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  • 1.
    Babusiaux, C.
    et al.
    Université Grenoble Alpes, CNRS, IPAG.
    Granvik, Mikael
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Department of Physics, University of Helsinki.
    Zwitter, T.
    University of Ljubljana, Faculty of Mathematics & Physics.
    Observational Hertzsprung-Russell diagrams2018In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 16, no A10Article in journal (Refereed)
    Abstract [en]

    Context. Gaia Data Release 2 provides high-precision astrometry and three-band photometry for about 1.3 billion sources over the full sky. The precision, accuracy, and homogeneity of both astrometry and photometry are unprecedented. Aims. We highlight the power of the Gaia DR2 in studying many fine structures of the Hertzsprung-Russell diagram (HRD). Gaia allows us to present many different HRDs, depending in particular on stellar population selections. We do not aim here for completeness in terms of types of stars or stellar evolutionary aspects. Instead, we have chosen several illustrative examples. Methods. We describe some of the selections that can be made in Gaia DR2 to highlight the main structures of the Gaia HRDs. We select both field and cluster (open and globular) stars, compare the observations with previous classifications and with stellar evolutionary tracks, and we present variations of the Gaia HRD with age, metallicity, and kinematics. Late stages of stellar evolution such as hot subdwarfs, post-AGB stars, planetary nebulae, and white dwarfs are also analysed, as well as low-mass brown dwarf objects. Results. The Gaia HRDs are unprecedented in both precision and coverage of the various Milky Way stellar populations and stellar evolutionary phases. Many fine structures of the HRDs are presented. The clear split of the white dwarf sequence into hydrogen and helium white dwarfs is presented for the first time in an HRD. The relation between kinematics and the HRD is nicely illustrated. Two different populations in a classical kinematic selection of the halo are unambiguously identified in the HRD. Membership and mean parameters for a selected list of open clusters are provided. They allow drawing very detailed cluster sequences, highlighting fine structures, and providing extremely precise empirical isochrones that will lead to more insight in stellar physics. Conclusions. Gaia DR2 demonstrates the potential of combining precise astrometry and photometry for large samples for studies in stellar evolution and stellar population and opens an entire new area for HRD-based studies.

  • 2.
    Binzel, R.P.
    et al.
    Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA; Chercheur Associé, IMCCE-Observatoire de Paris, France.
    DeMeo, F.E.
    Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA.
    Bus, S.J
    Univ. Hawaii.
    Tokunaga, A.
    Univ. Hawaii.
    Burbine, T.H.
    Mount Holyoke College.
    Lantz, C.
    Institut d'Astrophysique Spatiale, CNRS/Université Paris Saclay, France.
    Polishook, D.
    Weizmann Institute.
    Morbidelli, A.
    Université Côte d'Azur, Observatoire de la Côte d'Azur, CNRS, Lagrange, France.
    Birlan, M.
    IMCCE, Paris Observatory and Astronomical Institute of Romanian Academy, Bucharest, Romania.
    Vernazza, P.
    LAM–CNRS/AMU, Marseille, France.
    Burt, B.J
    Lowell Observatory.
    Moskovitz, N.
    Lowell Observatory.
    Slivan, S.M.
    Wellesley College.
    Thomas, C.A
    Northern Arizona University.
    Rivkin, A.S.
    Johns Hopkins University Applied Physics Laboratory.
    Hicks, M.D.
    Jet Propulsion Laboratory.
    Dunn, T.
    Colby College.
    Reddy, V.
    Univ. Arizona.
    Sanchez, J.A.
    Planetary Science Institute.
    Granvik, Mikael
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Univ. Helsinki.
    Kohout, T.
    Univ. Helsinki.
    Compositional Distributions and Evolutionary Processes for the Near-Earth Object Population: Results from the MIT-Hawaii Near-Earth Object Spectroscopic Survey (MITHNEOS)2019In: Icarus (New York, N.Y. 1962), ISSN 0019-1035, E-ISSN 1090-2643, Vol. 324, p. 41-76Article in journal (Refereed)
    Abstract [en]

    Advancing technology in near-infrared instrumentation and dedicated planetary telescope facilities have enabled nearly two decades of reconnoitering the spectral properties for near-Earth objects (NEOs). We report measured spectral properties for more than 1000 NEOs, representing >5 percent of the currently discovered population. Thermal flux detected below 2.5 microns allows us to make albedo estimates for nearly 50 objects, including two comets. Additional spectral data are reported for more than 350 Mars-crossing asteroids. Most of these measurements were achieved through a collaboration between researchers at the Massachusetts Institute of Technology and the University of Hawaii, with full cooperation of the NASA Infrared Telescope Facility (IRTF) on Mauna Kea. We call this project the MIT-Hawaii Near-Earth Object Spectroscopic Survey (MITHNEOS; myth-neos). While MITHNEOS has continuously released all spectral data for immediate use by the scientific community, our objectives for this paper are to: (1) detail the methods and limits of the survey data, (2) formally present a compilation of results including their taxonomic classification within a single internally consistent framework, (3) perform a preliminary analysis on the overall population characteristics with a concentration toward deducing key physical processes and identifying their source region for escaping the main belt. Augmenting our newly published measurements are the previously published results from the broad NEO community, including many results graciously shared by colleagues prior to formal publication. With this collective data set, we find the near-Earth population matches the diversity of the main-belt, with all main-belt taxonomic classes represented in our sample. Potentially hazardous asteroids (PHAs) as well as the subset of mission accessible asteroids (ΔV≤ 7 km/s) both appear to be a representative mix of the overall NEO population, consistent with strong dynamical mixing for the population that interacts most closely with Earth. Mars crossers, however, are less diverse and appear to more closely match the inner belt population from where they have more recently diffused. The fractional distributions of major taxonomic classes (60% S, 20% C, 20% other) appear remarkably constant over two orders of magnitude in size (10 km to 100 m), which is eight orders of magnitude in mass, though we note unaccounted bias effects enter into our statistics below about 500m. Given the range of surface ages, including possible refreshment by planetary encounters, we are able to identify a very specific space weathering vector tracing the transition from Q- to Sq- to S-types that follows the natural dispersion for asteroid spectra mapped into principal component space. We also are able to interpret a shock darkening vector that may account for some objects having featureless spectra. Space weathering effects for C-types are complex; these results are described separately by Lantz, Binzel, DeMeo. (2018, Icarus 302, 10-17). Independent correlation of dynamical models with taxonomic classes map the escape zones for NEOs to main-belt regions consistent with well established heliocentric compositional gradients. We push beyond taxonomy to interpret our visible plus near-infrared spectra in terms of the olivine and pyroxene mineralogy consistent with the H, L, and LL classes of ordinary chondrites meteorites. Correlating meteorite interpretations with dynamical escape region models shows a preference for LL chondrites to arrive from the ν6 resonance and H chondrites to have a preferential signature from the mid-belt region (3:1 resonance). L chondrites show some preference toward the outer belt, but not at a significant level. We define a Space Weathering Parameter as a continuous variable and find evidence for step-wise changes in space weathering properties across different planet crossing zones in the inner solar system. Overall we hypothesize the relative roles of planetary encounters, YORP spin-up, and thermal cycling across the inner solar system.

