arXiv subjects

Sarah Greenstreet

Publications and source records attributed to Sarah Greenstreet.

At least 19 recordsLinked to original sources

arXiv2026

Fast and Furious: Long-term orbit integrations with collocation integrator Lobbie

Efficient and accurate numerical integration methods are fundamental to studying long-term solar system dynamics, where numerical errors can accumulate over billions of orbital periods. In this work, we investigate the performance of our modification of Lobbie, a Lobatto collocation integrator for long-term simulations of the Solar System. We compare Lobbie against the widely used WHFast symplectic integrator and the high-order adaptive collocation integrator IAS15 implementations in the Rebound package. The performance of the integrator is evaluated using five benchmark problems: a circular two-body orbit integrated over 100 Myrs, two-body orbits with eccentricities up to 1-10^{-6} to test the adaptive step size control during repeated close encounters, the full eight-planet Solar System integrated over 100 Myrs, the four giant planets integrated over 10 Gyrs, and the eight-planet Solar System together with 50 asteroids on Aten-like orbits integrated over 1Myr to test the integrator's consistency in a chaotic, close-encounter-rich environment. Across all tests, Lobbie demonstrates excellent long-term stability and competitive computational performance. For full Solar System integrations, Lobbie achieves relative energy conservation at the level of 10^{-14} while outperforming IAS15 in computational efficiency and approaching the speed of WHFast at comparable accuracy. In the Solar System plus asteroids test, Lobbie also keeps different realizations of Jupiter's orbit consistent with each other to within about 1.5 km after 1 Myr of integration, two orders of magnitude better than IAS15, being twice faster. Our results demonstrate that Lobbie provides a powerful universal alternative to traditional symplectic mappings or Gauss-Radau collocation methods for long-term dynamical simulations in celestial mechanics.

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arXiv2026

Multi-year Ground-Based Survey Photometry of Active Comet 103P/Hartley 2 and Centaur (2060) Chiron: A Tale of Two Comets in the Pre-LSST Era

Comets and Centaurs trace the evolution of trans-Neptunian objects (TNOs) into the inner solar system. Their activity reflects the interplay between volatile sublimation, dust dynamics, and ring scattering. Yet the long-term behavior of individual objects is less constrained. To probe this evolutionary transition, we use wide-field survey photometry from the Asteroid Terrestrial-impact Last Alert System, Zwicky Transient Facility, and Las Cumbres Observatory observations of the Jupiter-family comet (JFC) 103P/Hartley 2 during its 2023/24 apparition, and the Centaur (2060) Chiron across 2020-2025, including its 2021 outburst. For 103P, heliocentric activity slopes are asymmetric about perihelion, with a steep inbound index ($n_{r,\rm pre}=-3.48\pm0.08$) and flatter outbound value ($n_{r,\rm post}=-1.16\pm0.04$), consistent with enhanced relative dust contribution post-perihelion. Reduced brightness versus prior apparitions matches reported secular fading trends. Dust mass-loss rates are $\sim4$-16 kg s$^{-1}$ for assumed grain properties. Colors exhibit a blueward trend near perihelion, consistent with enhanced gas contamination of the $g$-band, with possible phase-dependent scattering. A periodogram recovers a $\sim18.7$ hr activity-linked period near perihelion. For Chiron, subtracting a quiescent baseline reveals exponential decay from the 2021 outburst on a $\sim1.4$ yr timescale. Seasonal phase curves flatten from $β_o=0.150\pm0.034$ mag deg$^{-1}$ in 2021 to $\lesssim0.09$ mag deg$^{-1}$ by 2023-2025, converging with quiescent behavior. Broad-band colors remain unchanged at ATLAS ($c-o$)=0.22$\pm$0.09 mag. This extended activity suggests a new epoch of persistent, low-level activity and/or evolving ring-scattering. These objects bracket the TNO-to-JFC evolutionary sequence, with 103P near the volatile-depleted end, and Chiron still volatile-rich and capable of episodic activity.

