Jason H Steffen | University of Nevada, Las Vegas (original) (raw)

Papers by Jason H Steffen

Physical Review Letters, Jan 22, 2009

We report the first results from the GammeV search for chameleon particles, which may be created ... more We report the first results from the GammeV search for chameleon particles, which may be created via photon-photon interactions within a strong magnetic field. The chameleons are assumed to have matter effects sufficiently strong that they reflect from all solid surfaces of the apparatus, thus evading detection in our previous search for weakly-interacting axion-like particles. We implement a novel technique to create and trap the reflective particles within a jar and to detect them later via their afterglow as they slowly convert back into photons. We constrain the coupling of chameleons to photons as a function of chameleon mass for a wide class of chameleon theories.

ABSTRACT Experimentally probing the Planck scale can offer insights into understanding a quantum ... more ABSTRACT Experimentally probing the Planck scale can offer insights into understanding a quantum origin of spacetime. The Fermilab Holometer team will look for a new noise source arising from the Planck scale by using the precision of power-recycled Michelson interferometers. The two nested 40 meter interferometers may have a characteristic power spectral density based on the conjectured frequency independent Planckian noise. By cross-correlating the dark port signal of two nearby interferometers, we can rule out conventional noise sources that are not common to both devices. A common source of noise could be from the underlying spacetime itself. A positive result will lead to insights in theories of an emergent quantum spacetime. The Holometer team has finished construction and begun scientific commissioning. First results of the experiment are expected in Spring 2015.

arXiv (Cornell University), Jul 10, 2023

Monthly Notices of the Royal Astronomical Society, Jul 17, 2023

We study the formation of the TRAPPIST-1 (T1) planets starting shortly after Moon-sized bodies fo... more We study the formation of the TRAPPIST-1 (T1) planets starting shortly after Moon-sized bodies form just exterior to the ice line. Our model includes mass growth from pebble accretion and mergers, fragmentation, type-I migration, and eccentricity and inclination dampening from gas drag. We follow the composition evolution of the planets fed by a dust condensation code that tracks how various dust species condense out of the disc as it cools. We use the final planet compositions to calculate the resulting radii of the planets using a new planet interior structure code and explore various interior structure models. Our model reproduces the broader architecture of the T1 system and constrains the initial water mass fraction of the early embryos and the final relative abundances of the major refractory elements. We find that the inner two planets likely experienced giant impacts and fragments from collisions between planetary embryos often seed the small planets that subsequently grow through pebble accretion. Using our composition constraints we find solutions for a two-layer model, a planet comprised of only a core and mantle, that match observed bulk densities for the two inner planets b and c. This, along with the high number of giant impacts the inner planets experienced, is consistent with recent observations that these planets are likely dessicated. However, two-layer models seem unlikely for most of the remaining outer planets which suggests that these planets have a primordial hydrosphere. Our composition constraints also indicate that no planets are consistent with a core-free interior structure.

Monthly Notices of the Royal Astronomical Society, Jan 28, 2022

We present a fragmentation module and a composition tracking code for the-body code. Our fragment... more We present a fragmentation module and a composition tracking code for the-body code. Our fragmentation code utilises previous semi-analytic models and follows an implementation method similar to fragmentation for the-body code. In our-body simulations with fragmentation, we decrease the collision and planet formation timescales by inflating the particle radii by an expansion factor and experiment with various values of to understand how expansion factors affect the collision history and final planetary system. As the expansion factor increases, so do the rate of mergers which produces planetary systems with more planets and planets at larger orbits. Additionally, we present a composition tracking code which follows the compositional change of homogeneous bodies as a function of mass exchange and use it to study how fragmentation and the use of an expansion factor affects volatile delivery to the inner terrestrial disc. We find that fragmentation enhances radial mixing relative to perfect merging and that on average, as increases so does the average water mass fraction of the planets. Radial mixing decreases with increasing as collisions happen early on, before the bodies have time to grow to excited orbits and move away from their original location.

The Astrophysical Journal, Jan 14, 2016

Inspired by the close-proximity pair of planets in the Kepler-36 system, we consider two effects ... more Inspired by the close-proximity pair of planets in the Kepler-36 system, we consider two effects that may have important ramifications for the development of life in similar systems where a pair of planets may reside entirely in the habitable zone of the hosting star. Specifically, we run numerical simulations to determine whether strong, resonant (or non-resonant) planet-planet interactions can cause large variations in planet obliquity-thereby inducing large variations in climate. We also determine whether or not resonant interactions affect the rate of lithopanspermia between the planet pair-which could facilitate the growth and maintenance of life on both planets. We find that firstorder resonances do not cause larger obliquity variations compared with non-resonant cases. We also find that resonant interactions are not a primary consideration in lithopanspermia. Lithopanspermia is enhanced significantly as the planet orbits come closer together-reaching nearly the same rate as ejected material falling back to the surface of the originating planet (assuming that the ejected material makes it out to the location of our initial conditions). Thus, in both cases our results indicate that close-proximity planet pairs in multihabitable systems are conducive to life in the system.

arXiv (Cornell University), Aug 21, 2022

To more thoroughly study the effects of radiative forces on the orbits of small, astronomical bod... more To more thoroughly study the effects of radiative forces on the orbits of small, astronomical bodies, we introduce the Yarkovsky effect into , an extensional library for the N-body integrator. Two different versions of the Yarkovsky effect (the "Full Version" and the "Simple Version") are available for use, depending on the needs of the user. We provide demonstrations for both versions of the effect and compare their computational efficiency with another previously implemented radiative force. In addition, we show how this effect can be used in tandem with other features in by simulating the orbits of asteroids during the asymptotic giant branch phase of a 2 star. This effect is made freely available for use with the latest release of .

