Asteroid Tanning in the Solar Wind Salon

Asteroids tan fast in the solar wind (ESO)

In a study carried out by European Southern Observatory (ESO) scientists, it was found that asteroids are susceptible to sunburn. By comparing the material found inside meteorites here on the ground with the colour of asteroids floating in space, there is a huge difference; the asteroids in space are redder.

So far, this might not be too surprising, after all, the surface of Mars is red with ferrous oxides (rust), why shouldn’t asteroids be red too? Actually, asteroids aren’t necessarily made of the same stuff as Mars, and they aren’t getting tanned due to the Sun’s ultraviolet rays; asteroids are bathed in ionizing solar wind particles, causing the asteroid’s surfaces to redden over a period of time. And that period is short when compared with Solar System time scales. It only takes a million years for the surface of young asteroids (born from energetic asteroid collisions) to weather under the constant barrage of particles from the solar wind.

This has some interesting implications for asteroid studies. Possibly the most striking factor this study uncovers is the nature of near-Earth asteroids that have been observed exhibiting comparatively “young” surfaces, apparently free from solar wind reddening. Previously, astronomers have agreed that these young surfaces were down to recent asteroid collisions. However, the period of the solar wind tanning effect is much shorter than asteroid collision frequency. So even if two asteroids collided, in all likelihood, if we observed one of these asteroids, the solar wind would have weathered the surface back to its reddened state.

It turns out that some near-Earth asteroids have “young” surfaces due to gravitational interactions with planets as they pass. When this happens, the red dust is “shaken off”, revealing the untouched rock beneath.

For more, check out my article Young Asteroids Age Fast with a Solar Wind Tan on the Universe Today.

An Explanation For Solar Sigmoids

Hinode X-ray observation of a solar sigmoid (David McKenzie/Montana State University)
Hinode X-ray observation of a solar sigmoid (David McKenzie/Montana State University)

Sigmoids in the solar corona have been studied for many years, but little explanation of their formation or why they are often the seed of powerful solar flares have been forthcoming. Using high-resolution X-ray images from the Japanese-led solar mission Hinode (originally Solar-B), solar physicists have known that these very hot S-shaped structures are composed of many highly stressed magnetic flux tubes filled with energized plasma (also known as ‘fibrils’), but until now, little was known about the formation and flare eruption processes that occur in sigmoids.

Now, a team of solar physicists from the University of St Andrews believe they have found an answer using powerful magnetohydrodynamic (MHD) computer models, aiding our understanding of coronal dynamics and getting us one step closer to forecasting space weather…

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