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Mars is a cold and barren planet. Yet it is not too cold and perhaps not too baren to consider colonizing at some distant point in the future. But getting there will be fraught with hazards. One of the greatest challenges to overcome concerns the dangers associated with space weather. |
20 March 2005 | During the last few decades, human kind has made considerable strides toward a better understanding of the conditions and environment around Mars. We currently have several high-profile missions at Mars and several more are planned. The goal is to study the planet and develop the techniques that will enable us to eventually travel there in person.
One of the unavoidable hazards that will exist for any astronaut will be the potentially fatal effects of space weather. Solar flares and coronal mass ejections are capable of significantly elevating radiation levels in space. The reason why astronauts at the Earth are kept relatively safe is due to the powerful protective influence of the Earth's magnetic field. That field acts as a shield that deflects much of the radiation away from the domain of the astronauts. But Mars has no such shield; nor does the Moon. Astronauts traveling to either of these orbs place themselves at considerable risk should an energetic solar proton flare erupt in the right place on the Sun and at the right time. For example, during the intense solar flare storm that occurred in March 1989 (a series of extremely energetic solar flares associated with intense coronal mass ejections directed Earthward and toward Mars), astronauts walking on the Moon would have received enough radiation to produce potentially lethal radiation sickness.
A key ingredient to protecting the astronauts from the hazards of space radiation therefore involves developing the ability to predict the timing and intensity of space radiation storms. This is no easy task, since the intensity and timing of radiation depends in a large measure on the state of the space environment between the Sun and the Earth, the Moon, or Mars. A powerful solar flare alone is not always sufficient to produce intense space radiation storms at the Earth. Very often, intense space radiation storms are produced by the combination of powerful solar flares together with high velocity coronal mass ejections.
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This simple animation shows show the shock front of each coronal mass ejection is capable of accelerating energetic protons to higher energies (and hence higher velocities), resulting in intense space radiation storms at the Earth. |
Solar flares are capable of enhancing radiation levels in space all by themselves. However, if there are one or more coronal mass ejections enroute to humans in space, the energetic protons released by the solar flare can be further accelerated as they pass through the leading shock fronts of the coronal mass ejections. By the time the protons reach a spacecraft enroute to the Moon or Mars (or persons living on the Moon or Mars), they may be accelerated to significantly higher velocities and energies. As a result, they can pose a much greater health risk to astronauts inside (or out) of the protective shield of their spacecraft or habitat.
A recent analysis of our ability to predict the timing of energetic space radiation storms was performed by an international group of scientists using one of the most successful space weather prediction models, known as the HAF model (named after the last names of the researchers who helped to create it: Hakamada, Akasofu and Fry). This model is in use by some space weather forecasters to help determine when the potentially damaging effects of space weather storms may arrive at the Earth. Given that this model is capable of estimating the large-scale features of the solar wind (including the arrival of coronal mass ejections and other space weather disturbances), it is also used to predict the influence of space weather at other locations such as Mars, even if Mars is located very distant from the Earth.
Dr. Susan M. P. McKenna-Lawlor was the principle investigator of this study. She examined the intense flare storm of March 1989, when numerous strong solar flares were observed that affected both the Earth and Mars. It was during this same period of events that spectacular effects were observed at the Earth, including an intense period of auroral storm activity that was visible into the very low latitude regions, as well as a devastating power outage that kept millions of people in the dark in Quebec.
Had astronauts been on (or near) Mars during these events, they would have been plagued by an unusually long-duration (greater than 20 days) energetic space radiation storm that would have required protective measures (perhaps huddling inside a protective shielded bay within their spacecraft). A question that has remained open for years is why Mars experienced such a long-duration radiation storm?
Dr. McKenna-Lawlor used the HAF model to study this question, and to simulate whether it is possible to predict the arrival of space weather storms at Mars. She discovered that although Mars was generally poorly located to observe the high-velocity impacts of the coronal mass ejections that inflicted damage at the Earth, it was not immune to the effects of those coronal mass ejections. The shock fronts from those coronal mass ejections were strong enough (in some cases) to refract all the way around the Sun and reform on the side facing Mars. In addition, the combined interaction of several of the coronal mass ejections was found to be sufficient to produce proton acceleration toward Mars, which she and her colleagues concluded was the probable source of the long-duration space radiation storm observed at Mars.
The implications of this work are potentially far-ranging. Their work demonstrates that although it may be presently possible to predict the influence of space weather at planets other than our own with reasonable accuracy, the interaction and merging of multiple coronal mass ejections during strong solar flare storms can produce secondary effects such as long-duration space radiation hazards that can not be dismissed. Indeed, solid solutions to these hazards should be found before we place astronauts in spacecraft destined for locations as remote and unprotected as Mars or the Moon.
This research was published in the Journal of Geophysical Research, volume 110 on 17 March 2005 (A03102, doi:10.1029/2004JA010587, 2005) by the American Geophysical Union.
[1]Susan M. P. McKenna-Lawlor, M. Dryer, C. D. Fry, W. Sun, D. Lario, C. S. Deehr, B. Sanahuja, V. A. Afonin, M. I. Verigin, and G. A. Kotova (2005), Predictions of energetic particle radiation in the close Martian environment, J. Geophys. Res., 110, A03102, doi:10.1029/2004JA010587, 2005.
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