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arXiv2026

NSF-DOE Vera C. Rubin Observatory Observations of Interstellar Comet 3I/ATLAS (C/2025 N1)

We report on the observation and measurement of astrometry, photometry, morphology, and activityof the interstellar object 3I/ATLAS, also designated C/2025 N1 (ATLAS) with the NSF-DOE Vera C. Rubin Observatory. Comet 3I/ATLAS, the third known interstellar object, was discovered on UT 2025 July 1. Rubin Observatory had coincidentally collected images of the object's region of the sky during routine commissioning. Facilitated by Rubin's high resolution and large aperture, we successfully recovered object detections from Rubin observations spanning UT 2025 June 21 (10 days before discovery, when 3I/ATLAS was 4.5 au from the Sun) through the date of discovery, and we acquired additional images through UT 2025 July 20 as part of commissioning. We measure on-sky locations of 3I/ATLAS in Rubin ugrizy bands, with a typical precision of about 70 mas, and briefly describe the reason this is coarser than our measured static source astrometric precision of about 3 mas in Rubin images. We measure grizy magnitudes of 3I/ATLAS photometry at about 0.01 mag precision, detecting no short-term photometric variability above 0.01 mag. We derive an estimated near-nucleus dust-to-nucleus scattering cross-section ratio of eta >= 13 on UT 2025 July 2 based on Rubin photometry and an upper limit nucleus size computed from Hubble Space Telescope observations. We find Rubin colors of g - r = (0.657 +/- 0.013) mag, r - i = (0.235 +/- 0.018) mag, i - z = (0.147 +/- 0.042) mag, z - y = (0.047 +/- 0.052) mag. These data represent the earliest observations of this object by a large (>=8-meter class) telescope and illustrate the type of measurements (and discoveries) Rubin's Legacy Survey of Space and Time (LSST) will begin to provide after it begins in early 2026.

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arXiv2026

Sequential Fragmentation of C/2025 K1 (ATLAS) After Its Near-Sun Passage

Comet C/2025 K1 (ATLAS) reached perihelion at 0.33 au on 2025 October 8. Daily monitoring by the LCO Outbursting Objects Key Project revealed a major activity increase between November 2 and 4, accompanied by rapid changes in coma morphology. Serendipitous HST/STIS acquisition images obtained on November 8-10 captured the comet only days after this event and resolved five fragments, providing an early high-resolution view of a nucleus in the process of disruption. Fragment motions and morphologies indicate a hierarchical fragmentation sequence, including a slow secondary split of fragment II. Back extrapolation shows that both the primary and secondary breakups preceded their associated photometric outbursts by roughly one to three days. This consistent lag, together with the appearance of thin, short-lived arclets around fragment I in the first HST epoch, suggests that freshly exposed interior material warms rapidly but requires time before dust can be released efficiently. Given the comet's close perihelion passage, rotational instability driven by enhanced outgassing torques is a plausible contributor to nucleus disintegration and dust release, and may represent the primary source of the observed brightening. These combined ground- and space-based observations provide rare, time-resolved constraints on the thermal and structural evolution of a fragmented comet near perihelion and highlight the scientific value of capturing a nucleus within days of disruption, when thermal adjustment, dust mantle re-formation, and outgassing-driven torques jointly govern the onset of activity.

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arXiv2025

First Detection of Molecular Activity in the Largest Known Oort Cloud Comet: ALMA Imaging of C/2014 UN271 (Bernardinelli-Bernstein) at 16.6 au from the Sun

We report observations of comet C/2014 UN271 (Bernardinelli-Bernstein) carried out on UT 2024 March 8 and 17 at a heliocentric distance ($r_{\mathrm{H}}$) of 16.6 au using the Atacama Large Millimeter/Submillimeter Array (ALMA). The CO ($J$=2-1) line at 230 GHz was detected along with continuum emission from its dust coma and large ($\sim$140 km) nucleus, revealing the nature of the activity drivers and outgassing kinematics of the largest Oort cloud comet discovered to date. This work presents spectrally integrated flux maps, autocorrelation spectra, production rates, and parent scale lengths for CO and a stringent upper limit for the H$_2$CO production rate. CO outgassing displayed multiple active jets which evolved from one epoch to the next. The continuum emission was compact and spatially unresolved, and is consistent with thermal emission from the large nucleus and a tentative detection of a dust coma. Complementary optical observations provided activity context for the ALMA epochs, indicating that UN271 underwent an outburst in late February before returning to a quiescent brightness in mid--late March. These results represent the first secure detection of molecular activity reported in the literature for C/2014 UN271 and highlight the dynamic nature of this distantly active small world.

