arXiv subjects

Man-To Hui

Publications and source records attributed to Man-To Hui.

At least 19 recordsLinked to original sources

arXiv2026

Interstellar Object 3I/ATLAS Observed from Mars by China's Tianwen-1 Spacecraft

China's Tianwen-1 Mars orbiter successfully imaged the third interstellar object, 3I/ATLAS, during its close encounter with Mars using the onboard HiRIC CMOS camera. This is China's first deep-space observation of an astronomical object. These observations constitute the first imaging of this object from a vantage point significantly out of its orbital plane, providing a unique constraint on dust dynamics. Three observing epochs between 2025 September 30 and October 3 reveal clear changes in coma and tail morphology driven by the rapidly evolving viewing geometry. Comparison with Finson-Probstein dust dynamical models indicates that the coma is dominated by large grains with solar radiation pressure parameter $\beta \approx 10^{-3} $ - $10^{-2}$, corresponding to grain sizes of a few 100s $\mu$m. The extent of the sunward coma implies dust ejection velocities of $3$ - $10$ m s$^{-1}$. Despite the morphological evolution, the azimuthally averaged surface brightness profile remains nearly unchanged through the three epochs, transitioning from a radial slope near -1 close to the nucleus to slightly steeper than -1.5 at larger cometocentric distances, consistent with steady-state dust outflow accelerated by solar radiation pressure. Photometry yields an average $Af\rho \sim (2.0\pm0.2)\times10^4$ cm and a corresponding dust mass loss rate of $\dot{M} \sim 10^3$ kg s$^{-1}$.

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arXiv2026

Pre-perihelion Volatile Evolution of Interstellar Comet 3I/ATLAS Indicating Significant Contribution from Extended Source in the Coma

Interstellar comets provide rare opportunities for probing the diversity of refractory and volatile inventory around other stars. As the second ever interstellar comet, and the third interstellar object, 3I/ATLAS has been the focus of telescopic observations since its discovery in July 2025. Following the previous observations at multi-wavelengths, we present further radio observations of the 1665/1667 MHz ground-state OH lines and millimeter observations of the CO($J$=1-0) transition at 115.271 GHz that trace the coma $\rm H_2O$ and CO abundances, respectively. We derived OH production rates of $(1.32\pm0.47)\times10^{28}\ \rm s^{-1}$ at 2.27 au and $(1.89\pm0.37)\times10^{28}\ \rm s^{-1}$ at 1.96 au as well as an average CO production rate of $\rm (5.75\pm1.91) \times 10^{27}\, s^{-1}$ between 2.33 and 1.75 au, inferring a CO/$\rm H_2O$ ratio of ($28\pm11\%$). With the mean HCN production rate of $2.5\times 10^{25}\ \rm s^{-1}$ at 2.1 au reported by \citet{2025arXiv251120845R} and \citet{2025arXiv251002817C}, we infer a CO/HCN ratio of ($230\pm76$). By synthesizing water production rates measured with instruments of different apertures, we found that the sublimation from extended source in the coma contributes significantly to 3I's pre-perihelion water measurements, accounting for up to 80\% from 3 au to 2 au.

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arXiv2026

Nucleus and Postperihelion Activity of Interstellar Object 3I/ATLAS Observed by Hubble Space Telescope

We report the detection of the nucleus of interstellar object 3I/ATLAS, using a nucleus extraction technique on Hubble Space Telescope (HST) observations taken between December 2025 and January 2026. The product of the V-band geometric albedo, $p_V$, with the physical cross-section of the nucleus is $0.22 \pm 0.07$ km$^{2}$, which corresponds to an effective radius of $1.3 \pm 0.2$ km if assuming a comet-like albedo $p_{V} = 0.04$. This size is in agreement with an independent estimate based on the reported nongravitational acceleration and activity of the interstellar object. If the measured photometric variations are solely due to the rotation of an aspherical nucleus, the axis ratio must be $2:1$ or greater, and the rotation period $\gtrsim\!1$ hr. Leveraging the range of covered phase angles, we identified a significant opposition surge of $\sim\!0.2$ mag with a width of $3^{\circ} \pm 1^{\circ}$, which may include concurrent contributions from orbital plane crossing and tail projection, and determined a linear phase slope of $0.026 \pm 0.006$ mag degree$^{-1}$ for the coma dust. Compared to the preperihelion brightening trend, 3I faded more rapidly on the outbound leg, following an activity index of $4.5 \pm 0.3$, not unusual in the context of solar system comets. This activity asymmetry is further corroborated by a postperihelion coma surface brightness profile that is significantly shallower than its preperihelion counterpart. From discovery statistics, we infer that multiple interstellar objects resembling 3I probably went undetected prior to the discovery of 1I/`Oumuamua, unless the overall population possesses a steep size distribution.

