Picture this SELFI: A Maturation Project for a Submillimeter Enceladus Life Fundamentals Instrument (SELFI)

The Submillimeter Enceladus Life Fundamentals Instrument (SELFI) is a passive remote sensing submillimeter spectrometer being developed under NASA's Maturation of Instruments for Solar System Exploration (MatISSE) program. SELFI will advance submillimeter receiver technology beyond that of the Microwave Instrument for Rosetta Orbiter (MIRO) and the Submillimeter Wave Instrument (SWI) for the JUpiter ICy moons Explorer (JUICE). SELFI's science goals at Enceladus are to 1) investigate the chemical and isotopic compositions and corresponding densities of the plumes, the plume thermal structures, and the transport mechanisms within the plumes, and 2) characterize the source regions from which the plumes emerge. To satisfy these science objectives, SELFI will have fine radiometric resolution, high spectral resolution (resolving power R > 10⁶), multiple continuum channels with temperature sensitivity down to 10 K, and with high dynamical range, necessary to map Enceladus across its 30 K to 250 K temperature range.

SELFI will simultaneously observe fourteen molecular species in the Enceladus plumes that are important in the context of life and habitability of the subsurface ocean environment. These remote sensing measurements will:

- Assess the spatial and temporal variabilities in the plume chemical compositions;

- Provide insight into the subsurface ocean environment by monitoring H₂O, HDO, ∂¹⁸O, and ∂¹⁷O;

- Constrain the oxidation state of the surface ocean using H₂O₂and O₃, and;

- Utilize the SO₂and H₂S spectral signatures to constrain the impact arising from both the sea-floor volcanoes and pre-biotic molecules.

Moreover, the detection of the remaining molecular species is vital to better understand the ocean habitability - this also enables us to explore the chemical alteration processes arising from primordial volatiles that have been observed in comets. Lastly, the continuum observations correlate variations in plume activity with surface temperatures.

Under the MatISSE program, SELFI will advance - from TRL 4 to 6 - four key technologies of the RF-to-digital subsystem, which are:

- RF low noise amplifier design;

- Single-sideband (SSB) mixer and local oscillator (LO);

- IF assembly down-converter using monolithic microwave integrated circuit (MMIC) elements, and;

- Digital spectrometer electronics.