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Alfred Schachter

Koyal Group InfoMag - Planetary Scientists Create Global Geologic Map of Ganymede

Discovered in 1610, Ganymede has a diameter of 5,268 km, around 8 percent larger than that of Mercury and much larger than Pluto. The history of this largest moon in our Solar System can be divided into three phases: an early phase dominated by impact cratering and mixing of non-ice materials in the icy crust; a phase marked by great tectonic upheaval; and a late phase characterized by a gradual drop in heat flow and further impact cratering. The surface of Ganymede has been formed through a variety of processes and is a mix of two types of material: very old, highly cratered dark regions, and younger lighter regions.
“The dark/light distinction is based on sharp relative albedo contrasts at terrain boundaries, rather than on absolute albedo, because several other types of surface modification change the absolute albedo within these terrain classes. Dark materials cover 35 percent of Ganymede’s surface; almost the entire remainder of the surface is covered by light materials,” the researchers said in the description of the new map.
“Dark materials are heavily cratered, though not as heavily cratered as the surface of the neighboring satellite Callisto, suggesting that dark materials cannot be a primordial surface. At high resolution, dark materials are dominated by the downslope movement of loose dark regolith within impact craters and on the sides of bright ridges and hummocks. Observations suggest that dark materials are covered by a thin lag deposit of dark regolith derived by sublimation of a more ice-rich crust below. Dark materials commonly exhibit sets of concentric arcuate structures known as furrows. Furrows may be the remnants of ancient multi-ring impact basins, similar to intact impact basins on Callisto, such as Valhalla and Asgard.”
 “Light materials crosscut dark materials and exhibit a lower impact crater density, demonstrating that they were formed later. Light materials are subdivided into an intricate patchwork of crosscutting lineaments called grooves, mixed with areas of relatively smooth terrain.”
“At high resolution, most light materials are dominated by extensional faulting. Even light materials that appear to be smooth at low resolution are marked at high resolution by sets of parallel lineaments of apparent tectonic origin.”

“There is an open question on the extent to which light terrain is formed by cryovolcanic flooding of dark material with brighter ice versus tectonic destruction of preexisting surface features and exposure of brighter subsurface ice in fault scarps; it is certainly possible that both of these processes play important roles in the formation of light materials.”

Koyal Info Group Mag: History-Making Expedition Recruits New Scientists


The "Rising Star Expedition", known for its recent recovery of one of the largest troves of hominin (early human) fossils ever discovered in one place, is now ambitiously seeking new early-career scientists to study the more than 1,200 fossil elements retrieved from the site and now housed at the University of the Witwatersrand (Wits University) in Johannesburg, South Africa.


"The fossil material is an exceptional sample representing most of the parts of the skeleton, and our first task is to describe the material and place it into the context of hominin evolution," says John Hawks, a paleoanthropologist with the University of Wisconsin-Madison and a key member of the team that recovered the fossils during the Fall of 2013.


To that end, Professor Lee Berger of Wits University initiated an effort to recruit the best young minds he can find to help examine the finds and publish some of the first scientific observations, analyses and conclusions about the morphology, among other aspects, of the fragments, and what they might mean in terms of their place in the broad scope of human evolution. Berger has been at the forefront of major hominin fossil discoveries in South Africa, such as the recent Australopithecus sediba finds at the Malapa cave site.


"We are seeking early-career scientists with data and skill sets applicable to the study of any part of the anatomy of early hominins," say Berger and colleagues in the recently released announcement. "Participants must be willing to share these data and skills in a collaborative workshop designed to study, describe and publish these important hominin fossils."


While the workshop participants will receive mentoring from established senior scientists, their publications will be under their authorship and will be considered to be "high impact" publications.


The project is at least in part representative of Berger's philosophy of "open science", where scholars and scientists from all over the world are invited to play an active role in the process of research and discovery, expanding the perspectives, skills and knowledge sets brought to bear on finding the answers to important research questions. Traditionally, research on new finds in the field of paleoanthropology has often been conducted by a relatively closed set of scholars or scientists over a long period of time, resulting in new hypotheses or theories and conclusions that might have been different if 'more eyes' were brought to bear on the subjects of study.


The workshops are also intended to help build a bigger, brighter future for the science.


"We are recruiting an international team, and we are especially interested in building a group that will continue to produce great science in the future," says Hawks.


The trove of bones was first discovered in a south African cave system in October, 2013 by a pair of skilled cavers, who then alerted Berger. To investigate the cave and its contents, Berger spearheaded the assembly of an expeditionary group (called the "Rising Star Expedition") of scientists. Along with chief scientists, the group included six researchers (who Berger dubbed "underground astronauts") who were hand-picked to actually enter the cave system to excavate and remove the fossil bones. To qualify for this job, these team members had to have a master's degree or Ph.D. in paleontology, archaeology or a related field; they had to be experienced spelunkers, or cavers; and they had to be small enough to successfully and safely negotiate an 18-centimeter-wide opening leading to the targeted cave chamber. The effort has proven to be a great success, producing more than 1,200 fossil specimens representing a number of individuals initially identified as early hominins. The type of hominin is still unknown. It is one of the questions that the workshop project team hopes to answer.


There is more ahead. While excavating, the Rising Star team found evidence of articulated skeletons just below the levels where they were digging. These have yet to be recovered.


"Thousands of elements are left there", said Berger on a recent National Geographic weekend radio show. "We have excavated an area of only half the size of a normal breakfast table, and two or three inches deep, to recover more than a thousand elements of more than a dozen individuals.....and just underneath [that] surface, we find articulated remains -- their bodies are there, and that's what I had to close up."


Berger plans to return to the site for further excavation.


More information about the Rising Star Expedition can be acquired at the National Geographic website dedicated to covering the project. For scientists interested in applying for the Workshop, see this website for additional information.


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Source: http://popular-archaeology.com/issue/june-2013/article/history-making-expedition-recruits-new-scientists