In August of 2005, the Mars Express spacecraft was dutifully sending back data on the stratigraphy of the upper regions of the Martian crust when its signal kept getting interrupted. NASA scientists wanted to know why. Now, a study by Boston University College of Arts & Sciences researchers provides a clear answer.
The study, authored by Professor Paul Withers and graduate student Kamen Kozarev of the BU Astronomy Department along with colleagues from around the world, pinpointed the altitude where very high-voltage protons emitted during solar flares can most strongly interfere with radio signals. The study was published in the Journal of Geophysical Research.
The researchers analyzed ion and electron densities at various altitudes in the Martian atmosphere following a solar flare. Very high-energy protons ejected from the Sun during a flare can strike neutral atoms (usually carbon dioxide) in the atmosphere so hard that they knock loose an electron, creating a free electron and a positive ion. If enough of these electrons and ions build up in the atmosphere, they can interfere with radio waves. That is what was happening to the Mars Express.
"There must be lots of ionization to account for losing radio waves," said Withers. He and his colleagues created a model that will help scientists better understand and predict the effect of highly charged protons on the Martian atmosphere.
Withers also co-published a separate study in the Journal of Geophysical Research on the effect of ultraviolet (UV) light and x-rays on the Martian ionosphere (part of the upper atmosphere) following a solar flare. Withers, first author Anthony Lollo (BU College of Arts & Sciences '10), and BU Astronomy graduate students Katy Fallows, Zach Girazian, and Majd Matta, found an almost ten-fold increase in electron density at lower levels of the ionosphere during a solar flare. Like a highly charged proton, an x-ray can strike a gas molecule and knock an electron out.
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