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We used gravity mapping observations from NASA’s Gravity Recovery and Interior Laboratory (GRAIL) to detect, characterize and validate the presence of large impact craters buried beneath the lunar maria. In this paper we focus on two prominent anomalies detected in the GRAIL data using the gravity gradiometry technique. Our detection strategy is applied to both free-air and Bouguer gravity field observations to identify gravitational signatures that are similar to those observed over buried craters. The presence of buried craters is further supported by individual analysis of regional free-air gravity anomalies, Bouguer gravity anomaly maps, and forward modeling. Our best candidate, for which we propose the informal name of Earhart Crater, is approximately 200 km in diameter and forms part of the northwestern rim of Lacus Somniorum, The other candidate, for which we propose the informal name of Ashoka Anomaly, is approximately 160 km in diameter and lies completely buried beneath Mare Tranquillitatis. Other large, still unrecognized, craters undoubtedly underlie other portions of the Moon’s vast mare lavas.

NASA's GRAIL mission employed twin spacecraft in polar orbits around the Moon to measure the lunar gravity field at unprecedentedly high accuracy and resolution. The low spacecraft altitude in the extended mission enables the detection of small-scale surface or subsurface features. We analyzed these data for evidence of empty lava tubes beneath the lunar maria. We developed two methods, gradiometry and cross-correlation, to isolate the target signal of long, narrow, sinuous mass deficits from a host of other features present in the GRAIL data. Here, we report the discovery of several strong candidates that are either extensions of known lunar rilles, collocated with the recently discovered “skylight” caverns, or underlying otherwise unremarkable surfaces. Owing to the spacecraft polar orbits, our techniques are most sensitive to east-west trending near-surface structures and empty lava tubes with minimum widths of several kilometers, heights of hundreds of meters, and lengths of tens of kilometers.

We model the formation of lunar complex craters and investigate the effect of preimpact porosity on their gravity signatures. We find that while preimpact target porosities less than ~7% produce negative residual Bouguer anomalies (BAs), porosities greater than ~7% produce positive anomalies whose magnitude is greater for impacted surfaces with higher initial porosity. Negative anomalies result from pore space creation due to fracturing and dilatant bulking, and positive anomalies result from destruction of pore space due to shock wave compression. The central BA of craters larger than ~215 km in diameter, however, are invariably positive because of an underlying central mantle uplift. We conclude that the striking differences between the gravity signatures of craters on the Earth and Moon are the result of the higher average porosity and variable porosity of the lunar crust.

Analysis of transient deformation events in time series data observed via networks of continuous Global Positioning System (GPS) ground stations provide insight into the magmatic and tectonic processes that drive volcanic activity. Typical analyses of spatial positions originating from each station require careful tuning of algorithmic parameters and selection of time and spatial regions of interest to observe possible transient events. This iterative, manual process is tedious when attempting to make new discoveries and does not easily scale with the number of stations. Addressing this challenge, we introduce a novel approach based on a computer-aided discovery system that facilitates the discovery of such potential transient events. The advantages of this approach are demonstrated by actual detections of transient deformation events at volcanoes selected from the Alaska Volcano Observatory database using data recorded by GPS stations from the Plate Boundary Observatory network. Our technique successfully reproduces the analysis of a transient signal detected in the first half of 2008 at Akutan volcano and is also directly applicable to 3 additional volcanoes in Alaska, with the new detection of 2 previously unnoticed inflation events: in early 2011 at Westdahl and in early 2013 at Shishaldin. This study also discusses the benefits of our computer-aided discovery approach for volcanology in general. Advantages include the rapid analysis on multi-scale resolutions of transient deformation events at a large number of sites of interest and the capability to enhance reusability and reproducibility in volcano studies., Comment: Published in the Journal of Volcanology and Geothermal Research. 9 pages, 7 figures

Multiring basins, large impact craters characterized by multiple concentric topographic rings, dominate the stratigraphy, tectonics, and crustal structure of the Moon. Using a hydrocode, we simulated the formation of the Orientale multiring basin, producing a subsurface structure consistent with high-resolution gravity data from the Gravity Recovery and Interior Laboratory (GRAIL) spacecraft. The simulated impact produced a transient crater, ~390 kilometers in diameter, that was not maintained because of subsequent gravitational collapse. Our simulations indicate that the flow of warm weak material at depth was crucial to the formation of the basin’s outer rings, which are large normal faults that formed at different times during the collapse stage. The key parameters controlling ring location and spacing are impactor diameter and lunar thermal gradients.

This paper describes the development of a networked collaborative hypermedia system intended to support groups of writers and scholars in writing and publishing hypertext fiction and criticism. The current system supports the importation of individually-developed Storyspace hypertext documents into a MUD-based collaborative workspace for integration and expansion, and allows for the immediate publication of these dynamically-generated multimedia documents onto the World-Wide Web. In addition, we provide a forms-based writing and linking interface to the text, so that writers can write using either the MUD-based or the forms-based authoring tools. Since the HTML is generated dynamically from our underlying database, we have added the capabilities to: allow for user negotiation of content and bandwidth (e.g., only small versions of the pictures, with the audio and text in German, with movies), provide the bandwidth-intensive media from distributed mirror sites. This system is being used by dozens of students, writers, and theorists around the world to support such projects as: hypertext writing and theory classes at Brown and Vassar, a hypermedia version of David Blair's feature-length film, WAX or the Discovery of Television among the Bees, a collaborative women's hypertext fiction writing group, and the creation of an electronic journal to discuss the impact of technology on writing practice.

This paper describes our experiments with narrative structure in nonlinear, interactive and networked forms of media. Through these explorations, we have begun to anticipate what types of tools will be useful to tell stories in multi-user 3D immersive environments incorporating synthetic actors.

We describe the structure and development of WAXweb, a dynamic MOO-based hypermedia database which is being used as a VRML server. We also discuss the future of 3D MUD-like systems, describing the particular problems of highly-interactive, distributed 3D scenes. So that we can begin to experiment with these areas using commonly-available VRML browsers, this paper describes several extensions for VRML 1.x which will allow for simple dynamic multiuser interactions.

Animal studies have demonstrated that ventilation can be deferred for several minutes in witnessed arrest if chest compression is initiated promptly. It is unknown if this observation is also valid in situations of a “prolonged down time”. To assess whether immediate ventilation was essential following a prolonged down time arrest, six 20-30 kg, dogs were studied following ventricular fibrillation (VF). Chest compression (no ventilation) at 80-90/min was initiated after 6 min. Aortic pressure (pr) and blood gases were monitored. Pre-VF aortic pr; pH: PCPCO2 and O2 saturation (%02 sat) at room air were 136 ± 9.8/109 ± 8 mmHg; 7.38 ± 0.03; 37.9 ± 2.3; 97.5 ± 0.5% (M ± SEM). Following a 6 min downtime (DTl. there was no substantial change in arterial blood gases (graphs below). After 2 min of chest compression only the corresponding values were still 55 ± 13/21 ± 7 mmHg, 7.3 ± 0.0, 44.6 ± 1.6 and 90.8 ± 3.8%. Download : Download high-res image (65KB) Download : Download full-size image These data suggest that in a dog model. even following a prolonged down time, chest compression alone can maintain adequate gas exchange to sustain 02 saturation g90% for g2 minutes. The need for immediate ventilation during resuscitation must be reexamined.