inner six-year-old waited a lifetime and watched with joy as our space probes wrote a new book, one planet at a time, correcting our impressions of Venus, Mars and Jupiter, adding pictures of Uranus and Neptune. The final page was always missing, but now the day has come to add it. On Tuesday, we’ll visit Pluto.

Pluto (right) and its largest moon, Charon, seen from New Horizons, July 8, 2015

Honestly, it’s about time

NASA’s New Horizons spacecraft, traveling at 14.5 kilometers a second, has made the nine-and-a-half-year journey. With no way for the probe to slow down, the entire encounter will be over within hours. But everything it observes will be more than we know now.

New Horizons’ radio signal is so weak over such a distance that its data have to be transmitted at a snail’s pace. It will be October or November 2016 before all the pictures and all the measurements have arrived, and possibly well beyond that before any unexpected phenomena are completely understood. (Click for mission updates.)

It’s about time we got to Pluto. We could have saved ourselves the wait and been there in 1986, had Voyager 1 not taken a last-minute detour to look at Saturn’s moon Titan (which Voyager 2 inspected a year later). For decades, Pluto was thought of as nothing more than a random rock. How could it possibly be important? The few scientists who wanted to go there had their plans shot down repeatedly.

In the new millennium, they finally had enough evidence to make the case beyond simply being able to “complete the set”. More planet-sized objects were being discovered in our solar system — hundreds more — out beyond Neptune. Of these, Pluto is the closest, largest and easiest to observe. To understand this new class of planets and comprehend the solar system in the size we now know it to be, we need to get out to that part of space, called the Kuiper belt.

If all goes well this week, New Horizons will be sent onward to visit another object in the Kuiper belt. That’ll be a sweet reward for having to wait an extra 30 years.

A dwarf planet?

Pluto’s reclassification as a “dwarf planet” in 2006, eight months after New Horizons was launched, did not go down well with Alan Stern, the planetary scientist who campaigned hardest for, and ultimately led, the mission to Pluto. The decision was made in order to limit the number of bona-fide planets by excluding smaller objects, but the distinction is arbitrary, Stern says. “I can’t think of a single distinguishing characteristic that would set apart Pluto and other things that you’d call a planet, other than its size. So I like to say, you know, a chihuahua’s still a dog.”

I couldn’t agree more. So now that we’ve visited the whole solar system in its original lineup, it’s time to draw up a new list. Including all the planets, we’ve now got Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus, Neptune, Orcus, Pluto, Ixion, Salacia, Varuna, Haumea, Quaoar, Chaos, Makemake, Varda, Eris, and Sedna, plus 11 more in between that are known only by combinations of letters and numbers. With practice, your children should be able to memorize all of them as they dream of visiting even more distant worlds.