| 1. |
- Farnocchia, Davide, et al.
(författare)
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(523599) 2003 RM: The Asteroid that Wanted to be a Comet
- 2023
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Ingår i: The Planetary Science Journal. - : Institute of Physics (IOP). - 2632-3338. ; 4:2
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Tidskriftsartikel (refereegranskat)abstract
- We report a statistically significant detection of nongravitational acceleration on the subkilometer near-Earth asteroid (523599) 2003 RM. Due to its orbit, 2003 RM experiences favorable observing apparitions every 5 yr. Thus, since its discovery, 2003 RM has been extensively tracked with ground-based optical facilities in 2003, 2008, 2013, and 2018. We find that the observed plane-of-sky positions cannot be explained with a purely gravity-driven trajectory. Including a transverse nongravitational acceleration allows us to match all observational data, but its magnitude is inconsistent with perturbations typical of asteroids such as the Yarkovsky effect or solar radiation pressure. After ruling out that the orbital deviations are due to a close approach or collision with another asteroid, we hypothesize that this anomalous acceleration is caused by unseen cometary outgassing. A detailed search for evidence of cometary activity with archival and deep observations from the Panoramic Survey Telescope and Rapid Response System and the Very Large Telescope does not reveal any detectable dust production. However, the best-fitting H2O sublimation model allows for brightening due to activity consistent with the scatter of the data. We estimate the production rate required for H2O outgassing to power the acceleration and find that, assuming a diameter of 300 m, 2003 RM would require Q(H2O) similar to 10(23) molec s(-1) at perihelion. We investigate the recent dynamical history of 2003 RM and find that the object most likely originated in the mid-to-outer main belt (similar to 86% probability) as opposed to from the Jupiter-family comet region (similar to 11% probability). Further observations, especially in the infrared, could shed light on the nature of this anomalous acceleration.
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| 2. |
- Kastinen, Daniel
(författare)
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From meteors to space safety : dynamical models and radar measurements of space objects
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Every day the Earth's atmosphere is bombarded by 10-200 metric tons of dust-sized particles and larger pieces of material from space called meteoroids. Dust and meteoroids come from parent bodies such as comets and asteroids, which are remnants from the formation of the solar system. In addition to natural objects, geospace contains artificial satellites and space debris that needs to be monitored to reduce the risk of collisions. Studies of all these kinds of space objects form a cross-disciplinary research field that stretches from meteors to space safety. The primary goal of this thesis has been to rigorously connect measurements and their uncertainties with high-level analysis and dynamical simulations of distributions.An automated radar data analysis algorithm was developed for meteor head echo measurements. The analysis algorithm is able to produce realistic uncertainties for each individual meteor event, including the meteoroid orbit. Many of the resulting probability distributions are non-Gaussian, which needs to be accounted for. The analysis algorithm was applied to interferometric high-power large-aperture MU radar data in a case study on high altitude meteors. The study found that 74 out of 106,000 meteors appeared higher than 130 km and a few confirmed detections reached up to 150 km altitude.Comet 21P/Giacobini–Zinner is the parent body of the meteoroid stream giving rise to the October Draconid meteor shower. The meteoroid stream was simulated accounting for parent body orbital uncertainties to estimate meteor shower parameters. The simulation was able to model the unexpected mass distribution observed in the 2011 and 2012 October Draconids. It also successfully predicted a meteor outburst in 2018. Further, methods to reduce the computation time of meteoroid stream simulations using importance sampling were derived and implemented on a test model.EISCAT radar measurements were performed to study space debris from the Kosmos-1408 satellite, which had been destroyed and fragmented in orbit on 15 November, 2021. A novel method to estimate the size distribution of debris objects was developed. Data from two EISCAT radars were used to demonstrate a new initial orbit determination technique, yielding good agreement with known catalogue orbits. Finally, the detectability of near-Earth objects (NEOs) with the EISCAT~3D radar currently under construction was simulated. It was predicted that as many as seven temporarily captured NEOs, i.e. minimoons, could be discovered per year depending on the amount of allocated observation time. The predictions also show that hundreds of NEOs could be tracked yearly to improve their orbits.
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| 3. |
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| 4. |
- Lai, Ian-Lin, et al.