  • 3.
    Brown, A.G.A.
    et al.
    Leiden Observatory, Leiden University.
    Granvik, Mikael
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Department of Physics, University of Helsinki.
    Zwitter, T.
    University of Ljubljana, Faculty of Mathematics & Physics.
    Summary of the contents and survey properties2018In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 16, no A1Article in journal (Refereed)
    Abstract [en]

    Context. We present the second Gaia data release, Gaia DR2, consisting of astrometry, photometry, radial velocities, and information on astrophysical parameters and variability, for sources brighter than magnitude 21. In addition epoch astrometry and photometry are provided for a modest sample of minor planets in the solar system. Aims. A summary of the contents of Gaia DR2 is presented, accompanied by a discussion on the differences with respect to Gaia DR1 and an overview of the main limitations which are still present in the survey. Recommendations are made on the responsible use of Gaia DR2 results. Methods. The raw data collected with the Gaia instruments during the first 22 months of the mission have been processed by the Gaia Data Processing and Analysis Consortium (DPAC) and turned into this second data release, which represents a major advance with respect to Gaia DR1 in terms of completeness, performance, and richness of the data products. Results. Gaia DR2 contains celestial positions and the apparent brightness in G for approximately 1.7 billion sources. For 1.3 billion of those sources, parallaxes and proper motions are in addition available. The sample of sources for which variability information is provided is expanded to 0 : 5 million stars. This data release contains four new elements: broad-band colour information in the form of the apparent brightness in the G(BP) (330-680 nm) and G(RP) (630-1050 nm) bands is available for 1.4 billion sources; median radial velocities for some 7 million sources are presented; for between 77 and 161 million sources estimates are provided of the stellar effective temperature, extinction, reddening, and radius and luminosity; and for a pre-selected list of 14 000 minor planets in the solar system epoch astrometry and photometry are presented. Finally, Gaia DR2 also represents a new materialisation of the celestial reference frame in the optical, the Gaia-CRF2, which is the first optical reference frame based solely on extragalactic sources. There are notable changes in the photometric system and the catalogue source list with respect to Gaia DR1, and we stress the need to consider the two data releases as independent. Conclusions. Gaia DR2 represents a major achievement for the Gaia mission, delivering on the long standing promise to provide parallaxes and proper motions for over 1 billion stars, and representing a first step in the availability of complementary radial velocity and source astrophysical information for a sample of stars in the Gaia survey which covers a very substantial fraction of the volume of our galaxy.

  • 4.
    Brown, P.G.
    et al.
    Department of Physics and Astronomy, University of Western Ontario, London, Ontario, Canada. Centre for Planetary Science and Exploration, University of Western Ontario, London, Ontario,Canada.
    Vida, D.
    Department of Earth Sciences, University of Western Ontario, London, Ontario, Canada.
    Moser, D.E
    Jacobs Space Exploration Group, EV44/Meteoroid Environment Office, NASA Marshall Space Flight Center, Huntsville, Alabama, USA.
    Granvik, Mikael
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Department of Physics, University of Helsinki, Helsinki, Finland.
    Koshak, W.J
    NASA Marshall Space Flight Center, ST11 Robert Cramer Research Hall, Huntsville, Alabama, USA.
    Chu, D.
    Chesapeake Aerospace LLC, Grasonville, Maryland,USA.
    Steckloff, J.
    Planetary Science Institute, Tucson, Arizona, USA. Department of Aerospace Engineering and Engineering Mechanics, University of Texas at Austin, Austin, Texas, USA.
    Licata, A.
    Farmington Community Stargazers, Farmington Hills, Michigan, USA.
    Hariri, S.
    Department of Physics and Astronomy, Eastern Michigan University, Ypsilanti, Michigan, USA.
    Mason, J.
    Orchard Ridge Campus, Oakland Community College, Farmington Hills, Michigan,USA.
    Mazur, M.
    Department of Earth Sciences, University of Western Ontario, London, Ontario, Canada.
    Cooke, W.
    NASA Meteoroid Environment Office, Marshall Space Flight Center, Huntsville, Alabama, USA.
    Krzeminski, Z.
    Department of Physics and Astronomy, University of Western Ontario, London, Ontario, Canada.
    The Hamburg meteorite fall: Fireball trajectory, orbit, and dynamics2019In: Meteoritics and Planetary Science, ISSN 1086-9379, E-ISSN 1945-5100, Vol. 54, no 9, p. 2027-2045Article in journal (Refereed)
    Abstract [en]

    The Hamburg (H4) meteorite fell on 17 January 2018 at 01:08 UT approximately 10 km north of Ann Arbor, Michigan. More than two dozen fragments totaling under 1 kg were recovered, primarily from frozen lake surfaces. The fireball initial velocity was 15.83 ± 0.05 km s−1, based on four independent records showing the fireball above 50 km altitude. The radiant had a zenith angle of 66.14 ± 0.29° and an azimuth of 121.56 ± 1.2°. The resulting low inclination (<1°) Apollo‐type orbit has a large aphelion distance and Tisserand value relative to Jupiter (Tj) of ~3. Two major flares dominate the energy deposition profile, centered at 24.1 and 21.7 km altitude, respectively, under dynamic pressures of 5–7 MPa. The Geostationary Lightning Mapper on the Geostationary Operational Environmental Satellite‐16 also detected the two main flares and their relative timing and peak flux agree with the video‐derived brightness profile. Our preferred total energy for the Hamburg fireball is 2–7 T TNT (8.4–28 × 109 J), which corresponds to a likely initial mass in the range of 60–225 kg or diameter between 0.3 and 0.5 m. Based on the model of Granvik et al. (2018), the meteorite originated in an escape route from the mid to outer asteroid belt. Hamburg is the 14th known H chondrite with an instrumentally derived preatmospheric orbit, half of which have small (<5°) inclinations making connection with (6) Hebe problematic. A definitive parent body consistent with all 14 known H chondrite orbits remains elusive.