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arXiv2025

Dynamically New Comet C/2025 D1 (Groeller) with Record Perihelion Distance

We studied C/2025 D1 (Groeller), a long-period comet with an unprecedented perihelion distance of 14.1 au, using archival observations. The data reveals that it had been active at inbound heliocentric distances $r_{\rm H} \gtrsim 20$ au. Initially, the comet intrinsically brightened at $r_{\rm H} \gtrsim 16$ au, with brightening parameters comparable to those of other long-period comets. However, observations after late 2023 showed a gradual decay, despite the inbound trajectory of the comet. To our knowledge, such behaviours have not been observed for other long-period comets at similar heliocentric distances. We speculate that this might be linked to the onset of CO$_{2}$ sublimation and/or crystallisation processes. Alternatively, the activity source might have been exhausted. The surface brightness profile of the coma indicates a steady-state mass loss, implying supervolatile sublimation as the primary driver of the observed activity. Despite changes in the orbital plane angle, the circularly symmetric coma persisted throughout the observed period, indicative of the dominance of large grains in the coma. Assuming the activity trend is independent of bandpass, we found that comet was redder than many other solar system comets. Our model-dependent constraint estimates the nucleus radius to be $\gtrsim\!0.4$ km. We performed astrometric measurements, refined the orbital solution, and derived the original and future orbits of the comet. Our N-body integration, accounting for the Galactic tide, strongly favours that the comet is dynamically new, with its previous perihelion at $\gtrsim\!60$ au from the Sun $\gtrsim\!6$ Myr ago. It is highly likely that the comet will be lost from our solar system after the current apparition.

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arXiv2025

Pre-perihelion radio observations of comet 12P/Pons-Brooks with Tianma radio telescope

{The multiple outburst events of comet 12P/Pons-Brooks during its 2024 apparition offer a unique window into highly-active volatile releasing processes not observable during quiescent periods. We performed radio observations of comet 12P/Pons-Brooks with the Tianma-65m radio telescope, targeting the OH and NH$_3$ inversion lines at 18-cm and 1.3-cm, respectively. By monitoring 12P at different heliocentric distances on its inbound journey, we aim to provide insights into the comet's volatile composition and outburst behavior. Four observations were carried out between December 2023 and March 2024 when the comet was approaching the Sun from 2.22 AU to 1.18 AU. We conducted 18-cm OH lines observations on 4 single days using the cryogenically cooled receiver system of the telescope to derive $\rm H_{2}O$ production rate. During 12P's outburst on December 14, we also conducted observations targeting the $\rm NH_{3}$ emission. OH 18-cm lines were clearly detected with a signal-to-noise ratio of $\sim$4$\sigma$ (peak intensity). A tentative detection of $\rm NH_{3}$ was made at the $\sim$$3\sigma$ level during the outburst phase, but the detection needs to be further verified. Our observations provide information on the outgassing behavior of 12P/Pons-Brooks during its 2024 apparition. The water production rate of 12P, derived from the 18-cm OH lines is consistent with measurements obtained in other works. The possible detection of $\rm NH_{3}$ during an outburst suggests possible connections between subsurface volatile reservoir and the outburst mechanism. These results could further our understanding of the composition and activity of Halley-type comets.

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arXiv2025

Hubble Space Telescope Observations of the Interstellar Interloper 3I/ATLAS

We present high angular resolution observations of the third known interstellar interloper, 3I/ATLAS, from the Hubble Space Telescope. The object is clearly active at 3.8 au pre-perihelion, showing dust emitted from the hot Sun-facing side of the nucleus and a weak, radiation pressure swept tail away from the Sun. We apply a simple model to estimate the mass loss rate in dust as dM/dt = 12 sqrt(a) kg/s, where a is the mean particle size in microns. With 1 < a < 100, we infer dM/dt = 12 to 120 kg/s. A fit to the surface brightness distribution of the inner coma limits the effective radius of the nucleus to be r < 2.8 km, assuming red geometric albedo 0.04. Conversely, the nucleus cannot be smaller than 0.22 km in radius if its coma is supplied by sublimation of carbon monoxide, and must be larger if a less volatile molecule drives the mass loss.