(författare)
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Gas outflow and dust transport of comet 67P/Churyumov-Gerasimenko
- 2016
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Ingår i: Monthly notices of the Royal Astronomical Society. - : OXFORD UNIV PRESS. - 0035-8711 .- 1365-2966. ; 462, s. S533-S546
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Tidskriftsartikel (refereegranskat)abstract
- Because of the diurnal thermal cycle and the irregular shape of the nucleus, gas outflow of comet 67P/Churyumov-Gerasimenko could be highly anisotropic as indicated by the colliminated dust jet structures on the sunlit side. Based on the OSIRIS imaging observations of the outgassing effect, a simple model of surface sublimation can be constructed by taking into account the dependence on the solar insolation. With preliminary information on the time variability of the global gas production rate, a sequence of gas coma models can be generated at different epochs before and after perihelion. We also investigate different patterns of dust particle dynamics under the influences of nuclear rotation and gas drag. From these considerations, a consistent picture of the spatial distribution of dusty materials across the surface of comet 67P as it moves around the perihelion can be developed. It is found that because of the redeposition of the ejected dust from the Southern hemisphere to the Northern hemisphere during the southern summer season the Hapi region could gain up to 0.4 m while the Wosret region would lose up to 1.8 m of dust mantle per orbit.
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| 5. |
- Lee, Jui-Chi, et al.
(författare)
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Geomorphological mapping of comet 67P/Churyumov-Gerasimenko's Southern hemisphere
- 2016
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 462, s. S573-S592
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Tidskriftsartikel (refereegranskat)abstract
- In 2015 May, the Southern hemisphere of comet 67P/Churyumov-Gerasimenko became visible by the OSIRIS cameras on-board the Rosetta spacecraft. The resolution was high enough to carry out a detailed analysis of the surface morphology, which is quite different from the Northern hemisphere. Previous works show that fine particle deposits are the most extensive geological unit in the Northern hemisphere. In contrast, the Southern hemisphere is dominated by outcropping consolidated terrain. In this work, we provide geomorphological maps of the Southern hemisphere with the distinction of both geological units and linear features. The geomorphological maps described in this study allow us to gain a better understanding of the processes shaping the comet nucleus and the distribution of primary structures such as fractures and strata.
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| 6. |
- Massironi, Matteo, et al.
(författare)
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Geological map and stratigraphy of asteroid 21 Lutetia
- 2012
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Ingår i: Planetary and Space Science. - : Elsevier BV. - 0032-0633 .- 1873-5088. ; 66:1, s. 125-136
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Tidskriftsartikel (refereegranskat)abstract
- The OSIRIS (Optical, Spectroscopic, and Infrared Remote Imaging System) images acquired during the recent Rosetta fly-by of Lutetia (10th of July 2010), enabled us to unravel the long geological history of the asteroid. This is recorded on its highly varied surface which displays geological units of disparate ages. In particular, using images of the closest approach, five main regions (in turn subdivided into minor units) have been discriminated on the basis of crater density, overlapping and cross-cutting relationships, and presence of linear features (i.e., fractures, faults, grooves, troughs). Other regions, with still unclear stratigraphic position, were also recognized on images of lower resolution on the bases of geomorphological properties such as crater density, relationship with scarp and ridges, and sharp morphological boundaries. In this work the geological evolution of Lutetia surface is reconstructed through the description of its main units and related contacts. The oldest regions imaged during the closest approach (Achaia and Noricum) are pervasively affected by fractures and grooves and display surfaces so heavily cratered to be dated back to a period not far from the Late Heavy Bombardment (yielding Achaia a crater retention age of 3.6-3.7 Ga). A crater of 55 km diameter, named Massilia and corresponding to the Narbonensis region, cuts both Achaia and Noricum regions and probably represents the most prominent event of the Lutetia history. The considerable crater density on its floor and walls, the absence of discernable deposits related to the impact event, and the intense deformation of it floor - all attest to its relatively great age. The North Polar Cluster (Baetica region) is associated with smooth ejecta broadly mantling the surrounding units and displays few craters and no linear features, demonstrating its relatively young age (estimated at less than 300 Ma). The North Polar Crater Cluster is the product of superimposed impacts: the last one of 24 km of diameter excavated the pre-existing ejecta up to the bedrock which locally outcrops at the crater rim. The ejecta of this last impact were involved in several gravitational phenomena testified by the great variety of deposits made up of mega-boulders diamictons, fine materials, gravitational taluses and debris, and landslide accumulations. A part from the big cratering events generating Massilia and the North Polar Crater Cluster, the Lutetia geological history is also punctuated by minor events still recorded by its stratigraphic record well imaged by the closest approach data.