  • 5.
    Eyer, L.
    et al.
    Department of Astronomy, University of Geneva, Versoix, Switzerland .
    Granvik, Mikael
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Department of Physics, University of Helsinki, Helsinki, Finland.
    Zwitter, T.
    Faculty of Mathematics and Physics, University of Ljubljana, Ljubljana, Slovenia.
    Gaia Data Release 2 Variable stars in the colour-absolute magnitude diagram2019In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 623, article id 110Article in journal (Refereed)
    Abstract [en]

    Context. The ESA Gaia mission provides a unique time-domain survey for more than 1.6 billion sources with G less than or similar to 21 mag. Aims. We showcase stellar variability in the Galactic colour-absolute magnitude diagram (CaMD). We focus on pulsating, eruptive, and cataclysmic variables, as well as on stars that exhibit variability that is due to rotation and eclipses. Methods. We describe the locations of variable star classes, variable object fractions, and typical variability amplitudes throughout the CaMD and show how variability-related changes in colour and brightness induce "motions". To do this, we use 22 months of calibrated photometric, spectro-photometric, and astrometric Gaia data of stars with a significant parallax. To ensure that a large variety of variable star classes populate the CaMD, we crossmatched Gaia sources with known variable stars. We also used the statistics and variability detection modules of the Gaia variability pipeline. Corrections for interstellar extinction are not implemented in this article. Results. Gaia enables the first investigation of Galactic variable star populations in the CaMD on a similar, if not larger, scale as was previously done in the Magellanic Clouds. Although the observed colours are not corrected for reddening, distinct regions are visible in which variable stars occur. We determine variable star fractions to within the current detection thresholds of Gaia. Finally, we report the most complete description of variability-induced motion within the CaMD to date. Conclusions. Gaia enables novel insights into variability phenomena for an unprecedented number of stars, which will benefit the understanding of stellar astrophysics. The CaMD of Galactic variable stars provides crucial information on physical origins of variability in a way that has previously only been accessible for Galactic star clusters or external galaxies. Future Gaia data releases will enable significant improvements over this preview by providing longer time series, more accurate astrometry, and additional data types (time series BP and RP spectra, RVS spectra, and radial velocities), all for much larger samples of stars.

  • 6.
    Fedorets, Grigori
    et al.
    Department of Physics, University of Helsinki, Finland.
    Granvik, Mikael
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Department of Physics, University of Helsinki, Finland.
    Jones, R. Lynne
    DIRAC Institute, Department of Astronomy, University of Washington,Seattle, USA.
    Jurić, Mario
    DIRAC Institute, Department of Astronomy, University of Washington, Seattle, USA.
    Jedicke, Robert
    Institute for Astronomy, University of Hawaii, Honolulu, USA.
    Discovering Earth’s transient moons with the Large Synoptic Survey Telescope2020In: Icarus (New York, N.Y. 1962), ISSN 0019-1035, E-ISSN 1090-2643, Vol. 338, article id 113517Article in journal (Refereed)
    Abstract [en]

    Earth's temporarily-captured orbiters (TCOs) are a sub-population of near-Earth objects (NEOs). TCOs can provide constraints for NEO population models in the 1–10-metre-diameter range, and they are outstanding targets for in situ exploration of asteroids due to a low requirement on Δv. So far there has only been a single serendipitous discovery of a TCO. Here we assess in detail the possibility of their discovery with the upcoming Large Synoptic Survey Telescope (LSST), previously identified as the primary facility for such discoveries. We simulated observations of TCOs by combining a synthetic TCO population with an LSST survey simulation. We then assessed the detection rates, detection linking and orbit computation, and sources for confusion. Typical velocities of detectable TCOs will range from 1∘/day to 50∘/day, and typical apparent V magnitudes from 21 to 23. Potentially-hazardous asteroids have observational characteristics similar to TCOs, but the two populations can be distinguished based on their orbits with LSST data alone. We predict that a TCO can be discovered once every year with the baseline moving-object processing system (MOPS). The rate can be increased to one TCO discovery every two months if tools complementary to the baseline MOPS are developed for the specific purpose of discovering these objects. 

  • 7.
    Fedorets, Grigori
    et al.
    Department of Physics, University of Helsinki, Finland;Nordic Optical Telescope, La Palma, Santa Cruz de Tenerife, Spain .
    Muinonen, Karri
    Department of Physics, University of Helsinki, Finland;Finnish Geospatial Research Institute, Masala, Finland.
    Pauwels, Thierry
    Observatoire Royal de Belgique,Bruxelles, Belgium.
    Granvik, Mikael
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Department of Physics, University of Helsinki, Finland.
    Tanga, Paolo
    Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, Nice , France .
    Virtanen, Jenni
    Finnish Geospatial Research Institute, Masala, Finland.
    Berthier, Jérôme
    IMCCE, Institut de Mécanique Céleste et de Calcul des Éphémérides, Observatoire de Paris, PSL Research University, CNRS-UMR8028, Sorbonne Universités, UPMC Univ. Paris 06, Université de Lille, Paris, France .
    Carry, Benoit
    Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, Nice, France;IMCCE, Institut de Mécanique Céleste et de Calcul des Éphémérides, Observatoire de Paris, PSL Research University, CNRS-UMR8028, Sorbonne Universités, UPMC Univ. Paris 06, Université de Lille, Paris, France.
    David, Pedro
    IMCCE, Institut de Mécanique Céleste et de Calcul des Éphémérides, Observatoire de Paris, PSL Research University, CNRS-UMR8028, Sorbonne Universités, UPMC Univ. Paris 06, Université de Lille, Paris, France .
    Dell’Oro, Aldo
    INAF, Osservatorio Astrofisico di Arcetri, Firenze, Italy .
    Mignard, François
    Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, Nice, France.
    Petit, Jean-Marc
    Observatoire de Besançon, UMR CNRS 6213, Besançon, France .
    Spoto, Federica
    Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, Nice, France.
    Thuillot, William
    IMCCE, Institut de Mécanique Céleste et de Calcul des Éphémérides, Observatoire de Paris, PSL Research University, CNRS-UMR8028, Sorbonne Universités, UPMC Univ. Paris 06, Université de Lille, Paris, France .
    Optimizing asteroid orbit computation for Gaia with normal points2018In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 620, article id A101Article in journal (Refereed)
    Abstract [en]

