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Outreach Observations of Uranus and Neptune in support of NASA’s New Horizons Mission

Presentation #115.04 in the session Community Science and Public Engagement in Planetary Science, Astronomy, and Solar Eclipses (Oral Presentation)

Published onOct 23, 2023
Outreach Observations of Uranus and Neptune in support of NASA’s New Horizons Mission

NASA’s New Horizons (NH) spacecraft observed Uranus and Neptune from its position in the outer solar system (>56 au) in September 2023 at high phase angles not otherwise attainable, concurrent with HST. The NH Project solicited simultaneous observations by the global amateur astronomy community to support this event. NH observed Uranus from 12:15 UT on Sept. 16 – 6:27 UT on Sept. 17 (17.2 hours) and Neptune from 7:35 UT on Sept. 22 – 16:59 UT on Sept. 23 (32.4 hours). Viewed from NH, the observation phase angles were 43° and 80°, respectively. These NH data provide new insights into the atmospheric radiation balance of both planets and are also geometrically similar to many exoplanet studies from ground- and Earth-orbit facilities. Key questions NH seeks to address with these observations include: What are the energy budgets and heat balances for each of these planets and what roles do water and convection play in their atmospheres? What fraction of incident sunlight does each planet absorb and how does this compare with the thermal energy each planet emits? While NH did not spatially resolve these planets, the new data significantly reduce uncertainties in the Voyager solar phase curve, while providing additional red/blue wavelength discrimination; the NH Multispectral Visible Imaging Camera (MVIC) extends observations to 0.98 µm. Concurrent observations from Earth at low phase angles (<3°) – even the week before and after spacecraft observations – from relatively modest 0.3-0.5-m class telescopes, can produce images that reveal atmospheric structure on these distant worlds. These contemporaneous observations will help break degeneracies in how the atmospheric aerosols scatter, better constraining their size and optical depth and reducing the number of free parameters. The observations of Uranus could include measuring the current brightness distribution across the planet, as well as the possible presence of discrete clouds. For Neptune, they include characterizing unusually bright features. They also provide a better temporal baseline for – and even help interpret – the originating mechanism(s) for structure in the NH and HST measurements. The NH observations of Uranus and Neptune will be downlinked later in 2023; here we report on the participation to date from the amateur community.

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