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Gregory Laughlin

Publications and source records attributed to Gregory Laughlin.

At least 37 records · Page 2Linked to original sources
arXiv2021

The Aligned Orbit of the Eccentric Warm Jupiter K2-232b

Measuring the obliquity distribution of stars hosting warm Jupiters may help us to understand the formation of close-orbiting gas giants. Few such measurements have been performed due to practical difficulties in scheduling observations of the relatively infrequent and long-duration transits of warm Jupiters. Here, we report a measurement of the Rossiter-McLaughlin effect for K2-232b, a warm Jupiter (M_P=0.39 M_Jup) on an 11.17-day orbit with an eccentricity of 0.26. The data were obtained with the Automated Planet Finder during two separate transits. The planet's orbit appears to be well-aligned with the spin axis of the host star, with a projected spin-orbit angle of lambda = -11.1+/-6.6 deg. Combined with the other available data, we find that high obliquities are almost exclusively associated with planets that either have an orbital separation greater than 10 stellar radii or orbit stars with effective temperatures hotter than 6,000K. This pattern suggests that the obliquities of the closest-orbiting giant planets around cooler stars have been damped by tidal effects.

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arXiv2021

Assessing the Formation of Solid Hydrogen Objects in Starless Molecular Cloud Cores

The properties of the first-discovered interstellar object (ISO), 1I/2017 (`Oumuamua), differ from both Solar System asteroids and comets, casting doubt on a protoplanetary disk origin. In this study, we investigate the possibility that it formed with a substantial H2 ice component in the starless core of a giant molecular cloud. While interstellar solid hydrogen has yet to be detected, this constituent would explain a number of the ISO's properties. We consider the relevant processes required to build decameter-sized, solid hydrogen bodies and assess the plausibility of growth in various size regimes. Via an energy balance argument, we find that the most severe barrier to formation is the extremely low temperature required for the favorability of molecular hydrogen ice. However, if deposition occurs, we find that the turbulence within starless cores is conducive for growth into kilometer-sized bodies on sufficiently short timescales. Then, we analyze mass loss in the interstellar medium and determine the necessary size for a hydrogen object to survive a journey to the Solar System as a function of ISO age. Finally, we discuss the implications if the H2 explanation is correct, and we assess the future prospects of ISO science. If hydrogen ice ISOs do exist, our hypothesized formation pathway would require a small population of porous, 100 micron dust in a starless core region that has cooled to 2.8K via adiabatic expansion of the surrounding gas and excellent shielding from electromagnetic radiation and cosmic rays.

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arXiv2020

A collage of small planets from the Lick Carnegie Exoplanet Survey : Exploring the super-Earth and sub-Neptune mass regime

Analysis of new precision radial velocity (RV) measurements from the Lick Automated Planet Finder (APF) and Keck HIRES have yielded the discovery of three new exoplanet candidates orbiting two nearby K dwarfs not previously reported to have companions (HD 190007 & HD 216520). We also report new velocities from both the APF and the Planet Finder Spectrograph (PFS) for the previously reported planet host stars GJ 686 and HD 180617 and update the corresponding exoplanet orbital models. Of the newly discovered planets, HD 190007 b has a period of 11.72 days, an RV semi-amplitude of K = 5.64$\pm$0.55 m s$^{-1}$, a minimum mass of 16.46$\pm$1.66 $\rm M_{\oplus}$, and orbits the slightly metal-rich, active K4 dwarf star HD 190007 (d = 12.7 pc). HD 216520 b has an orbital period of 35.45 days, an RV semi-amplitude of K = 2.28$\pm$0.20 m s$^{-1}$, and a minimum mass of 10.26$\pm$0.99 $\rm M_{\oplus}$, while HD 216520 c has an orbital period of P = 154.43 days, an RV semi-amplitude of K = 1.29$\pm0.22$ m s$^{-1}$, and a minimum mass of 9.44$\pm$1.63 $\rm M_{\oplus}$. Both of these planets orbit the slightly metal-poor, inactive K0 dwarf star HD 216520 (d = 19.6 pc). We find that our updated best fit models for HD 180617 b and GJ 686 b are in good agreement with the previously published results. For HD 180617 b we obtain an orbital period of 105.91 days, an RV semi-amplitude of K = 2.696$\pm$0.22 m s$^{-1}$, and a minimum mass of 2.214$\pm$1.05 $\rm M_{\oplus}$. For GJ 686 b we find the orbital period to be 15.53 days, the RV semi-amplitude to be K = 3.00$\pm$0.18 m s$^{-1}$, and the minimum mass to be 6.624$\pm$0.432 $\rm M_{\oplus}$. Using an injection-recovery exercise, we find that HD 190007 b and HD 216520 b are unlikely to have additional planets with masses and orbital periods within a factor of two, in marked contrast to $\sim$85\% of planets in this mass and period range found with Kepler.