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arXiv2025

Great comet C/2023 A3 (Tsuchinshan-ATLAS): dust loss before perihelion

In this study, the dust loss of comet C/2023 A3 (Tsuchinshan-ATLAS) is investigated through the analysis of archival images. By measuring the surface brightness profile of the coma, we determined that the comet maintained nearly in a steady state during the observations. Analysis of the dust distribution perpendicular to the orbital plane reveals that the ejection velocity is $v_{\perp}\sim(65\pm5)\,\beta^{1/2}$ m s$^{-1}$, where $\beta$ is inversely proportional to the size of the dust grains. From the dust scattering cross-section measurement, we estimated the upper limit of the nucleus radius to be $\sim\!5.9\pm0.2$ km, assuming a geometric albedo of 0.04. Based on the extrapolation of the scattering cross-section over time, the onset time of significant dust activity is estimated to be 25 July 2022, corresponding to a heliocentric distance of 9.1 au, with the activity mechanism at this distance likely being the phase transition from amorphous to crystalline ice. Our simulation reveals that the minimum dust size is \SI{20}{\micro\meter} and the size distribution index is $s = 3.4$ in tail. The dust loss rate is determined to be $(1.7 \pm 0.8) \times 10^2$ kg s$^{-1}$, based on the derived average size of the particles and the rate of change of the scattering cross-section over time. Through a simplistic model, we evaluate that the nucleus of the comet remains stable against tidal effects, sublimation, and rotational instability, and disfavour the fate of disintegration. The result is consistent with observations that the nucleus has survived.

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arXiv2024

2019 UO$_{14}$: A Transient Trojan of Saturn

Saturn has long been the only giant planet in our solar system without any known Trojan members. In this paper, with serendipitous archival observations and refined orbit determination, we report that 2019 UO$_{14}$ is a Trojan of the gas giant. However, the object is only a transient Trojan currently librating around the leading Lagrange point $L_4$ of the Sun-Saturn system in a period of $\sim\!0.7$ kyr. Our N-body numerical simulation shows that 2019 UO$_{14}$ was likely captured as a Centaur and became trapped around $L_4$ $\sim\!2$ kyr ago from a horseshoe coorbital. The current Trojan state will be maintained for another millennium or thereabouts before transitioning back to a horseshoe state. Additionally, we characterize the physical properties of 2019 UO$_{14}$. Assuming a linear phase slope of $0.06 \pm 0.01$ mag/deg, the mean $r$-band absolute magnitude of the object was determined to be $H_r = 13.11 \pm 0.07$, with its color measured to be consistent with those of Jupiter and Neptune Trojans and not statistically different from Centaurs. Although the short-lived Saturn Trojan exhibited no compelling evidence of activity in the observations, we favour the possibility that it could be an active Trojan. If confirmed, 2019 UO$_{14}$ would be marked as the first active Trojan in our solar system. We conservatively determine the optical depth of dust within our photometric aperture to be $\lesssim\!10^{-7}$, corresponding to a dust mass-loss rate to be $\lesssim\!1$ kg s$^{-1}$, provided that the physical properties of dust grains resemble Centaur 29P/Schwassmann-Wachmann 1.

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arXiv2024

Serendipitous Archival Observations of A New Ultra-distant Comet C/2019 E3 (ATLAS)

We identified a new ultra-distant comet C/2019 E3 (ATLAS) exhibiting preperihelion cometary activity at heliocentric distances $\gtrsim\!20$ au, making it the fourth member of this population after C/2010 U3 (Boattini), C/2014 UN$_{271}$ (Bernardinelli-Bernstein), and C/2017 K2 (PANSTARRS). From serendipitous archival data, we conducted analyses of the comet, finding that the activity was consistent with steady-state behaviour, suggestive of sublimation of supervolatiles, that the cross-section of dust increased gradually on the inbound leg of the orbit, varying with heliocentric distances as $r_{\rm H}^{-1.5 \pm 0.4}$, and that the dust was produced at a rate of $\gtrsim\!10^2$ kg s$^{-1}$ within the observed timespan. Our modelling of the largely symmetric morphology of the comet suggests that the dust environment was likely dominated by mm-scale dust grains ejected at speeds $\lesssim\!0.4$ m s$^{-1}$ from the sunlit hemisphere of the nucleus. Assuming a typical geometric albedo of 0.05 and adopting several simplistic thermophysical models, we estimated the nucleus to be at least $\sim\!3$ km across. We also measured the colour of the comet to be consistent with other long-period comets, except being slightly bluer in $g-r$. With our astrometric measurements, we determined an improved orbit of the comet, based upon which we derived that the comet is dynamically new and that its perihelion distance will further shrink due to the Galactic tide. We conclude the paper by comparing the known characteristics of the known ultra-distant comets.

