Boulders in Formation on Comet 67P/Churyumov-Gerasimenko

The standing “stones” of Comet 67P. Courtesy: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Scientists from the OSIRIS camera team for the European Space Agency’s Rosetta mission have released a rare image of the surface showing a most impressive site: a group of three icy boulders (one of which is about 30 meters/about 90 feet) across, standing upright on the rugged surface of the comet. The image (which was obtained last September and is only NOW being made public) shows these objects riding along on the comet at the rim of a small surface depression.  They appear to be only slightly attached to the comet itself.

A balancing rock formation at the Garden of the Gods in Colorado, for comparison to the stnading stones of Comet 67P. Courtesy AHodges7 via Wikipedia.

Why these rocks are only tenuously attached is still something of a mystery, nor do the scientists completely understand how they formed. Somehow some sort of cometary activity causes surface boulders to move around on the surface. These aren’t the first boulder-type objects to be seen on the comet; earlier in the mission, scientists identified a rubble pile that was roughly the shape of a pyramid, and they nicknamed it “Cheops”).

Balanced rocks are nothing new on Earth. You may have seen them as you traveled around the American Southwest or Australia, or other places where erosion has cut into stone. Erosion forces include wind, water, and the action of glaciers.

The standing stones we know about on our planet are connected to the underlying rock by small “necks” of rock.  In the case of Comet 67P, there are a number of forces and activities at work that could be producing and moving these boulders around the surface.  There aren’t any good answers yet as to why and how these boulders exist, but the team intends to continue monitoring them as the mission proceeds.

The Rosetta mission is doing a long-term study of this comet, and will move along with it as Comet 67P rounds the Sun during its perihelion (closest approach) on August 13, 2015. Already, it has taught and shown us more about comets in a few months than years of Earth-based observations. As a former comet researcher, I find the mission to be a dream come true because we finally really get to truly “ride along” with a comet as it does its thing. Stay tuned—I’m sure there’ll be more great images coming out. If you want to follow along, surf over to the Rosetta mission site for the latest news.

We Stand on the Threshold of Discovery

New Horizons spots all five of Pluto’s known moons. Courtesy New Horizons mission/NASA/ Johns Hopkins APL

Ten years ago the New Horizons spacecraft lifted off on the journey of a lifetime—aimed at Pluto and beyond. This week, less than 60 days before its closest approach to the famous dwarf planet, the spacecraft is less than an astronomical unit away from its main target. It’s running just fine, and searching for new moons and a possible ring system around Pluto. It has already spotted Nyx and Kerberos, the dimmest of Pluto’s known moons. Any moons or rings that it finds from here on out are worlds that have never before been seen.

The mission to Pluto is catching people’s hearts and minds, and not just because Pluto has been the center of discussion about its planetary status. This distant world has always been something of a goalpost in solar system studies. Until the discovery of more-distant dwarf planets in the Kuiper Belt, Pluto was considered the frontier—the last stop before the stars. In a sense, it still is. New Horizons will swing by Pluto and Charon, and possibly two other smaller worlds in a few years, but after that, the mission’s adventure lies in the stars.

New Horizons is guiding our view of a distant, cold, lonely part of the solar system. From here on out, each of its images will show us something we’ve never seen before now. Its collection of instruments will tell scientists what the conditions are like at this lonely outpost: how cold it is, what the solar heliospheric influence is in this region of the solar system, and possibly what’s hiding beneath the surfaces of Pluto and Charon. Not to mention what’s ON those surfaces. Will we see craters? Geysers? Giant canyons? Cracks?

What do we already know? Pluto’s surface itself is quite reflective, like a fresh snowfall. It also has large markings that range from bright to dark. The surface is covered with ice made up of molecular hydrogen as well as varying amounts of what are called “hydrocarbons”. These are methane and ethane, along with carbon monoxide ices. As of now, that’s about all the scientists know. But, again, in the coming weeks, the view is going to improve dramatically.

What’s happening with the atmosphere of Pluto? We know that much of the thin blanket of air around Pluto is leaving this world through a process called hydrodynamic escape. What drives that?

What’s going on beneath Pluto’s surface? And, for that matter, beneath Charon’s? New Horizons won’t be able to peek beneath the ices, but it can measure the masses of both worlds, and that will give incredible insight into what’s happening in the cores of these two worlds.

From here on out, Pluto is going to surprise us each week and I’ve been following this story and writing about the mission for many months now. If you’ve been following my Pluto and New Horizons stories on this blog, or reading my work at, you’ve seen how fascinating this system is. This mission has been a long time coming. The science teams are already busy with data about the Pluto system that is streaming back to Earth each day. I’m ready to learn more, and I hope you are, too. Stay tuned!