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arXiv2025

Pluto Geologic Map: Use of Crater Data to Understand Age Relationships

Pluto's surface displays a wide variety of geologic units from smooth plains to extremely rugged mountainous expanses. These terrains range in age from young, actively resurfaced regions (no observable craters even in the highest-resolution New Horizons images) to old, heavily cratered, eroded regions. Here we expand upon the crater data analysis and the independent crater data set used in the production of a 1:7M scale geologic map of Pluto that is to be published by the United States Geologic Survey (USGS). We present both relative ages based on crater spatial density (number of craters in a given size bin per km^2) and also quantitative ages (e.g., 2 Ga) using the estimated impactor flux onto Pluto. The techniques presented here were developed specifically for the information available from a USGS geologic map, where smaller craters are mapped as points only (no specific diameter information per crater). We developed a new type of visualization, called a distributed R-plot, to understand the relative ages of the geologic units. The uncertainties in the current knowledge of the Kuiper belt populations and impactor flux at Pluto propagate to large uncertainties in the estimated quantitative ages (~a factor of two). However, both relative and quantitative ages from crater analysis were still valuable tools in developing the sequence of geologic events. Pluto has large areas of crater-free young terrains (13 units making up ~27% of mapped higher-resolution surface area), with widely varying morphologies, indicating a variety of resurfacing mechanisms, both exogenic and endogenic, likely active into Pluto's recent past or present.

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arXiv2025

Tuning the Legacy Survey of Space and Time (LSST) Observing Strategy for Solar System Science: Incremental Templates in Year 1

The Vera C. Rubin Observatory is due to commence the 10-year Legacy Survey of Space and Time (LSST) at the end of 2025. To detect transient/variable sources and identify solar system objects (SSOs), the processing pipelines require templates of the static sky to perform difference imaging. During the first year of the LSST, templates must be generated as the survey progresses, otherwise SSOs cannot be discovered nightly. The incremental template generation strategy has not been finalized; therefore, we use the Metric Analysis Framework (MAF) and a simulation of the survey cadence (one_snap_v4.0_10yrs}) to explore template generation in Year 1. We have assessed the effects of generating templates over timescales of days-weeks, when at least four images of sufficient quality are available for $\geq90\%$ of the visit. We predict that SSO discoveries will begin $\sim$2-3 months after the start of the survey. We find that the ability of the LSST to discover SSOs in real-time is reduced in Year 1. This is especially true for detections in areas of the sky that receive fewer visits, such as the North Ecliptic Spur (NES), and in less commonly used filters, such as the $u$ and $g$-bands. The lack of templates in the NES dominates the loss of real-time SSO discoveries; across the whole sky the MAF Main-Belt asteroid (MBA) discovery metric decreases by up to $63\%$ compared to the baseline observing strategy, whereas the metric decreases by up to $79\%$ for MBAs in the NES alone.

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arXiv2024

Rubin ToO 2024: Envisioning the Vera C. Rubin Observatory LSST Target of Opportunity program

The Legacy Survey of Space and Time (LSST) at Vera C. Rubin Observatory is planned to begin in the Fall of 2025. The LSST survey cadence has been designed via a community-driven process regulated by the Survey Cadence Optimization Committee (SCOC), which recommended up to 3% of the observing time to carry out Target of Opportunity (ToO) observations. Experts from the scientific community, Rubin Observatory personnel, and members of the SCOC were brought together to deliver a recommendation for the implementation of the ToO program during a workshop held in March 2024. Four main science cases were identified: gravitational wave multi-messenger astronomy, high energy neutrinos, Galactic supernovae, and small potentially hazardous asteroids possible impactors. Additional science cases were identified and briefly addressed in the documents, including lensed or poorly localized gamma-ray bursts and twilight discoveries. Trigger prioritization, automated response, and detailed strategies were discussed for each science case. This document represents the outcome of the Rubin ToO 2024 workshop, with additional contributions from members of the Rubin Science Collaborations. The implementation of the selection criteria and strategies presented in this document has been endorsed in the SCOC Phase 3 Recommendations document (PSTN-056). Although the ToO program is still to be finalized, this document serves as a baseline plan for ToO observations with the Rubin Observatory.

