Target of Opportunity Observation of an Episodic Storm on Uranus
Abstract
We propose a TOO observation of Uranus to capture the formation process of a dark anticyclonic vortex during an episodic convective storm. The planet Uranus continues to exhibit increased atmospheric activity after the 2007 equinox, likely in response to extreme insolation change (Hammel et al. 2005, Icarus 175, 284, Sromovsky et al. 2009, Icarus 203, 265, Sromovsky et al. 2007, Icarus 192, 558, Sromovsky et al. 2012, Icarus 220, 6). We hypothesize that Uranian dark spots emerge from an episodic outburst, and predict that such a spot will form in the near future. The historical record makes references to such discrete structures (both bright and dark) on Uranus during previous equinoctial apparitions (Alexander 1965; the last equinox occurred in 1965). Furthermore, northern high-latitudes are now coming into view after 40+ years of winter darkness, exhibiting unusual activities (Sromovsky et al. 2012, Icarus 220, 694). Our TOO will be triggered by amateur observations; the best amateur facilities are now able to resolve the disk of Uranus and detect such activity if it is very large or has very high contrast. Amateurs also have access to a great many nights of telescope time. If a discrete cloud feature on Uranus is reported through these networked professional and amateur ground-based observations, we propose to obtain follow-up images with Hubble's WFC3. The proposed TOO images will permit determination of detailed structure of the feature at visible wavelengths, and provide vertical and horizontal constraints on the feature's scattering properties. Hubble is the only facility that can provide such information at visible wavelengths.All WFC3 exposures have CR-SPLIT=NO to reduce overhead. POS-TARG offsets for quad filter WFC3 exposures have been specified to place target approximately 20 arcseconds closer to center of array relative to "optimal" aperture locations. This places the planet approximately 10 arcseconds towards the center of the array relative to the "QUAD-FIX" fiducial points. This has been done to reduce telescope move magnitudes (between different quads), while still leaving a 512 x 512 pixel area around the target outside of the quad filter vignetted regions.
- Publication:
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HST Proposal
- Pub Date:
- October 2014
- Bibcode:
- 2014hst..prop13712S