研究目的
To detect and study Europa's visible-wavelength atomic oxygen aurora to understand its atmospheric composition and variability.
研究成果
The first detection of Europa's visible-wavelength oxygen aurora confirms an O2-dominated atmosphere with column densities of (1–9)×10^14 cm^?2, consistent with previous UV studies. The non-detection of other emissions rules out high O/O2 mixing ratios and supports the potential for future detection of water plumes using optical aurorae.
研究不足
Observations were limited by weather conditions (e.g., cloud cover during Keck observations), high background noise from Jupiter's scattered light, and the need for Europa to be in eclipse. The electron density variability introduces uncertainty in derived column densities, and the non-detection of certain emissions (e.g., 5577 ?) limits constraints on mixing ratios.
1：Experimental Design and Method Selection:
Observations were conducted using the Keck I telescope and Hubble Space Telescope (HST) to capture optical spectra of Europa during eclipses by Jupiter, targeting auroral emissions at specific wavelengths. Data reduction involved standard pipelines for calibration and background subtraction.
2：Sample Selection and Data Sources:
Europa was observed on six occasions in February–April 2018 while in Jupiter's shadow to avoid reflected sunlight interference.
3：List of Experimental Equipment and Materials:
HST with STIS CCD and G750M grating, Keck I telescope with HIRES spectrograph, using specific slit sizes and spectral settings.
4：Experimental Procedures and Operational Workflow:
For HST, images were taken in dither positions, split for cosmic ray removal, and processed using calstis pipeline. For Keck, observations involved offset tracking, bias correction, flat fielding, and wavelength calibration with Thorium–Argon lamps.
5：Data Analysis Methods:
Emission brightness was extracted using apertures matching Europa's disk size, with uncertainties derived from noise in emission-free regions. Ratios of emission lines were calculated to infer atmospheric composition.
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