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arXiv2020

Lunar Exploration as a Probe of Ancient Venus

An ancient Venusian rock could constrain that planet's history, and reveal the past existence of oceans. Such samples may persist on the Moon, which lacks an atmosphere and significant geological activity. We demonstrate that if Venus' atmosphere was at any point thin and similar to Earth's, then asteroid impacts transferred potentially detectable amounts of Venusian surface material to the Lunar regolith. Venus experiences an enhanced flux relative to Earth of asteroid collisions that eject lightly-shocked ($\lesssim 40$ GPa) surface material. Initial launch conditions plus close-encounters and resonances with Venus evolve ejecta trajectories into Earth-crossing orbits. Using analytic models for crater ejecta and \textit{N}-body simulations, we find more than $0.07\%$ of the ejecta lands on the Moon. The Lunar regolith will contain up to 0.2 ppm Venusian material if Venus lost its water in the last 3.5 Gyr. If water was lost more than 4 Gyr ago, 0.3 ppm of the deep megaregolith is of Venusian origin. About half of collisions between ejecta and the Moon occur at $\lesssim6$ km s$^{-1}$, which hydrodynamical simulations have indicated is sufficient to avoid significant shock alteration. Therefore, recovery and isotopic analyses of Venusian surface samples would determine with high confidence both whether and when Venus harbored liquid oceans and/or a lower-mass atmosphere. Tests on brecciated clasts in existing Lunar samples from Apollo missions may provide an immediate resolution. Alternatively, regolith characterization by upcoming Lunar missions may provide answers to these fundamental questions surrounding Venus' evolution.

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arXiv2020

EXPRES I. HD~3651 an Ideal RV Benchmark

The next generation of exoplanet-hunting spectrographs should deliver up to an order of magnitude improvement in radial velocity precision over the standard 1 m/s state of the art. This advance is critical for enabling the detection of Earth-mass planets around Sun-like stars. New calibration techniques such as laser frequency combs and stabilized etalons ensure that the instrumental stability is well characterized. However, additional sources of error include stellar noise, undetected short-period planets, and telluric contamination. To understand and ultimately mitigate error sources, the contributing terms in the error budget must be isolated to the greatest extent possible. Here, we introduce a new high cadence radial velocity program, the EXPRES 100 Earths program, which aims to identify rocky planets around bright, nearby G and K dwarfs. We also present a benchmark case: the 62-d orbit of a Saturn-mass planet orbiting the chromospherically quiet star, HD 3651. The combination of high eccentricity (0.6) and a moderately long orbital period, ensures significant dynamical clearing of any inner planets. Our Keplerian model for this planetary orbit has a residual RMS of 58 cm/s over a $\sim 6$ month time baseline. By eliminating significant contributors to the radial velocity error budget, HD 3651 serves as a standard for evaluating the long term precision of extreme precision radial velocity (EPRV) programs.

