SETI Institute Weekly Colloquium - Upcoming Speakers
Brown dwarfs are sub-stellar objects that occupy the region of parameter space between gas giant planets, like Jupiter, and the smallest bona fide stars. Since brown dwarfs never achieve sustained core hydrogen fusion, they are destined to cool over cosmic timescales from thousands to hundreds of degrees Kelvin. Observations and models of these strange worlds reveal hydrogen-dominated atmospheres with a variety of trace molecular species, as well as metal, dust, and salt condensates.
Recent surveys and targeted observations have revealed that a substantial fraction of brown dwarfs have a brightness that varies in time, with some variations as large as 30% at certain wavelengths. In this presentation, Dr. Robinson will review the atmospheric physics of brown dwarfs and the current state of variability observations, and he will discuss the various processes that likely cause brown dwarf variability, which include dynamical effects, temporally- and spatially-varying clouds, and associated atmospheric temperature fluctuations.
It has been proposed that in Gale Crater, where the Curiosity rover landed in August 2012, lakes developed to various depths after the large central mound (informally referred to as Mt. Sharp) had evolved to a form close to its current topography. Using a combination of CTX and HiRISE imagery and CTX, HiRISE and HRSC topography, we have documented a sequence of rising and falling lake levels, thereby providing a possible relative timeline of the hydrologic events within Gale crater. Assuming that the entrance canyon deposits (the canyon which the Curiosity rover will ascend once it reaches Mt. Sharp) records a back-stepping sequence of fans and deltas, then a corresponding hydrologic sequence is suggested. After the formation of a gilbert-type delta exiting an 84-km long incised valley (Farah Vallis) that drains 270,000 km2 to the south of Gale, and a corresponding lake with an average depth of 700 meters, the inflow of water from Farah Vallis fell or ceased. The lake level dropped considerably, to an elevation at least below the entrance canyon deposits. At a later time, local precipitation drove gully erosion of the Gale rim, and amplified by renewed Farah Vallis runoff, caused a rising lake level that produced deltas on the western rim of Gale and the entrance canyon deposits on Mt. Sharp. This hydrologic system shut down sufficiently abruptly that the deltas did not cut down as the lake evaporated. The time gap between these two lake forming events, perhaps driven by different hydrologic systems, is not yet established. Fan deposition around Gale crater, including the Peace Vallis fan near the rover’s landing site, likely occurred after these large lakes disappeared. This has implications for understanding regional paleo-climates on Mars after the Noachian, as well as providing context for the geology and sedimentology along the Curiosity rover traverse.
Jeff Moore will give a pre-encounter view of our expectations for the New Horizons flyby of Pluto.
Dr. Militzer will briefly review the interior structure of different types of planets and discuss how it is affected by the miscibility of various planetary materials. Results from recent ab initiocomputer simulations will be presented that focus on the miscibility properties of four systems: hydrogen-helium mixtures in gas giant planets, hydrogen-water mixtures in ice giants, silicate-iron mixtures in the interiors of terrestrial planets.
Finally Dr. Militzer will discuss his recent model of Jupiter’s interior that he and his team are putting together before NASA’s Juno spacecraft inserts into orbit about this planet next year.