New Horizons UV Observations of the Interplanetary and Interstellar Medium
Abstract
The Alice ultraviolet spectrograph on the New Horizons (NH) spacecraft has been performing routine observations of interplanetary medium (IPM) atomic hydrogen Lyman-α (Lyα) emission in the outer solar system, since well before the Pluto flyby in 2015. The observations include regularly spaced great-circle scans of the sky and pointed spectra near the downstream and upstream flow directions of interstellar H atoms. The NH Alice data agree quite well with Voyager observations made ~30 years previously at lower sensitivity. In particular, the decrease of IPM Lyα brightness in the upstream-looking direction as a function of spacecraft distance from the Sun follows an expected 1/r dependence, but with an extra added constant brightness of ~40 Rayleighs (Gladstone et al., Geophys. Res. Lett., 45, 8022, 2018). This additional brightness is a possible signature of the hydrogen wall at the heliopause or of a more distant galactic background. Besides constraining interplanetary medium hydrogen, the Alice spectra also provide useful constraints on other atomic species via resonance line emissions, since they cover a wavelength range of 52-187 nm. Initial results from recent Alice observations are presented here. Future observations are planned at a cadence of roughly twice per year. This research was supported by NASA contract NASW02008 to SwRI.
- Publication:
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American Astronomical Society Meeting Abstracts #235
- Pub Date:
- January 2020
- Bibcode:
- 2020AAS...23521107G