Seminars for Scientists

In the fifty years since the launch of Mariner 4, an armada of missions with progressively more sophisticated instrumentation has transformed our view of Mars, revealing a planet of outsized features with a complex geologic history and extraordinary climatological variations. Despite the wealth of observations, knowledge of the interior has been largely limited to inferences… Read more »

The behavior exhibited by dynamical systems is strongly influenced by the presence or absence of conserved quantities. When numerically modeling these systems, obtaining the correct long-term qualitative behavior requires retaining conservation laws in the numerical update rule. One method for constructing conservative numerical models is to derive the algorithm from a variational principle discretely analogous… Read more »

Though often considered a minor species, nitric oxide (NO) plays several key roles in the thermosphere. It terminates the ion-neutral chemistry due to its low ionization potential. Its long lifetime enables it to be transported to the middle atmosphere where it will catalytically destroy ozone. And as the primary heteronuclear species, infrared radiation from vibrationally excited… Read more »

The moon, like many objects in flowing plasma, gives rise to a rarefied quasineutral plasma wake that attracts ions along the magnetic field giving rise to beam-like ion distributions, known theoretically since the 1960s, and observed by satelites. Recent particle in cell simulations of the wake at realistic mass ratio show ion-disrupting instabilities grow in… Read more »

The Interstellar Boundary Explorer (IBEX) launched in Oct. 2008 and the observations by the Voyager spacecraft provided truly remarkable advances in heliospheric research. While Voyager provided in situ measurements of the plasma conditions on leaving our solar system, IBEX imaged the interactions occurring at the boundary of our heliosphere in all directions in space by… Read more »

Philae is a comet Lander, part of Rosetta which is a Cornerstone Mission of the ESA Horizon 2000 programme. In August 2014 Rosetta did rendezvous with comet 67P/Churyumov-Gerasimenko (CG) after a 10 year cruise. Both its nucleus and coma have been studied allowing the selection of a landing site for Philae. Philae was separated from the Rosetta… Read more »

By the time eukaryotic life or photosynthesis evolved on Earth, the Martian surface had become extremely inhospitable – cold, hyperarid, acidic, oxidizing and bathed in UV radiation. But, the subsurface of Mars could potentially have contained a vast microbial biosphere. Data from recent missions have revealed spectacular views of materials exhumed from the subsurface by… Read more »

Space weathering refers to the alterations suffered by solid materials when directly exposed (i.e. no atmosphere) to the space environment. The classic example is the weathering of the lunar regolith in which common rock-forming minerals decompose into glassy aggregates with nanophase iron. The lunar nanophase iron produces a characteristic spectral red slope. But how do… Read more »

All stars are believed to possess expanding outer atmospheres known as stellar winds. The continual evaporation of gas from stars has a significant impact on stellar and planetary evolution, and also on the larger-scale evolution of gas and dust in galaxies. Despite more than a half-century of study, though, the basic mechanisms responsible for producing… Read more »

The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft will end its mission at the end of April, crashing into the surface after four years in orbit and over a decade in space.  One of its instruments, the Mercury Atmospheric and Surface Composition Spectrometer (MASCS), was built here at LASP. In this talk I… Read more »

The present understanding of cirrus cloud microphysics and their radiative effects is limited, which is an important key for improving climate models. An optimal estimation-based algorithm using three infrared bands of the Moderate Resolution Imaging Spectroradiometer (MODIS) to retrieve cirrus radiative and microphysical properties has been developed. This IR method is suitable when cloud optical… Read more »

Organics and water-ice coexist in many parts of our solar system and in the interstellar medium, particularly where the temperatures are low. Interstellar ice grains, protoplanetary disks, evolved planetary systems consisting of outer planetary icy bodies, and small bodies like Kuiper Belt Objects and Oort Cloud – the birth places of comets, all these icy… Read more »

The Atmospheric Imaging Assembly (AIA) telescope on board the Solar Dynamics Observatory (SDO) provides coronal EUV imaging over a broader temperature sensitivity range than the previous generations of instruments (EUVI, EIT, and TRACE). Differential emission measure tomography (DEMT) of the solar corona based on AIA data is presented here for the first time. The main… Read more »

Impact craters are the most ubiquitous geological process in the solar system. Their uses as tools for understanding solid bodies in our solar system include: (1) age dating of planetary surfaces and geological processes, (2) informants of subsurface stratigraphy and geophysical properties of the crust, and (3) the physics of the impact process. In this… Read more »

The Mars Atmosphere and Volatile Evolution (MAVEN) mission is designed to explore the Mars upper atmosphere and its interactions with the Sun and solar wind. It’s goal is to understand the processes controlling the structure and composition of the upper atmosphere and ionosphere, to determine the escape rate of gas to space at the present… Read more »

An inverse correlation between the observed solar wind and the rate of expansion of magnetic flux tubes (FTE) within photosphere and inner corona was shown to exist by Levine et al. (1977). Wang and Sheeley, through a series of papers in the 1990s, established an empirical relationship between solar wind speed and FTE, suggesting that… Read more »

The rich dynamics of the Saturn ring and moon systems offer unique opportunities to study the evolution of the planet and its surrounding bodies. For instance, seismology of Saturn is made possible by the gravitational interaction between Saturn and its rings, in which density waves in the rings are excited by Lindblad resonances with Saturn’s… Read more »

The geologic history of the Solar System builds on an extensive record of impact flux models, crater counts, and ~270 kg of lunar samples analyzed in terrestrial laboratories. However, estimates of impactor flux may be biased by the fact that most of the dated Apollo samples were only tenuously connected to an assumed geologic context. Moreover, uncertainties… Read more »

A wealth of information about the climate cycle and ice budget of Mars is recorded within the layers of Martian polar caps. Using primarily subsurface observations with the Shallow Radar (SHARAD) instrument on board Mars Reconnaissance Orbiter (MRO), along with optical observations of the surface, we study the stratigraphic record of the ice caps to… Read more »

The Mars ultraviolet aurora was discovered in 2005 when observing the nightside limb with the SPICAM UV spectrometer on board ESA’s Mars Express (MEx) satellite. It was characterized by the transient presence of the CO Cameron bands between 140 and 180 nm and the CO2+ doublet near 289 nm which are normally absent on the… Read more »

Global energy balance models of the Martian atmosphere have predicted that throughout Martian history, for a range of initial total carbon dioxide inventories, the Martian atmosphere may be unstable relative to surface condensation. This is commonly referred to as atmospheric collapse. Since a collapsed state may limit the amount of time available for physical and… Read more »