arXiv subjects

P. Lacerda

Publications and source records attributed to P. Lacerda.

17 recordsLinked to original sources

arXiv2025

Considerations on the process of target selection for the Comet Interceptor mission

Comet Interceptor is an ESA science mission with payload contributions from ESA Member States and with an international participation by JAXA. It is the first mission that is being designed, built, and potentially launched before its target is known. This approach will enable the spacecraft to perform the first mission to a Long Period Comet from the Oort Cloud, as these comets have fleeting visits to the inner Solar System lasting only months to years from first discovery, too short for the usual process of mission development to be followed. In this paper we describe a number of factors that need to be considered in selecting a target for the mission, including scientific, orbital, spacecraft and instrument constraints, and discussion of different prioritisation strategies. We find that, in the case where we have a choice of targets, our decisions will mostly be driven by orbital information, which we will have relatively early on, with information on the activity level of the comet an important but secondary consideration. As cometary activity levels are notoriously hard to predict based on early observations alone, this prioritisation / decision approach based more on orbits gives us confidence that a good comet that is compatible with the spacecraft constraints will be selectable with sufficient warning time to allow the mission to intercept it.

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arXiv2025

Centaur Nuclei: Sizes, Shapes, Spins, and Structure

We present a wide-ranging but in-depth analysis of Centaurs, focusing on their physical and structural aspects. Centaurs, originating from the Scattered Disk and Kuiper Belt, play a crucial role in our understanding of Solar System evolution. We first examine how biases in discovery and measurement affect our understanding of the Centaur size distribution. In particular we address the strong dependence of the census on perihelion distance and the broad distribution of Centaur geometric albedos. We explore the rotational characteristics derived from lightcurves, revealing a diverse range of spin rates and photometric variabilities, with most Centaurs showing low amplitude lightcurves, suggesting near-spherical shapes. Additionally, we investigate the relationships between Centaur orbital parameters, surface colors, and physical properties, noting a lack of correlation between rotational dynamics and orbital evolution. We also address the influence of sublimation-driven activity on Centaur spin states, and the rarity of contact binaries. We then discuss some observational and modeling limitations from using common observations (e.g. visible or infrared photometry) to determine diameters and shapes. Following that, we give some points on understanding how Centaur diameters and shapes can reveal the `primitive' nature of the bodies, emphasizing the important role occultation observations play. We also then assess how the Centaur size distribution we see today has been influenced by the collisions in both the primordial Kuiper Belt and in the subsequent Scattered Disk. Finally, we end the chapter with a short narrative of future prospects for overcoming our current limitations in understanding Centaur origins and evolution.

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arXiv2025

Secular brightness curves of 272 comets

We investigate the brightening behavior of long-period comets as a function of dynamical age, defined by the original reciprocal semimajor axis, $1/a_0$. Our goal is to test long-standing claims about comet behavior using a large number of available measurements. We use a large set of photometric observations to compute and analyze global and local brightening curves for 272 long-period comets. Observed magnitudes are fitted with a linear model in log heliocentric distance, from which we derive brightening parameters for each comet. We categorize the sample into dynamically new, intermediate, and old comets, comparing their brightening behavior. We also examine the relationships between dynamical age and other orbital and physical parameters. Dynamically new comets are seen to brighten more slowly than old comets, particularly within 3 au from the Sun. The brightening rate of new comets appears to vary with heliocentric distance. New comets are intrinsically brighter than old comets, and exhibit a tighter correlation between brightening parameters.

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arXiv2020

TNOs are Cool! A Survey of the transneptunian Region XV. Physical characteristics of 23 resonant transneptunian and scattered disk objects

The goal of this work is to determine the physical characteristics of resonant, detached and scattered disk objects in the transneptunian region, observed mainly in the framework of the "TNOs are Cool!" Herschel Open Time Key Program. Based on thermal emission measurements with the Herschel/PACS and Spitzer/MIPS instruments we determine size, albedo, and surface thermal properties for 23 objects using radiometric modelling techniques. This is the first analysis in which the physical properties of objects in the outer resonances are determined for a notable sample. In addition to the results for individual objects, we have compared these characteristics with the bulk properties of other populations of the transneptunian region. The newly analyzed objects show a large variety of beaming factors, indicating a diversity of thermal properties, and in general, they follow the albedo-colour clustering identified earlier for Kuiper belt objects and Centaurs, further strengthening the evidence for a compositional discontinuity in the young Solar System.

