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Recent Podcast
Chandra's Archives Come to Life
Chandra's Archives Come to Life
Every year, NASA's Chandra X-ray Observatory looks at hundreds of objects throughout space to help expand our understanding of the Universe. (2014-10-22)


Ice Core Records: From Volcanoes to Supernovas

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Narrator (April Hobart, CXC)
To study space, scientists usually use telescopes in high and dry places atop mountains. Or they gather their data remotely from observatories far away in space. There are other ways, however, to learn about the cosmos.

Researchers have been traveling for decades to some of the coldest places on the planet – Antarctica and Greenland – to uncover some of the secrets from space that have been left behind on Earth.

Dr. Gisela Dreschoff is one of those scientists. Since the 1970s, Dr. Dreschoff, a professor at University of Kansas, has been traveling to these harsh and remote locations to conduct her science.

Dr. Dreschoff:
I've been going to Antarctica (South Pole). I probably spent a total of two years at the South Pole, but each season only a little bit, so 13 times in Antarctica. I’ve been at Vostok Station and several seasons in the Arctic.

Narrator:
Dr. Dreschoff originally went to Antarctica to study gamma ray radiation coming from space.

Dr. Dreschoff:
I was actually doing, with my colleague Zeller, a remote sensing project, and determining the radiation background of Antarctica using a gamma ray spectrometer and helicopters and C130s and so on. And so we did that for several years, and so as background, as we were flying over ice, there’s nothing coming from below in terms of radiation, and so all we were measuring was radiation coming from space.

Narrator:
Soon, Dr. Dreschoff began looking at ice cores, cut from hundreds or even thousands of feet below the frozen surface, for other clues about the cosmos. Scientists study ice cores to track phenomena that happened in the Earth’s past including climate variability, forest fires, and volcanic activity. Dr. Dreschoff, however, was interested in effects from the Sun. She began looking for so-called solar proton events, where there is an outburst from the Sun.

Dr. Dreschoff:
The charged particles coming from the sun, we figured, should produce ionization of the atmosphere. And so especially what I was interested in was individual solar proton events. General solar activity had been suggested from auroral activity once before, but I wanted to see if it was possible to see individual solar proton events, because then that would mean, if we could see those, it would mean the signal was real, that you know, it could only have come from the sun.

Narrator:
Charged particles from solar activity follow the Earth’s magnetic field lines and enter the atmosphere above the polar regions. The particles ionize nitrogen and oxygen, generating oxides of nitrogen called nitrates as the end product.

Dr. Dreschoff:
We figured that any particles, energetic particles, charged particles, coming into the polar atmosphere should generate ionization, ionization of nitrogen and oxygen. When that is ionized, it easily forms chemical bonds, oxides of nitrogen, and the ultimate oxidation product is NO3.

Narrator:
Dr. Dreschhoff explains why the polar regions are the best place on Earth to look for this type of signature from space.

Dr. Dreschoff:
Polar stratosphere, it gets so cold during the winter, it freezes out, and when it freezes out, it comes down to the surface as gravitational sedimentation, so it comes out quite fast, fast compared to any diffusive processes. So that means if there are gigantic, and there are, gigantic eruptions on the sun called solar proton events, when these protons enter the polar atmosphere they come spiraling down the open magnetic field lines in the polar regions, so they easily make it into the deeper atmosphere.

Narrator:
However, Dr. Dreschhoff began to wonder if signals from even farther away in space could be detected in the ice cores. She started to look for traces of historic supernova explosions, including those tied to famous supernova remnants observed by Chandra and other telescopes today.

Dr. Dreschoff:
Looking at the two Antarctic cores, and looking at the signal, and comparing these two cores, we found that there are particular impulsive events, nitrate events, which within our dating error, (which means for South Pole about ten years of dating error and for Vostok thirty years of dating error), within these error bars, these peaks corresponded. We compared 1200 years, because South Pole is only 1200 years, so 1200 years at the South Pole with 1200 years at Vostok Station, and there we found a peak near 1006, 1054 (Crab Nebula), 1320 and 1572 and 1604, which would be Kepler and before that Tycho and so on.

Narrator:
It is very important for astronomers to know precisely when these supernovas exploded. While there are some historic accounts by people who may have witnessed these stars exploding hundreds of years ago, having another line of evidence would be very exciting. Still, Dr. Dreschhoff cautions that her data are not conclusive, and like most scientists, she needs more data.

Dr. Dreschoff:
I certainly cannot say 100%. Nobody can. Okay? First of all, as I said, here we are with a number of impulsive nitrate events, and embedded in that, let’s say, are supernova signals. Now, if I have just one core, well, it can be pretty good if my data are very good. If I have two cores, or three, then it becomes pretty good, you know it’s getting better and better, but you can never be absolutely certain. Never.

Narrator:
So here we have two seemingly separate fields of science – geology and astrophysics – coming together to try to solve some very intriguing questions. In our next episode, we’ll learn more about Dr. Dreschoff’s research and the controversy surrounding perhaps the most famous supernova explosion of all time: Cassiopeia A.