The last approach image taken by New Horizons before closest approach. As the planetary community waits with bated breath for tonight's downlink, we consider this sparkling new image - the best view yet of the furthest object from our sun yet observed by spacecraft. Pluto, a world in its own right, no matter what label we put on it.
Like many of my colleagues, I got up early this morning to witness an event billed as the "completion of our initial reconnaissance of the solar system." Just before 8 in the morning, Eastern Daylight Time, the New Horizons spacecraft - our very first New Frontiers mission - made its closest approach to the (now) Dwarf Planet Pluto.
From an outsider's perspective, I can imagine that one of the most puzzling aspects of this event was the very non-event of it. Sure there were scads of folks with tiny American flags counting down and cheering at the Applied Physics Lab in Laurel, MD. The NASA brass was there too - Charlie Bolton, the Administrator himself, was giving interviews along with the other principals and there was a media circus of lights and cameras.
But really, the action was rather remote. There was no confirmation of success via satellite, no breathtaking images poping up on the screen. Despite the atmosphere feeling much more like a spacecraft landing than a pure flyby, it stands in stark contrast to the three landing events in which I have participated, even Huygens landing on Saturn's moon Titan.
And how could it not? Pluto, out beyond the orbit of Neptune is over 4.5 hours away by radio wave, and, no doubt, the team doesn't wish to waste precious minutes near close encounter slewing the spacecraft away from its prize to transmit what they have seen so far back to earth. Even if they did it would be after noon when they arrived. Later still as, certainly, after all this time, New Horizons will have sufficient discipline programmed in to collect togther the best of the best before sending back home for us tonight.
Thus the true celebration will take place later today in a worldwide event called Plutopalooza. I will be participating in the York University Astronomy Club's edition. This morning's event was instead more about having a picture of cheering scientists to go with the morning press, and also a meetup for the true believers. Perish the thought, but we don't yet know how things went. While there is joy, and perhaps a bit of relief that the time of encounter has finally arrived - I can tell you from experience that it is tinged with a hint of sick anticipation still. That won't be dispelled until tonight.
But as we wait for word from the spacecraft, we have a beautiful new picture to wonder at. Anticipating the need to fill that data vacuum, the team held back their best approach image which I have reproduced at the top of this post. It shows the feature now famous around the world as "the Heart" and a surprising range of coloration across the surface. It is almost as if the dwarf planet is streaked with paint. But the coloring agent here are different volatiles - likely some nitrogen, methane, ammonia and other trace compounds.
Unfortunately for a planetary scientist like myself, we already know that the atmosphere will be thin. Pluto is several decades beyond perihelion now and is headed out towards the far part of its orbit. But what remains on the surface was likely forged, at least in part, during those 'warmer and wetter times.' In fact, the red coloration led to Bolden describing Pluto as "the other red planet."
But all references to Mars aside, Pluto is indeed its own world with its own fascinating geology. The image above doesn't give the whole picture, but it is clear enough for us to know that the close encounter images will reveal many different processes operating on the body and competing with each other to leave their mark on its surface.
We had a hint of this. Neptue's moon Triton (pictured below) is thought to be a captured Kuiper Belt Object, and was far more active and more varied than had been suspected from previous telescopic observation. Here there were frostier areas littered across its vaguely reddish surface and the enigmatic cantaloupe terrain (at upper left) which might be tectonic. Dark streaks cut across the surface of the body, the remnants of nitrogen geysers erupting out into space driven by a solid state greenhouse effect. Could this perhaps be the source of the darker "Whale" terrain to the left of Pluto's "Heart?" Both bodies have a bit of a mottled or scalloped appearance, especially in the interfaces between different terrain types. This is also seen in other sublimation driven landscapes, such as on Comets and the "Swiss-cheese" terrain of the Martian southern polar cap.
Not surprisingly, there are also differences between Pluto and Triton. While they share a similar coloration, likely as the result of similar processing and similar composition, in other ways they are unalike. The bluish-greenish frostiness near the terminator on Triton does not have a clear analog, at least not in images captured thus far. For its part, Pluto also has significantly more dark terrain on its surface and more crater-like features. For much more than that, we will have to await this evening.
New Horizons is the first of the New Frontiers Missions (Juno is NF2 and Osiris-Rex is NF3). Meant to be more responsive than a Flagship, yet better funded and more complex than a Discovery-Class mission, it's impressive what we've seen so far and I can't wait to see what's yet to come from this new class of exploration mission.
Oh, and for those of you just coming upon the field - not to worry about that "completing the reconnaissance of the solar system" remark, there will be plenty of exploring left to do. Mariner 4, the first fly-by of Mars, revealed only a moon-like cratered highland. This is certainly not how we think of that planet today. Mariner 10 saw less than half of Mercury's surface - a map that was not completed until 30 years later by Messenger.
Even after New Horizons, a good chunk of Pluto remains in darkness. While we're unlikely to be back within the next few decades, perhaps even within my lifetime, who knows what mysteries might be lurking there? That's the thrill of planetary, and it's days like today where we finally fill in the map a little bit more which makes this area of such great interest to me.