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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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arXiv2022

Fragment Dynamics in Active Asteroid 331P/Gibbs

We present a dynamical analysis of the fragmented active asteroid 331P/Gibbs. Using archival images taken by the Hubble Space Telescope from 2015 to 2018, we measured the astrometry of the primary and the three brightest (presumably the largest) components. Conventional orbit determination revealed a high-degree of orbital similarity between the components. We then applied a fragmentation model to fit the astrometry, obtaining key parameters including the fragmentation epochs and separation velocities. Our best-fit models show that Fragment B separated from the primary body at a speed of $\sim$1 cm s$^{-1}$ between 2011 April and May, whereas two plausible scenarios were identified for Fragments A and C. The former split either from the primary or from Fragment B, in 2011 mid-June at a speed of $\sim$8 cm s$^{-1}$, and the latter split from Fragment B either in late 2011 or between late 2013 and early 2014, at a speed of $\sim$0.7-0.8 cm s$^{-1}$. The results are consistent with rotational disruption as the mechanism causing the cascading fragmentation of the asteroid, as suggested by the rapid rotation of the primary. The fragments constitute the youngest known asteroid cluster, providing us with a great opportunity to study asteroid fragmentation and formation of asteroid clusters.

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arXiv2022

Perihelion Activity of (3200) Phaethon Is Not Dusty: Evidence from STEREO/COR2 Observations

We present an analysis of asteroid (3200) Phaethon using coronagraphic observations from 2008 to 2022 by the COR2 cameras onboard the twin Solar TErrestrial RElations Observatory (STEREO) spacecraft. Although undetected in individual images, Phaethon was visible in stacks combined from the same perihelion observations, yet only at small ($\lesssim$30\deg) but not large ($\gtrsim$150\deg) phase angles. The observations are in line with the contribution from a bare nucleus, thereby seriously contradicting the interpretation based on HI-1 observations that attributes the perihelion activity to the ejection of \micron-sized dust. We obtained an upper limit to the effective cross-section of \micron-sized dust to be $\lesssim \! 10^{5}$ m$^{2}$, at least three orders of magnitude smaller than earlier estimates based on HI-1 data. On the contrary, the COR2 observations cannot rule out the existence of mm-sized or larger debris around Phaethon. However, the fact that no postperihelion debris tail has ever been detected for Phaethon suggests the unimportance of such dust in the perihelion activity. We thus conclude that the perihelion activity of Phaethon is highly unlikely relevant to the ejection of dust. Rather, we deduce that the activity is associated with gas emissions, possibly Fe I and/or Na D lines. To verify our conjecture and to fully understand the perihelion activity of Phaethon, more observations at small heliocentric distances are desired. We compile a list of observing windows ideal for the search of gas emissions of the asteroid from ground telescopes. The best opportunities will be during total solar eclipses.

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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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arXiv2022

The Lingering Death of Periodic Near-Sun Comet 323P/SOHO

We observed near-Sun comet 323P/SOHO for the first time using ground and space telescopes. In late December 2020, the object was recovered at Subaru showing no cometary features on its way to perihelion. However, in our postperihelion observations it developed a long narrow tail mimicking a disintegrated comet. The ejecta, comprised of at least mm-sized dust with power-law size distribution index $3.2 \pm 0.2$, was impulsively produced shortly after the perihelion passage, during which $\gtrsim$0.1-10% of the nucleus mass was shed due to excessive thermal stress and rotational disruption. Two fragments of $\sim$20 m in radius (assuming a geometric albedo of 0.15) were seen in HST observations from early March 2021. The nucleus, with an effective radius of $86 \pm 3$ m (the same albedo assumed) and an aspect ratio of $\sim$0.7, has a rotation period of 0.522 hr, which is the shortest for known comets in the solar system and implies cohesive strength $\gtrsim$10-100 Pa in the interior. The colour of the object was freakish, and how it changed temporally has never been previously observed. Using our astrometry, we found a strong nongravitational effect following a heliocentric dependency of $r_{\rm H}^{-8.5}$ in the transverse motion of the object. Our N-body integration reveals that 323P has a likelihood of 99.7% to collide with the Sun in the next two millennia driven by the $\nu_6$ secular resonance.

