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Clues from Solar Studies

Earth Science in Space 1



The Sun in extreme ultraviolet light, as seen by the SOHO spacecraft.

NASA image

These days you can't watch the news from space without someone asking, what good does this multimillion-dollar stuff do when the money is better spent on Earth. (As if we had sent the money to space aliens!) Actually, people have always been asking that, but the answers have changed. For geology—the science most closely tied to our material prosperity—the payoff from space research has grown and grown.

The early U.S. and Soviet space programs were a mixture of Cold-War nationalism and "right stuff" barnstorming. Only aviators were recruited, though no actual flying skill was required until the Space Shuttle Columbia's first re-entry on April 14, 1981. Only on the very last Moon mission did NASA send an actual geologist, Harrison Schmitt, there to examine the rocks in the field.

Nowadays, space money is being spent more usefully. Let's take a look at some of the ways that space research benefits Earth science, and vice versa.

Eyes on the Sun

Consider the Sun. Now that we have a fair grasp of Earth's 4.6-billion-year history, there are facts we need to nail down about the Sun. What has it done during that time span? How steadily does it shine? What do its activities do to Earth's climate and magnetism?

The Sun's gross structure and life story are well described from fundamental nuclear physics as well as the study of thousands of other similar stars. We figure the young Sun had to be somewhat dimmer than it is today, like a fluorescent bulb that's just turned on, but for the last couple billion years it's been pretty steady.

But as usual in science, answering a basic question leads to many more detailed ones. We need to know more about the inner structure of the Sun, and one promising way to do that is to use the same technique there we apply on Earth, namely seismology.

The Sun doesn't quake the way Earth does, having no rocks to rupture, but it does shake from its own energetic movements of gas and plasma, and once it shakes it oscillates—it ringsthe way Earth does after large earthquakes. The steady eyes of satellite cameras are keeping track of the Sun's ringing, and the techniques of seismology are being applied by helioseismologists in an undertaking no one foresaw in the days of Sputnik.

Solar Flickers and Flutters

The same satellite observations are being combed for clues to a more immediate question: solar variability. The Sun changes its output slightly (about 0.1 percent) over the course of its sunspot cycle. That is known to affect the global climate. But how much does the Sun vary over geologic time scales? We know of a few recent flickers, for instance the Maunder minimum of the 17th century. This was a 70-year period when sunspots disappeared entirely and parts of the world endured unusually cold weather. Apparently the Sun grew dimmer by a fraction of a percent during that time.

It would be nice to know more about such events, like how to predict them, much the way we are beginning to forecast the annual Atlantic hurricane seasons or the more irregular El Niño climatic disruptions. But it would also be good knowledge for interpreting the geologic record. That is, since we can routinely measure subtle isotopic changes with great accuracy to study volcanic activity and ocean currents in the past, can we detect ancient solar flickering as well? Only with excellent data from space can we move forward with this intricate inquiry.

PS: The Sun is connected to activity even farther out in space. A vigorous Sun helps shield Earth from galactic cosmic rays, which in turn affects the production of things like carbon-14 (important for age dating of ancient materials). A quiet Sun increases our cosmic dosage. More on that in Part 2.

Next page > Radioisotopes: Geologic Dates from Space > Page 2, 3, 4, 5, 6, 7

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