American Astronomical Society Meeting Abstracts #225, 2015

arXiv (Cornell University), Mar 25, 2023

Tidally locked worlds provide a unique opportunity for constraining the probable climates of cert... more Tidally locked worlds provide a unique opportunity for constraining the probable climates of certain exoplanets. They are unique in that few exoplanet spin and obliquity states are known or will be determined in the near future: both of which are critical in modeling climate. A recent study shows the dynamical conditions present in the TRAPPIST-1 system make rotation and large librations of the substellar point possible for these planets, which are usually assumed to be tidally locked. We independently confirm the tendency for planets in TRAPPIST-1-like systems to sporadically transition from tidally locked libration to slow rotation using N-body simulations. We examine the nature and frequency of these spin states to best inform energy balance models which predict the temperature profile of the planet's surface. Our findings show that tidally locked planets with sporadic rotation are able to be in both long-term persistent states and states with prolonged transient behavior: where frequent transitions between behaviors occur. Quasi-stable spin regimes, where the planet exhibits one spin behavior for up to hundreds of millennia, are likely able to form stable climate systems while the spin behavior is constant. 1D energy balance models show that tidally locked planets with sporadic rotation around M-dwarfs will experience a relatively small change in substellar temperature due to the lower albedo of ice in an infrared dominant stellar spectrum. The exact effects of large changes in temperature profiles on these planets as they rotate require more robust climate models, like 3D global circulation models, to better examine.

arXiv (Cornell University), Mar 31, 2023

Despite the importance of Jupiter and Saturn to Earth's formation and habitability, there has not... more Despite the importance of Jupiter and Saturn to Earth's formation and habitability, there has not yet been a comprehensive observational study of how giant exoplanets correlate with the architectural properties of close-in, sub-Neptune-sized exoplanets. This is largely because transit surveys are particularly insensitive to planets at orbital separations 1 au, and so their census of Jupiter-like planets is incomplete, inhibiting our study of the relationship between Jupiter-like planets and the small planets that do transit. To investigate the relationship between close-in, small and distant, giant planets, we conducted the Kepler Giant Planet Survey (KGPS). Using the W. M. Keck Observatory High Resolution Echelle Spectrometer, we spent over a decade collecting 2844 radial velocities (RVs; 2167 of which are presented here for the first time) of 63 Sunlike stars that host 157 transiting planets. We had no prior knowledge of which systems would contain giant planets beyond 1 au, making this survey unbiased with respect to previously detected Jovians. We announce RV-detected companions to 20 stars from our sample. These include 13 Jovians (< < M M i M 0.3 sin 13 J J , 1 au < a < 10 au), eight nontransiting sub-Saturns, and three stellarmass companions. We also present updated masses and densities of 84 transiting planets. The KGPS project leverages one of the longest-running and most data-rich collections of RVs of the NASA Kepler systems yet, and it will provide a basis for addressing whether giant planets help or hinder the growth of sub-Neptune-sized and terrestrial planets. Future KGPS papers will examine the relationship between small, transiting planets and their longperiod companions.

arXiv (Cornell University), Jun 2, 2019

Partial condensation of dust from the Solar nebula is likely responsible for the diverse chemical... more Partial condensation of dust from the Solar nebula is likely responsible for the diverse chemical compositions of chondrites and rocky planets/planetesimals in the inner Solar system. We present a forward physical-chemical model of a protoplanetary disc to predict the chemical compositions of planetary building blocks that may form from such a disc. Our model includes the physical evolution of the disc and the condensation, partial advection, and decoupling of the dust within it. The chemical composition of the condensate changes with time and radius. We compare the results of two dust condensation models: one where an element condenses when the midplane temperature in the disc is lower than the 50% condensation temperature (T 50) of that element and the other where the condensation of the dust is calculated by a Gibbs free energy minimization technique assuming chemical equilibrium at local disc temperature and pressure. The results of two models are generally consistent with some systematic differences of ∼ 10% depending upon the radial distance and an element's condensation temperature. Both models predict compositions similar to CM, CO, and CV chondrites provided that the decoupling timescale of the dust is on the order of the evolution timescale of the disc or longer. If the decoupling timescale is too short, the composition deviates significantly from the measured values. These models may contribute to our understanding of the chemical compositions of chondrites, and ultimately the terrestrial planets in the solar system, and may constrain the potential chemical compositions of rocky exoplanets.

NASA's exoplanet mission is the world's premier instrument for the discovery and study of... more NASA's exoplanet mission is the world's premier instrument for the discovery and study of planets orbiting distant stars. As the nominal mission comes to a close, Kepler has discovered nearly 2500 planet candidates, confirmed dozens of multi-planet systems, provided important insights into the orbital architectures of planetary systems, identified specific systems that challenge theories of planet formation and dynamical evolution, has revolutionized our understanding of stellar interiors, and is gearing to measure the frequency of Earth-like planets in the habitable zones of Sun-like stars in its extended mission phase. I present the most recent results from the Kepler mission.