Evolving Perspectives on the Atmosphere and Climate of Mars
Dr. Richard Zurek, JPL
Abstract: The planet Mars has both fascinated and tantalized humankind since the invention of the telescope and now well into the age of exploration from space. The first of three waves of space missions to Mars were flyby spacecraft that returned images of a heavily cratered planet with a thin atmosphere, suggesting Mars was more like the Moon than an older Earth. However, Mariner 9, the first spacecraft to orbit another planet, found vast channel and valley networks carved into its surface, as well as towering volcanoes, suggesting that ancient Mars was once much more Earth-like. Subsequent missions have landed on the planet and new orbiters have probed the planet at ever increasing spatial resolution and spectral coverage. As a result of the latest round of space exploration, Mars is revealed to be a complex, diverse planet— one whose climate has changed dramatically over time from an ancient atmosphere where water was active on its surface to a drier, thinner atmosphere shaped by periodic ice ages, to the present atmosphere where dynamic change continues today.
Dr. Zurek is the Chief Scientist in the Mars Program Office, Project Scientist, MRO.
Exploring Impact Heating of the Early Martian Climate
Kathryn Steakley, NMSU
ABSTRACT: Geological evidence implies that Mars may have had a more warm and wet environment during the late Noachian / early Hesperian era (3.5–3.8 billion years ago), but climate models struggle to reproduce such warm conditions. Prior studies with one-dimensional atmospheric models indicate that the water and energy from impacts could provide enough greenhouse warming to raise temperatures above the freezing point of liquid water for many years. We will use the NASA Ames Research Center Mars GCM to characterize potential atmospheric changes induced by impactors ranging in diameter from 50 m to 100 km on a range of early Mars surface pressure scenarios (10-mbar, 100-mbar, 300-mbar, 1-bar, 2-bar, 3-bar). Our objectives are 1) to examine the temperature behavior of the early Martian climate following impacts and determine if environmental conditions on its surface could support liquid water for extended periods of time, and 2) to quantify precipitation rates and examine rainfall patterns on a simulated early Martian surface following impacts and determine if this mechanism is possibly responsible for the formation of observed river valley networks on Mars. Examining climate conditions after impacts with a GCM will allow us to test a potential mechanism for heating the early Martian atmosphere, constrain the magnitude and temporal duration of these potential heating events, and provide insight regarding the availability of liquid water on early Mars which is relevant to its past habitability.
Star formation in the vicinity of the supermassive black hole at the Galactic Centre
Dr. Mark Wardle, Macquarie University
The disruptive tidal field near supermassive black holes overcomes the self-gravity of objects that are less dense than the Roche density. This was once expected to suppress star formation within several parsecs of Sgr A*, the four million solar mass black hole at the centre of the Galaxy. It has since become apparent that things are not this simple: Sgr A* is surrounded by a sub-parsec-scale orbiting disk of massive stars, indicating a star formation event occurred a few million years ago. And on parsec scales, star formation seems to be happening now: there are proplyd candidates and protostellar outflow candidates, as well as methanol and water masers that in the galactic disk would be regarded as sure-fire signatures of star formation. In this talk, I shall consider how star formation can occur so close to Sgr A*.
The stellar disk may be created through the partial capture of a molecular cloud as it swept through the inner few parsecs of the galaxy and temporarily engulfed Sgr A*. This rather naturally creates a disk of gas with the steep surface density profile of the present stellar disk. The inner 0.04 pc is so optically thick that it cannot fragment, instead accreting onto Sgr A* in a few million years; meanwhile the outer disk fragments and creates the observed stellar disk. The isolated young stellar objects found at larger distances, on the other hand, can be explained by stabilisation of clouds or cloud cores by the high external pressure that permeates the inner Galaxy. A virial analysis shows that clouds are indeed tidally disrupted within 0.5 pc of Sgr A*, but outside this the external pressure allows self-gravitating clouds to survive, providing the raw material for ongoing star formation.
Observations of Solar System Bodies with the VLA and ALMA
Dr. Bryan Butler, NRAO
Observations of solar system bodies at wavelengths from submm to meter wavelengths provide important and unique information about those bodies. Such observations probe to depths unreachable at other wavelengths – typically of order 10-20 wavelengths for bodies with solid surfaces, and as deep as tens of bars for those with thick atmospheres (the giant planets). In the past five years, two instruments have been commissioned which have revolutionized the ability to make very sensitive, high-resolution observations at these wavelengths: the Karl G. Jansky Very Large Array (VLA) and the Atacama Large Millimeter/Submillimeter Array (ALMA). I will present a discussion of results over the past five years from observations from both the VLA and ALMA. These include observations of the atmospheres of all of the giant planets, the rings of Saturn, and the surfaces of many icy bodies in the outer solar system. I will also present plans for the Next Generation Very Large Array (ngVLA), the next step for millimeter to centimeter wavelength interferometry.
Giant Planet Shielding of the Inner Solar System Revisited: Blending Celestial Mechanics with Advanced Computation
Dr. William Newman, UCLA
The Earth has sustained during the last billion years as many as five catastrophic collisions with asteroids and comets which led to widespread species extinctions. Our own atmosphere was literally blown away 4.5 billion years ago by a collision with a Mars-sized impactor. However, collisions with comets originating in the outer solar system accreted much of the present-day atmosphere. Relatively advanced life on our planet is the beneficiary of a number of impact events during Earth’s history which built our atmosphere without destroying a large fraction of terrestrial life. Using very high precision Monte Carlo integration methods to explore the orbital evolution over hundreds of millions of years followed by the application of celestial mechanical techniques, the presentation will explain directly how Earth was shielded by the combined influence of Jupiter and Saturn, assuring that only 1 in 100,000 potential collisions with the Earth will materialize.