“The interesting feature in this case is that the process could possibly be important on much smaller scales, as well, with spicules, for example,” says Peter. This will be the task of future work with numerical models that have higher spatial resolution and the further comparison with observations.
After many decades of coronal research it is now agreed, beyond a doubt, that, fundamentally, the magnetic fields supply sufficient energy to heat the corona. Peter qualifies this: “But we still don’t know how this energy is transferred to the coronal plasma on the centimeter or meter scale.” Even his simulations can’t clarify this, because they compute the events on large scales of hundreds of kilometers. The solar researchers are in a similar situation to meteorologists: although their models can predict where it will rain with a certain probability, they can’t compute the drop formation in the cloud.
The researchers are pinning great hopes on a new solar observatory, the Solar Orbiter, which the European Space Agency ESA decided to build in the fall of 2011. The space telescope will be launched in 2017 and will orbit the Sun on an elliptical trajectory at a minimum distance of 42 million kilometers. This corresponds to less than one-third of the distance between Earth and Sun. Never before has a space laboratory come so close to our Sun. Furthermore, the orbit will be so strongly inclined with respect to the solar equator that it will also be possible to observe the Sun’s poles for the first time.
The Max Planck Institute in Lindau is involved with four of the ten scientific instruments. The institute is supervising the development of a magnetograph that will measure the magnetic field and the plasma velocity. Moreover, a spectrometer based on the experience gained with SUMER will investigate the corona with unparalleled accuracy and very high temporal resolution.
The scientists don’t have much time: They have to deliver the instruments to ESA in 2015. And before they do, they must perform lots of experiments – “For example with materials and optics that survive the very high temperatures and very heavy particle bombardment from the solar wind and flares,” explains Eckart Marsch, one of the initiators of the Solar Orbiter. The observatory will come so close to the Sun that the space probe’s heat shield will reach 500 degrees Celsius.
At this close distance, it will also be possible to measure the original properties of the particles in situ, and in the precise same state in which they come from the surface of the Sun and fly off into interplanetary space along the magnetic field lines. One of the aims is to calculate the trajectories of the particles back to their origin on the Sun, in order to gain a better understanding of how waves and turbulences propagate in the solar wind.
This would enable the researchers to study the close interaction of the plasma with the active magnetic field of the Sun and its heliosphere. This data would then be incorporated into the 3-D modeling of the particle propagation. “One of the main motivations behind the Solar Orbiter is to understand the microphysics of the corona,” says Marsch, who is looking forward to a golden age of solar research.
That part of the universe between the different planets of the solar system. This space is occupied by planetoids and gas, as well as interplanetary dust and particles of the solar wind.
A gas that is partially or completely comprised of ions and electrons, that is, of free charge carriers. To put it simply, a plasma is electrically conducting and is often described as the fourth state of matter. More than 99 percent of visible matter in the universe is in the plasma state.
Regions that are around 1,500 degrees Celsius cooler than the undisturbed visible solar surface (photosphere). Owing to the low temperature, they appear dark in contrast. Sunspots are caused by disturbances in the solar magnetic field. They often appear in groups, and many are larger than our Earth. Furthermore, their number follows, on average, an 11-year cycle.
A stream of charged particles - mainly protons, electrons and helium nuclei (alpha particles) - that the Sun continuously blows into space. The speed of the solar wind is around 400 kilometers per second, but it can also reach 900 kilometers per second.