Skimming through the Sun's atmosphere

The surface of the Sun is an incredibly violent place that it is difficult for theorists to model or for experimentalists to reproduce on Earth. However, a paper in Science this week by Cooper Downs at the Predictive Science Inc. in San Diego and his colleagues show how a comet's close encounter with the Sun in 2011 can help us.

The Sun's surface is not only a very hot environment, but it's also subject to very strong magnetic fields produced by the Sun's interior. It is these magnetic fields that can trigger some of the most violent processes in the Sun, such as coronal mass ejections - the ejection of vast clouds of gas at very high speed, which can trigger the northern and southern lights if the collide with the Earth's magnetic field.

It is a difficult environment to model, both because of the infeasibility of building spacecraft that could survive the temperatures they would encounter flying through the Sun's atmosphere, and because of the difficult of reproducing anything so extreme in laboratories on Earth.

However, it is an environment we would very much like to be able to reproduce on Earth, as nuclear fusion reactions - reproducing the processes by which the Sun generates its energy - could be a future solution to the Earth's energy crisis.

Writing in the journal Science this week, Cooper Downs points out that even if it is difficult for us to send probes to travel through the Sun's atmosphere, nature provided just such a probe for us in 2011. In December of that year, comet 2011 W3 Lovejoy skimmed through the Sun's atmosphere, leaving a wake of steam and dust behind it, rather like the condensation trails that aircraft leave behind them.

Subsequently, this line of material has warped and distorted under the influence of the Sun's heat and magnetic field. By studying exactly how it behaves, Downs and his colleagues have produced estimates for how the Sun's magnetic field varies along the line. This is particularly valuable since magnetic field do not produce light of their own, and are normally invisible to telescopes.

Understanding how the Sun behaves is a formidable challenge and these observations are only one step along the way. Nonetheless, they provide theorists with a novel piece of data with which to constrain their models.