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arXiv2024

Analysing the Onset of Cometary Activity by the Jupiter-Family Comet 2023 RN3

We utilize serendipitous observations from the Asteroid Terrestrial-impact Last Alert System (ATLAS) and the Zwicky Transient Facility (ZTF) in addition to targeted follow-up observations from the Las Cumbres Observatory (LCO) and Liverpool Telescope to analyze the first observed instance of cometary activity by the newly-discovered Jupiter-family comet C/2023 RN3 (ATLAS), whose orbital dynamics place it close to residing on a Centaur-like orbit. Across our 7-month baseline, we observe an epoch of cometary activity commencing in August 2023 with an increase in brightness of >5.4 mag. The lightcurve of 2023 RN3 indicates the presence of continuous cometary activity across our observations, suggesting the onset of a new period of sustained activity. We find no evidence of any outbursts on top of the observed brightening, nor do we find any significant color evolution across our observations. 2023 RN3 is visibly extended in LCO and Liverpool Telescope observations, indicating the presence of a spatially-extended coma. Numerical integration of 2023 RN3's orbit reveals the comet to have recently undergone a slight increase in semimajor axis due to a planetary encounter with Jupiter, however whether this orbital change could trigger 2023 RN3's cometary activity is unclear. Our estimate for the maximum dust production metric of Afrho ~400 cm is consistent with previous measurements for the Jupiter-family comet and Centaur populations.

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arXiv2024

The Discovery and Evolution of a Possible New Epoch of Cometary Activity by the Centaur (2060) Chiron

Centaurs are small Solar System objects on chaotic orbits in the giant planet region, forming an evolutionary continuum with the Kuiper belt objects and Jupiter-family comets. Some Centaurs are known to exhibit cometary activity, though unlike comets this activity tends not to correlate with heliocentric distance and the mechanism behind it is currently poorly understood. We utilize serendipitous observations from the Asteroid Terrestrial-impact Last Alert System (ATLAS), Zwicky Transient Facility (ZTF), Panoramic Survey Telescope and Rapid Response System (Pan-STARRS), Dark Energy Survey (DES), and Gaia in addition to targeted follow-up observations from the Las Cumbres Observatory, TRAnsiting Planets and PlanetesImals Small Telescope South (TRAPPIST-South), and Gemini North telescope to analyze an unexpected brightening exhibited by the known active Centaur (2060) Chiron in 2021. This is highly indicative of a cometary outburst. As of 2023 February, Chiron has still not returned to its pre-brightening magnitude. We find Chiron's rotational lightcurve, phase curve effects, and possible high-albedo surface features to be unlikely causes of this observed brightening. We consider the most likely cause to be an epoch of either new or increased cometary activity, though we cannot rule out a possible contribution from Chiron's reported ring system, such as a collision of as-yet unseen satellites shepherding the rings. We find no evidence for coma in our Gemini or TRAPPIST-South observations, though this does not preclude the possibility that Chiron is exhibiting a coma that is too faint for observation or constrained to the immediate vicinity of the nucleus.

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arXiv2023

Jupiter's Metastable Companions

Jovian co-orbitals share Jupiter's orbit in 1:1 mean motion resonance. This includes $>$10,000 so-called Trojan asteroids surrounding the leading (L4) and trailing (L5) Lagrange points, viewed as stable groups dating back to planet formation. Via a massive numerical study we identify for the first time some Trojans which are certainly only `metastable'; instead of being primordial, they are recent captures from heliocentric orbits into moderately long-lived (10 kyr - 100 Myr) metastable states that will escape back to the scattering regime. We have also identified (1) the first two jovian horseshoe co-orbitals that exist for many resonant libration periods, and (2) eight jovian quasi-satellites with metastable lifetimes of 4-130 kyr. Our perspective on the Trojan population is thus now more complex as Jupiter joins the other giant planets in having known metastable co-orbitals which are in steady-state equilibrium with the planet-crossing Centaur and asteroid populations, in agreement with theoretical estimates.