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| 7. |
- Massironi, Matteo, et al.
(författare)
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Two independent and primitive envelopes of the bilobate nucleus of comet 67P
- 2015
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 526:7573, s. 402-405
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Tidskriftsartikel (refereegranskat)abstract
- The factors shaping cometary nuclei are still largely unknown, but could be the result of concurrent effects of evolutionary(1,2) and primordial processes(3,4). The peculiar bilobed shape of comet 67P/Churyumov-Gerasimenko may be the result of the fusion of two objects that were once separate or the result of a localized excavation by outgassing at the interface between the two lobes(5). Here we report that the comet's major lobe is enveloped by a nearly continuous set of strata, up to 650 metres thick, which are independent of an analogous stratified envelope on the minor lobe. Gravity vectors computed for the two lobes separately are closer to perpendicular to the strata than those calculated for the entire nucleus and adjacent to the neck separating the two lobes. Therefore comet 67P/Churyumov-Gerasimenko is an accreted body of two distinct objects with 'onion-like' stratification, which formed before they merged. We conclude that gentle, low-velocity collisions occurred between two fully formed kilometre-sized cometesimals in the early stages of the Solar System. The notable structural similarities between the two lobes of comet 67P/Churyumov-Gerasimenko indicate that the early-forming cometesimals experienced similar primordial stratified accretion, even though they formed independently.
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| 8. |
- Pajola, Maurizio, et al.
(författare)
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Aswan site on comet 67P/Churyumov-Gerasimenko : Morphology, boulder evolution, and spectrophotometry
- 2016
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 592
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Tidskriftsartikel (refereegranskat)abstract
- Aims. We provide a detailed morphological analysis of the Aswan site on comet 67P/Churyumov-Gerasimenko (67P). We derive the size-frequency distribution of boulders >= 2 m and correlate this distribution with the gravitational slopes for the first time on a comet. We perform the spectral analysis of this region to understand if possible surface variegation is related to the different surface textures observable on the different units. Methods. We used two OSIRIS Narrow Angle Camera (NAC) image data sets acquired on September 19 and 22, 2014, with a scale of 0.5 m/px. Gravitational slopes derived from the 3D shape model of 67P were used to identify and interpret the different units of the site. By means of the high-resolution NAC data sets, boulders >= 2.0 m can be unambiguously identified and extracted using the software ArcGIS. Coregistered and photometrically corrected color cubes were used to perform the spectral analyses, and we retrieved the spectral properties of the Aswan units. Results. The high-resolution morphological map of the Aswan site (0.68 km(2)) shows that this site is characterized by four different units: fine-particle deposits located on layered terrains, gravitational accumulation deposits, taluses, and the outcropping layered terrain. Multiple lineaments are identified on the Aswan cliff, such as fractures, exposed layered outcrops, niches, and terraces. Close to the terrace margin, several arched features observed in plan view suggest that the margin progressively retreats as a result of erosion. The size-frequency of boulders >= 2 m in the entire study area has a power-law index of -3.9 +0.2/-0.3 (1499 boulders >= 2 m/km(2)), suggesting that the Aswan site is mainly dominated by gravitational events triggered by sublimation and/or thermal insolation weathering causing regressive erosion. The boulder size-frequency distribution versus gravitational slopes indicates that when higher gravitational slope terrains are considered, only boulders <= 10 m are identified, as well as steeper power-slope indices. In addition, no boulders >= 2 m are observed on slopes >= 50 degrees. This may indicate that larger blocks detached from a sublimating cliff cannot rest at these slopes and consequently fall down. The spectral analysis performed on the site shows that despite different morphologic units, no spectral differences appear in the multiple textures. This may confirm a redistribution of particles across the nucleus as a consequence of airfall, whether coming from Hapi or from the southern hemisphere when it is active during perihelion.
