The Cassini visual and infrared mapping spectrometer (VIMS) investigation is a multidisciplinary study of the Saturnian system. Visual and near-infrared imaging spectroscopy and high-speed spectrophotometry are the observational techniques. The scope of the investigation includes the rings, the surfaces of the icy satellites and Titan, and the atmospheres of Saturn and Titan. In this paper, we will elucidate the major scientific and measurement goals of the investigation, the major characteristics of the Cassini VIMS instrument, the instrument calibration, and operation, and the results of the recent Cassini flybys of Venus and the Earth-Moon system.

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The opposition effect, the sharp surge in brightness of an astronomical object observed near zero phase angle, which has been known for more than a century, has generally been explained by shadow hiding. The reflectances of several Apollo lunar soil samples have been measured as a function of phase angle in linearly and circularly polarized light. All samples exhibited a decrease in the linear polarization ratio and an increase in the circular polarization ratio in the opposition peak. This provides unequivocal proof that most of the lunar opposition effect is caused by coherent backscatter, not shadow hiding. This result has major implications for the interpretation of photometric observations of bodies in the solar system, including the Earth.

Observations of Saturn's satellite Enceladus using Cassini's Visual and Infrared Mapping Spectrometer instrument were obtained during three flybys of Enceladus in 2005. Enceladus' surface is composed mostly of nearly pure water ice except near its south pole, where there are light organics, CO2, and amorphous and crystalline water ice, particularly in the region dubbed the "tiger stripes." An upper limit of 5 precipitable nanometers is derived for CO in the atmospheric column above Enceladus, and 2% for NH3 in global surface deposits. Upper limits of 140 kelvin (for a filled pixel) are derived for the temperatures in the tiger stripes.

Abstract. She provided intellectual guidance for the entire project, developing agenda for the weekly phone calls and for the two stakeholder meetings. She developed the analytical framework for understanding risks in community-engaged research and played a major role in all of the drafts of the manuscripts. She provided content expertise in research ethics and human subjects protections. Mr. Loup was the research associate for this project and worked with Dr. Ross in the intellectual development of the three manuscripts. He also worked on multiple draft revisions, performed library searches, organized weekly conference calls for the writing group, and coordinated the two stakeholder meetings. Dr. Nelson was a key member of the writing group; attended both stakeholder meetings and many phone meetings; and commented, critiqued, and provided detailed constructive criticisms on numerous drafts. He provided content expertise in human subjects protection. The work reported in this article was conducted prior to Dr. Nelson joining the U.S. Food and Drug Administration, and do not represent the views and/or policies of the FDA or the Department of Health and Human Services. Dr. Botkin was a key member of the writing group; attended both stakeholder meetings and many phone meetings; and commented, critiqued, and provided detailed constructive criticisms on numerous drafts. Dr. Kost was a key member of the writing group; attended the initial stakeholder meeting and many phone meetings; commented, critiqued, and provided detailed constructive criticisms on numerous drafts; and provided content expertise in human subject protections and research subject advocacy. Mr. Smith was a key member of the writing group; attended both stakeholder meetings and many phone meetings; and commented, critiqued, and provided detailed constructive criticisms on numerous drafts. He provided content expertise on the role of community research partners and helped ensure that the manuscripts provided a balance between the needs of the academic research community and their community partners. Dr. Gehlert worked with Dr. Ross as a content expert in community-engaged research. Dr. Gehlert was instrumental in inviting a broad range of stakeholders and helped ensure that the manuscripts reflected current communityengaged research practice and policy.

Spectra from Cassini's Visual and Infrared Mapping Spectrometer reveal that the horizontal structure, height, and optical depth of Titan's clouds are highly dynamic. Vigorous cloud centers are seen to rise from the middle to the upper troposphere within 30 minutes and dissipate within the next hour. Their development indicates that Titan's clouds evolve convectively; dissipate through rain; and, over the next several hours, waft downwind to achieve their great longitude extents. These and other characteristics suggest that temperate clouds originate from circulation-induced convergence, in addition to a forcing at the surface associated with Saturn's tides, geology, and/or surface composition.

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Titan is the only satellite in our Solar System with a dense atmosphere. The surface pressure is 1.5 bar (ref. 1) and, similar to the Earth, N2 is the main component of the atmosphere. Methane is the second most important component, but it is photodissociated on a timescale of 10(7) years (ref. 3). This short timescale has led to the suggestion that Titan may possess a surface or subsurface reservoir of hydrocarbons to replenish the atmosphere. Here we report near-infrared images of Titan obtained on 26 October 2004 by the Cassini spacecraft. The images show that a widespread methane ocean does not exist; subtle albedo variations instead suggest topographical variations, as would be expected for a more solid (perhaps icy) surface. We also find a circular structure approximately 30 km in diameter that does not resemble any features seen on other icy satellites. We propose that the structure is a dome formed by upwelling icy plumes that release methane into Titan's atmosphere.