arXiv subjects

Phoebe Sandhaus

Publications and source records attributed to Phoebe Sandhaus.

3 recordsLinked to original sources

arXiv2026

Effects of Outer Giant Planets on In Situ Formation of Inner Super-Earths

Recent studies have found an observational correlation between the presence of outer giant planets and inner super-Earths, which implies that outer giants do not suppress the formation of super-Earths. We simulate late-stage in situ planet formation in the presence of outer giant planets using $N$-body simulations. We investigate the effects of two sets of outer giants: the four Solar System giant planets and three dynamically active giant planets. Compared to systems without outer giants, we find that systems with the Solar System giants tend to form inner super-Earths that are more compact, coplanar, and circular, while the systems with the dynamically active giants form inner super-Earths that are more eccentric, inclined, and widely spaced, with lower intrinsic multiplicity. Including a contribution from systems that form with dynamically active giant planets allows us to match observable quantities of super-Earths, including their two component eccentricity distribution. However, matching the observed population requires different formation conditions prior to the giant impact stage for systems with vs. without giant planets. In our model, observed super-Earths that form in the presence of dynamically active outer giants emerge from disks with lower solid surface densities and without a depleted gas stage, suggesting that the giant planets may have reduced, but not prevented, delivery and/or accretion of solids in the inner disk. With a large enough sample of inner and outer systems, we could break down occurrence rates of inner super-Earths based on the properties of outer giants, and vice versa, and then compare these conditional probabilities with simulations.

astro-ph.EP↗

arXiv2026

Effects of Pebble Accretion Isolation Mass on Observable Exoplanet Properties

The Kepler Mission has discovered a plethora of planetary systems with super-Earth sized planets. These systems exhibit many properties, from widely-spaced planets with non-negligible eccentricities and inclinations, to tightly-spaced, coplanar, and nearly circular multi-planet systems. The observable properties of these systems, such as planet-planet spacings, multiplicity and orbital morphology, can be strongly influenced by the initial conditions of formation. These conditions affect the early growth of planetary embryos in the gas disk phase through pebble and/or planetesimal accretion, which then affects the final growth of planets during the giant impact stage. In this work, we investigate how assumptions of different limiting embryo isolation masses during early stages of planet formation affect the final properties of super-Earth planets within the inner disk, comparing our mock-observed results to each other, as well as to the Kepler sample. We test several models of pebble accretion isolation mass, including pebble isolation, flow isolation, and migration feedback isolation and otherwise adopt the same parameters for the gas disk. We find that while each model can match at least one distribution of observables in the Kepler catalog, they fall short of matching all distributions simultaneously, even with extreme reweighting. Our inability to match all observations suggests that the initial conditions and/or modeled effects in our simulations that we held fixed should be investigated. This exploration sheds light on how planetary systems evolve and the processes that influence the wide range of system parameters we observe today, helping place our own Solar System in context.

astro-ph.EP↗

arXiv2022

A Search for Radio Technosignatures at the Solar Gravitational Lens Targeting Alpha Centauri

Stars provide an enormous gain for interstellar communications at their gravitational focus, perhaps as part of an interstellar network. If the Sun is part of such a network, there should be probes at the gravitational foci of nearby stars. If there are probes within the solar system connected to such a network, we might detect them by intercepting transmissions from relays at these foci. Here, we demonstrate a search across a wide bandwidth for interstellar communication relays beyond the Sun's innermost gravitational focus at 550 AU using the Green Bank Telescope (GBT) and Breakthrough Listen (BL) backend. As a first target, we searched for a relay at the focus of the Alpha Centauri AB system while correcting for the parallax due to Earth's orbit around the Sun. We searched for radio signals directed at the inner solar system from such a source in the L and S bands. Our analysis, utilizing the turboSETI software developed by BL, did not detect any signal indicative of a non-human-made artificial origin. Further analysis excluded false negatives and signals from the nearby target HD 13908. Assuming a conservative gain of 10^3 in L-band and roughly 4 times that in S-band, a ~1 meter directed transmitter would be detectable by our search above 7 W at 550 AU or 23 W at 1000 AU in L-band, and above 2 W at 550 AU or 7 W at 1000 AU in S-band. Finally, we discuss the application of this method to other frequencies and targets.

astro-ph.IM↗