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arXiv2017

Rotation of Cometary Nuclei: New Lightcurves and an Update of the Ensemble Properties of Jupiter-Family Comets

We report new lightcurves and phase functions for nine Jupiter-family comets (JFCs). They were observed in the period 2004-2015 with various ground telescopes as part of the Survey of Ensemble Physical Properties of Cometary Nuclei (SEPPCoN) as well as during devoted observing campaigns. We add to this a review of the properties of 35 JFCs with previously published rotation properties. The photometric time-series were obtained in Bessel R, Harris R and SDSS r' filters and were absolutely calibrated using stars from the Pan-STARRS survey. This specially-developed method allowed us to combine data sets taken at different epochs and instruments with absolute-calibration uncertainty down to 0.02 mag. We used the resulting time series to improve the rotation periods for comets 14P/Wolf, 47P/Ashbrook-Jackson, 94P/Russell, and 110P/Hartley 3 and to determine the rotation rates of comets 93P/Lovas and 162P/Siding-Spring for the first time. In addition to this, we determined the phase functions for seven of the examined comets and derived geometric albedos for eight of them. We confirm the known cut-off in bulk densities at $\sim$0.6 g $\mathrm{cm^{-3}}$ if JFCs are strengthless. Using the model of Davidsson (2001) for prolate ellipsoids with typical density and elongations, we conclude that none of the known JFCs require tensile strength larger than 10-25 Pa to remain stable against rotational instabilities. We find evidence for an increasing linear phase function coefficient with increasing geometric albedo. The median linear phase function coefficient for JFCs is 0.046 mag/deg and the median geometric albedo is 4.2 per cent.

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arXiv2017

The 67P/Churyumov-Gerasimenko observation campaign in support of the Rosetta mission

We present a summary of the campaign of remote observations that supported the European Space Agency's Rosetta mission. Telescopes across the globe (and in space) followed comet 67P/Churyumov-Gerasimenko from before Rosetta's arrival until nearly the end of mission in September 2016. These provided essential data for mission planning, large-scale context information for the coma and tails beyond the spacecraft, and a way to directly compare 67P with other comets. The observations revealed 67P to be a relatively `well behaved' comet, typical of Jupiter family comets and with activity patterns that repeat from orbit-to-orbit. Comparison between this large collection of telescopic observations and the in situ results from Rosetta will allow us to better understand comet coma chemistry and structure. This work is just beginning as the mission ends -- in this paper we present a summary of the ground-based observations and early results, and point to many questions that will be addressed in future studies.

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arXiv2017

TNOs are Cool: a survey of the Transneptunian Region XII. Thermal light curves of Haumea, 2003 VS2 and 2003 AZ84 with Herschel Space Observatory-PACS

Time series observations of the dwarf planet Haumea and the Plutinos 2003VS2 and 2003AZ84 with Herschel/PACS are presented in this work. Thermal emission of these trans-Neptunian objects were acquired as part of the TNOs are Cool Herschel Space Observatory key programme. We search for the thermal light curves at 100 and 160um of Haumea and 2003AZ84, and at 70 and 160um for 2003VS2 by means of photometric analysis of the PACS data. The goal of this work is to use these thermal light curves to obtain physical and thermophysical properties of these icy Solar System bodies. Haumea's thermal light curve is clearly detected at 100 and 160um. The effect of the reported dark spot is apparent at 100um. Different thermophysical models were applied to these light curves, varying the thermophysical properties of the surface within and outside the spot. Although no model gives a perfect fit to the thermal observations, results imply an extremely low thermal inertia (< 0.5 MKS) and a high phase integral (> 0.73) for Haumea's surface. We note that the dark spot region appears to be only weakly different from the rest of the object, with modest changes in thermal inertia and/or phase integral. The thermal light curve of 2003VS2 is not firmly detected at 70 and at 160um but a thermal inertia of 2+/-0.5 MKS can be derived from these data. The thermal light curve of 2003AZ84 is not firmly detected at 100um. We apply a thermophysical model to the mean thermal fluxes and to all the Herschel/PACS and Spitzer/MIPS thermal data of 2003AZ84, obtaining a close to pole-on orientation as the most likely for this TNO. For the three TNOs, the thermal inertias derived from light curve analyses or from the thermophysical analysis of the mean thermal fluxes confirm the generally small or very small surface thermal inertias of the TNO population, which is consistent with a statistical mean value of 2.5+/-0.5 MKS.