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arXiv2022

Hubble Space Telescope Detection of the Nucleus of Comet C/2014 UN$_{271}$ (Bernardinelli-Bernstein)

We present a high-resolution observation of distant comet C/2014 UN$_{271}$ (Bernardinelli-Bernstein) using the {\it Hubble Space Telescope} on 2022 January 8. The signal of the nucleus was successfully isolated by means of the nucleus extraction technique, with an apparent $V$-band magnitude measured to be $21.64 \pm 0.11$, corresponding to an absolute magnitude of $8.62 \pm 0.11$. The product of the visual geometric albedo with the effective radius squared is $p_V R_n^2$ = 159$\pm$16 km$^2$. If the ALMA observation by Lellouch et al. (2022) refers to a bare nucleus, we derive a visual geometric albedo of $0.034 \pm 0.008$ and an effective diameter of $137 \pm 15$ km. If dust contamination of the ALMA signal is present at the maximum allowed level (24%), we find nucleus diameter $119 \pm 13$ km and albedo of $0.044 \pm 0.011$. In either case, we confirm that C/2014 UN$_{271}$ is the largest long-period comet ever detected. Judging from the measured surface brightness profile of the coma, whose logarithmic gradient varies azimuthally between $\sim$1 and 1.7 in consequence of solar radiation pressure, the mass production is consistent with steady-state production but not with impulsive ejection, as would be produced by an outburst. Using aperture photometry we estimated an enormous (albeit uncertain) mass-loss rate of $\sim$10$^3$ kg s$^{-1}$ at a heliocentric distance of $\sim$20 au.

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arXiv2021

The Second Earth Trojan 2020 XL$_{5}$

The Earth Trojans are co-orbitals librating around the Lagrange points $L_4$ or $L_5$ of the Sun-Earth system. Although many numerical studies suggest that they can maintain their dynamical status and be stable on timescales up to a few tens of thousands of years or even longer, they remain an elusive population. Thus far only one transient member (2010 TK$_7$) has been discovered serendipitously. Here, we present a dynamical study of asteroid 2020 XL$_5$. With our meticulous followup astrometric observations of the object, we confirmed that it is a new Earth Trojan. However, its eccentric orbit brings it close encounters with Venus on a frequent basis. Based on our N-body integration, we found that the asteroid was captured into the current Earth Trojan status in the 15th century, and then it has a likelihood of 99.5% to leave the $L_4$ region within the next $\sim$10 kyr. Therefore, it is most likely that 2020 XL$_5$ is dynamically unstable over this timescale.

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arXiv2021

Disintegration of Long-Period Comet C/2019 Y4 (ATLAS): I. Hubble Space Telescope Observations

Near-Sun Comet C/2019 Y4 (ATLAS) is the first member of a long-period comet group observed to disintegrate well before perihelion. Here we present our investigation into this disintegration event using images obtained in a 3-day {\it Hubble Space Telescope} (\hst) campaign. We identify two fragment clusters produced by the initial disintegration event, corresponding to fragments C/2019 Y4-A and C/2019 Y4-B identified in ground-based data. These two clusters started with similar integrated brightness, but exhibit different evolutionary behavior. C/2019 Y4-A was much shorter-lived compared to C/2019 Y4-B, and showed signs of significant mass-loss and changes in size distribution throughout the 3-day campaign. The cause of the initial fragmentation is undetermined by the limited evidence but crudely compatible with either the spin-up disruption of the nucleus or runaway sublimation of sub-surface supervolatile ices, either of which would lead to the release of a large amount of gas as inferred from the significant bluing of the comet observed shortly before the disintegration. Gas can only be produced by the sublimation of volatile ices, which must have survived at least one perihelion passage at a perihelion distance of $q=0.25$~au. We speculate that Comet ATLAS is derived from the ice-rich interior of a non-uniform, kilometer-wide progenitor that split during its previous perihelion. This suggests that comets down to a few kilometers in diameter can still possess complex, non-uniform interiors that can protect ices against intense solar heating.

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arXiv2020

Outburst and Splitting of Interstellar Comet 2I/Borisov

We present Hubble Space Telescope observations of a photometric outburst and splitting event in interstellar comet 2I/Borisov. The outburst, first reported with the comet outbound at 2.8 AU (Drahus et al.~2020), was caused by the expulsion of solid particles having a combined cross-section about 100 sq. km and a mass in 0.1 mm sized particles about 2e7 kg. The latter corresponds to 1e-4 of the mass of the nucleus, taken as a sphere of radius 500 m. A transient ``double nucleus'' was observed on UT 2020 March 30 (about three weeks after the outburst), having a cross-section about 0.6 sq. km and corresponding dust mass 1e5 kg. The secondary was absent in images taken on and before March 28, and in images taken on and after April 03. The unexpectedly delayed appearance and rapid disappearance of the secondary are consistent with an origin through rotational bursting of one or more large (meter-sized) boulders under the action of outgassing torques, following their ejection from the main nucleus. Overall, our observations reveal that the outburst and splitting of the nucleus are minor events involving a negligible fraction of the total mass: 2I/Borisov will survive its passage through the planetary region largely unscathed.

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