    Context. In addition to the systematic observations of known solar-system objects (SSOs), a continuous processing of new discoveries requiring fast responses is implemented as the short-term processing of Gaia SSO observations, providing alerts for ground-based follow-up observers. The common independent observation approach for the purposes of orbit computation has led to unrealistically large ephemeris prediction uncertainties when processing real Gaia data. Aims. We aim to provide ground-based observers with a cloud of sky positions that is shrunk to a fraction of the previously expected search area by making use of the characteristic features of Gaia astrometry. This enhances the efficiency of Gaia SSO follow-up network and leads to an increased rate of asteroid discoveries with reasonably constrained orbits with the help of ground-based follow-up observations of Gaia asteroids. Methods. We took advantage of the separation of positional errors of Gaia S SO observations into a random and systematic component. We treated the Gaia observations in an alternative way by collapsing up to ten observations that correspond to a single transit into a single so-called normal point. We implemented this input procedure in the Gaia S SO short-term processing pipeline and the OpenOrb software. Results. We validate our approach by performing extensive comparisons between the independent observation and normal point input methods and compare them to the observed positions of previously known asteroids. The new approach reduces the ephemeris uncertainty by a factor of between three and ten compared to the situation where each point is treated as a separate observation. Conclusions. Our new data treatment improves the sky prediction for the Gaia SSO observations by removing low-weight orbital solutions. These solutions originate from excessive curvature of observations, introduced by short-term variations of Gaia attitude on the one hand, and, as a main effect, shrinking of systematic error bars in the independent observation case on the other hand. We anticipate that a similar approach may also be utilized in a situation where observations from a single observatory dominate.

  • 8.
    Granvik, Mikael
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Department of Physics, University of Helsinki.
    Brown, Peter
    Department of Physics and Astronomy, University of Western Ontario.
    Identification of meteorite source regions in the solar system2018In: Icarus (New York, N.Y. 1962), ISSN 0019-1035, E-ISSN 1090-2643, Vol. 311, p. 271-287Article in journal (Refereed)
    Abstract [en]

    Over the past decade there has been a large increase in the number of automated camera networks that monitor the sky for fireballs. One of the goals of these networks is to provide the necessary information for linking meteorites to their pre-impact, heliocentric orbits and ultimately to their source regions in the solar system. We re-compute heliocentric orbits for the 25 meteorite falls published to date from original data sources. Using these orbits, we constrain their most likely escape routes from the main asteroid belt and the cometary region by utilizing a state-of-the-art orbit model of the near-Earth-object population, which includes a size-dependence in delivery efficiency. While we find that our general results for escape routes are comparable to previous work, the role of trajectory measurement uncertainty in escape-route identification is explored for the first time. Moreover, our improved size-dependent delivery model substantially changes likely escape routes for several meteorite falls, most notably Tagish Lake which seems unlikely to have originated in the outer main belt as previously suggested. We find that reducing the uncertainty of fireball velocity measurements below  ∼ 0.1 km/s does not lead to reduced uncertainties in the identification of their escape routes from the asteroid belt and, further, their ultimate source regions. This analysis suggests that camera networks should be optimized for the largest possible number of meteorite recoveries with measured speed precisions of order 0.1 km/s.

  • 9.
    Harju, Jorma
    et al.
    Department of Physics, University of Helsinki, Finland. Max-Planck-Institut für extraterrestrische Physik, Garching, Germany.
    Lehtinen, Kimmo
    Finnish Geospatial Research Institute FGI, Masala, Finland.
    Romney, Jonathan
    Long Baseline Observatory, Socorro, USA.
    Petrov, Leonid
    Astrogeo Center, Falls Church, USA.
    Granvik, Mikael
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Department of Physics, University of Helsinki, Finland.
    Muinonen, Karri
    Department of Physics, University of Helsinki, Finland. Finnish Geospatial Research Institute FGI, Masala, Finland.
    Bach, Uwe
    Max-Planck-Institut für Radioastronomie, Bonn, Germany.
    Poutanen, Markku
    Finnish Geospatial Research Institute FGI, Masala, Finland.
    Radio Interferometric Observation of an Asteroid Occultation2018In: Astronomical Journal, ISSN 0004-6256, E-ISSN 1538-3881, Vol. 156, no 4, p. 1-10, article id 155Article in journal (Refereed)
    Abstract [en]

    The occultation of the radio galaxy 0141+268 by the asteroid(372)Palma on 2017 May 15 was observed using sixantennas of the Very Long Baseline Array(VLBA). The shadow of Palma crossed the VLBA station at Brewster,Washington. Owing to the wavelength used, and the size and the distance of the asteroid, a diffraction pattern in theFraunhofer regime was observed. The measurement retrieves both the amplitude and the phase of the diffractedelectromagnetic wave. This is thefirst astronomical measurement of the phase shift caused by diffraction. Themaximum phase shift is sensitive to the effective diameter of the asteroid. The bright spot at the shadow’s center,the so called Arago–Poisson spot, is clearly detected in the amplitude time-series, and its strength is a goodindicator of the closest angular distance between the center of the asteroid and the radio source. A sample ofrandom shapes constructed using a Markov chain Monte Carlo algorithm suggests that the silhouette of Palmadeviates from a perfect circle by 26±13%. The best-fitting random shapes resemble each other, and we suggesttheir average approximates the shape of the silhouette at the time of the occultation. The effective diameterobtained for Palma, 192.1±4.8 km, is in excellent agreement with recent estimates from thermal modeling ofmid-infrared photometry. Finally, our computations show that because of the high positional accuracy, a singleradio interferometric occultation measurement can reduce the long-term ephemeris uncertainty by an order ofmagnitude.

