Pluto’s Surface Has Changed Over Time

So, Pluto has a second set of mountains along one edge of Tombaugh Regio (the heart-shaped region). The planet continues to stun all of us with amazing views sent back by New Horizons, and the mountains are just the latest in a long string of discoveries to come. I can’t say I’m totally surprised to see them; I remember a geology teacher once saying where there’s one mountain range on a world, shaped by some kind of internal process, there’s bound to be another.

These mountains aren’t quite as high as the Norgay Montes, first seen on July 15th, but they’re still pretty spectacular-looking. They rise up to perhaps only a kilometer or so, but they look quite sharp, standing out in relief against the bright landscape. It looks like they may be younger than the surrounding landscape, but that’s just my guess. If so, then this surface is changing, indeed!

The thing that caught my eye after I checked out the mountains was that very interesting interface between the dark region and the brighter material that makes up Sputnik Planum (which is part of Tombaugh Regio). At first glance, I could tell that there’s been some filling in of craters by the white material. That’s another clue that the lighter-colored landscape is much younger than the darker regions. In fact, the team suspects the dark region is billions of years old, while the lighter landscape is less than a hundred million years old. That’s pretty young in planetary science terms, when you think about it. The solar system formed some 4.56 BILLION years ago, so this surface has only been around for a short time compared the age of the Sun and other worlds.

What Could Be Causing the Mountains on Pluto?

As I mentioned in my article of a few days back, called  Pluto is Geologically Active, mountain-building processes here on Earth are driven by plate tectonics, which is itself driven by heat and motions beneath the planet’s crust. We don’t know yet what’s driving it on Pluto. The planet is just about 70 percent rock, so it might be that there’s activity in the interior related to decay of radioactive materials or some other process.

If that activity generates or is driven by heat, that would affect the icy surface, possibly causing mountains to form in some way, and ices to flow to create smoothed-over landscapes. Remember, the ices on Pluto are largely nitrogen and methane, and those can melt and/or sublimate at pretty low temperatures, so you wouldn’t need a lot of heat. I look forward to hearing a more nuanced and scientifically informed interpretation of the images from the New Horizons team.

There will be a science press conference on the 24th (you can watch at NASA.TV), and I suspect we’ll hear more about those mountains and the dichotomy between the dark and light regions of the planet. So, as I like to say, stay tuned!

Note: the spacecraft has gathered 50 gigabits of data, which it will be sending back over the ever-increasing distance between it and the Earth over the next 16 months. At times, the spacecraft will be returning various types of data, not all of it imaging. However, the team will be releasing images as often as they can, generally once a week or so. The best way to keep up with the news from New Horizons is to check out www.nasa.gov/newhorizons and/or pluto.jhuapl.edu — where you’ll find images, videos, and discussions of the latest Pluto scientific discoveries.

What’s at Work on this Distant Planet?

As Pluto comes into sharper focus through the eyes of New Horizons, we’re seeing more definition of the dark and light areas on this distant world. The lighter areas are very likely ice patches, but the dark ones are more intriguing. The most interesting image THIS week, shows four distinct markings that look like craters, or mountains, or… something on one side of the planet. What could be causing these dark markings?

Think about this: Pluto is covered with ices — water, nitrogen, and methane. That means it’s a cold place, indeed. At a surface temperature range of -287 to -369, that’s cold enough for nitrogen and methane to freeze out and coat the landscape. Of course, water is frozen as well.

Nitrogen and methane are susceptible to what’s called “irradiation” by sunlight, and in particular, the ultraviolet radiation emitted by the Sun. That process darkens the two ices and can create molecules called “tholins”. If you could be there and pick up some of this stuff, it might be as Carl Sagan once described: “A complex, organic goo.” Astronomers have found a great deal of evidence of these tholins on Pluto, which could account for the reddish color and dark markings we’re seeing.

Patterns of Tholins?

These tholins aren’t new discoveries. We’ve seen them on other our solar system moons such as Iapetus at Saturn and Umbriel at Uranus. They’re also present in the atmosphere of Titan. So, it makes sense that we’d see them at Pluto, too. And, they’re very likely what is forming the dark areas we’re seeing and turning the overall surface a nice red color. Now, why they’re in those exact configurations? Maybe there are vents or some other sources in those areas that periodically spew water ice over the other types of ice. Maybe those dark areas are where the water ice has gone away, leaving leaving behind the sun-darkened ice.

That’s my educated guess, and I can’t wait to see if it’s right or wrong. If it’s wrong, then, wow — maybe there’s something even MORE interesting going on there than everybody expects. In any case, I’m just part of the “Public Imaging Team”, taking my best educated guess at what’s going on there.

The image I’ve posted here was released on July 1 and was part of a pair taken on June 25 and June 27th. I’ve overprocessed it a wee bit just to bring out the light and dark areas, so don’t read too much into the image based on what I’ve done. In point of fact, the day they were released,  Principal Investigator Alan Stern made it clear that the team was really puzzled by all the dark and light markings on the planet. I suspect they won’t be for long!

It might be tempting to say, “Oh, those look like craters!” Or “Mountains on Pluto!”, the truth is, nobody quite knows yet what they are. The good news is, there are more images on the way, and in 11 days (or less) we’ll know exactly what those things are. Go New Horizons!

To learn more about Pluto’s coloration and markings, check out NASA’s Pluto: The Other Red Planet page. It goes into more scientific detail about the darkening of Pluto’s surface. They’ve also posed a GIF animation/movie of the rotation of Pluto and Charon during the time the last released images were taken.