Spin and shape analyses for the slowly rotating asteroid (39420) 2084 T-2

The investigation of rotation of asteroids is an important means to deriving information about their physical properties and processes using ground-based instrumentation. The rotation rate distribution imply the significance of non-gravitational forces depending on the size of the asteroid. The absence of certain rotation rates in the asteroid population poses constraints on the inner structure of asteroids of different sizes. The majority of rotation periods of asteroids solved from photometric lightcurves belong to fast rotators. The observation time required for obtaining an accurate period estimate is substantially longer for a slowly rotating asteroid than for a rapidly rotating asteroid. Therefore, lightcurve surveys with limited observation time which allocate the same amount of time for all asteroids, are expected to only produce accurate periods for asteroids with short rotation periods. This thesis concentrates on various aspects of asteroid rotation. Methods used to obtain asteroid rotation periods and shape models are discussed. Also, physical mechanisms affecting the rotation of asteroids are considered. The focus is on the main-belt objects and slowly rotating bodies. The Thousand Asteroid Lightcurve Survey (Masiero et al. 2009) carried out with the Canada-France-Hawaii Telescope was one of the first systematic asteroid lightcurve surveys. One of the objects selected for follow-up was Hungaria asteroid (39420) 2084 T-2. Masiero et al. (2009) quoted a rotation period of 105 ± 21 h which is a relatively inaccurate solution, especially compared to the solutions for the fast rotators. In this work we present an updated period fit as well as a possible convex shape solution (Kaasalainen \& Torppa 2001, Kaasalainen et al. 2001) for the asteroid. The possibility that the investigated asteroid is a close binary or a non-principal-axis rotator is also discussed.Asteroidien pyörimistä tutkitaan jotta saataisiin tietoa asteroidien fysikaalista ominaisuuksista ja prosesseista. Pyörimisperiodijakauma eri asteroidikokoluokissa kuvaa ei-gravitaatiovoimien merkitystä riippuen asteroidin koosta. Tiettyjen pyörimistilojen puuttuminen pyörimisjakaumasta asettaa rajoituksia erikokoisten asteroidien sisäiselle rakenteelle. Suurin osa fotometrisistä valokäyristä saaduista asteroidien pyörimisperiodeista on ratkaistu nopeasti pyöriville kappaleille. Hitaasti pyörivän asteroidin pyörimisperiodin ratkaiseminen vaatii huomattavasti enemmän havaintoaikaa kuin nopeasti pyörivän kappaleen. Näin ollen valokäyräseurantaohjelmissa, joissa havaintoaikaa jaetaan tasaisesti asteroidien kesken, vain nopeasti pyöriville asteroideille on mahdollista ratkaista tarkkoja pyörimisperiodeja. Tutkielma keskittyy asteroidien pyörimisen eri näkökohtiin. Tutkielmassa kuvaillaan erilaisia metodeja, joiden avulla voidaan määrittää asteroidien pyörimisperiodeja ja muotomalleja. Lisäksi tutkielmassa käsitellään fysikaalisia mekanismeja, jotka vaikuttavat asteroidien pyörimiseen. Painopiste on päävyöhykeasteroideissa ja hitaasti pyörivissä kappaleissa. Canada-France-Hawaii -kaukoputkella toteutettu TALCS-seurantaohjelma (Masiero et al. 2009) oli yksi ensimmäisistä systemaattisista asteroidien valokäyräseurantaohjelmista. Yksi valituista asteroideista on Hungaria-populaation asteroidi (39420) 2084 T-2. Masiero et al. (2009) antaa pyörimisperiodin tulokseksi 105 ± 21 tuntia, mikä on suhteellisen epätarkka tulos verrattuna saatuihin nopeasti pyörivien asteroidien periodien virherajoihin. Tässä työssä esitellään päivitetty perioditulos sekä ehdotus asteroidin konveksiksi muotomalliksi (Kaasalainen & Torppa 2001, Kaasalainen et al. 2001). Lisäksi arvoidaan, onko kyseinen kohde mahdollisesti kaksoisasteroidi ja pyöriikö se pääakselinsa ympäri