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arXiv2023

Photometry of the Didymos system across the DART impact apparition

On 26 September 2022, the Double Asteroid Redirection Test (DART) spacecraft impacted Dimorphos, the satellite of binary near-Earth asteroid (65803) Didymos. This demonstrated the efficacy of a kinetic impactor for planetary defense by changing the orbital period of Dimorphos by 33 minutes (Thomas et al. 2023). Measuring the period change relied heavily on a coordinated campaign of lightcurve photometry designed to detect mutual events (occultations and eclipses) as a direct probe of the satellite's orbital period. A total of 28 telescopes contributed 224 individual lightcurves during the impact apparition from July 2022 to February 2023. We focus here on decomposable lightcurves, i.e. those from which mutual events could be extracted. We describe our process of lightcurve decomposition and use that to release the full data set for future analysis. We leverage these data to place constraints on the post-impact evolution of ejecta. The measured depths of mutual events relative to models showed that the ejecta became optically thin within the first ~1 day after impact, and then faded with a decay time of about 25 days. The bulk magnitude of the system showed that ejecta no longer contributed measurable brightness enhancement after about 20 days post-impact. This bulk photometric behavior was not well represented by an HG photometric model. An HG1G2 model did fit the data well across a wide range of phase angles. Lastly, we note the presence of an ejecta tail through at least March 2023. Its persistence implied ongoing escape of ejecta from the system many months after DART impact.

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arXiv2023

Splitting of Long-Period Comet C/2018 F4 (PANSTARRS)

Long-period comet C/2018 F4 (PANSTARRS) was observed to show duplicity of its inner region in 2020 September, suggestive of a splitting event. We here present analyses of our observations of the comet taken from the LOOK project and the University of Hawaii 2.2 m telescope after the discovery of the splitting. The two fragments Components A and B, estimated to be $\sim\!60$ m to 4 km in radius, remained highly similar to each other in terms of brightness, colour, and dust morphology throughout our observing campaign from 2020 September to 2021 December. Our fragmentation model yielded that the two components split at a relative speed of $3.00 \pm 0.18$ m s$^{-1}$ in 2020 late April, implying a specific energy change of $\left(5.3 \pm 2.8 \right) \times 10^3$ J kg$^{-1}$, and that Component B was subjected to a stronger nongravitational acceleration than Component A in both the radial and normal directions of the orbit. The obtained splitting time is broadly consistent with the result from the dust morphology analysis, which further suggested that the dominant dust grains were millimeter-sized and ejected at speed $\sim\!2$ m s$^{-1}$. We postulate that the pre-split nucleus of the comet consisted of two lobes resembling the one of 67P, or that the comet used to be a binary system like main-belt comet 288P. Regardless, we highlight the possibility of using observations of split comets as a feasible manner to study the bilobate shape or binarity fraction of cometary nuclei.

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arXiv2023

Tuning the Legacy Survey of Space and Time (LSST) Observing Strategy for Solar System Science

The Vera C. Rubin Observatory is expected to start the Legacy Survey of Space and Time (LSST) in early to mid-2025. This multi-band wide-field synoptic survey will transform our view of the solar system, with the discovery and monitoring of over 5 million small bodies.The final survey strategy chosen for LSST has direct implications on the discoverability and characterization of solar system minor planets and passing interstellar objects. Creating an inventory of the solar system is one of the four main LSST science drivers. The LSST observing cadence is a complex optimization problem that must balance the priorities and needs of all the key LSST science areas. To design the best LSST survey strategy, a series of operation simulations using the Rubin Observatory scheduler have been generated to explore the various options for tuning observing parameters and prioritizations. We explore the impact of the various simulated LSST observing strategies on studying the solar system's small body reservoirs. We examine what are the best observing scenarios and review what are the important considerations for maximizing LSST solar system science. In general, most of the LSST cadence simulations produce +/-5% or less variations in our chosen key metrics, but a subset of the simulations significantly hinder science returns with much larger losses in the discovery and light curve metrics.

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arXiv2023

Orbital Period Change of Dimorphos Due to the DART Kinetic Impact

The Double Asteroid Redirection Test (DART) spacecraft successfully performed the first test of a kinetic impactor for asteroid deflection by impacting Dimorphos, the secondary of near-Earth binary asteroid (65803) Didymos, and changing the orbital period of Dimorphos. A change in orbital period of approximately 7 minutes was expected if the incident momentum from the DART spacecraft was directly transferred to the asteroid target in a perfectly inelastic collision, but studies of the probable impact conditions and asteroid properties indicated that a considerable momentum enhancement ($β$) was possible. In the years prior to impact, we used lightcurve observations to accurately determine the pre-impact orbit parameters of Dimorphos with respect to Didymos. Here we report the change in the orbital period of Dimorphos as a result of the DART kinetic impact to be -33.0 +/- 1.0 (3$σ$) minutes. Using new Earth-based lightcurve and radar observations, two independent approaches determined identical values for the change in the orbital period. This large orbit period change suggests that ejecta contributed a significant amount of momentum to the asteroid beyond what the DART spacecraft carried.

