5 research outputs found
A search for technosignatures from 14 planetary systems in the Kepler field with the Green Bank Telescope at 1.15-1.73 GHz
Analysis of Kepler mission data suggests that the Milky Way includes billions
of Earth-like planets in the habitable zone of their host star. Current
technology enables the detection of technosignatures emitted from a large
fraction of the Galaxy. We describe a search for technosignatures that is
sensitive to Arecibo-class transmitters located within ~420 ly of Earth and
transmitters that are 1000 times more effective than Arecibo within ~13 000 ly
of Earth. Our observations focused on 14 planetary systems in the Kepler field
and used the L-band receiver (1.15-1.73 GHz) of the 100 m diameter Green Bank
Telescope. Each source was observed for a total integration time of 5 minutes.
We obtained power spectra at a frequency resolution of 3 Hz and examined
narrowband signals with Doppler drift rates between +/-9 Hz/s. We flagged any
detection with a signal-to-noise ratio in excess of 10 as a candidate signal
and identified approximately 850 000 candidates. Most (99%) of these candidate
signals were automatically classified as human-generated radio-frequency
interference (RFI). A large fraction (>99%) of the remaining candidate signals
were also flagged as anthropogenic RFI because they have frequencies that
overlap those used by global navigation satellite systems, satellite downlinks,
or other interferers detected in heavily polluted regions of the spectrum. All
19 remaining candidate signals were scrutinized and none were attributable to
an extraterrestrial source.Comment: 15 pages, 5 figures, accepted for publication in the Astronomical
Journa
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The Crusts of Mars, Tethys, and Mimas: Geophysical Exploration of Historic Heat Flow
The evolution of a planetary body often determines and is determined by its thermal properties. In my first project, I explore the consequences of heating upon pore closure, allowing me to estimate the heat flow through the Martian crust during the latest significant pore generation event—likely large basin-forming impacts. We apply a pore closure model developed for the Moon to Mars and take into account the geological processes that may alter the depth of a transition between porous and competent crust. If the 8–11 km deep discontinuity in seismic wave speed detected by the InSight lander marks the base of the uppermost porous layer of the Martian crust, then the heat flux at the time the porosity was created must exceed 60 mW m^−2, indicating a time prior to 4 Ga. Then, I explore how the global shape of an icy satellite allows us to infer its heat budget and interior—including the presence or absence of a subsurface global ocean. I apply this method in my second and third projects to Tethys and Mimas, respectively. We assume spatial variations in tidal heating are responsible for thickness or temperature variations in an isostatic ice shell, which manifests as surface topography. For Saturn’s moon Tethys, our best-fit models require Pratt isostasy and obliquity tides, with a normalized moment of inertia 0.340-0.345 and an average surface heat flux 1-2 mW m^−2. Then, we find that to account for its hydrostatic shape, Mimas’ normalized moment of inertia is 0.375, indicating a relatively undifferentiated world. Its remaining topography is consistent with a ∼30 km thick conductive ice shell in Airy isostasy atop a weakly convecting ∼30 km thick layer that itself mantles a ∼140 km radius ice-rock interior. For neither satellite do we find an ocean. However, the total power and pattern inferred to produce both satellites’ shapes from tidal heating indicate an ancient era of high obliquity. The common thread of all three projects is the flow of heat, and how our understanding of it can be revealed by or can reveal properties of the planetary bodies we study