Studies of Asteroids with Exiguous Astrometry from Synoptic Surveys

Astrometry, i.e., the study of positions of stellar-appearing heavenly bodies, is the basis for all astronomical research. Each generation of new astronomical surveys delivers new insights into the structure of the Universe, including our Solar System. Small bodies of the Solar System, asteroids and comets, are the populations which reveal the initial conditions, overall structure, and previous processes shaping the Solar System. With the incremental development of the impressive survey programmes, certain types of objects will always be on the threshold of discoveries. Therefore, only a small number of data for these objects will ever be available. In this thesis, two such Solar System populations are investigated: Earth's temporary natural satellites, and asteroids discovered by the Gaia mission. The statistical properties and steady-state population of two sub-populations of Earth's natural satellites, temporarily-captured orbiters and flybys, are assessed. The challenges for detection and prospects for future investigation of Earth's natural satellites are discussed. Also, the detectability of Earth's temporarily-captured orbiters with the upcoming Large Synoptic Survey Telescope is investigated, raising the importance of dedicated treatment for small fast-moving objects in the processing. One of the many fields of astronomy where ESAs Gaia mission makes an important contribution is the discovery of newly discovered asteroids. Candidates for newly discovered asteroids are processed daily and distributed to follow-up observers. A new statistical orbital inversion method, random-walk ranging, is developed. Additionally, the method to improve follow-up predictions by lowering the effect of systematic errors is introduced. This thesis gives an overview of the phenomenon of the temporary capture of asteroids by planets. The statistical ranging-based orbital inversion methods are discussed. The advancements in the fields of stellar and asteroid astronomy over the ages, and respective breakthroughs in the relevant fields of astronomy are assessed.Astrometria, eli tähtimäisten taivaankappaleiden paikanmittaukseen keskittyvä tieteenala toimii perustana koko tähtitieteen tutkimukselle. Alati kehittyvät tähtitieteelliset seurantaohjelmat tuovat ilmi uusia näkökulmia maailmankaikkeuden rakenteeseen, sisältäen myös oman aurinkokuntamme. Aurinkokunnan pienkappaleiden, asteroidien ja komeettojen, populaatiot ovat avainasemassa paljastamassa aurinkokunnan alkuperäisiä olosuhteita yleisrakennetta ja aurinkokuntaa muokanneita menneitä prosesseja. Vaikuttavasta seurantaohjelmien harppauksisesta kehityksestä huolimatta tietyt kohteet tulevat aina olemaan hankalasti havaittavissa. Näin ollen näistä kohteista kerättävä data tulee aina olemaan määrältään hyvin vähäistä. Tässä väitöskirjassa tarkastellaan kahta aurinkokunnan pienkappalepopulaatiota, joista on ainoastaan harvoja havaintoja: Maapallon väliaikaisesti kaappautuvia kuita, sekä Gaia-mission löytämiä uusia asteroideja. Maapallon väliaikaisesti kaappautuvat kuut jakaantuvat kahteen alapopulaatioon: kiertäjiin ja ohilentäjiin. Molempien alapopulaation tilastolliset ominaisuudet ja pysyväispopulaatiot on määritelty. Maapallon väliaikaisesti kaappautuvien kuiden havaitsemisen ongelmat ja niitä koskevan tutkimuksen tulevaisuudennäkymiä on avattu. Myös väliaikaisesti kaappautuvien kuiden havaitsevuutta tulevan sukupolven LSST-teleskoopin avulla on tutkittu, korostaen pienten nopeasti liikkuvien kohteiden erityiskohtelun merkitystä datan käsittelyssä. Euroopan avaruusjärjestön Gaia-missiolla on tärkeä panos moneen tähtitieteen osa-alueeseen. Yksi näistä osa-alueista on entuudestaan tuntemattomien asteroidien havaitseminen. Uudet asteroidiehdokkaat käsitellään automaattisesti, ja niiden paikkaennusteet jaetaan jatkohavaitsijoille päivittäin. Gaia-mission asteroidihavaintoja varten on yhtäältä kehitetty uusi radanlaskentamenetelmä, ja toisaalta rakennettu metodi, jonka tarkoituksena on pienentää satunnaisvirheiden vaikutusta radanlaskentaan, mikä johtaa pienempiin ja helpommin hallittaviin ennusteisiin jatkohavaitsijoille. Tämän väitöskirjan johdanto-osiossa käsitellään yleisesti asteroidien väliaikaista kaappautumista planeettajärjestelmiin ja tilastollisia radanlaskentamenetelmiä. Lisäksi väitöskirjassa pohditaan tähti- ja asteroidiastrometrian historiallista kehitystä ja sen vaikutusta muihin tähtitieteen osa-alueisiin läpi vuosisatojen

Taxonomy of Asteroids From the Legacy Survey of Space and Time Using Neural Networks

The Legacy Survey of Space and Time (LSST) is one of the ongoing or future surveys, together with the Gaia and Euclid missions, which will produce a wealth of spectrophotometric observations of asteroids. This article shows how deep learning techniques with neural networks can be used to classify the upcoming observations, particularly from LSST, into the Bus-DeMeo taxonomic system. We report here a success ratio in classification up to 90.1% with a reduced set of Bus-DeMeo types for simulated observations using the LSST photometric filters. The scope of this work is to introduce tools to link future observations into existing Bus-DeMeo taxonomy.Peer reviewe