  • 10.
    Helmi, A.
    et al.
    University of Groningen, Kapteyn Astron Institute.
    Granvik, Mikael
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Department of Physics, University of Helsinki.
    Zwitter, T.
    University of Ljubljana, Faculty of Mathematics & Physics.
    Gaia Data Release 2: Kinematics of globular clusters and dwarf galaxies around the Milky Way2018In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 16, no A12Article in journal (Refereed)
    Abstract [en]

    Aims. The goal of this paper is to demonstrate the outstanding quality of the second data release of the Gaia mission and its power for constraining many different aspects of the dynamics of the satellites of the Milky Way. We focus here on determining the proper motions of 75 Galactic globular clusters, nine dwarf spheroidal galaxies, one ultra-faint system, and the Large and Small Magellanic Clouds. Methods. Using data extracted from the Gaia archive, we derived the proper motions and parallaxes for these systems, as well as their uncertainties. We demonstrate that the errors, statistical and systematic, are relatively well understood. We integrated the orbits of these objects in three different Galactic potentials, and characterised their properties. We present the derived proper motions, space velocities, and characteristic orbital parameters in various tables to facilitate their use by the astronomical community. Results. Our limited and straightforward analyses have allowed us for example to (i) determine absolute and very precise proper motions for globular clusters; (ii) detect clear rotation signatures in the proper motions of at least five globular clusters; (iii) show that the satellites of the Milky Way are all on high-inclination orbits, but that they do not share a single plane of motion; (i v) derive a lower limit for the mass of the Milky Way of 9.1(-2.6)(+6.2) x 10(11) M-circle dot based on the assumption that the Leo I dwarf spheroidal is bound; (v) derive a rotation curve for the Large Magellanic Cloud based solely on proper motions that is competitive with line-of-sight velocity curves, now using many orders of magnitude more sources; and (v i) unveil the dynamical effect of the bar on the motions of stars in the Large Magellanic Cloud. Conclusions. All these results highlight the incredible power of the Gaia astrometric mission, and in particular of its second data release.

  • 11.
    Jenniskens, Peter
    et al.
    SETI Institute, Carl Sagan Center, Mountain View, California, USA. NASA Ames Research Center, Moffett Field, California,USA.
    Granvik, Mikael
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. University of Helsinki, Department of Physics, Helsinki, Finland.
    The Creston, California, meteorite fall and the origin of L chondrites2019In: Meteoritics and Planetary Science, ISSN 1086-9379, E-ISSN 1945-5100, Vol. 54, no 4, p. 699-720Article in journal (Refereed)
    Abstract [en]

    It has been proposed that all L chondrites resulted from an ongoing collisional cascade of fragments that originated from the formation of the ~500 Ma old asteroid family Gefion, located near the 5:2 mean‐motion resonance with Jupiter in the middle Main Belt. If so, L chondrite pre‐atmospheric orbits should be distributed as expected for that source region. Here, we present contradictory results from the orbit and collisional history of the October 24, 2015, L6 ordinary chondrite fall at Creston, CA (here reclassified to L5/6). Creston's short 1.30 ± 0.02 AU semimajor axis orbit would imply a long dynamical evolution if it originated from the middle Main Belt. Indeed, Creston has a high cosmic ray exposure age of 40–50 Ma. However, Creston's small meteoroid size and low 4.23 ± 0.07° inclination indicate a short dynamical lifetime against collisions. This suggests, instead, that Creston originated most likely in the inner asteroid belt and was delivered via the ν6 resonance. The U‐Pb systematics of Creston apatite reveals a Pb‐Pb age of 4,497.1 ± 3.7 Ma, and an upper intercept U‐Pb age of 4,496.7 ± 5.8 Ma (2σ), circa 70 Ma after formation of CAI, as found for other L chondrites. The K‐Ar (age ~4.3 Ga) and U,Th‐He (age ~1 Ga) chronometers were not reset at ~500 Ma, while the lower intercept U‐Pb age is poorly defined as 770 ± 320 Ma. So far, the three known L chondrites that impacted on orbits with semimajor axes a <2.0 AU all have high (>3 Ga) K‐Ar ages. This argues for a source of some of our L chondrites in the inner Main Belt. Not all L chondrites originate in a continuous population of Gefion family debris stretching across the 3:1 mean‐motion resonance.

  • 12.
    Katz, D.
    et al.
    GEPI, Observatoire de Paris, Université PSL, CNRS.
    Granvik, Mikael
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Department of Physics, University of Helsinki.
    Zwitter, T.
    University of Ljubljana, Faculty of Mathematics & Physics.
    Gaia Data Release 2: Mapping the Milky Way disc kinematics2018In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 16, no A11Article in journal (Refereed)
    Abstract [en]

