SETI Institute Weekly Colloquium
At the Microsoft Campus in Mountain view
1065 La Avenida St, Mountain View CA
FREE and open to the public. Tuesdays, noon to 1pm
The coldest known exoplanets are still much hotter than the gas giant planets in our own Solar System. Pushing to colder temperatures requires observing in the thermal infrared (3-5 microns) where self-luminous gas-giants peak in brightness.
Dr. Skemer will present observational studies characterizing the atmospheres of the coldest exoplanets and the coldest brown dwarf. These observations include a planet whose metallicity is higher than its host star, and a 250 K brown dwarf which shows signs of water clouds. Additionally, he will describe a new instrument that can obtain spectroscopy of directly imaged planets from 3-5 microns.
Thanks to numerous ground and space-based surveys, we are now aware of over 3300 planets orbiting other stars, with another nearly 2500 candidates from the Kepler Mission awaiting confirmation. The Universe is teeming with rocky and gaseous bodies. How did these planet systems form and evolve toward their present configurations? The answer to this question lies in the study of young planets and their formation environments. In this talk Dr. Cody will show how high-precision time series data from space telescopes is beginning to illuminate the conditions surrounding planet formation and the star-disk connection.
Progress is being made on two fronts. First, high cadence photometry of accreting young stars is revealing the structure of inner circumstellar disks on spatial scales inaccessible to direct imaging. In some cases, we are able to observe occultations by coherent dust clumps which may be the precursors to planetesimals. Second, the onset of the K2 mission is enabling an unprecedented search for exoplanets at ages of a few to 100 million years. Dr. Cody will present a selection of exquisite photometric time series from several recent campaigns, highlighting the case of K2-33b, a recently discovered transiting planet around a newborn star in the Upper Scorpius region.
Dwarf galaxies tend to form stars inefficiently. Yet, blue compact dwarf (BCD) galaxies are a subset of dwarf galaxies that have intense and concentrated star formation (compared to typical dwarf galaxies). BCDs are thought to require a large disturbance to trigger their burst of star formation. A common theory is that the enhanced star formation in a BCD is the result of an interaction with another galaxy or a dwarf-dwarf galaxy merger. However, many BCDs are relatively isolated from other galaxies, making an interaction or a merger a less likely starburst trigger.
As part of the atomic hydrogen dwarf galaxy survey, LITTLE THINGS*, Dr. Ashley has studied the gaseous properties of six BCDs. Atomic hydrogen data allow us to explore the velocity fields and morphologies of the gas in BCDs, which may contain signatures of star formation triggers, such as gas consumption, a past merger, and interaction with previously undetected companions. If BCDs have formed through gas consumption or dwarf-dwarf mergers, then they would be useful analogs for galaxy formation in the early universe. Also, learning which large disturbance has triggered the burst of star formation in BCDs could be useful for understanding and modeling how/whether BCDs evolve into/from other types of dwarf galaxies.
The understanding of the early stages of planet formation from a disk of orbiting particles is an ongoing challenge for astrophysics and planetary science. Dr. Marcus will address the importance of instabilities in the particle disk as a link in the planetary formation chain.
Without instabilities, gas around a forming protostar remains in orbit, and the final star cannot form; dust grains cannot accumulate to form planets; and the compositions of meteorites cannot be explained. Unfortunately, the Keplerian motion within a disk is assumed by most astrophysicists to be stable by Rayleigh’s theorem because the angular momentum of the disk increases with increasing radius.
Dr. Marcus will show that there is a new purely hydrodynamic instability that is violent and destabilizes the protoplanetary disk, filling it with turbulence. The essential ingredients of the new instability are rotation, shear, and vertical density stratification, so the instability can occur in stratified Boussinesq (or fully compressible) Couette flows. The new instability occurs at critical layers where neutrally-stable eigenmodes are singular in the inviscid limit (but finite, with a width that scales as the Reynolds number Re to the -1/3 power when viscosity is present) and requires an initial finite-amplitude perturbation. In a flow initialized with weak Kolmogorov noise with initial Mach number Ma, when Ma > Re-1/2 (~10-7 in a protoplanetary disk) the instability will be triggered and create turbulence and large-volume and large-amplitude vortices that fill the disk. When the initial perturbation is an isolated vortex, the vortex triggers a new generation of vortices at the nearby critical layers. After this second generation of vortices grows large, it triggers a third generation. The triggering of subsequent generations continues ad infinitum in a self-similar manner creating a 3D lattice of turbulent 3D vortices.
Pluto's main atmospheric species, N2, is also frozen on its surface, as are its minor atmospheric species, CH4 and CO. The New Horizons spacecraft found complicated and intriguing evidence for a dynamically interacting surface and atmosphere. The REX instrument shows a planetary boundary layer that depends on whether there's N2 ice available to sublimate.
Altitude appears to be a factor in the distribution of both N2 and CH4 ice, with N2 favoring lower altitudes (higher pressures, so higher condensation temperatures), whereas some high ridges are coated in CH4 frost. Sublimation may be responsible for some of the stranger geologic forms on Pluto. Finally, preserved landforms may point to earlier ages with more widespread volatile ice coverage or higher surface pressures.
Dr. Young will talk about the evidence, and some of the ways New Horizons is influencing how we think about Pluto's atmosphere and surface.
It is widely accepted that the occurrence of methane (CH4) in the Martian atmosphere may imply the presence of active geological sources, i.e. gas emission structures in the Martian soil and subsoil. In other words, gas seepage, a process well known on Earth, should exist on Mars. The concept of gas seepage,although obvious for many geologists, especially those working in gas geochemistry and petroleum geology, is ignored or poorly known by Mars methane science community. The seminar will offer a discussion on the fundamentals of seepage, its potential occurrence on Mars (via microseepage, mud volcanoes, faults, degassing from serpentinized rocks) and possible detection techniques. Basic concepts on potential methane origin on Mars (biotic vs abiotic) will be discussed and clarified, considering some confusion and misinterpretations in present literature.
Giuseppe Etiopeis a senior researcher, geologist, at the Istituto Nazionale di Geofisica e Vulcanologia in Rome, Italy. He works on the origin, occurrence, and migration of gas in the geosphere, with particular reference to biotic hydrocarbons in sedimentary basins and abiotic gas in serpentinized ultramafic rocks. He studies the origin of methane, gas seepage phenomena and their implications for the environment, energy resource exploration and planetary geology (methane on Mars). He published 164 articles and a Springer’s book on “Natural Gas Seepage”. H index: 27 (Web of Science); 32 (Google Scholar).
In the last few years we have found that Mars' south polar cap has as much carbon-dioxide as Mars' current atmosphere. This raises numerous questions about how this massive deposit formed and what Mars was like when it was in the atmosphere. Using a combination of methods including spacecraft imagery, radar, and modeling we can start to answer some of these questions. Carver Bierson will discuss evidence that these deposits may have formed over several cycles of Mars atmosphere collapsing onto the surface and then sublimating back into the atmosphere.