1.7% 0.3% 0.003%

Credit: NASA 1 2 6 7 16 H He C N S Carbon Nitrogen Sulfur

Source: Irwin (2009). of our : , composition, and structure, Chichester, UK: Praxis Publishing Ltd. URANUS DR. LEIGH FLETCHER Uranus is an , meaning that its chemical makeup differs from University of Leicester and , with strong enrichment in elements like carbon, nitrogen, sulfur, and oxygen, mixed with an atmosphere of hydrogen and helium. These elements were likely mixed into Uranus as it was forming billions of years ago, while being bombarded by the ice-rich building blocks in the outer solar system. All of these Dr. Leigh Fletcher is a planetary scientist key elements are found as molecules in a reduced form (i.e., combined with specializing in the exploration of our hydrogen) to form , , , and . To make solar system’s giant planets via robotic matters even more complex, the atmosphere of Uranus is so that these missions and groundbased . gases condense to form . The topmost clouds, seen in rare uranian He is a Royal Society University Research storms and atmospheric outbursts, comprise methane ice crystals. Beneath the Fellow (URF) and Associate Professor in methane ice clouds, we find a main deck of hydrogen sulfide ice. We can Planetary Sciences at the University of see the impacts of the hydrogen sulfide in our astronomical data, but if you had Leicester. He earned a Natural Science the misfortune to fly through the uranian clouds, you’d be quickly overwhelmed degree from Cambridge and a Ph.D. in by a pungent “rotten egg” smell. Deeper into the interior, we’d expect to find Planetary Physics from Oxford, and has water clouds — but these are so deep down that no or groundbased since worked as a NASA fellow at the Jet have ever been Propulsion Laboratory and as a Research capable of detecting them. Fellow at Oxford. His research uses The water might be in the spectroscopy of planetary atmospheres form of an exotic hot and from the to the and , using the unique signatures of black ice, which might be atmospheric gases and clouds to determine the global patterns of the most common form of and composition and how their climates vary with time. This research can reveal water in our solar system. the atmospheric dynamics, chemistry, and origins of these diverse giant planets. Its properties remain very Fletcher received the 2016 Harold C. Urey prize from the Division for Planetary mysterious, and future Sciences of the American Astronomical Society for outstanding achievements Two views of Uranus in the infrared as observed by the Keck missions to the ice are in by an early career scientist. He is a Co-Investigator on the in 2012 showing clouds of methane ices above needed to explore this exotic Cassini mission to Saturn and the JUpiter ICy Explorer (JUICE) mission a main cloud deck of hydrogen-sulfide ice. Uranus exhibits a mixture of chemical elements. banded structure, just like the other giant planets of our solar to Jupiter, and is a passionate advocate for future exploration of the distant ice system. Credit: NASA/ESA/L. A. Sromovsky/P. M. Fry/H. B. giants. He currently leads a planetary atmospheres team at the University of Hammel/I. de Pater/K. A. Rages. Leicester, funded by the Royal Society, the Science and Technology Facilities Council (STFC), and the European Research Council. You can follow his research on Twitter (@LeighFletcher).

Founded at the height of the program in 1968, the Lunar and Planetary Institute (LPI) is an The year 2019 marks the 150th anniversary of Dmitri Mendeleev’s development of the Periodic intellectual leader in lunar and planetary science. LPI’s mission is to advance understanding of the System and has been proclaimed the “International Year of the Periodic Table of Chemical solar system by providing exceptional science, service, and inspiration to the world. The research Elements” (IYPT2019). carried out at LPI supports NASA’s efforts to explore the solar system. www.iypt2019.org www.lpi.usra.edu