    Context. The second Gaia data release (Gaia DR2) contains high-precision positions, parallaxes, and proper motions for 1.3 billion sources as well as line-of-sight velocities for 7.2 million stars brighter than G(RVS) = 12 mag. Both samples provide a full sky coverage. Aims. To illustrate the potential of Gaia DR2, we provide a first look at the kinematics of the Milky Way disc, within a radius of several kiloparsecs around the Sun. Methods. We benefit for the first time from a sample of 6.4 million F-G-K stars with full 6D phase-space coordinates, precise parallaxes (sigma((omega) over bar)/(omega) over bar <= 20%), and precise Galactic cylindrical velocities (median uncertainties of 0.9-1.4 km s(-1) and 20% of the stars with uncertainties smaller than 1 km s(-1) on all three components). From this sample, we extracted a sub-sample of 3.2 million giant stars to map the velocity field of the Galactic disc from similar to 5 kpc to similar to 13 kpc from the Galactic centre and up to 2 kpc above and below the plane. We also study the distribution of 0.3 million solar neighbourhood stars (r < 200 pc), with median velocity uncertainties of 0.4 km s(-1), in velocity space and use the full sample to examine how the over-densities evolve in more distant regions. Results. Gaia DR2 allows us to draw 3D maps of the Galactocentric median velocities and velocity dispersions with unprecedented accuracy, precision, and spatial resolution. The maps show the complexity and richness of the velocity field of the galactic disc. We observe streaming motions in all the components of the velocities as well as patterns in the velocity dispersions. For example, we confirm the previously reported negative and positive galactocentric radial velocity gradients in the inner and outer disc, respectively. Here, we see them as part of a non-axisymmetric kinematic oscillation, and we map its azimuthal and vertical behaviour. We also witness a new global arrangement of stars in the velocity plane of the solar neighbourhood and in distant regions in which stars are organised in thin substructures with the shape of circular arches that are oriented approximately along the horizontal direction in the U - V plane. Moreover, in distant regions, we see variations in the velocity substructures more clearly than ever before, in particular, variations in the velocity of the Hercules stream. Conclusions. Gaia DR2 provides the largest existing full 6D phase-space coordinates catalogue. It also vastly increases the number of available distances and transverse velocities with respect to Gaia DR1. Gaia DR2 offers a great wealth of information on the Milky Way and reveals clear non-axisymmetric kinematic signatures within the Galactic disc, for instance. It is now up to the astronomical community to explore its full potential.

  • 13.
    Mignard, F.
    et al.
    Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange.
    Granvik, Mikael
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Department of Physics, University of Helsinki.
    Zwitter, T.
    University of Ljubljana, Faculty of Mathematics & Physics.
    Gaia Data Release 2: The celestial reference frame (Gaia-CRF2)2018In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 16, no A14Article in journal (Refereed)
    Abstract [en]

    Context. The second release of Gaia data (Gaia DR2) contains the astrometric parameters for more than half a million quasars. This set defines a kinematically non-rotating reference frame in the optical domain. A subset of these quasars have accurate VLBI positions that allow the axes of the reference frame to be aligned with the International Celestial Reference System (ICRF) radio frame. Aims. We describe the astrometric and photometric properties of the quasars that were selected to represent the celestial reference frame of Gaia DR2 (Gaia-CRF2), and to compare the optical and radio positions for sources with accurate VLBI positions. Methods. Descriptive statistics are used to characterise the overall properties of the quasar sample. Residual rotation and orientation errors and large-scale systematics are quantified by means of expansions in vector spherical harmonics. Positional differences are calculated relative to a prototype version of the forthcoming ICRF3. Results. Gaia-CRF2 consists of the positions of a sample of 556 869 sources in Gaia DR2, obtained from a positional cross-match with the ICRF3-prototype and AllWISE AGN catalogues. The sample constitutes a clean, dense, and homogeneous set of extragalactic point sources in the magnitude range G similar or equal to 16 to 21 mag with accurately known optical positions. The median positional uncertainty is 0.12 mas for G < 18 mag and 0.5 mas at G = 20 mag. Large-scale systematics are estimated to be in the range 20 to 30 mu as. The accuracy claims are supported by the parallaxes and proper motions of the quasars in Gaia DR2. The optical positions for a subset of 2820 sources in common with the ICRF3-prototype show very good overall agreement with the radio positions, but several tens of sources have significantly discrepant positions. Conclusions. Based on less than 40% of the data expected from the nominal Gaia mission, Gaia-CRF2 is the first realisation of a non-rotating global optical reference frame that meets the ICRS prescriptions, meaning that it is built only on extragalactic sources. Its accuracy matches the current radio frame of the ICRF, but the density of sources in all parts of the sky is much higher, except along the Galactic equator.

  • 14.
    Schwamb, Megan E.
    et al.
    Gemini Observatory, Northern Operations Center, Hilo, USA.
    Hsieh, Henry
    Planetary Science Institute, Tucson, USA.
    Bannister, Michele T.
    Queen's University Belfast, Belfast, UK.
    Bodewits, Dennis
    Auburn University, Auburn, USA.
    Chesley, Steven R
    California Institute of Technology, Pasadena, USA.
    Fraser, Wesley C.
    Queen's University Belfast, Belfast, UK.
    Granvik, Mikael
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. University of Helsinki, Finland.
    Jones, R. Lynne
    University of Washington, Seattle, USA.
    Jurić, Mario
    University of Washington, Seattle, USA.
    Kelley, Michael S.P.
    University of Maryland, USA.
    Ragozzine, Darin
    Brigham Young University, Provo, USA.
    Trilling, David E.
    Northern Arizona University, Flagstaff, USA.
    Volk, Kathryn
    University of Arizona, Tucson, USA.
    A Software Roadmap for Solar System Science with the Large Synoptic Survey Telescope2019In: Research Notes of the AAS, E-ISSN 2515-5172, Vol. 3, no 3, article id 51Article in journal (Refereed)
    Abstract [en]

    The 8.4 m Large Synoptic Survey Telescope (LSST) will provide an unprecedented view of the Solar System (Ivezić et al. 2008; LSST Science Collaboration et al. 2009). LSST will detect millions of asteroids and tens of thousands of distant Solar System bodies, within approximately 16 and 24.5 mag (in r-band). Over a ten year period, most of these minor planets will receive hundreds of observations divided between 6 filters (ugrizy). What specifically LSST project will deliver for Solar System detections will soon be updated in the LSST Data Products Definition Document (DPDD; Jurić et al. 2013). A preliminary version of the new LSST Solar System data products schema is available at http://ls.st/ssd and http://ls.st/oug.

    The LSST Solar System Science Collaboration (SSSC; http://www.lsstsssc.org) produced a science roadmap (Schwamb et al. 2018) which outlines the collaboration's highest ranked research priorities utilizing LSST. To achieve these science goals, the SSSC has identified crucial software products and tools that will be required but will not be provided by the LSST project. These will have to be developed by the SSSC and the broader planetary community. To spur this effort, we present below this list of LSST community software development tasks.

