Short arc orbit determination and imminent impactors in the <i>Gaia</i> era

Spoto, F.; Vigna, Alessio Del; Milani, Andrea; Tommei, Giacomo; Tanga, P.; Mignard, F.; Carry, B.; Thuillot, W.; David, Pedro

doi:10.1051/0004-6361/201732104

Cited by 24 publications

(40 citation statements)

References 29 publications

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“…Astrometric data exist since the discovery of Phaethon by the Infrared Astronomical Satellite in October 1983 (Green & Kowal 1983). As of July 2018, 4782 astrometric observations have been reported to the Minor Planet Center by ground-based observatories and 28 observations by the WISE spacecraft.…”

Section: Astrometric Observations and Orbit Determinationmentioning

confidence: 99%

(3200) Phaethon: Bulk density from Yarkovsky drift detection

Hanuš¹,

Vokrouhlický²,

Delbò³

et al. 2018

A&A

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Context. The recent close approach of the near-Earth asteroid (3200) Phaethon offered a rare opportunity to obtain high-quality observational data of various types. Aims. We used the newly obtained optical light curves to improve the spin and shape model of Phaethon and to determine its surface physical properties derived by thermophysical modeling. We also used the available astrometric observations of Phaethon, including those obtained by the Arecibo radar and the Gaia spacecraft, to constrain the secular drift of the orbital semimajor axis. This constraint allowed us to estimate the bulk density by assuming that the drift is dominated by the Yarkovsky effect. Methods. We used the convex inversion model to derive the spin orientation and 3D shape model of Phaethon, and a detailed numerical approach for an accurate analysis of the Yarkovsky effect. Results. We obtained a unique solution for Phaethon's pole orientation at (318 • , −47 • ) ecliptic longitude and latitude (both with an uncertainty of 5 • ), and confirm the previously reported thermophysical properties (D = 5.1 ± 0.2 km, Γ = 600±200 J m −2 s −0.5 K −1 ). Phaethon has a top-like shape with possible north-south asymmetry. The characteristic size of the regolith grains is 1−2 cm. The orbit analysis reveals a secular drift of the semimajor axis of −(6.9±1.9)×10 −4 au Myr −1 . With the derived volume-equivalent size of 5.1 km, the bulk density is 1.67±0.47 g cm −3 . If the size is slightly larger ∼ 5.7 − 5.8 km, as suggested by radar data, the bulk density would decrease to 1.48 ± 0.42 g cm −3 . We further investigated the suggestion that Phaethon may be in a cluster with asteroids (155140) 2005 UD and (225416) 1999 YC that was formed by rotational fission of a critically spinning parent body. Conclusions. Phaethon's bulk density is consistent with typical values for large (> 100 km) C-complex asteroids and supports its association with asteroid (2) Pallas, as first suggested by dynamical modeling. These findings render a cometary origin unlikely for Phaethon.

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Section: Astrometric Observations and Orbit Determinationmentioning

confidence: 99%

(3200) Phaethon: Bulk density from Yarkovsky drift detection

Hanuš¹,

Vokrouhlický²,

Delbò³

et al. 2018

A&A

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“…Unfortunately, this is precisely the case of very small asteroids observed only shortly before a close approach or an impact with the Earth (the so-called imminent impactors). With the aim to address the issue, three dedicated systems have recently been developed: SCOUT (at JPL/NASA, [6]), NEORANGER (at University of Helsinki, [7]) and NEOScan (at University of Pisa/SpaceDyS, [8]). Taking the latter as an example, NEOScan consults the NEOCP of the Minor Planet Center (MPC) every two minutes, extracting and analysing data through the use of algorithms based on the Admissible Region (AR), a tool widely used also in the field of space debris orbit determination ( [9,10]).…”

