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Space science in the realm of the giant planets and beyond, as conducted by Southwest Research Institute (SwRI), is active beyond the asteroid belt.

New Horizons Mission to Pluto

The New Horizons mission to Pluto was conceived at SwRI-Boulder and launched toward Pluto in January 2006. The spacecraft is now well beyond the orbit of Saturn, and will fly past Pluto and its moons Charon, Nix, and Hydra (the last two co-discovered by Boulder staff) in July 2015, greatly improving our understanding of these worlds and icy dwarf planets in general.

New Horizons Discoveries

New Horizons made its first discoveries in early 2007, when it flew past Jupiter at a range of 2 million km and used the giant planet’s gravity to speed the journey to Pluto. The spacecraft’s images of Jupiter itself revealed new details of its complex storm systems, including unprecedented near-infrared time-lapse views of ammonia-rich thunderstorms being torn apart by the planet’s intense winds. New Horizons obtained some of the best-ever images of Jupiter’s faint ring system, discovering a series of mysterious clumps of ring material. Images of its volcanic moon Io documented an enormous eruption from the volcano Tvashtar, obtaining movies of its 350-km-high plume. These close-up observations were supplemented using the Hubble Space Telescope and ground-based telescopes. The peculiar lumpy atmosphere of Io and charged particles that escape Io and fill the Jovian magnetosphere are subjects of additional ground-based and spacecraft investigations.

Pluto's Atmosphere

	Europa rises past the limb of Jupiter as seen by the New Horizons spacecraft.

Even as it awaits the New Horizons flyby, Pluto is under regular scrutiny from Earth. Pluto’s atmosphere was discovered in 1988 by means of stellar occultation, in which a planetary body passes between the observer and a background star. A subsequent pair of occultations in 2002 revealed, surprisingly, that the atmospheric pressure had doubled despite Pluto’s increasing distance from the Sun. To further study these changes, the Boulder staff formed an occultation group in 2002, with members who have since traveled the world — wherever a star happens to cast Pluto’s shadow on the Earth — to record five subsequent Pluto occultations using a combination of local observatories and portable telescopes. These data are detailing changes in the structure, dynamics and shape of Pluto’s atmosphere, paving the way for New Horizons’ 2015 close-up view.

NASA's Cassini Spacecraft Orbits Saturn

Somewhat closer to home, NASA’s Cassini spacecraft has been orbiting the ringed planet Saturn since 2004, providing unprecedented information about the planet and its moons. Staff members have been involved both in planning Cassini’s observations and in understanding many facets of the data.

Volcanic Activity on Enceladus

	The active "tiger stripe" fractures at the south pole of Enceladus glow with internal heat in this composite, false-color image from the Saturn-orbiting Cassini spacecraft. Image courtesy NASA/JPL/GSFC/SwRI/SSI

In July 2005, Cassini’s Composite Infrared Spectrometer (CIRS) revealed enormous amounts of thermal radiation from tectonic fractures at the south pole of Saturn’s small moon Enceladus — one of a series of observations by multiple Cassini instruments that revealed Enceladus to be only the third world in the solar system, after Earth and Jupiter’s Io, known to be currently volcanically active. The high heat flux and geological activity near the moon’s south pole is driven by tidal flexing of Enceladus due to its eccentric orbit around Saturn. Follow-on theoretical work suggests that Enceladus has an ocean beneath its ice shell. Energy created by tidally driven raising and lowering of the ice shell by tens of meters each day is transported to the surface by solid-state convection, which provides a natural explanation for the intense heat, volcanism and deformation.

Atmospheric Comparisons: Titan to Earth

Most exotic of all Saturn’s moons is Titan. By far the largest moon, wrapped in a smoggy atmosphere almost five times as dense as Earth’s, Titan also exhibits many of the same weather phenomena as Earth. The air is mostly nitrogen, similar to Earth’s atmosphere, but the predominant volatile compound is methane, not water. Titan conditions permit methane to condense as both ice and liquid, so methane likely participates in a cycle similar to Earth’s hydrological cycle. Atmospheric simulations indicate that a critical level of methane is required to initiate convective clouds. The relatively clear region where the Huygens probe landed in 2005 was far below this threshold. These clouds, which appear to be similar to terrestrial thunderstorms, can also produce centimeters to hundreds of centimeters of precipitation in only a few hours — sufficient to carve the river-like channel features observed across much of Titan’s surface.

Seasons on Saturn

	Saturn's narrow F ring and broad A ring were photographed by the Cassini spacecraft soon after Saturn's August 2009 equinox. Shadows are cast onto the rings by thick clumps within or at the edges of empty gaps in the A ring. Image courtesy NASA/JPL/SSI

Like Earth, Saturn has seasons. During the first five years of Cassini’s mission, Saturn’s southern hemisphere experienced summer. In August 2009, the Sun crossed to the northern hemisphere and briefly illuminated Saturn’s rings edge-on. During this event, which occurs just once every 15 years, the rings and moons cast shadows on each other. Most parts of the rings are only about 10 meters thick, due to the energy lost during collisions between ring particles. However, observations of the rings planned by SwRI Cassini scientists and colleagues during this year’s "equinox" have shown that some parts of the rings are not meters, but several kilometers, thick.

For more information about our outer solar system research capabilities, or how you can contract with SwRI, please contact Robert Grimm, Ph.D., at rgrimm@swri.org or (720) 240-0149.

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Southwest Research Institute^® (SwRI^®), headquartered in San Antonio, Texas, is a multidisciplinary, independent, nonprofit, applied engineering and physical sciences research and development organization with 11 technical divisions.

December 28, 2012