Discovering Earth’s transient moons with the Large Synoptic Survey Telescope

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.Peer reviewe

Earth’s Minimoons : Opportunities for Science and Technology

Twelve years ago the Catalina Sky Survey discovered Earth's first known natural geocentric object other than the Moon, a few-meter diameter asteroid designated 2006 RH120. Despite significant improvements in ground-based telescope and detector technology in the past decade the asteroid surveys have not discovered another temporarily-captured orbiter (TCO; colloquially known as minimoons) but the all-sky fireball system operated in the Czech Republic as part of the European Fireball Network detected a bright natural meteor that was almost certainly in a geocentric orbit before it struck Earth's atmosphere. Within a few years the Large Synoptic Survey Telescope (LSST) will either begin to regularly detect TCOs or force a re-analysis of the creation and dynamical evolution of small asteroids in the inner solar system. The first studies of the provenance, properties, and dynamics of Earth's minimoons suggested that there should be a steady state population with about one 1- to 2-m diameter captured objects at any time, with the number of captured meteoroids increasing exponentially for smaller sizes. That model was then improved and extended to include the population of temporarily-captured flybys (TCFs), objects that fail to make an entire revolution around Earth while energetically bound to the Earth-Moon system. Several different techniques for discovering TCOs have been considered but their small diameters, proximity, and rapid motion make them challenging targets for existing ground-based optical, meteor, and radar surveys. However, the LSST's tremendous light gathering power and short exposure times could allow it to detect and discover many minimoons. We expect that if the TCO population is confirmed, and new objects are frequently discovered, they can provide new opportunities for (1) studying the dynamics of the Earth-Moon system, (2) testing models of the production and dynamical evolution of small asteroids from the asteroid belt, (3) rapid and frequent low delta-v missions to multiple minimoons, and (4) evaluating in-situ resource utilization techniques on asteroidal material. Here we review the past decade of minimoon studies in preparation for capitalizing on the scientific and commercial opportunities of TCOs in the first decade of LSST operations.Peer reviewe

Physical and dynamical properties of the unusual V-type asteroid (2579) Spartacus

Context. Asteroid (2579) Spartacus is a small V-type object located in the inner main belt. This object shows spectral characteristics unusual for typical Vestoids, which may indicate an origin deeper than average within Vesta or an origin from an altogether different parent body. Aims. Our main goal is to study the origin of Spartacus. We derive the spin of Spartacus and a convex shape model of Spartacus in order to increase the knowledge of the body's physical properties. The rotational parameters are then used to investigate dynamical evolution of the object as well as to distinguish regions sampled by spectral observations to determine whether its surface displays heterogeneity. Methods. We collected lightcurves available from the literature (oppositions of 2009, 2012) and obtained additional photometric observations at various telescopes in 2016, 2017, and 2018. We used the lightcurve inversion method to derive a spin and convex shape model. We have collected spectral observations over two rotational periods of Spartacus and determined its spectral parameters using the modified Gaussian model (MGM). We then dynamically integrated the orbital elements of Spartacus, taking into account existing information, including its thermal properties, size and the derived spin axis orientation. Results. We find two models for (2579) Spartacus: (a) lambda = 312 degrees +/- 5 degrees, beta = -57 degrees +/- 5 degrees and (b) lambda = 113 degrees +/- 5 degrees, beta = -60 degrees +/- 5 degrees both retrograde. We find that the drift direction for Spartacus is consistent with separation from Vesta, and after a backward integration of 1 Gyr the asteroid reaches the boundary of the family. We did not observe spectral variations with rotation, thus the body most likely has a homogeneous surface. Additionally, new spectral analysis indicates that the 1.0 and 2.0 mu m band centers are within ranges that are typical for Vestoids while the area ratio of these bands is about half that of typical Vestoids. Conclusions. The asteroid (2579) Spartacus is in retrograde rotation and has a drift direction consistent with an origin from Vesta. The revised spectral band centers are within ranges typical for Vestoids, while band area ratio (BAR) is unusually low compared to that of other V-types. The dynamical model shows that the asteroid could have migrated to its current location from the edges of the Vesta family within 1 Gyr, but an origin from an earlier impact on Vesta could also be plausible.Peer reviewe