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arXiv2020

Evidence that 1I/2017 U1 (`Oumuamua) was composed of molecular hydrogen ice

`Oumuamua (I1 2017) was the first macroscopic ($l\sim100\,{\rm m}$) body observed to traverse the inner solar system on an unbound hyperbolic orbit. Its light curve displayed strong periodic variation, and it showed no hint of a coma or emission from molecular outgassing. Astrometric measurements indicate that 'Oumuamua experienced non-gravitational acceleration on its outbound trajectory, but energy balance arguments indicate this acceleration is inconsistent with a water ice sublimation-driven jet of the type exhibited by solar system comets. We show that all of `Oumaumua's observed properties can be explained if it contained a significant fraction of molecular hydrogen (H$_{2}$) ice. H$_{2}$ sublimation at a rate proportional to the incident solar flux generates a surface-covering jet that reproduces the observed acceleration. Mass wasting from sublimation leads to monotonic increase in the body axis ratio, explaining `Oumuamua's shape. Back-tracing `Oumuamua's trajectory through the Solar System permits calculation of its mass and aspect ratio prior to encountering the Sun. We show that H$_{2}$-rich bodies plausibly form in the coldest dense cores of Giant Molecular Clouds, where number densities are of order $n\sim10^5$, and temperatures approach the $T=3\,{\rm K}$ background. Post-formation exposure to galactic cosmic rays implies a $τ\sim 100$ Myr age, explaining the kinematics of `Oumuamua's inbound trajectory.

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arXiv2020

Energy Optimization in Extrasolar Planetary Systems: The Transition from Peas-in-a-Pod to Runaway Growth

Motivated by the trends found in the observed sample of extrasolar planets, this paper determines tidal equilibrium states for forming planetary systems --- subject to conservation of angular momentum, constant total mass, and fixed orbital spacing. In the low-mass limit, valid for superearth-class planets with masses of order $m_{\rm p}\sim10M_\oplus$, previous work showed that energy optimization leads to nearly equal mass planets, with circular orbits confined to a plane. The present treatment generalizes previous results by including the self-gravity of the planetary bodies. For systems with sufficiently large total mass $m_{\scriptstyle T}$ in planets, the optimized energy state switches over from the case of nearly equal mass planets to a configuration where one planet contains most of the material. This transition occurs for a critical mass threshold of approximately $m_{\scriptstyle T} \ge m_{\scriptstyle C}\sim40M_\oplus$ (where the value depends on the semimajor axes of the planetary orbits, the stellar mass, and other system properties). These considerations of energy optimization apply over a wide range of mass scales, from binary stars to planetary systems to the collection of moons orbiting the giant planets in our solar system.

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arXiv2019

Hidden Planets: Implications from 'Oumuamua and DSHARP

The discovery of 'Oumuamua (1I/2017 U1), the first interstellar interloper, suggests an abundance of free-floating small bodies whose ejection into galactic space cannot be explained by the current population of confirmed exoplanets. Shortly after 'Oumuamua's discovery, observational results from the DSHARP survey illustrated the near-ubiquity of ring/gap substructures within protoplanetary disks, strongly suggesting the existence of a vast population of as-yet undetected wide-separation planets that are capable of efficiently ejecting debris from their environments. These planets have $a \gtrsim 5$ au and masses of order Neptune's or larger, and they may accompany $\sim$50% of newly formed stars (Zhang et al. 2018). We combine the DSHARP results with statistical constraints from current time-domain surveys to quantify the population of detectable icy planetesimals ejected by disk-embedded giant planets through gravity assists. Assessment of the expected statistical distribution of interstellar objects is critical to accurately plan for and interpret future detections. We show that the number density of interstellar objects implied by 'Oumuamua is consistent with 'Oumuamua itself having originated as an icy planetesimal ejected from a DSHARP-type system via gravity assists, with the caveat that 'Oumuamua's lack of observed outgassing remains in strong tension with a cometary origin. Under this interpretation, 'Oumuamua's detection points towards a large number of long-period giant planets in extrasolar systems, supporting the hypothesis that the observed gaps in protoplanetary disks are carved by planets. In the case that 'Oumuamua is an ejected cometary planetesimal, we conclude that LSST should detect up to a few interstellar objects per year of 'Oumuamua's size or larger and over 100 yr$^{-1}$ for objects with $r > 1\,{\rm m}$.

