Bulletin of the American Physical Society
APS April Meeting 2017
Volume 62, Number 1
Saturday–Tuesday, January 28–31, 2017; Washington, DC
Session Y6: Exoplanets and Planetary Science |
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Sponsoring Units: DAP Chair: Eric Ford, Pennsylvania State University Room: Virginia C |
Tuesday, January 31, 2017 1:30PM - 1:42PM |
Y6.00001: Odd Harmonics in Exoplanet Photometry: Weather or Artifact? Victoria Chayes, Nicholas Cowan, \'Elie Bouffard, Hal Haggard In the Fourier decomposition of light curves of exoplanets observed by the Kepler mission, one expects to see power in the first mode, from the planet orbiting the star, and the second mode, from ellipsoidal variations. Observations of power in the third mode of planets such as HAT-P-7b and Kepler-13Ab are as of yet unexplained. Using a spherical harmonic basis we analyze planet maps to find their corresponding light curves and show that no planet observed edge-on can produce these third harmonics with either reflected light or thermal emissions. Further numerical and analytic calculations put upper bounds on the power in the third mode that can be produced by planets not transiting perfectly edge-on, or with time-variable maps. We find the expected order of magnitude of these contributions to be at most two orders of magnitude below the first harmonic. The North-South asymmetric features or time-variable maps that could produce such harmonics would suggest exoplanetary weather if observed. However, more careful analysis of tidal effects on the stars of HAT-P-7b and Kepler-13Ab suggest that these particular harmonics are stellar in origin. [Preview Abstract] |
Tuesday, January 31, 2017 1:42PM - 1:54PM |
Y6.00002: Stable Orbits for Exomoons in Earth's Cousin (Kepler-452b) Orbiting a Sun-like Star Niyousha Davachi, Marialis Rosario Franco, Sergio Garza, Dr. Zdzislaw E. Musielak Kepler 452b, also nicknamed Earth's cousin, was discovered orbiting the habitable zone (HZ) of a G2 Star (Jenkins et al. 2015). This exoplanet is considered a super Earth, with a mass of 5 \textpm 2 M$\oplus $ and a radius of 1.11 R$\oplus $; and is arguably the first rocky, habitable exoplanet to orbit a sun-like star. With a period of 385 days, conditions are prompt to be similar to those of Earth, and while Kepler-452b orbits the HZ of its parent star, its habitability could also be affected by the presence of an exomoon. Motivated by the need to understand conditions of habitability and orbital stability of Kepler-45b, we have performed a series of N-body integrations to examine the possibility of the exoplanet hosting an exomoon(s). Our results give a range of physical parameters leading to stable orbits for exomoons around this habitable super Earth. [Preview Abstract] |
Tuesday, January 31, 2017 1:54PM - 2:06PM |
Y6.00003: Analysis of Mars Express Ionogram Data via a Multilayer Artificial Neural Network Collin Wilkinson, Arron Potter, Greg Palmer, Firdevs Duru fduru@coe.edu Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS), which is a low frequency radar on the Mars Express (MEX) Spacecraft, can provide electron plasma densities of the ionosphere local at the spacecraft in addition to densities obtained with remote sounding. The local electron densities are obtained, with a standard error of about 2{\%}, ~by measuring the electron plasma frequencies with an electronic ruler on ionograms, which are plots of echo intensity as a function of time and frequency. This is done by using a tool created at the University of Iowa (Duru et al., 2008). This approach is time consuming due to the rapid accumulation of ionogram data. In 2013, results from an algorithm-based analysis of ionograms were reported by Andrews et al., but this method did not improve the human error. In the interest of fast, accurate data interpretation, a neural network (NN) has been created based on the Fast Artificial Neural Network C libraries. This NN consists of artificial neurons, with 4 layers of 12960, 10000, 1000 and 1 neuron(s) each, consecutively. This network was trained using 40 iterations of 1000 orbits. The algorithm-based method of Andrews et al. had a standard error of \textasciitilde 40{\%}, while the neural network has achieved error on the order of \textasciitilde 20{\%}. [Preview Abstract] |
Tuesday, January 31, 2017 2:06PM - 2:18PM |
Y6.00004: Local Heliospheric and Interstellar Radiation Environment of Planet X. John Cooper The orbit and aphelion direction of the putative Planet X at mass \textasciitilde 10 M$_{\mathrm{E}}$ has been inferred earlier from orbital modeling of Sedna and other distant Kuiper Belt Objects. The centroid of possible aphelion locations at 10$^{\mathrm{3}}$ AU lies within the heliotail potentially extending thousands of AU downstream from the direction of interstellar neutral flow into the heliosphere. The only spacecraft now heading in that general direction is Pioneer 10, long silent since last contact in January 2003 at 82 AU from the Sun. The Interstellar Background Explorer (IBEX) has from Earth orbit, however, been mapping energetic neutral atom (ENA) emissions from the outer heliosphere, including in the heliotail direction. Angular resolutions of the IBEX ENA maps are too coarse to resolve Planet X itself but could inform on larger-scale particle flux environments of distant objects within the heliotail. Present Voyager 1 energetic particle measurements in the outer heliosheath will eventually be joined by Voyager 2 bulk plasma measurements at ion energies below 10 keV for more complete characterization of particle flux distributions. These distributions can then be used to model external radiation interactions with the more distant objects of our solar system, potentially including Planet X. [Preview Abstract] |
Tuesday, January 31, 2017 2:18PM - 2:30PM |
Y6.00005: Titan's Topside Ionospheric Composition: Cassini Plasma Spectrometer Ion Mass Spectrometer Measurements Edward Sittler, Richard Hartle, Ashraf Ali, John Cooper, Alexander Lipatov, David Simpson, Menelaos Sarantos, Dennis Chornay, Todd Smith We present ion composition measurements of Titan's topside ionosphere using both T9 and T15 Cassini Plasma Spectrometer (CAPS) Ion Mass Spectrometer (IMS) measurements. The IMS is able to make measurements of Titan's ionosphere due to ionospheric outflows as originally reported for the T9 flyby. This allows one to take advantage of the unique capabilities of the CAPS IMS which measures both the mass-per-charge (M/Q) of the ions and the fragments of the ions produced inside the sensor such as carbon, nitrogen and oxygen fragments. Specific attention will be given to such ions as NH4$+$, N$+$, O$+$, CH4$+$, CxHy$+$, and HCNH$+$ ions as examples. The CAPS IMS uses a time-of-flight (TOF) technique which accelerates ions up to 14.6 kV, so they can pass through ultra-thin carbon foils. Neutral fragments are used to measure the ion M/Q and positive fragments to measure the atomic components. We preliminarily find, by using IMS measurements of T9 and T15 ionospheric outflows, evidence for methane group ions, nitrogen ions, ammonium ions, water group ions and CnHm$+$ ions with n $=$ 2, 3, and 4 within Titan's topside ionosphere. [Preview Abstract] |
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