Minimoons & drifters

International audienceWe will present an overview of our recent work on understanding the population of natural objects that are temporarily captured in the Earth-Moon system. We use the term 'minimoon' to refer to objects that i) have negative total energy (kinetic potential) relative to the Earth-Moon barycenter that ii) make at least one full revolution around the barycenter in a co-rotating frame relative to the Earth-Sun axis iii) while they are within 3 Earth Hill-sphere radii. There has been one confirmed minimoon, the 2-3 meter diameter object designated 2006 RH_{120} that was discovered by the Catalina Sky Survey [1]. That object's size, capture duration, geocentric trajectory, and pre-and post-capture heliocentric orbits are in perfect agreement with the minimoon model proposed by Granvik et al. (2012) [2]. We expect that there are one or two 1 to 2 meter diameter minimoons in the steady state population at any time and about a dozen larger than 50 cm diameter. Minimoons have an average lifetime of about 9 months. 'Drifters' are like minimoons except that they do not fulfill the requirement of making at least one revolution in the Earth-Moon system. The population of drifters is about 10× the minimoon population so that the largest drifter in the steady state is about 5-10 meters in diameter and there are perhaps ten of about 1 meter diameter at any time. The combined population of minimoons and drifters, henceforth 'cis-lunar objects' (CLO), provide a formerly unrecognized opportunity for scientific exploration and testing concepts for in-situ resource utilization [3]. They could provide large samples of main-belt asteroids that are unaffected by passage through Earth's atmosphere or weathering on the ground, with the added convenience of already being gravitationally bound in the Earth-Moon system. The CLOs provide interesting challenges for rendezvous missions because of their limited lifetime and non-elliptical trajectories while they are bound objects [4]. The problem is that detecting the CLOs is difficult -- they are small, captured for only limited time periods, and their apparent rates of motion are more like artificial satellites than the more distant NEOs [5]. New technology may enable the detection of a small number of CLOs from the ground in the next few years [5,6] but the only way to discover a reliable stream of these interesting objects is from a space-based platform

Minimoons & drifters

International audienceWe will present an overview of our recent work on understanding the population of natural objects that are temporarily captured in the Earth-Moon system. We use the term 'minimoon' to refer to objects that i) have negative total energy (kinetic potential) relative to the Earth-Moon barycenter that ii) make at least one full revolution around the barycenter in a co-rotating frame relative to the Earth-Sun axis iii) while they are within 3 Earth Hill-sphere radii. There has been one confirmed minimoon, the 2-3 meter diameter object designated 2006 RH_{120} that was discovered by the Catalina Sky Survey [1]. That object's size, capture duration, geocentric trajectory, and pre-and post-capture heliocentric orbits are in perfect agreement with the minimoon model proposed by Granvik et al. (2012) [2]. We expect that there are one or two 1 to 2 meter diameter minimoons in the steady state population at any time and about a dozen larger than 50 cm diameter. Minimoons have an average lifetime of about 9 months. 'Drifters' are like minimoons except that they do not fulfill the requirement of making at least one revolution in the Earth-Moon system. The population of drifters is about 10× the minimoon population so that the largest drifter in the steady state is about 5-10 meters in diameter and there are perhaps ten of about 1 meter diameter at any time. The combined population of minimoons and drifters, henceforth 'cis-lunar objects' (CLO), provide a formerly unrecognized opportunity for scientific exploration and testing concepts for in-situ resource utilization [3]. They could provide large samples of main-belt asteroids that are unaffected by passage through Earth's atmosphere or weathering on the ground, with the added convenience of already being gravitationally bound in the Earth-Moon system. The CLOs provide interesting challenges for rendezvous missions because of their limited lifetime and non-elliptical trajectories while they are bound objects [4]. The problem is that detecting the CLOs is difficult -- they are small, captured for only limited time periods, and their apparent rates of motion are more like artificial satellites than the more distant NEOs [5]. New technology may enable the detection of a small number of CLOs from the ground in the next few years [5,6] but the only way to discover a reliable stream of these interesting objects is from a space-based platform

Precovery Observations Confirm the Capture Time of Asteroid 2020 CD3 as Earth's Minimoon

Asteroid 2020 CD3 was discovered on 2020 February 15 by the Catalina Sky Survey while it was temporarily captured in a geocentric orbit before escaping Earth's Hill sphere on 2020 March 7. We searched archival images and found precoveries of 2020 CD3 from the Dark Energy Camera and Catalina Sky survey. The Dark Energy Camera images yielded three observations on 2019 January 17, while the Catalina Sky Survey images yielded four observations on 2019 January 24 from the Mt. Lemmon telescope and four observations on 2018 May 9 from the Mt. Bigelow telescope. These precovery observations allowed us to refine the orbit of 2020 CD3 and determine that it was captured in a geocentric orbit on 2017 September 15 after a close approach to the Moon at a distance of 11,974 ± 10 km. We analyzed the trajectory of 2020 CD3 to look for potential Earth impacts within the next 100 years and find a ≳1% probability of an impact between 2061 and 2120 depending on nongravitational force model assumptions. The small size of 2020 CD3, about 1 to 2 m, makes any potential impact harmless. © 2021. The American Astronomical Society. All rights reserved.Immediate accessThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]