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arXiv2019

The Case for a Large-Scale Occultation Network

We discuss the feasibility of and present initial designs and approximate cost estimates for a large ($N\sim2000$) network of small photometric telescopes that is purpose-built to monitor $V \lesssim 15$ Gaia Mission program stars for occultations by minor solar system bodies. The implementation of this network would permit measurement of the solar system's tidal gravity field to high precision, thereby revealing the existence of distant trans-Neptunian objects such as the proposed "Planet Nine." As a detailed example of the network capabilities, we investigate how occultations by Jovian Trojans can be monitored to track the accumulation of gravitational perturbations, thereby constraining the presence of undetected massive solar system bodies. We also show that the tidal influence of Planet Nine can be discerned from that of smaller, nearer objects in the Kuiper belt. Moreover, ephemerides for all small solar system bodies observed in occultation could be significantly improved using this network, thereby improving spacecraft navigation and refining Solar System modeling. Finally, occultation monitoring would generate direct measurements of size distributions for asteroid populations, permitting a better understanding of their origins.

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arXiv2019

On the Anomalous Acceleration of 1I/2017 U1 `Oumuamua

We show that the $P\sim8\,{\rm h}$ photometric period and the astrometrically measured $A_{\rm ng}\sim2.5\times10^{-4}\,{\rm cm\,s^{-2}}$ non-gravitational acceleration (at $r\sim1.4\,{\rm AU}$) of the interstellar object 1I/2017 (`Oumuamua) can be explained by a nozzle-like venting of volatiles whose activity migrated to track the sub-solar location on the object's surface. Adopting the assumption that `Oumuamua was an elongated $a\times b \times c$ ellipsoid, this model produces a pendulum-like rotation of the body and implies a long semi-axis $a\sim 5A_{\rm ng}P^2/4π^2 \sim 260\,{\rm m}$. This scale agrees with the independent estimates of `Oumuamua's size that stem from its measured brightness, assuming an albedo of $p\sim0.1$, appropriate to ices that have undergone long-duration exposure to the interstellar cosmic ray flux. Using ray-tracing, we generate light curves for ellipsoidal bodies that are subject to both physically consistent sub-solar torques and to the time-varying geometry of the Sun-Earth-`Oumuamua configuration. Our synthetic light curves display variations from chaotic tumbling and changing cross-sectional illumination that are consistent with the observations, while avoiding significant secular changes in the photometric periodicity. If our model is correct, `Oumuamua experienced mass loss that wasted $\sim 10\%$ of its total mass during the $\sim 100\,{\rm d}$ span of its encounter with the inner Solar System and had an icy composition with a very low $[{\rm C}/{\rm O}]\lesssim 0.003$. Our interpretation of `Oumuamua's behavior is consistent with the hypothesis that it was ejected from either the outer regions of a planetesimal disk after an encounter with an embedded $M_{\rm p} \sim M_{\rm Nep}$ planet or from an exo-Oort cloud.

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arXiv2019

Obliquity-Driven Sculpting of Exoplanetary Systems

NASA's Kepler mission revealed that $\sim 30\%$ of Solar-type stars harbor planets with sizes between that of Earth and Neptune on nearly circular and co-planar orbits with periods less than 100 days. Such short-period compact systems are rarely found with planet pairs in mean-motion resonances (MMRs) -- configurations in which the planetary orbital periods exhibit a simple integer ratio -- but there is a significant overabundance of planet pairs lying just wide of the first-order resonances. Previous work suggests that tides raised on the planets by the host star may be responsible for forcing systems into these configurations by draining orbital energy to heat. Such tides, however, are insufficient unless there exists a substantial and as-yet unidentified source of extra dissipation. Here we show that this cryptic heat source may be linked to "obliquity tides" generated when a large axial tilt (obliquity) is maintained by secular resonance-driven spin-orbit coupling. We present evidence that typical compact, nearly-coplanar systems frequently experience this mechanism, and we highlight additional features in the planetary orbital period and radius distributions that may be its signatures. Extrasolar planets that maintain large obliquities will exhibit infrared light curve features that are detectable with forthcoming space missions. The observed period ratio distribution can be explained if typical tidal quality factors for super-Earths and sub-Neptunes are similar to those of Uranus and Neptune.