Section: Introductionmentioning

confidence: 99%

New Tools for the Optimized Follow-Up of Imminent Impactors

Mochi

Tommei

2021

Universe

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The solar system is populated with, other than planets, a wide variety of minor bodies, the majority of which are represented by asteroids. Most of their orbits are comprised of those between Mars and Jupiter, thus forming a population named Main Belt. However, some asteroids can run on trajectories that come close to, or even intersect, the orbit of the Earth. These objects are known as Near Earth Asteroids (NEAs) or Near Earth Objects (NEOs) and may entail a risk of collision with our planet. Predicting the occurrence of such collisions as early as possible is the task of Impact Monitoring (IM). Dedicated algorithms are in charge of orbit determination and risk assessment for any detected NEO, but their efficiency is limited in cases in which the object has been observed for a short period of time, as is the case with newly discovered asteroids and, more worryingly, imminent impactors: objects due to hit the Earth, detected only a few days or hours in advance of impacts. This timespan might be too short to take any effective safety countermeasure. For this reason, a necessary improvement of current observation capabilities is underway through the construction of dedicated telescopes, e.g., the NEO Survey Telescope (NEOSTEL), also known as “Fly-Eye”. Thanks to these developments, the number of discovered NEOs and, consequently, imminent impactors detected per year, is expected to increase, thus requiring an improvement of the methods and algorithms used to handle such cases. In this paper we present two new tools, based on the Admissible Region (AR) concept, dedicated to the observers, aiming to facilitate the planning of follow-up observations of NEOs by rapidly assessing the possibility of them being imminent impactors and the remaining visibility time from any given station.

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“…The pre-release of star positions and proper motions appearing in the second data release (DR2) (Gaia Collaboration et al 2016, 2018b has demonstrated the reality of the expected improvement, with successful, accurate predictions of the occultation path for several objects, including Pluto and other TNOs such as the New Horizons mission target (486958) Arrokoth (Buie et al 2018;Porter et al 2018;Ortiz et al 2019;Buie et al 2020). Spoto et al (2017) have tested the use of observed occultations as astrometric measurements, which have an accuracy comparable to that of the target star.…”

Section: Introductionmentioning

confidence: 99%

A survey for occultation astrometry of main belt: expected astrometric performances

Ferreira

Tanga

Machado

et al. 2020

A&A

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Context. Occultations of stars by asteroids are an efficient method to study the properties of minor bodies, and can be exploited as tools to derive very precise asteroid astrometry relative to the target star. With the availability of stellar astrometry thanks to the ESA mission Gaia, the frequency of good predictions and the quality of the astrometry have been strongly enhanced. Aims. Our goal is to evaluate the astrometric performance of a systematic exploitation of stellar occultations, with a homogeneous data set and a given instrument setup. As a reference instrument, we adopt the example of a robotic 50 cm telescope, which is under construction at the Observatoire de la Côte d’Azur. We focus in particular on single-chord occultations. Methods. We created a data set of simulated light curves, that are modelled by a Bayesian approach. To build the final statistics, we considered a list of predicted events over a long time span, and stellar astrometry from Gaia data release 2. Results. We derive an acceptable range of observability of the events, with clear indications of the expected errors in terms of timing uncertainties. By converting the distribution of such errors to astrometric uncertainties, we show that the precision on a single chord can reach levels equivalent to the performance of Gaia (sub-milli-arcseconds). The errors on the asteroid position are dominated by the uncertainty on the position of the occultation chord with respect to the barycentre of the object. Conclusions. The limiting factor in the use of occultation astrometry is not the light curve uncertainty, but our knowledge of the asteroid's shape and size. This conclusion is valid in a wide range of flux drops and magnitudes of the occulted star. The currently increasing knowledge of the shape, spin properties, and size, must be used to mitigate this source of error.

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Short arc orbit determination and imminent impactors in the Gaia era

Cited by 24 publications

References 29 publications

(3200) Phaethon: Bulk density from Yarkovsky drift detection

(3200) Phaethon: Bulk density from Yarkovsky drift detection

New Tools for the Optimized Follow-Up of Imminent Impactors

A survey for occultation astrometry of main belt: expected astrometric performances

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