I’ve been interested in rocks since I was a kid. Our family would go for rides in the mountains to explore. I’d come home with collections of rocks and crystals in my pockets and on the floor of the station wagon. I remember getting one particularly cool-looking crystal-embedded rock while on a trip to Rocky Mountain National Park. I just started at it like it was a huge treasure. That rock got lost in a family move not long after I collected it. However, it was really inspiring and I remember it after all these years.

How Did a Rock Get Started? It’s a Long Story

One thing that I used to do was look at a rock and think, “Where did you come from?” Of course, the first answer was “the park” or “the mountain”. Then, after learning more about how rocks form, I’d think about the formation process that brought the rock to me. We lived (and still live) on the edge of what was an ocean that existed hundreds of millions of years ago. Eventually (and there’s a long geologic history you can read in the famous Roadside Geology of Colorado), the oceans receded and dried up.

That left behind huge deposits of sandstones. Mountain-building processes pushed up the ancestral Rockies. they eroded away, eventually. Then, another round of mountain formation created the current Rockies. The rocks you find around here can be sandstones and shales, created from deep water deposits and shoreline areas. Or, maybe they’re granites and other rocks formed in conjunction with volcanic activity and the pushing-up of peaks to form the Rockies.

So, the rocks I used to find were probably sandstones. However, the one with the crystals clearly had formed differently from the red rocks I had collected first. And, among the rocks, we’d find fossils and, in some places, we could go and find sharks’ teeth just lying around. So, clearly, the region I grew up in had some history to it.

Everything Starts in Chemical Elements

It wasn’t until college and a chemistry class that I learned about the elements that formed the rocks and crystals I used to collect. A rock that I thought was pretty boring turned out to be feldspar, like the one in the picture here. It’s a common rock, but with an interesting history. If you ever pick one up, you’re holding a collection of elements. They can be potassium, aluminum, silicon, oxygen, sodium, or calcium in varying combinations. And, to get to BE a rock, they had to be part of volcanic activity. That could have been a flow, or when a flow impinged on another rock.

And, actually, feldspars can be found in sedimentary rocks. Those are created as other rocks erode and eventually get cemented together in layers. I won’t get into the technicality here, because it’s a lot. But, the creation of what looks like a simple pebble or rock belies a lot of activity.

Chemical Elements Started Somewhere, Too

The thing to remember is those chemical elements. They all came from someplace here on Earth. However, they didn’t start here. They GOT to Earth because some of them existed in the cloud that gave birth to our star and our planet. And, how did they get in the cloud? Well, they formed in other stars, for the most part. All but the hydrogen. That was created in the Big Bang, nearly 14 billion years ago.

So, that rock you hold in your hand? It came from space. Maybe not directly, like a meteorite, but through a long process. It included starbirth, star death, and wandering in a nebula. Then, it’s elements came together to form protoplanets. They slammed together to make a planet, which then experienced its own evolutionary history.

The next time you pick up a rock, ponder it a while. Think about its journey from space to your hand. and, then, think about the similarities it has with YOU. Because you, too, formed from chemical elements.

And me? I still pick up rocks. I have one rock from nearly every continent on Earth. And, they keep me company as I write about the cosmos from my office in mountains that formed millions of years ago to supply rocks for me to ponder.

A long time ago, I studied comets during my years in graduate school. We studied cometary plasma tails, and found a lot of interesting things. But, we didn’t know at the time that a comet can have an aurora. That all changed with the in-depth study of Comet 67P/Churyumov-Gerasimenko. The Rosetta mission studied that comet in great detail, including emissions from and around the nucleus. Among those emissions: far-ultraviolet light that is generated when electrically charged particles from the Sun interact with the gassy coma surrounding a cometary nucleus.

From Dayglow to Cometary Aurorae

Initially, scientists interpreted the far-UV emissions as part of the “dayglow” surrounding the comet. When they re-analyzed the data, they found the emissions. The solar wind remains the culprit, just as it plays a role in forming the plasma tail of a comet. Charged particles in the solar wind interact with the gases in the coma. That actually causes water and other molecules to break apart and the resulting atoms give off far-ultraviolet light. And, that’s what forms the aurora around the comet.

Implications of Cometary Aurorae

Of course, the formation of such emissions at a comet tells scientists something about the solar wind, its particle loads and intensities. Studying what happens at a comet can give better insight into changes in the solar wind over time. It’s particularly important for understanding space weather, which is caused by the solar wind and its interactions with planetary magnetospheres. Space weather is a natural phenomenon and can affect satellites and astronauts in orbit around Earth. It would definitely have an effect on missions beyond Earth, too.

Back when we were studying comets and their plasma tails, we depended on a solar-orbiting spacecraft called Ulysses. It gave us information about the solar wind as it left the Sun. That allowed us to follow the effects of the solar wind on the comets we were studying. In particular, it helps shape the plasma tail, and disturbances in the solar wind definitely showed up at the comets some hours or days later.

New Data, New Ways of Seeing Comets

The Rosetta spacecraft is now “one” with the comet it studied. Its data adds a whole new dimension to what we know about comets and their interactions with the solar wind. Up until this discovery, I am not sure people thought about cometary aurorae. But, then again, back in the 1990s, we never thought comets could have x-ray emissions. Those were discovered by the Rœntgen X-ray Satellite and Rossi X-ray Timing Explorer at comet C/Hyakutake 1996 B2 and are also thought to be due to an interaction between the comet and the solar magnetic field entrained in the solar wind. This recent discovery is another in a long line of unexpected surprises about comets.