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arXiv2018

Obliquity Tides May Drive WASP-12b's Rapid Orbital Decay

Recent analyses have revealed a mystery. The orbital period of the highly inflated hot Jupiter, WASP-12b, is decreasing rapidly. The rate of inspiral, however, is too fast to be explained by either eccentricity tides or equilibrium stellar tides. While dynamical stellar tides are possible, they require a subgiant structure for the star, whereas stellar models point toward a main sequence host. Here, we show that these hitherto irreconcilable observations might be explained by planetary obliquity tides if planet b's spin vector is trapped in a high-obliquity state maintained by a secular spin-orbit resonance with an unseen exterior perturbing planet. We derive constraints on the obliquity ($ε\gtrsim50^{\circ}$), reduced tidal quality factor ($Q^{\prime}\sim10^{6}-10^{7}$), and perturbing planet parameters ($M_{2}\sim10-20M_{\oplus}$, $a_2\lesssim0.04\,{\rm AU}$) required to generate the observed orbital decay. Direct N-body simulations that include tidal and spin dynamics reinforce the plausibility of the scenario. Furthermore, we show that the resonance could have been captured when planet b's obliquity was small, making the proposed sequence of events easy to explain. The hypothetical perturbing planet is within the limits of current radial velocity constraints on the system yet is also detectable. If it exists, it could provide evidence in favor of the in situ formation hypothesis for hot Jupiters.

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arXiv2018

An orbital window into the ancient Sun's mass

Models of the Sun's long-term evolution suggest that its luminosity was substantially reduced 2-4 billion years ago, which is inconsistent with substantial evidence for warm and wet conditions in the geological records of both ancient Earth and Mars. Typical solutions to this so-called "faint young Sun paradox" consider changes in the atmospheric composition of Earth and Mars, and while attractive, geological verification of these ideas is generally lacking-particularly for Mars. One possible underexplored solution to the faint young Sun paradox is that the Sun has simply lost a few percent of its mass during its lifetime. If correct, this would slow, or potentially even offset the increase in luminosity expected from a constant-mass model. However, this hypothesis is challenging to test. Here, we propose a novel observational proxy of the Sun's ancient mass that may be readily measured from accumulation patterns in sedimentary rocks on Earth and Mars. We show that the orbital parameters of the Solar system planets undergo quasi-cyclic oscillations at a frequency, given by secular mode g_2-g_5, that scales approximately linearly with the Sun's mass. Thus by examining the cadence of sediment accumulation in ancient basins, it is possible distinguish between the cases of a constant mass Sun and a more massive ancient Sun to a precision of greater than about 1 per cent. This approach provides an avenue toward verification, or of falsification, of the massive early Sun hypothesis.

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arXiv2018

Dissecting Latency in the Internet's Fiber Infrastructure

The recent publication of the `InterTubes' map of long-haul fiber-optic cables in the contiguous United States invites an exciting question: how much faster would the Internet be if routes were chosen to minimize latency? Previous measurement campaigns suggest the following rule of thumb for estimating Internet latency: multiply line-of-sight distance by 2.1, then divide by the speed of light in fiber. But a simple computation of shortest-path lengths through the conduits in the InterTubes map suggests that the conversion factor for all pairs of the 120 largest population centers in the U.S.\ could be reduced from 2.1 to 1.3, in the median, even using less than half of the links. To determine whether an overlay network could be used to provide shortest paths, and how well it would perform, we used the diverse server deployment of a CDN to measure latency across individual conduits. We were surprised to find, however, that latencies are sometimes much higher than would be predicted by conduit length alone. To understand why, we report findings from our analysis of network latency data from the backbones of two Tier-1 ISPs, two scientific and research networks, and the recently built fiber backbone of a CDN.