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| 9. |
- Pajola, Maurizio, et al.
(författare)
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Size-frequency distribution of boulders >= 7 m on comet 67P/Churyumov-Gerasimenko
- 2015
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 583
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Tidskriftsartikel (refereegranskat)abstract
- Aims. We derive for the first time the size-frequency distribution of boulders on a comet, 67P/Churyumov-Gerasimenko (67P), computed from the images taken by the Rosetta/OSIRIS imaging system. We highlight the possible physical processes that lead to these boulder size distributions. Methods. We used images acquired by the OSIRIS Narrow Angle Camera, NAC. on 5 and 6 August 2014. The scale of these images (2.44-2.03 m/px) is such that boulders >= 7 m can be identified and manually extracted from the datasets with the software ArcGIS. We derived both global and localized size-frequency distributions. The three-pixel sampling detection, coupled with the favorable shadowine of the surface (observation phase angle ranging from 48 to 53), enables unequivocally detecting boulders scattered all over the illuminated side of 67P. Results. We identify 3546 boulders larger than 7 m on the imaged surface (36.4 km(2)), with a global number density of nearly 100/km(2) and a cumulative size-frequency distribution represented by a power-law with index of -3.6 +0.2/-0.3. The two lobes of 67P appear to have slightly different distributions, with an index of -3.5 +0.2/-0.3 for the main lobe (body) and -4.0 +0.31-0.2 for the small lobe (head). The steeper distribution of the small lobe might be due to a more pervasive fracturing. The difference of the distribution for the connecting region (neck) is much more significant, with an index value of -2.2 +0.2/-0.2. We propose that the boulder field located in the neck area is the result of blocks falling from the contiguous Hathor cliff. The lower slope of the size-frequency distribution we see today in the neck area might be due to the concurrent processes acting on the smallest boulders, such as i) disintegration or fragmentation and vanishing through sublimation; ii) uplifting by gas drag and consequent redistribution; and iii) burial beneath a debris blanket. We also derived the cumulative size-frequency distribution per km(2) of localized areas on 67P. By comparing the cumulative size-frequency distributions of similar geomorphological settings, we derived similar power-law index values. This suggests that despite the selected locations on different and often opposite sides of the comet, similar sublimation or activity processes, pit formation or collapses, as well as thermal stresses or fracturing events occurred on multiple areas of the comet, shaping its surface into the appearance we see today.
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| 10. |
- Pajola, Maurizio, et al.
(författare)
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The southern hemisphere of 67P/Churyumov-Gerasimenko : Analysis of the preperihelion size-frequency distribution of boulders >= 7m
- 2016
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 592
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Tidskriftsartikel (refereegranskat)abstract
- Aims. We calculate the size-frequency distribution of the boulders on the southern hemisphere of comet 67P Churyumov-Gerasimenko (67P), which was in shadow before the end of April 2015. We compare the new results with those derived from the northern hemisphere and equatorial regions of 67P, highlighting the possible physical processes that lead to these boulder size distributions. Methods. We used images acquired by the OSIRIS Narrow Angle Camera (NAC) on 2 May 2015 at a distance of 125 km from the nucleus. The scale of this dataset is 2.3 m/px; the high resolution of the images, coupled with the favorable observation phase angle of 62 degrees, provided the possibility to unambiguously identify boulders >= 7 m on the surface of 67P and to manually extract them with the software ArcGIS. We derived the size-frequency distribution of the illuminated southern hemisphere. Results. We found a power-law index of -3.6 +/- 0.2 for the boulders on the southern hemisphere with a diameter range of 7-35 m. The power-law index is equal to the one previously found on northern and equatorial regions of 67P, suggesting that similar boulder formation processes occur in both hemispheres. The power-law index is related to gravitational events triggered by sublimation and/or thermal fracturing causing regressive erosion. In addition, the presence of a larger number of boulders per km(2) in the southern hemisphere, which is a factor of 3 higher with respect to the northern hemisphere, suggests that the southernmost terrains of 67P are affected by a stronger thermal fracturing and sublimating activity, hence possibly causing larger regressive erosion and gravitational events.
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