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arXiv2016

The Pan-STARRS 1 Discoveries of five new Neptune Trojans

In this work we report the detection of seven Neptune Trojans (NTs) in the Pan-STARRS 1 (PS1) survey. Five of these are new discoveries, consisting of four L4 Trojans and one L5 Trojan. Our orbital simulations show that the L5 Trojan stably librates for only several million years. This suggests that the L5 Trojan must be of recent capture origin. On the other hand, all four new L4 Trojans stably occupy the 1:1 resonance with Neptune for more than 1 Gyr. They can, therefore, be of primordial origin. Our survey simulation results show that the inclination width of the Neptune Trojan population should be between $7^{\circ}$ and $27^{\circ}$ at $>$ 95% confidence, and most likely $\sim 11^{\circ}$. In this paper, we describe the PS1 survey, the Outer Solar System pipeline, the confirming observations, and the orbital/physical properties of the new Neptune Trojans.

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arXiv2016

Near-infrared spatially resolved spectroscopy of (136108) Haumea's multiple system

The transneptunian region of the solar system is populated by a wide variety of icy bodies showing great diversity. The dwarf planet (136108) Haumea is among the largest TNOs and displays a highly elongated shape and hosts two moons, covered with crystalline water ice like Hamuea. Haumea is also the largest member of the sole TNO family known to date. A catastrophic collision is likely responsible for its unique characteristics. We report here on the analysis of a new set of observations of Haumea obtained with SINFONI at the ESO VLT. Combined with previous data, and using light-curve measurements in the optical and far infrared, we carry out a rotationally resolved spectroscopic study of the surface of Haumea. We describe the physical characteristics of the crystalline water ice present on the surface of Haumea for both regions, in and out of the Dark Red Spot (DRS), and analyze the differences obtained for each individual spectrum. The presence of crystalline water ice is confirmed over more than half of the surface of Haumea. Our measurements of the average spectral slope confirm the redder characteristic of the spot region. Detailed analysis of the crystalline water-ice absorption bands do not show significant differences between the DRS and the remaining part of the surface. We also present the results of applying Hapke modeling to our data set. The best spectral fit is obtained with a mixture of crystalline water ice (grain sizes smaller than 60 micron) with a few percent of amorphous carbon. Improvements to the fit are obtained by adding ~10% of amorphous water ice. Additionally, we used the IFU-reconstructed images to measure the relative astrometric position of the largest satellite Hi`iaka and determine its orbital elements. An orbital solution was computed with our genetic-based algorithm GENOID and our results are in full agreement with recent results.

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arXiv2016

Comet formation in collapsing pebble clouds. What cometary bulk density implies for the cloud mass and dust-to-ice ratio

Comets are remnants of the icy planetesimals that formed beyond the ice line in the Solar Nebula. Growing from micrometre-sized dust and ice particles to km-sized objects is, however, difficult because of growth barriers and time scale constraints. The gravitational collapse of pebble clouds that formed through the streaming instability may provide a suitable mechanism for comet formation. We study the collisional compression of cm-sized porous ice/dust-mixed pebbles in collapsing pebble clouds. For this, we developed a collision model for pebbles consisting of a mixture of ice and dust, characterised by their dust-to-ice mass ratio. Using the final compression of the pebbles, we constrain combinations of initial cloud mass, initial pepple porosity, and dust-to-ice ratio that lead to cometesimals which are consistent with observed bulk properties of cometary nuclei. We find that observed high porosity and low density of ~0.5 g/cc of comet nuclei can only be explained if comets formed in clouds with mass approximately M>1e18 g. Lower mass clouds would only work if the pebbles were initially very compact. Furthermore, the dust-to-ice ratio must be in the range of between 3 and 9 to match the observed bulk properties of comet nuclei. (abridged version)

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arXiv2015

Sputtering of Oxygen Ice by Low Energy Ions

Naturally occurring ices lie on both interstellar dust grains and on celestial objects, such as those in the outer solar system. These ices are continu- ously subjected to irradiation by ions from the solar wind and/or cosmic rays, which modify their surfaces. As a result, new molecular species may form which can be sputtered off into space or planetary atmospheres. We determined the experimental values of sputtering yields for irradiation of oxygen ice at 10 K by singly (He+, C+, N+, O+ and Ar+) and doubly (C2+, N2+ and O2+) charged ions with 4 keV kinetic energy. In these laboratory experiments, oxygen ice was deposited and irradiated by ions in an ultra high vacuum chamber at low temperature to simulate the environment of space. The number of molecules removed by sputtering was observed by measurement of the ice thickness using laser interferometry. Preliminary mass spectra were taken of sputtered species and of molecules formed in the ice by temperature programmed desorption (TPD). We find that the experimental sputtering yields increase approximately linearly with the projectile ion mass (or momentum squared) for all ions studied. No difference was found between the sputtering yield for singly and doubly charged ions of the same atom within the experimental uncertainty, as expected for a process dominated by momentum transfer. The experimental sputter yields are in good agreement with values calculated using a theoretical model except in the case of oxygen ions. Preliminary studies have shown molecular oxygen as the dominant species sputtered and TPD measurements indicate ozone formation.

