June 9, 2015

The European Space Agency, or ESA, has chosen three final candidates as possibilities for an upcoming medium-class science mission, including the Turbulence Heating ObserveR, or THOR, mission -- which incorporates a key instrument built at NASA's Goddard Space Flight Center in Greenbelt, Maryland.
If chosen as the final candidate, THOR would orbit Earth observing the interaction of Earth's magnetic field with the steady stream of particles from the sun, called the solar wind. THOR would address a fundamental problem in space plasma physics – the study of the charged gases that fill up space -- concerned with how plasma is heated and how the energy subsequently dissipates. By studying the solar wind, the investigation would study the underlying physical mechanisms of plasma behavior under turbulent conditions. This would shed light on plasma elsewhere in space as well, helping to understand a key interaction between planets and their host stars.
NASA Goddard will contribute a fast electron plasma analyzer system to THOR. This system is patterned closely after the Fast Plasma Investigation now aboard the recently launched Magnetospheric Multiscale, or MMS, mission. This unique plasma analyzer is 100 times faster than any that have ever flown in the solar wind. It thus enables THOR to measure plasma properties at the time and distance scales needed to truly quantify this turbulent energy dissipation – scales never before observed in space.
"It is tremendously gratifying that the MMS fast plasma architecture, on which so many have worked so hard, is seen to be an key element of the THOR mission," said Tom Moore, project scientist for MMS at NASA Goddard.
ESA chose two additional mission concepts to be explored further: one to study exoplanets, called Atmospheric Remote-Sensing Infrared Exoplanet Large-survey (Ariel), and one to study the X-ray universe, called the X-ray Imaging Polarimetry Explorer (Xipe).

Image: This instrument is part of the Fast Plasma Investigation flying on NASA's Magnetospheric Multiscale, or MMS, mission. A similar instrument built at NASA Goddard might fly on a mission currently being considered by ESA -- called the Turbulence Heating ObserveR, or THOR.