February 2014

Tuesday, Feb 4
3:45 pm
LPL Graduate Student Colloquium: Margaret Landis and Sarah Peacock
Margaret Landis
Graduate Student in the Department of Planetary Sciences
A Review of: "Reading the Climate Record of the Martian Polar Layered Deposits"
Hvidberg et al. 2012, Icarus 221

Sarah Peacock
Graduate Student in the Department of Planetary Sciences
A Review of: "The Ultraviolet Radiation Environment Around M Dwarf Exoplanet Host Stars"
France et al. 2013, Astrophysical Journal 763
Kuiper Space Sciences: Room 312
Monday, Feb 10
12:00 pm — 1:00 pm
CANCELED Brown Bag: Dr. Colin Dundas
Dr. Colin Dundas
Research Geologist
Astrogeology Science Center, USGS

Host: Shane Byrne
Kuiper Space Sciences: Room 309
Tuesday, Feb 11
3:45 pm
LPL Colloquium: Dr. Walter Harris
Dr. Walter Harris
Associate Professor
University of Arizona - Lunar and Planetary Laboratory

The Big Shock That Wasn't: Or Was It?

The heliopause is the broad region marking the transition from space defined by the outflowing solar wind and rarefied local interstellar medium (LISM). This region is far too remote for easy in situ study, but fairly simple to conceptualize theoretically. In the classic model the heliopause itself is a standoff between counter-flowing regions with different plasma pressures and densities. Inside the heliopause, the solar wind decelerates across a termination shock and as it encounters the barrier itself. Outside the heliopause, the LISM encounters a similar process, starting with an upstream bowshock and ending with a pile up of plasma at the interface.

The past two decades have marked a sea change in our understanding of this region. Remote observations with the SOHO and Voyager spacecraft have mapped the spatial distribution and velocity of the incoming neutral LISM flow. At the same time, direct, in situ measurements of penetrating LISM from Ulysses and of energetic neutrals produced at the heliopause by IBEX have combined with termination shock and heliospause crossings by the Voyager spacecraft to produce a detailed map of the interface region shape. Combined these have greatly increased our understanding of the magnetic and plasma properties of the region immediately beyond the solar system.

In 2012 a new controversy emerged from an IBEX measurement of heliospheric hydrogen and helium that suggested the relative velocity between the LISM and the solar system is lower than previously thought. The lower velocity, when combined with models of the density, temperature, and magnetic field of the LISM suggested that the plasma Mach number was <1, in which case the long assumed upstream bow shock did not exist.

In this presentation, I will discuss the origins and basis for both the original assumption of a bow shock and the results that suggest it is not present. I will also discuss more recent observations and modeling that indicate flaws in both the original IBEX measurement of heliospheric neutrals and the modeling that led to the no-shock condition, and I will discuss new measurements that could be made to resolve the controversy.
Kuiper Space Sciences: Room 312
Monday, Feb 17
4:00 pm — 5:00 pm
TAP Colloquium: Sean M. Couch
Sean M. Couch
University of Chicago

At the Edge of Explosion: Simulating the Violent Deaths of Massive Stars
Core-collapse supernovae (CCSNe) are the luminous explosions that herald the death of massive stars. Neutron stars, pulsars, magnetars, and black holes are all born in these explosions. Observations show that certain CCSNe share a common progenitor with long gamma-ray bursts. CCSNe are also largely responsible for the production of heavy elements throughout the universe and for driving galactic chemical evolution. Despite the importance of CCSNe to our understanding of many aspects of the universe, the mechanism that reverses stellar core collapse and drives these explosions is not fully understood. I will discuss the current state-of-the-art in CCSN theory and simulation, with an emphasis on my work on three-dimensional CCSN simulations. Tremendous insights about the CCSN mechanism are being gained from these simulations, including the pesky result that 3D simulations are even less prone to explosion than 2D. I will highlight my recent work showing the tremendous importance of realistic progenitor structure for the CCSN mechanism and discuss new physics frontiers in CCSN theory that have the potential to reveal a successful explosion mechanism.
Kuiper Space Sciences: Room 308
Tuesday, Feb 18
3:45 pm — 4:45 pm
LPL Graduate Student Colloquium: Patrick Harner and Xianyu Tan
Patrick Harner
Graduate Student in the Department of Planetary Sciences
Martian Carbonates Hiding in Plain Sight? VNIR Spectra of Hydrated Carbonates

Xianyu Tan
Graduate Student in the Department of Planetary Sciences
A Review of: "3D Climate Modeling of Close-in Land Planets: Circulation Patterns, Climate Moist Bistability, and Habitability"
Kuiper Space Sciences: Room 312
Monday, Feb 24
12:00 pm — 1:00 pm
Brown Bag Colloquium: Dr. Gilda Ballester
Dr. Gilda Ballester
Associate Staff Scientist
U of A Lunar and Planetary Laboratory