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arXiv2015

The formation of the solar system

The solar system started to form about 4.56 Gyr ago and despite the long intervening time span, there still exist several clues about its formation. The three major sources for this information are meteorites, the present solar system structure and the planet-forming systems around young stars. In this introduction we give an overview of the current understanding of the solar system formation from all these different research fields. This includes the question of the lifetime of the solar protoplanetary disc, the different stages of planet formation, their duration, and their relative importance. We consider whether meteorite evidence and observations of protoplanetary discs point in the same direction. This will tell us whether our solar system had a typical formation history or an exceptional one. There are also many indications that the solar system formed as part of a star cluster. Here we examine the types of cluster the Sun could have formed in, especially whether its stellar density was at any stage high enough to influence the properties of today's solar system. The likelihood of identifying siblings of the Sun is discussed. Finally, the possible dynamical evolution of the solar system since its formation and its future are considered.

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arXiv2014

Pan-STARRS 1 observations of the unusual active Centaur P/2011 S1(Gibbs)

P/2011 S1 (Gibbs) is an outer solar system comet or active Centaur with a similar orbit to that of the famous 29P/Schwassmann-Wachmann 1. P/2011 S1 (Gibbs) has been observed by the Pan-STARRS 1 (PS1) sky survey from 2010 to 2012. The resulting data allow us to perform multi-color studies of the nucleus and coma of the comet. Analysis of PS1 images reveals that P/2011 S1 (Gibbs) has a small nucleus $< 4$ km radius, with colors $g_{P1}-r_{P1} = 0.5 \pm 0.02$, $r_{P1}-i_{P1} = 0.12 \pm 0.02$ and $i_{P1}-z_{P1} = 0.46 \pm 0.03$. The comet remained active from 2010 to 2012, with a model-dependent mass-loss rate of $\sim100$ kg s$^{-1}$. The mass-loss rate per unit surface area of P/2011 S1 (Gibbs) is as high as that of 29P/Schwassmann-Wachmann 1, making it one of the most active Centaurs. The mass-loss rate also varies with time from $\sim 40$ kg s$^{-1}$ to 150 kg s$^{-1}$. Due to its rather circular orbit, we propose that P/2011 S1 (Gibbs) has 29P/Schwassmann-Wachmann 1-like outbursts that control the outgassing rate. The results indicate that it may have a similar surface composition to that of 29P/Schwassmann-Wachmann 1. Our numerical simulations show that the future orbital evolution of P/2011 S1 (Gibbs) is more similar to that of the main population of Centaurs than to that of 29P/Schwassmann-Wachmann 1. The results also demonstrate that P/2011 S1 (Gibbs) is dynamically unstable and can only remain near its current orbit for roughly a thousand years.

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arXiv2013

TNOs are Cool: A survey of the trans-Neptunian region. VIII. Combined Herschel PACS and SPIRE observations of 9 bright targets at 70--500 micron

Transneptunian objects (TNOs) are bodies populating the Kuiper Belt and they are believed to retain the most pristine and least altered material of the solar system. The Herschel Open Time Key Program entitled "TNOs are Cool: A survey of the trans-Neptunian region" has been awarded 373 h to investigate the albedo, size distribution and thermal properties of TNOs and Centaurs. Here we focus on the brightest targets observed by both the PACS and SPIRE multiband photometers: the dwarf planet Haumea, six TNOs (Huya, Orcus, Quaoar, Salacia, 2002 UX25, and 2002 TC302), and two Centaurs (Chiron and Chariklo). Flux densities are derived from PACS and SPIRE instruments using optimised data reduction methods. The spectral energy distribution obtained with the Herschel PACS and SPIRE instruments over 6 bands (centred at 70, 100, 160, 250, 350, and 500 $μ$m), and with Spitzer-MIPS at 23.7 and 71.4 $μ$m has been modelled with the NEATM thermal model in order to derive the albedo, diameter, and beaming factor. For the Centaurs Chiron and Chariklo and for the 1000 km sized Orcus and Quaoar, a thermophysical model was also run to better constrain their thermal properties. We derive the size, albedo, and thermal properties, including thermal inertia and surface emissivity, for the 9 TNOs and Centaurs. Several targets show a significant decrease in their spectral emissivity longwards of $\sim$300 $μ$m and especially at 500 $μ$m. Using our size estimations and the mass values available in the literature, we also derive the bulk densities for the binaries Quaoar/Weywot (2.18$^{+0.43}_{-0.36}$ g/cm$^3$), Orcus/Vanth (1.53$^{+0.15}_{-0.13}$ g/cm$^3$), and Salacia/Actea (1.29$^{+0.29}_{-0.23}$ g/cm$^3$). Quaoar's density is similar to that of the other dwarf planets Pluto and Haumea, and its value implies high contents of refractory materials mixed with ices.

