The MUSE mission approved by NASA

There are still several secrets about the Solar corona that astronomers must unveil. The corona is the uppermost solar atmosphere, made by low-density gas with temperatures as high as a few million degrees (as a comparison, the plasma in photosphere and chromosphere is at about 5600 K and 10000 K, respectively). The energy required to heat the gas up to this temperature is stored by the magnetic field, and then thought to be often released during phenomena occurring on small spatial scales and called “magnetic-reconnection events”, due to rapid changes in the topology of the magnetic field lines. In fact, the hottest plasma and the most violent phenomena in the Solar corona, such as flares, occur in the regions with intense magnetic fields, called “active regions”.

Some of the phenomena related to the solar magnetic activity may have important consequences for Earth, such as the solar wind and the coronal mass ejections. These phenomena, in fact, release charged particles in the interstellar space. These particles, once trapped by the Earth magnetic field, can cause harmless and spectacular phenomena, such as the aurorae, or potentially dangerous phenomena such as geomagnetic storms. The study of these phenomena is of great interest, as proved by the fact that they are the subject of a new-born branch of physics, called “Space Weather”.

The perfect instrument that would allow us to study in details the physical processes involved in the magnetic solar activity should be capable of acquiring spectroscopic observations over a wide range of spatial scales, from the small scales at which the magnetic energy is released (≤ 0.5”), to the typical size of the active regions (>100”), with rapid sampling necessary to follow the variability of these phenomena on timescales of 20 sec. This is the concept of the mission MUlti-slit Solar Explorer (MUSE), which has been recently approved by NASA as a “Medium-class Explorer” mission, with a budget of $192 milions. MUSE will be equipped with a spectrograph and a camera. The spectrograph (MUSE 37-slits Spectrograph) will observe in three UV bands, designed in order to detect the typical emission of highly ionized Iron atoms, typical of active regions, and it has an innovative design of 37 parallel slits which will acquire spectra simultaneously. The camera (MUSE Context Imager) will provide images with a time cadence of 4 seconds, and with a resolution of 0.33″ over a field of view of 580″×290″. MUSE observations will allow us a significant step forward our understanding of the interaction between plasma and magnetic fields in the Solar corona, which is a unique laboratory in the Universe for such a studies. The principal investigator of MUSE is B. De Pontieu, of the Lockheed Martin Advanced Technology Center of Palo Alto, California. Among the collaborators there are F. Reale and P. Pagano of the University of Palermo, and A. Petralia of INAF – Astronomical Observatory of Palermo. MUSE is described in details in the paper: “Probing the physics of the solar atmosphere with the Multi-slit Solar Explorer (MUSE): I. Coronal Heating“, appeared on The Astrophysical Journal.

The figure (click here to visualize the entire image) shows an illustration of how MUSE will observe the details of an active region. The panels also show the temporal cadence of the observations, the field of view, the type of the emission observed and the plasma temperature which will be probed.