Extended upper atmospheres of hot Jupiters from the perspective of UV transit observations with HST

The hot-Jupiter HD 209458b was the first exoplanet on which an extended upper atmosphere was discovered in H I reaching out to Roche-lobe distances. Many theoretical studies have followed that can explain the H I Lyman-alpha line transit absorption: the immense stellar extreme-UV and X-ray input should heat and drive a hydrodynamic outflow in the upper atmosphere, and the effects of magnetic-field plasma confinement and stellar-wind interaction have also been explored. Detection of other species can provide further constrains to our understanding of the system, and the heavy and abundant species of O I and C II, which should be dragged along by the lighter but dominant H I and H II gas, have also been observed. Their measured absorption depths require either heating by a higher stellar XUV flux than minimum solar values, additional super-solar abundances, and/or super-thermal processes broadening the absorption line profiles. HST/COS observations have been reported resolving a broad C II line absorption, but, unfortunately, we will show these results to be uncertain because the reference off-transit stellar data were not consecutive to the in-transit observation and suffer from significant stellar flux variations.

We will also show new evidence of an unexpectedly low activity on the star HD 209458 that is also long-term, revealing a significantly lower XUV flux to the planet than assumed in all previous models. This requires a re-evaluation of the energetics and super-thermal processes at play (and of the possible abundances). We will also present a new detection of Mg I in the upper atmosphere of the planet, but not of Mg II as would be expected. This detection provides new constrains and requires further study of the recombination rates that would be expected from current models. It also supports the previously proposed notion that Si and Mg are not effectively removed by condensation into silicates in the lower atmosphere of HD 209458b (in agreement with optical transit data). However, contrary to a previous claim of detection of Si III based on the above COS observations, our re-analysis of that data as well as of archival HST/STIS data shows a negative detection in these ions. The silicon may be present but at a different ionization state.

We will finish by presenting HST FUV observations of HD 189733b, a hot Jupiter that orbits close to a very active star. H I has been detected on the hotter upper atmosphere of this planet, and more recently OI has also been detected with COS. These neutrals are not as extended as on HD 209458b because of the larger photo-ionization rates. A great variation is seen in H I, which should be related to the large variability of the active star. A tentative C II detection shows an apparent early-ingress absorption, potentially revealing a magnetospheric signature, but the detection requires further confirmation due to the possibility of a stellar variation during the observations.

Clearly, the parameter space characterizing the upper atmospheres of hot Jupiters is vast, and new observations will be critical in our understanding of these systems.
Kuiper Space Sciences: Room 309
Tuesday, Feb 25
3:45 pm
LPL Colloquium: Dr. Gilda Ballester
Dr. Gilda Ballester
Associate Staff Scientist
U of A Lunar and Planetary Laboratory

Surprisingly great variety in the lower atmospheres of hot Jupiters as observed with HST
Hot Jupiters remain the most accessible of exoplanets for transit (and eclipse) studies, but their characterization is still in the early stages. We are using HST for an optical and near-IR spectral transit survey of eight hot Jupiters spanning the 1000-3000 K regime. Our recent results emphasize the great variety in the atmospheres of these planets.

Transit absorption signatures show the radius at which the atmosphere becomes optically thick to absorbing and scattering species. The optical (~0.3-1.0 micron) spectra are sensitive to scattering by molecular hydrogen and by aerosols, as well as to the strong Na I and K I D-lines that are expected to be prominent on these planets. The near-IR spectra sample the 1.4-micron water band also expected to be prominent for a solar-abundance (C/O<1) hot Jupiter.

Some results were initially unexpected, such as the detection on condensates on the hottest planet Wasp-12b, but they are beginning to be understood based on the temperature regime that spans the condensation of different species, on the day-to-night temperature contrast which is pronounced in the hottest targets, and on the strong ~1 day 3D dynamics on these tidally-locked planets. Nevertheless, large differences are also observed in the clarity of the atmospheres of planets with fairly similar effective temperatures. Another key result is that the aerosols can mute or totally obscure the 1.4-micron water band absorption in some planets, and thus interfere with the interpretation of C/O ratios based solely on IR transit data.

An unexpectedly large diversity is also seen in the alkalis. In some planets, a strong, high-altitude Na I absorption is detected that requires super-solar abundances, while no corresponding K I absorption is observed. Processes such as photo-ionization could be explored to enhance the Na/K neutral abundance ratios at these altitudes. In sharp contrast, however, the opposite Na I and K I absorption ratio is also observed. The planet with the strongest K I absorption has an effective temperature that is too high for the predicted path of Na condensation as Na2S, so unexpected element-to-element metallicity variations and chemical/condensation schemes must the explored in future models.
Kuiper Space Sciences: Room 312