  • 15.
    Siltala, L.
    et al.
    Department of Physics, University of Helsinki, Helsinki, Finland. Nordic Optical Telescope, de La Palma, Santa Cruz de Tenerife, Spain.
    Granvik, Mikael
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Department of Physics, University of Helsinki, Helsinki, Finland.
    Asteroid mass estimation with the robust adaptive Metropolis algorithm2020In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 633, article id A46Article in journal (Refereed)
    Abstract [en]

    Context. The bulk density of an asteroid informs us about its interior structure and composition. To constrain the bulk density, one needs an estimated mass of the asteroid. The mass is estimated by analyzing an asteroid’s gravitational interaction with another object, such as another asteroid during a close encounter. An estimate for the mass has typically been obtained with linearized least-squares methods, despite the fact that this family of methods is not able to properly describe non-Gaussian parameter distributions. In addition, the uncertainties reported for asteroid masses in the literature are sometimes inconsistent with each other and are suspected to be unrealistically low.

    Aims. We aim to present a Markov-chain Monte Carlo (MCMC) algorithm for the asteroid mass estimation problem based on asteroid-asteroid close encounters. We verify that our algorithm works correctly by applying it to synthetic data sets. We use astrometry available through the Minor Planet Center to estimate masses for a select few example cases and compare our results with results reported in the literature.

    Methods. Our mass-estimation method is based on the robust adaptive Metropolis algorithm that has been implemented into the OpenOrb asteroid orbit computation software. Our method has the built-in capability to analyze multiple perturbing asteroids and test asteroids simultaneously.

    Results. We find that our mass estimates for the synthetic data sets are fully consistent with the ground truth. The nominal masses for real example cases typically agree with the literature but tend to have greater uncertainties than what is reported in recent literature. Possible reasons for this include different astrometric data sets and weights, different test asteroids, different force models or different algorithms. For (16) Psyche, the target of NASA’s Psyche mission, our maximum likelihood mass is approximately 55% of what is reported in the literature. Such a low mass would imply that the bulk density is significantly lower than previously expected and thus disagrees with the theory of (16) Psyche being the metallic core of a protoplanet. We do, however, note that masses reported in recent literature remain within our 3-sigma limits.

    Results. The new MCMC mass-estimation algorithm performs as expected, but a rigorous comparison with results from a least-squares algorithm with the exact same data set remains to be done. The matters of uncertainties in comparison with other algorithms and correlations of observations also warrant further investigation.

  • 16.
    Solin, O.
    et al.
    Department of Physics, University of Helsinki, Helsinki, Finland.
    Granvik, Mikael
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Department of Physics, University of Helsinki, Helsinki, Finland.
    Monitoring near-Earth-object discoveries for imminent impactors2018In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 616, article id A176Article in journal (Refereed)
    Abstract [en]

    Aims. We present an automated system called NEORANGER that regularly computes asteroid-Earth impact probabilities for objects on the Minor Planet Center’s (MPC) Near-Earth-Object Confirmation Page (NEOCP) and sends out alerts of imminent impactors to registered users. In addition to potential Earth-impacting objects, NEORANGER also monitors for other types of interesting objects such as Earth’s natural temporarily-captured satellites.

    Methods. The system monitors the NEOCP for objects with new data and solves, for each object, the orbital inverse problem, which results in a sample of orbits that describes the, typically highly-nonlinear, orbital-element probability density function (PDF). The PDF is propagated forward in time for seven days and the impact probability is computed as the weighted fraction of the sample orbits that impact the Earth.

    Results. The system correctly predicts the then-imminent impacts of 2008 TC3 and 2014 AA based on the first data sets available. Using the same code and configuration we find that the impact probabilities for objects typically on the NEOCP, based on eight weeks of continuous operations, are always less than one in ten million, whereas simulated and real Earth-impacting asteroids always have an impact probability greater than 10% based on the first two tracklets available.

  • 17.
    Spoto, F.
    et al.
    Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange.
    Granvik, Mikael
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Department of Physics, University of Helsinki.
    Zwitter, T.
    University of Ljubljana, Faculty of Mathematics & Physics.
    Gaia Data Release 2: Observations of solar system objects2018In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 16, no A13Article in journal (Refereed)
    Abstract [en]

    Context. The Gaia spacecraft of the European Space Agency (ESA) has been securing observations of solar system objects (SSOs) since the beginning of its operations. Data Release 2 (DR2) contains the observations of a selected sample of 14,099 SSOs. These asteroids have been already identified and have been numbered by the Minor Planet Center repository. Positions are provided for each Gaia observation at CCD level. As additional information, complementary to astrometry, the apparent brightness of SSOs in the unfiltered G band is also provided for selected observations. Aims. We explain the processing of SSO data, and describe the criteria we used to select the sample published in Gaia DR2. We then explore the data set to assess its quality. Methods. To exploit the main data product for the solar system in Gaia DR2, which is the epoch astrometry of asteroids, it is necessary to take into account the unusual properties of the uncertainty, as the position information is nearly one-dimensional. When this aspect is handled appropriately, an orbit fit can be obtained with post-fit residuals that are overall consistent with the a-priori error model that was used to define individual values of the astrometric uncertainty. The role of both random and systematic errors is described. The distribution of residuals allowed us to identify possible contaminants in the data set (such as stars). Photometry in the G band was compared to computed values from reference asteroid shapes and to the flux registered at the corresponding epochs by the red and blue photometers (RP and BP). Results. The overall astrometric performance is close to the expectations, with an optimal range of brightness G similar to 12 - 17. In this range, the typical transit-level accuracy is well below 1 mas. For fainter asteroids, the growing photon noise deteriorates the performance. Asteroids brighter than G similar to 12 are affected by a lower performance of the processing of their signals. The dramatic improvement brought by Gaia DR2 astrometry of SSOs is demonstrated by comparisons to the archive data and by preliminary tests on the detection of subtle non-gravitational effects.