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arXiv2011

Integral-field spectroscopy of (90482) Orcus-Vanth

Aims. We seek to constrain the surface composition of the Trans-Neptunian Object (90482) Orcus and its small satellite Vanth, as well as their mass and density. Methods. We acquired near-infrared spectra (1.4-2.4 μm) of (90482) Orcus and its companion Vanth using the adaptive-optics-fed integral-field spectrograph SINFONI mounted on Yepun/UT4 at the European Southern Observatory Very Large Telescope. We took advantage of a very favorable appulse (separation of only 4") between Orcus and the UCAC2 29643541 star (R = 11.6) to use the adaptive optics mode of SINFONI, allowing both components to be spatially resolved and Vanth colors to be extracted independently from Orcus. Results. The spectrum of Orcus we obtain has the highest signal-to-noise ratio to date, and we confirm the presence of H2O ice in crystalline form, together with the presence of an absorption band at 2.2 μm. We set an upper limit of about 2% for the presence of methane, and 5% for ethane. Because the methane alone cannot account for the 2.2 μm band, the presence of ammonia is suggested to the level of a couple of percent. The colors of Vanth are found slightly redder than those of Orcus, but the large measurement uncertainties forbid us from drawing conclusions on the origin of the pair (capture or co-formation). Finally, we reset the orbital phase of Vanth around Orcus, and confirm the orbital parameters derived by Brown et al. (2010, AJ 139).

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arXiv2010

"TNOs are cool": A survey of the trans-neptunian region. II. The thermal lightcurve of (136108) Haumea

Thermal emission from Kuiper Belt object (136108) Haumea was measured with Herschel-PACS at 100 and 160 micrometers for almost a full rotation period. Observations clearly indicate a 100-micrometer thermal lightcurve with an amplitude of a factor of ~ 2, which is positively correlated with the optical lightcurve. This confirms that both are primarily due to shape effects. A 160-micrometer lightcurve is marginally detected. Radiometric fits of the mean Herschel- and Spitzer- fluxes indicate an equivalent diameter D ~ 1300 km and a geometric albedo p_v ~ 0.70-0.75. These values agree with inferences from the optical lightcurve, supporting the hydrostatic equilibrium hypothesis. The large amplitude of the 100-micrometer lightcurve suggests that the object has a high projected a/b axis ratio (~ 1.3) and a low thermal inertia as well as possible variable infrared beaming. This may point to fine regolith on the surface, with a lunar-type photometric behavior. The quality of the thermal data is not sufficient to clearly detect the effects of a surface dark spot.

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arXiv2010

"TNOs are Cool": A survey of the trans-Neptunian region I. Results from the Herschel Science Demonstration Phase (SDP)

The goal of the Herschel Open Time Key programme "TNOs are Cool!" is to derive the physical and thermal properties for a large sample of Centaurs and trans-Neptunian objects (TNOs), including resonant, classical, detached and scattered disk objects. We present results for seven targets either observed in PACS point-source, or in mini scan-map mode. Spitzer-MIPS observations were included for three objects. The sizes of these targets range from 100 km to almost 1000 km, five have low geometric albedos below 10%, (145480) 2005 TB190 has a higher albedo above 15%. Classical thermal models driven by an intermediate beaming factor of $η$=1.2 or $η$-values adjusted to the observed colour temperature fit the multi-band observations well in most cases. More sophisticated thermophysical models give very similar diameter and albedo values for thermal inertias in the range 0-25 Jm-2s-0.5K-1, consistent with very low heat conductivities at temperatures far away from the Sun. The early experience with observing and model strategies will allow us to derive physical and thermal properties for our complete Herschel TNO sample of 140 targets as a benchmark for understanding the solar system debris disk, and extra-solar ones as well.

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