There have been four successful robotically operated Mars rovers, all managed by the Jet Propulsion Laboratory: Sojourner, Opportunity, Spirit and Curiosity. On January 24, 2016, NASA reported that current studies on Mars by Curiosity and Opportunity (the latter now defunct) would be searching for evidence of ancient life, including a biosphere based on autotrophic, chemotrophic or chemolithoautotrophic microorganisms, as well as ancient water, including fluvio-lacustrine environments (plains related to ancient rivers or lakes) that may have been habitable. The search for evidence of habitability, taphonomy (related to fossils), and organic carbon on Mars is now a primary NASA objective. In June 2018, Opportunity went out of contact after going into hibernation mode in a dust storm. NASA declared the end of the Opportunity mission on February 13, 2019, after numerous failures to wake up the rover.
"Ganymede's ocean might be organized like a Dagwood sandwich," commented Dr. Steve Vance in a May 1, 2014 statement. Dr. Vance, of NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California, went on to explain the weird moon's resemblance to the Blondie cartoon character's famous multi-layered sandwiches. The study, headed by Dr. Vance, provides new theoretical indications for the team's "club sandwich" model, originally proposed in 2013. The research appears in the journal Planetary and Space Science. Simply put, resistance to the creation of a space frontier originates with the insecurities of Western leaders. First, it is clear that everything changes with the emergence of a frontier. Established power structures are usually shaken, not reinforced. (If this is not clear, try reading Walter Prescott Webb's The Great Frontier, particularly the last chapter, and Divided We Stand: The Crisis of a Frontierless Democracy, by the same author.) The precise chemical composition of these very alien lakes and seas remained unknown until 2014, when Cassini's radar instrument detected Ligeia Mare, now known to be Titan's second-largest hydrocarbon-filled lake. Ligeia Mare is brimming with an abundance of sloshing methane, and this enormous liquid reservoir is approximately the same size as two of Earth's Great Lakes combined--Lake Michigan and Lake Huron. Many planetary scientists think that the seabed of Ligeia Mare may be blanketed with a thick layer of sludge that is composed of organic-rich compounds.