The Jupiter InfraRed Auroral Mapper

JIRAM will be the second image spectrometer to explore Jupiter after NIMS, the Near-Infrared Mapping Spectrometer, which operated on the NASA Galileo mission in 1995. JIRAM is the first Italian instrument of this kind to be sent to Jupiter. It belongs to a family of image spectrometers, which are currently flying on the ESA Rosetta and Venus Express missions as well as the NASA Dawn mission. The "first born" of this family is the visual channel of VIMS on Cassini.

The primary goal of JIRAM is to probe the upper layers of Jupiter's atmosphere down to pressures of 5-7 bars at infrared wavelengths in the 2- 5 μm interval using an imager and a spectrometer. The possibility of performing images, spectra or spectral images due to the simultaneous presence of the imager and the spectrometer inside JIRAM's optical head, allows great flexibility and the possibility to implement the appropriate mode for each mission phase.

By means of its high contrast imaging and spectroscopy, JIRAM will study the dynamics and chemistry of auroral regions and their link to Jupiter's magnetic field and magnetosphere. JIRAM will image the auroras using wavelengths around 3.4 μm where the emission of the H3+ ion in the polar region is strong. This wavelength overlaps a deep methane absorption band. As a result, one can image Jupiter's ionosphere at this wavelength with a large signal-to-noise ratio against the planet, otherwise darkened by absorption due to methane in its atmosphere. H3+ is formed in the Jovian ionosphere by the (hydrogen) ion-molecule reaction (H2+ + H2 —> H3+ + H) that follows ionization of molecular H2 by the charged particles falling on Jupiter and coupled with its strong magnetic field.

Jupiter emits radiation from its interior and is relatively brilliant around the 5 μm wavelength. However, the atmospheric gases, in particular methane (CH4), water (H2O), ammonia (NH3) and phosphine (PH3) modulate the transmission of such radiation by partial absorption which then leaves a signature of their presence in the atmosphere. Areas known as hot spots with higher radiation emission have been identified on Jupiter where the atmosphere is clearer and the inner part of the planet can be observed. JIRAM will study the Jovian hot spots in order to determine their vertical structure and hence, test their formation mechanisms. It will also measure the emitted thermal radiation from Jupiter's atmosphere to map water moist convection and determine the water abundance and other constituents at depths corresponding to the water clouds.

The JIRAM instrument is being developed by scientists from the Italian National Institute for Astrophysics. JIRAM is funded by the Italian Space Agency. The prime contractor for the hardware development is Galileo Avionica.