Probing Exoplanet Atmospheric Properties from Phase Variations and Polarization
Laura Mayorga, NMSU
The study of exoplanets is evolving past simple transit and Doppler method discovery and characterization. One of the many goals of the upcoming mission WFIRST-AFTA is to directly image giant exoplanets with a coronagraph. We undertake a study to determine the types of exoplanets that missions such as WFIRST will encounter and what instruments these missions require to best characterize giant planet atmospheres. We will first complete a benchmark study of how Jupiter reflects and scatters light as a function of phase angle. We will use Cassini flyby data from late 2000 to measure Jupiter’s phase curve, spherical albedo, and degree of polarization. Using Jupiter as a comparison, we will then study a sample of exoplanet atmosphere models generated to explore the atmospheric parameter space of giant planets and estimate what WFIRST might observe. Our study will provide valuable refinements to Jupiter-like models of planet evolution and atmospheric composition. We will also help inform future missions of what instruments are needed to characterize similar planets and what science goals will further our knowledge of giant worlds in our universe.
Searching for Dwarf Satellites around Milky Way – Analog Galaxies with the SAGA survey
Ben Weiner, Steward Observatory
Dwarf satellites of massive galaxies are a probe of many issues in galaxy evolution and cosmology, including the nature of low-mass galaxies, star formation at early times, accretion into halos, and the abundance of low-mass dark matter halos. Much attention has been devoted to the number and nature of Milky Way and M31 dwarf satellites, especially the “missing satellites problem.” However, we know very little about dwarf satellites outside the Local Group below the mass of the LMC, and we don’t know if the MW and M31 satellite systems are typical. The SAGA (Satellites Around Galactic Analogs) survey collaboration aims to address this with both observational and theoretical studies of satellite abundances and properties around Milky Way analog central galaxies. I will present results from our MMT/Hectospec wide field spectroscopic surveys for satellites. We have surveyed the fields of several nearby galaxies that are similar to the Milky Way to detect and spectroscopically confirm dwarf satellites. We find a range of numbers of satellites, suggesting that there is a significant variance in halo histories. We also find that not all dwarf systems resemble the Milky Way and M31 systems. I will discuss these results and some of the implications on the life cycle of satellites that we can infer from satellite abundances and properties, including their images and spectra.
Diagnosing the SEEDS of Planet Formation
John Wisniewski, University of Oklahoma
Circumstellar disks provide a useful astrophysical diagnostic of the formation and early evolution of exoplanets. It is commonly believed that young protoplanetary disks serve as the birthplace of planets, while older debris disks can provide insight into the architecture of exoplanetary systems. In this talk, I will discuss how one can use high contrast imaging techniques to spatially resolve nearby circumstellar disk systems, and how this imagery can be used to search for evidence of recently formed planetary bodies. I will focus on results from the Strategic Exploration of Exoplanets and Disks with Subaru (SEEDS) project, as well as some ongoing follow-up work.
On the Edge: Exoplanets with Orbital Periods Shorter Than a Peter Jackson Movie
Brian Jackson, Boise State Univeristy
From wispy gas giants to tiny rocky bodies, exoplanets with orbital periods of several days and less challenge theories of planet formation and evolution. Recent searches have found small rocky planets with orbits reaching almost down to their host stars’ surfaces, including an iron-rich Mars-sized body with an orbital period of only four hours. So close to their host stars that some of them are actively disintegrating, these objects’ origins remain unclear, and even formation models that allow significant migration have trouble accounting for their very short periods. Some are members of multi-planet system and may have been driven inward via secular excitation and tidal damping by their sibling planets. Others may be the fossil cores of former gas giants whose atmospheres were stripped by tides.
In this presentation, I’ll discuss the work of our Short-Period Planets Group (SuPerPiG), focused on finding and understanding this surprising new class of exoplanets. We are sifting data from the reincarnated Kepler Mission, K2, to search for additional short-period planets and have found several new candidates. We are also modeling the tidal decay and disruption of close-in gaseous planets to determine how we could identify their remnants, and preliminary results suggest the cores have a distinctive mass-period relationship that may be apparent in the observed population. Whatever their origins, short-period planets are particularly amenable to discovery and detailed follow-up by ongoing and future surveys, including the TESS mission.
The Orbital and Planetary Phase Variations of Jupiter-Sized Planets: Characterizing Present and Future Giants
Laura Mayorga, NMSU
It is commonly said that exoplanet science is 100 years behind planetary science. While we may be able to travel to an exoplanet in the future, inferring the properties of exoplanets currently relies on extracting as much information as possible from a limited dataset. In order to further our ability to characterize, classify, and understand exoplanets as both a population and as individuals, this thesis makes use of multiple types of observations and simulations.
Firstly, direct-imaging is a technique long used in planetary science and is only now becoming feasible for exoplanet characterization. We present our results from analyzing Jupiter’s phase curve with Cassini/ISS to instruct the community in the complexity of exoplanet atmospheres and the need for further model development. The planet yields from future missions may be overestimated by today’s models. We also discuss the need for optimal bandpasses to best differentiate between planet classes.
Secondly, photometric surveys are still the best way of conducting population surveys of exoplanets. In particular, the Kepler dataset remains one of the highest precision photometric datasets and many planetary candidates remain to be characterized. We present techniques by which more information, such as a planet’s mass, can be extracted from a transit light curve without expensive ground- or space-based follow-up observations.
Finally, radial-velocity observations have revealed that many of the larger “planets” may actually be brown dwarfs. To understand the distinction between a brown dwarf and an exoplanet or a star, we have developed a simple, semi-analytic viscous disk model to study brown dwarf evolutionary history. We present the rudimentary framework and discuss its performance compared to more detailed numerical simulations as well as how additional physics and development can determine the potential observational characteristics that will differentiate between various formation scenarios.
Exoplanet science has already uncovered a plethora of previously unconsidered phenomenon. To increase our understanding of our own planet, as well as the other various possible end cases, will require a closer inspection of our own solar system, the nuanced details of exoplanet data, refined simulations, and laboratory astrophysics.