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I wish I could remember who said that planets are the ashes of stars; it’s not quite as lovely as “We are all starstuff,” but it’s certainly encapsulates the process that has to occur in order to get the raw materials for planets. You start out with a cloud of dust and gas in interstellar space; some of that dust and gas is from earlier generation of stars. Some of the materials start to stick together, and then more of them. Eventually, if enough of them stick together (and I’m greatly simplifying the process), you get a world.

Once a planet is formed (ignore the fact that I’ve skipped over a few millions of years of accretion), the process isn’t done just because the planetesimals are done banging together.

Nope, world-building continues, just in different directions and by different processes. On early Earth, there was a surface to be tended to. It got bashed in by incoming bits of stuff left over from the accretion days. In fact, everything with a hard surface in the inner solar system was cratered by incoming bits of interplanetary debris. There’s very little evidence of that bombardment (which geologists call the “late, heavy bombardment”) that you can see openly on Earth’s surface today (unless you know what you’re looking for), but you can see more obvious evidence for it in the cratered surfaces of Mercury and the Moon (for example).

Kilauea Caldera and Halema`uma`u Crater on the Big Island of Hawaii, courtesy of the USGS Volcano Observatory. — Kilauea Caldera and Halema`uma`u Crater on the Big Island of Hawai'i, courtesy of the USGS Volcano Observatory.

Of more interest to us here on contemporary Earth are the processes of tectonism and volcanism, particularly volcanism. There are volcanoes scattered around the Earth’s surface (both on the continents and under the ocean waves), and they do a good job of building up Earth’s surface.

You can visit a place in Hawai’i where the Earth is created new each day. Lava pours out of this volcano, and under the ocean surface a few miles off the coast of the Big Island, another island is being built, entirely through the hard work of another volcano. I’ve hiked over the most active of Hawai’i’s volcanoes and it is a sobering reminder of the creative (and destructive) forces at work in the planet-building and maintenance game. And, of course, there are other volcanoes on Earth which do a great job of re-paving the surfaces of planets and moons (think Io, at Jupiter, or the ice volcanoes of Triton and other icy moons in the outer solar system).

I mentioned tectonism up there… it’s a short term for a complex set of actions in our Earth’s crust (and on other “hard body” planets and moons, too). Essentially on Earth, the crust is divided into chunks called “plates” and those plates are in motion. You and I are riding along on a plate right now. There are dozens of plates in the Earth’s crust. In some of the places where they meet we see volcanoes formed as rock is heated by the friction of two plates rubbing together. In other places one plate dives under another. In other places,they spread apart, like giant conveyor belts carrying the continents away from each other.

Seafloor spreading at boundary of two plates. For more about plate motions, read here

Tectonics are also “blamed” for things like earthquakes, which also reshape the surface of the land. Tectonics builds mountains by shoving huge slabs of Earth’s surface up into peaks. What takes them down? Another surfaces-shaping force called “erosion” (or, what planetary scientists like to call “weathering”). Flowing water, blowing winds, the action of sand on a surface—all these erode the surface on Earth. So do sulfuric acid droplets (so-called “acid rain.”). And, you can see evidence of these forces on other planets. Take a look at Mars sometime and see what erosion, tectonics, and volcanism have done to its desolate surface. Or, check out some of the moons of Jupiter or Saturn. Tectonism and volcanism at work there, too.

When it comes to building planets, as you can see, the work doesn’t stop when the accretion and bombardment do.

A friend was telling me about a conversation she had with a family member who criticized her for studying science when “there’s so much more you could do with your life.” My friend asked the family member what the relative thought she should be doing, and the response was about like this: become a doctor, or a nurse—a profession that helps people. Another choice, as the relative suggested to my friend, was to settle down and have kids and forget all about science. When my friend pushed her relative on the subject a bit more, the real truth came out: the relative said that science was against religion and that when you compared the two, religion was always better.

Putting aside the obvious contradiction that becoming a doctor or a nurse does require one to study science (actually become a scientist of the body), the idea that one can compare science and religion—even without the clearly biased opinion of the relative—seems like comparing apples and rocks. In other words, there’s no comparison.

But, I got to thinking about the subtext of the relative’s concerns (again, aside from the clearly sexist assumption that a woman studying science should really be home having babies, something which I’ve always thought is a choice best left to the woman in question), and I see another meaning here. What the relative might really have been asking is “What good is your science?” In other words, what good is astronomy? What use does it have? To a person unschooled in science, or even afraid of it, those are important questions.

But, they’re also fair questions, provided you don’t go around looking for answers that aren’t biased for or against the study of science. It’s a question that I’m sure lots of government officials and elected representatives ask whenever they see a federal budget that includes so many dollars for astronomy research.

Let’s drill down a little more, though, and ask “of what use is a star?” That’s something that astronomy helps us discover. And, in uncovering the use of a star, we discover links to … ourselves!

From the surface of our planet, the star looks like a point of light. It might be part of a constellation, a star pattern in the sky.

Polaris (which we all know is the North Star for at least a few thousand more years) helps us determine where north is in the sky, in essence, which direction the north pole of our planet is pointing. If we study Polaris’s light through special instruments (spectrometers or spectrographs), we can tell what its chemical makeup is; that is, what chemical elements are in its atmosphere. We can also find out, as HST did, more information about its companion star.

So, in this case, a star is a pathfinder for directions on our planet, and it can tell us something about itself. As we study more stars, we find that they all seem to have some things in common: they were born in clouds of hydrogen gas, they shine (and we can measure their luminosities and use those measurements to tell us how far away they are), and they have different sizes and colors. The sizes and colors tell us something about their masses, compositions, and their life cycles.

HST studies young stars in nearby galaxy

The more stars you study, the more you learn about the environments in which they’re born. What are their birthplaces? Gas and dust clouds, called nebulae. We find them throughout our own galaxy, and as the image above shows, we see them in other galaxies, too. Throughout their lives, stars enrich their environments by blowing stellar winds rich with elements into interstellar space. When they die, they recycle themselves. Other stars form from the interstellar gas and dust clouds that are left behind when a star dies. And, some of those stars form with planets around them. In our case, the Sun formed from the debris of ancient, long-gone stars. Without the remnants of star death, our star, and particularly our planet, would not have been possible. And, as you may have heard, life on our planet contains atoms that first existed in stars. As Carl Sagan once said, “WE are star stuff.”

Galaxies themselves form from the coalescence of smaller galaxies (dwarfs) of stars, and each star in those galaxies goes through the same birth, life, and death processes that we’ve observed in our own Milky Way Galaxy.

And, the earliest stars that ever shone, more than 13 billion years ago, lit up the universe in a sort of cosmic “first light” that has been reverberating across the light-years ever since.

The technologies we use to study stars are important. Not only do they let us look to outer space for answers, but in some cases, those machines and the computer chips and sensors they use, also benefit humans in many ways. The most obvious use I can think of off the top of my head is the example of sensors built for the Space Telescope Imaging Spectrograph. It turns out they’re also useful for imaging breast cancers. I find that quite poetic: that technology humans developed to look at light from distant objects is also helping humans, who are, after all, part of the cosmic dance that produces galaxies, nebulae, stars, planets, and humans.

So, of what use is a star? Look at your hand, your arm, the face of your loved one, and tell me how poor the universe would be if stars hadn’t formed, lived, and died, leaving their remains to provide the building blocks of more stars, our planet, and eventually, the life upon it.

The Spacewriter's Ramblings

Building a Planet

Of What Use is a Star?

Exploring Science and the Cosmos