Asteroid Vesta - Images from the Dawn Spacecraft

With the New Horizons spacecraft hurtling toward its 2014 encounter with Pluto, and with the Dawn spacecraft now at its most up-close and personal encounter with Vesta, we are in the process of learning scads of information about two objects that are among the poorest understood and least explored bodies in the Solar System.

Before NASA's Dawn settled into orbit around the asteroid Vesta—the second largest object in the Main Asteroid Belt, after the Dwarf Planet Ceres—we knew very little about it. That it is mega-mountain of rock 330 miles across that rotates rather quickly in space and is slightly egg-shaped, these things we knew—but not much more.

What Dawn has revealed to us, however, is a tiny world with unexpected complexities, inside and out.

Inside, Vesta's anatomy may not be unlike Earth and the other Terrestrial planets, which all developed cores heavy with iron and mantles and crusts made of lighter silicate rocks when they were young and molten. This "differentiation" occurs for the same reason that gold particles sink to the bottom of a gold-pan as a prospector shakes the water-sand slurry back and forth: the gold is denser, the sand lighter, so the materials separate.

Outside, Vesta's surface offers amazing landscape vista opportunities for a future robot lander or astronaut: complex topography of valleys, cliffs, troughs, ridges, and a huge mountain, with elevation differences deviating above and below the global average elevation by as much as 15 miles—that's three Mount Everests, or two Marianas Trenches!

Parts of the surface resemble some of the basaltic formations of cooled lava in Hawaii, suggesting that, long ago, there may have been active volcanoes on Vesta, spewing out lava to shape the young surface.

What a sight it must have been—and it makes me smile when I think about the children's book "The Little Prince." My favorite part of that story was the description of how the Prince, on his little asteroid world (which was only twenty or thirty feet across, I'd guess), cooked his meals on a frying pan held over a miniature volcano, which he made sure to keep clean and functional with a periodic cleaning using a giant Q-tip….

All of these revelations—the core/mantle differentiation, complicated geography, possible tectonic features, and signs of past volcanism–have prompted some scientists to ask, should Vesta be reclassified as a Dwarf Planet, along with Ceres, Pluto, and the others thus dubbed?

I have on my desk at work a letter from a 3rd Grader. It starts, "I think Pluto should be a planet (not a Dwarf Planet)…." The letter continues in richer detail and quite a bit of passionate defense of Pluto, but I was struck by the fact that this 3rd Grader was, at the time Pluto was originally "demoted," three years old. (And some thought the Pluto controversy would end with the previous generation of kids….)

But it did get me wondering. If Dawn has changed our view of Vesta from a mere large asteroid to something maybe worthy of promotion to Dwarf Planet, what might New Horizons do to our current view of Pluto? I'm not suggesting the International Astronomical Union will reinstate Pluto as a planet when we get our first up-close images of its surface—after all, no matter what Pluto's surface may hold in store for us, this Dwarf Planet can't meet one of the three conditions for planethood: being massive enough to clear the region of space in which it revolves. Alas, Pluto shares its orbital space with other objects.

But I fully expect that New Horizons will change our perspective on Pluto, as Dawn is doing for Vesta. The more we learn of the rich details of mysterious places like these, the more, I think, we regard them as "worlds"—regardless of their classification as asteroid, dwarf planet, or planet.

Artist's concept of a Pluto landscape, with moon Charon on
the horizon. NASA.

Observations of Pluto have been made by Hubble before, bringing us the most detailed images of that small world ever taken. Still, the images reveal little more than variations in shading, and in the most recent observations, some color.
The recent images show the dwarf planet from different angles, grabbed at different times as Pluto slowly rotates, once about every six days. The darker areas have been characterized as having a "molasses" color—I'm assuming that means very dark brown, as that's the color of molasses in the bottle in our kitchen.

So, is Pluto's surface oozing with syrupy sugars? First of all, nothing should be oozing at all under the temperatures Pluto routinely experiences. Since Pluto reached its closest approach to the Sun back in the 1980s—something that happens only every 248 years—temperatures have risen to their highest in our lifetimes, and are now up to about -385 degrees Fahrenheit. Yeah, minus. Global warming on Pluto….

While scientists don't yet know what the deep brown regions are, some expect it has something to do with Pluto's methane, the existence of which we've known for some time from spectroscopic measurements. Methane is a hydrocarbon—an "organic molecule"–whose chemistry is part of the basis of life on Earth.

That's not to say there's life on Pluto—but one theory about the molasses-colored patches is that it may be some sort of tar-like substance that has developed over millions of years from the Sun's weak rays interacting with Pluto's methane. Over its seasonal and orbital gyrations, Pluto's methane cycles from being frozen solid on the ground to being a gas and forming a thin atmosphere; right now that atmosphere is as thick as it's ever been in our lifetimes.

Will astronauts in the distant future have to worry about getting stuck in something sticky when they walk around on Pluto? Too early to tell….

Since childhood I've been fascinated by Pluto—probably more for our lack of knowing it than for anything we actually know (which isn't a whole lot: small, cold, dark, slow, patchy brown, methane, three moons; that's the lion's-share of our knowledge). It's a place of mystery, not unlike Mars and Venus, or Jupiter's Galilean moons, were long ago (like in my childhood), before we sent spacecraft to see them up close, and before we had the powerful eye of Hubble. Mars, at least, we're getting to know pretty well; it still holds plenty of mysteries, but somehow feels not so far removed, and familiar.

And, something else is on the horizon in the exploration of Pluto: in five years, NASA's New Horizons spacecraft will whiz by and in a few short hours collect an amount of information that will absolutely dwarf all that we have learned since Pluto was discovered in 1930. It's like the treks of Pioneer and Voyager all over again, back in the 1970s and 1980s, when we first visited the Gas Giant planets, and moons like Io and Europa went from being fuzzy blobs with variations in surface shading and color to worlds with craters and volcanoes and ice fissures and…well, let's just say I can hardly wait to get that up-close glimpse of Pluto.

37.8148 -122.178