Positive outcome from the CLASP-II solar physics experiment that involved IRSOL

On April 11, 2019, at the NASA facility at the White Sands Missile Range in New Mexico (USA), the successful launch of a sounding rocket was performed as part of the “Chromospheric LAyer Spectro-Polarimeter” experiment (CLASP-II). The experiment also involved the the Istituto Ricerche Solari (IRSOL, associated with USI) in the theoretical interpretation of the data. This activity requires also the application of sophisticated computational methods, for the development of which IRSOL collaborates closely with the Institute of Computational Sciences (ICS) at the USI Faculty of Informatics.

CLASP-II is an international collaboration led by NASA's Marshall Space Flight Center (USA), the National Astronomical Observatory of Japan (NAOJ, Tokyo, Japan), the Instituto de Astrofísica de Canarias (IAC, Tenerife, Spain) and the Institut d’Astrophysique Spatiale (IAS, Orsay, France). Additional partners are the Astronomical Institute of the Academy of Sciences of the Czech Republic (ASCR), the Istituto Ricerche Solari Locarno (IRSOL, Switzerland), Lockheed Martin Solar & Astrophysics Laboratory (Palo Alto, USA), Stockholm University (Sweden), and the Rosseland Center for Solar Physics Research (Oslo, Norway).

The goal of CLASP-II was to provide new spectro-polarimetric observations of a particular layer of the solar atmosphere, the chromosphere. This complex region is at the core of several key problems, and its investigation is today one of the main priorities in solar physics research. One of the most interesting and debated aspects of the chromosphere is undoubtedly its magnetism. The contribution of IRSOL to the experiment concerns the theoretical interpretation of the CLASP-II data, with the aim of extracting as much information as possible on the magnetism of the upper solar chromosphere.

The acquisition of this information requires the comparison of the data provided by CLASP-II with the results of theoretical simulations performed in three-dimensional models of the solar atmosphere. These simulations are extremely complex, and require the use of powerful calculation tools, for the development of which it is essential to combine complementary skills in the fields of solar physics and computational sciences. This is precisely the objective of the "Sinergia" project of the Swiss National Fund for Scientific Research (SFNS) currently underway, involving IRSOL (Dr. Luca Belluzzi, member of the CLASP-II project), ICS (Prof. Rolf Krause), and IAC (Prof. Trujillo Bueno, principal investigator of the CLASP-II project and responsible for the theoretical part of the experiment).  

Solar magnetic fields can be investigated by exploiting the signatures that they leave in a particular property of light: the polarization. CLASP-II succeeded in providing unprecedented measurements of the intensity and polarization of ultraviolet light emerging from the upper chromosphere. These unique observations will now be exploited to get new precious information on the strength and orientation of the magnetic fields present in this region of the solar atmosphere. This kind of information is crucial for understanding, for instance, the physical mechanisms that trigger high-energy solar phenomena, like flares or coronal mass ejections. If directed towards the Earth, these explosive events may be dangerous for astronauts, or may damage the electronic devices aboard satellites, on which our technology-dependent society strongly relies. 

Solar radiation at ultraviolet wavelengths cannot be observed from ground, and for this reason a suborbital rocket experiment has been proposed within the framework of the NASA's Sounding Rocket Program. Sounding rockets are simpler and more affordable than satellite missions, and offer a great opportunity to scientists to test new ideas and achieve rapid results. CLASP-II was launched on Thursday, April 11, at 12:51pm (local time) from the White Sands desert in New Mexico, aboard a NASA's Black Brandt IX sounding rocket. The rocket reached an altitude of 170 miles (about 273 km), before descending by parachute. The payload was recovered in good condition. The measurement was perfectly performed during the five minutes of observation: both the pointing system and the spectropolarimeter worked very well. A first analysis of the data has shown a good agreement with the theoretical predictions.