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arXiv2018

HD 202772A B: A Transiting Hot Jupiter Around A Bright, Mildly Evolved Star In A Visual Binary Discovered By Tess

We report the first confirmation of a hot Jupiter discovered by the Transiting Exoplanet Survey Satellite (TESS) mission: HD 202772A b. The transit signal was detected in the data from TESS Sector 1, and was confirmed to be of planetary origin through radial-velocity measurements. HD 202772A b is orbiting a mildly evolved star with a period of 3.3 days. With an apparent magnitude of V = 8.3, the star is among the brightest known to host a hot Jupiter. Based on the 27days of TESS photometry, and radial velocity data from the CHIRON and HARPS spectrographs, the planet has a mass of 1.008+/-0.074 M_J and radius of 1.562+/-0.053 R_J , making it an inflated gas giant. HD 202772A b is a rare example of a transiting hot Jupiter around a quickly evolving star. It is also one of the most strongly irradiated hot Jupiters currently known.

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arXiv2018

Transiting Exoplanet Monitoring Project (TEMP). I. Refined System Parameters and Transit Timing Variations of HAT-P-29b

We report the photometry of six transits of the hot Jupiter HAT-P-29b obtained from 2013 October to 2015 January. We analyze the new light curves, in combination with the published photometric, and Doppler velocimetric, and spectroscopic measurements, finding an updated orbital ephemeris for the HAT-P-29 system, $T_{\rm C}[0]= 2456170.5494(15)\,[\rm{BJD_{TDB}}]$ and $P=5.723390(13) \,{\rm days}$. It is $17.63\,{\rm s}$ ($4.0\,σ$) longer than the previously published value, amounting to errors exceeding $2.5\,\rm{hrs}$ at the time of writing (on UTC 2018 June 1). The measured transit mid-times for HAT-P-29b show no compelling evidence of timing anomalies from a linear model, which rules out the presence of a perturbers with masses greater than $0.6$, $0.7$, $0.5$, and $0.4\,{\rm M_\oplus}$ near the $1:2$, $2:3$, $3:2$, and $2:1$ resonances with HAT-P-29b, respectively.

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arXiv2018

Reassessing Exoplanet Light Curves with a Thermal Model

We present a uniform assessment of existing near-infrared Spitzer Space Telescope observations of planet-bearing stars. Using a simple four-parameter blackbody thermal model, we analyze stars for which photometry in at least one of Spitzer's IRAC bands has been obtained over either the entirety or a significant fraction of the planetary orbit. Systems in this category comprise ten well-studied systems with Hot Jupiters on circular or near-circular orbits (HAT-P-7, HD 149026, HD 189733, HD 209458, WASP-12, WASP-14, WASP-18, WASP-19, WASP-33, and WASP-43), as well as three stars harboring planets on significantly eccentric orbits (GJ 436, HAT-P-2, and HD 80606). We find that our simple model, in almost all cases, accurately reproduces the minimum and maximum planetary emission, as well as the phase offsets of these extrema with respect to transits/secondary eclipses. For one notable exception, WASP-12 b, adding an additional parameter to account for its tidal distortion is not sufficient to reproduce its photometric features. Full-orbit photometry is available in multiple wavelengths for 10 planets. We find that the returned parameter values for independent fits to each band are largely in agreement. However, disagreements in night-side temperature suggest distinct atmospheric layers, each with their own characteristic minimum temperature. In addition, a diversity in albedos suggests variation in opacity of the photospheres. While previous works have pointed out trends in photometric features based on system properties, we cannot conclusively identify analogous trends for physical model parameters. To make the connection between full-phase data and physical models more robust, a higher signal-to-noise must come from both increased resolution and a careful treatment of instrumental systematics.

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