Mark Showalter

Mark Showalter
Senior Research Scientist
Curriculum Vitae: 
Discipline: 
Planetary Astronomy

Planetary astronomer Mark Showalter is rabid about rings. While everyone knows about Saturn’s spectacular ring system, it’s often forgotten that Jupiter, Uranus, and Neptune are also encircled by fainter and narrower rings. Each of these systems interacts closely with a family of small, inner moons. Showalter works on some of NASA’s highest-profile missions to the outer planets, including Cassini, now orbiting Saturn, and New Horizons, which flew past Jupiter en route to its 2015 encounter with Pluto. He has even searched for the rings of Mars, although so far with no success. Known for his persistence in planetary image analysis, Mark's work on the earlier Voyager mission led to his discovery of Jupiter’s faint, outer “gossamer” rings and Saturn’s tiny ring-moon, Pan.

Mark was recently granted three more years to study the system of rings and moons orbiting Uranus with the Hubble Space Telescope. He has been leading a team of astronomers in this investigation off and on since 2002. This work has already led to the discovery of two small moons and two faint rings. He enjoyed the opportunity to name the moons "Mab" and "Cupid," after characters from Shakespeare's plays. For the next few years, he hopes that this work will illuminate the subtle interactions at work within a dense pack of moons and rings that circle the planet. The system shows signs of chaotic motion, which means that the orbits are slightly unpredictable and collisions between moons can occur on time scales as short as one million years. That may sound like a long time, but it is astonishingly short for a system that is more than 4 billion years old.

Rings and the faint moons that interact with them are more than just local anomalies. They serve as dynamical laboratories where we can observe some of the same processes that operate, albeit on much larger scales, in galaxies and during the formation of planetary systems.

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Observations of the Pluto System During the New Horizons Encounter Epoch

Observations of the Pluto System During the New Horizons Encounter Epoch

Observations and Dynamics of Ring-Moon Systems

The Cassini data sets have provided remarkable new insights about the processes at work among the rings and small moons of Saturn. Guided by these discoveries, we will seek out and investigate related phenomena in the ring-moon systems orbiting Jupiter, Uranus, Neptune and Pluto. We will employ data from Voyager, Cassini and New Horizons, complemented by the best publicly available data from HST and from the W. M. Keck Telescope. We will apply new and powerful image analysis techniques that should enable us to obtain significant new results from old data.

Precision Pointing Reconstruction and Backplanes in Support of Cassini Remote Sensing Science

The objective of this proposal is to generate several higher-order data products that will substantially reduce the level of effort required to analyze Cassini's optical remote sensing data sets (ISS, VIMS, CIRS and UVIS), by eliminating the need for most scientists to perform their own navigation and geometric reconstruction.

Initial Analysis of Pluto's Tiniest Moon

This is an unsolicited proposal to perform the initial scientific analysis of Pluto’s tiniest moons, the recently-discovered “P4” (S/2011 (134340) 1; Showalter et al. 2011) and “P5” (S/2012 (134340) 1; Showalter et al. 2012b). It will enable the P.I. to determine the bodies’ orbits, shapes and sizes based on all of the available Hubble data, using established measurement and modeling techniques. The results of this analysis will be published promptly and will be presented at a scientific workshop about the Pluto system in July 2013.

Orbital Evolution and Stability of the Inner Uranian Moons

Orbital Evolution and Stability of the Inner Uranian Moons

CIRS Investigations of Planetary Rings

This is a new, five-year proposal to support the work of CIRS co-investigator Dr. Mark Showalter on behalf of the Cassini Project. It is a successor to our current cooperative agreement, NNX06AC85A. The predecessor agreement has supported the Cassini-related activities of Dr. Showalter and his SETI Institute colleagues Dr. Stu Pilorz, Robert French and, briefly, Dr. Nicolas Altobelli. This report provides a brief summary of our accomplishments during the previous agreement and outlines our plans for the years ahead. The Cassini Mission is now expected to continue into 2017, so this proposal describes our planned work for most of the remainder of the Cassini tour. Our activities encompass conducting fundamental scientific research with the CIRS data, plus meeting a large and continuing set of responsibilities for mission operations and planning.

Orbital Evolution and Stability of the Inner Uranian Moons

Orbital Evolution and Stability of the Inner Uranian Moons

New Horizons Mission Planning Support: A Deep Search for Faint Rings of Pluto

New Horizons Mission Planning Support: A Deep Search for Faint Rings of Pluto

Preserving Voyager's Legacy: Image Calibration and Geometry Reconstruction

The Voyager flybys remain our best source of data for the Uranus and Neptune systems, and provide key reference points for continuing studies of Jupiter and Saturn. However, because the Voyager mission pre-dates NASA's focus on archiving, the data sets remain difficult to use. We propose to modernize the Voyager data sets by (a) producing calibrated and geometrically corrected versions of all the images; (b) generating accurate, continuous "C kernels" describing the pointing of the instruments during each Voyager flyby; and (c) using this information to generate detailed geometric indices describing the contents of the Voyager images and spectra. The resulting volumes of derived products will be delivered to the Planetary Data System. This work will ensure that the Voyager data sets remain easily usable by the scientific community for many decades to come.

Orbital Evolution and Stability of the Inner Uranian Moons

Orbital Evolution and Stability of the Inner Uranian Moons

The Rings Node for the Planetary Data System

Continued improvements in the Planetary Data System, specifically the Rings Node, including development of an interactive website to engage the public about the diversity and significance of planetary ring systems.