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arXiv2022

A LOOK at Outbursts of Comet C/2014 UN$_{271}$ (Bernardinelli-Bernstein) Near 20 au

Cometary activity may be driven by ices with very low sublimation temperatures, such as carbon monoxide ice, which can sublimate at distances well beyond 20 au. This point is emphasized by the discovery of Oort cloud comet C/2014 UN$_{271}$ (Bernardinelli-Bernstein), and its observed activity out to $\sim$26 au. Through observations of this comet's optical brightness and behavior, we can potentially discern the drivers of activity in the outer solar system. We present a study of the activity of comet Bernardinelli-Bernstein with broad-band optical photometry taken at 19-20 au from the Sun (2021 June to 2022 February) as part of the LCO Outbursting Objects Key (LOOK) Project. Our analysis shows that the comet's optical brightness during this period was initially dominated by cometary outbursts, stochastic events that ejected $\sim10^7$ to $\sim10^8$ kg of material on short (< 1 day) timescales. We present evidence for three such outbursts occurring in 2021 June and September. The nominal nuclear volumes excavated by these events are similar to the 10-100 m pit-shaped voids on the surfaces of short-period comet nuclei, as imaged by spacecraft. Two out of three Oort cloud comets observed at large pre-perihelion distances exhibit outburst behavior near 20 au, suggesting such events may be common in this population. In addition, quiescent CO-driven activity may account for the brightness of the comet in 2022 January to February, but that variations in the cometary active area (i.e., the amount of sublimating ice) with heliocentric distance are also possible.

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arXiv2022

The LCO Outbursting Objects Key Project: Overview and Year 1 Status

The LCO Outbursting Objects Key (LOOK) Project uses the telescopes of the Las Cumbres Observatory (LCO) Network to: (1) to systematically monitor a sample of Dynamically New Comets over the whole sky, and (2) use alerts from existing sky surveys to rapidly respond to and characterize detected outburst activity in all small bodies. The data gathered on outbursts helps to characterize each outburst's evolution with time, assess the frequency and magnitude distribution of outbursts in general, and contributes to the understanding of outburst processes and volatile distribution in the Solar System. The LOOK Project exploits the synergy between current and future wide-field surveys such as ZTF, PanSTARRS, and LSST as well as rapid-response telescope networks such as LCO, and serves as an excellent testbed for what will be needed the much larger number of objects coming from Rubin Observatory. We will describe the LOOK Project goals, the planning and target selection (including the use of NEOexchange as a Target and Observation Manager or "TOM"), and results from the first phase of observations, including the detection of activity and outbursts on the giant comet C/2014 UN271 (Bernardinelli-Bernstein) and the discovery and follow-up of outbursts on comets. Within these outburst discoveries, we present a high cadence of 7P/Pons-Winnecke with days, a large outburst on 57P/duToit-Neujmin-Delporte, and evidence that comet P/2020 X1 (ATLAS) was in outburst when discovered.

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arXiv2021

OSSOS. XXIII. 2013 VZ70 and the Temporary Coorbitals of the Giant Planet

We present the discovery of 2013 VZ70, the first known horseshoe coorbital companion of Saturn. Observed by the Outer Solar System Origins Survey (OSSOS) for 4.5 years, the orbit of 2013 VZ70 is determined to high precision, revealing that it currently is in `horseshoe' libration with the planet. This coorbital motion will last at least thousands of years but ends ~10 kyr from now; 2013 VZ70 is thus another example of the already-known `transient coorbital' populations of the giant planets, with this being the first known prograde example for Saturn (temporary retrograde coorbitals are known for Jupiter and Saturn). We present a theoretical steady state model of the scattering population of trans-Neptunian origin in the giant planet region (2--34 au), including the temporary coorbital populations of the four giant planets. We expose this model to observational biases using survey simulations in order to compare the model to the real detections made by a set of well-characterized outer Solar System surveys. While the observed number of coorbitals relative to the scattering population is higher than predicted, we show that the number of observed transient coorbitals of each giant planet relative to each other is consistent with a transneptunian source.

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