  • 18.
    Torppa, Johanna
    et al.
    Space Systems Finland.
    Granvik, Mikael
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. Department of Physics, University of Helsinki.
    Penttilä, Antti
    Department of Physics, University of Helsinki.
    Reitmaa, Jukka
    Space Systems Finland.
    Tudose, Violeta
    Space Systems Finland.
    Pelttari, Leena
    Space Systems Finland.
    Muinonen, Karri
    Department of Physics, University of Helsinki.
    Bakker, Jorgo
    European Space Astronomy Center.
    Navarro, Vicente
    European Space Astronomy Center.
    O’Mullane, William
    European Space Astronomy Center.
    Added-value interfaces to asteroid photometric and spectroscopic data in the Gaia database2018In: Advances in Space Research, ISSN 0273-1177, E-ISSN 1879-1948, Vol. 62, no 2, p. 464-476Article in journal (Refereed)
    Abstract [en]

    We present two added-value interfaces (AVIs) for analyzing photometric and spectroscopic data observed by the Gaia satellite. The Gaia Added-Value Interface for Temporal Analysis (GAVITEA) is used to calculate an estimate for the spin state and shape of an asteroid from its photometric data, and the Gaia Added-Value Interface for Spectral Classification (GAVISC) provides tools to define the taxonomic type and surface absorption coefficient based on spectroscopic asteroid data. Computations are mainly carried out using well-known methods of asteroid data analysis but the AVIs also offer the possibility to test novel methods that are specifically developed for analyzing temporally sparse photometric data, typical for Gaia.

  • 19.
    Unsalan, Ozan
    et al.
    University of Istanbul, Vezneciler, Fatih Istanbul, Turkey. Ege University, Bornova, Izmir, Turkey.
    Jenniskens, Peter
    SETI Institute, Mountain View, California, USA. NASA Ames Research Center, Moffett Field, California, USA.
    Granvik, Mikael
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. University of Helsinki, Helsinki, Finland.
    Schmedemann, Nico
    Freie Universit at Berlin, Berlin, Germany. Max Planck Institute for Solar System Research, Gottingen, Germany.
    The Sariçiçek howardite fall in Turkey: Source crater of HED meteorites on Vesta and impact risk of Vestoids2019In: Meteoritics and Planetary Science, ISSN 1086-9379, E-ISSN 1945-5100, Vol. 54, no 5, p. 953-1008Article in journal (Refereed)
    Abstract [en]

    The Sariçiçek howardite meteorite shower consisting of 343 documented stones occurred on September 2, 2015 in Turkey and is the first documented howardite fall. Cosmogenic isotopes show that Sariçiçek experienced a complex cosmic‐ray exposure history, exposed during ~12–14 Ma in a regolith near the surface of a parent asteroid, and that an ~1 m sized meteoroid was launched by an impact 22 ± 2 Ma ago to Earth (as did one‐third of all HED meteorites). SIMS dating of zircon and baddeleyite yielded 4550.4 ± 2.5 Ma and 4553 ± 8.8 Ma crystallization ages for the basaltic magma clasts. The apatite U‐Pb age of 4525 ± 17 Ma, K‐Ar age of ~3.9 Ga, and the U,Th‐He ages of 1.8 ± 0.7 and 2.6 ± 0.3 Ga are interpreted to represent thermal metamorphic and impact‐related resetting ages, respectively. Petrographic; geochemical; and O‐, Cr‐, and Ti‐isotopic studies confirm that Sariçiçek belongs to the normal clan of HED meteorites. Petrographic observations and analysis of organic material indicate a small portion of carbonaceous chondrite material in the Sariçiçek regolith and organic contamination of the meteorite after a few days on soil. Video observations of the fall show an atmospheric entry at 17.3 ± 0.8 km s−1 from NW; fragmentations at 37, 33, 31, and 27 km altitude; and provide a pre‐atmospheric orbit that is the first dynamical link between the normal HED meteorite clan and the inner Main Belt. Spectral data indicate the similarity of Sariçiçek with the Vesta asteroid family (V‐class) spectra, a group of asteroids stretching to delivery resonances, which includes (4) Vesta. Dynamical modeling of meteoroid delivery to Earth shows that the complete disruption of a ~1 km sized Vesta family asteroid or a ~10 km sized impact crater on Vesta is required to provide sufficient meteoroids ≤4 m in size to account for the influx of meteorites from this HED clan. The 16.7 km diameter Antionia impact crater on Vesta was formed on terrain of the same age as given by the 4He retention age of Sariçiçek. Lunar scaling for crater production to crater counts of its ejecta blanket show it was formed ~22 Ma ago.

  • 20.
    Ye, Quanzhi
    et al.
    California Institute of Technology, Pasadena, USA. The University of Western Ontario, London, Ontario, Canada..
    Granvik, Mikael
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology. University of Helsinki, Finland.
    Debris of Asteroid Disruptions Close to the Sun2019In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 873, no 2, article id 104Article in journal (Refereed)
    Abstract [en]

    The under-abundance of asteroids on orbits with small perihelion distances suggests that thermally driven disruption may be an important process in the removal of rocky bodies in the solar system. Here we report our study of how the debris streams arise from possible thermally driven disruptions in the near-Sun region. We calculate that a small body with a diameter 0.5 km can produce a sufficient amount of material to allow the detection of the debris at the Earth as meteor showers, and that bodies at such sizes thermally disrupt every ~2 kyr. We also find that objects from the inner parts of the asteroid belt are more likely to become Sun-approachers than those from the outer parts. We simulate the formation and evolution of the debris streams produced from a set of synthetic disrupting asteroids drawn from Granvik et al.'s near-Earth object population model, and find that they evolve 10–70 times faster than streams produced at ordinary solar distances. We compare the simulation results to a catalog of known meteor showers on Sun-approaching orbits. We show that there is a clear overabundance of Sun-approaching meteor showers, which is best explained by a combining effect of comet contamination and an extended disintegration phase that lasts up to a few thousand years. We suggest that a few asteroid-like Sun-approaching objects that brighten significantly at their perihelion passages could, in fact, be disrupting asteroids. An extended period of thermal disruption may also explain the widespread detection of transiting debris in exoplanetary systems.

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