'Oumuamua (1I/2017 U1) is the first known object of interstellar origin to have entered the Solar System on an unbound and hyperbolic trajectory with respect to the Sun
. Various physical ...observations collected during its visit to the Solar System showed that it has an unusually elongated shape and a tumbling rotation state
and that the physical properties of its surface resemble those of cometary nuclei
, even though it showed no evidence of cometary activity
. The motion of all celestial bodies is governed mostly by gravity, but the trajectories of comets can also be affected by non-gravitational forces due to cometary outgassing
. Because non-gravitational accelerations are at least three to four orders of magnitude weaker than gravitational acceleration, the detection of any deviation from a purely gravity-driven trajectory requires high-quality astrometry over a long arc. As a result, non-gravitational effects have been measured on only a limited subset of the small-body population
. Here we report the detection, at 30σ significance, of non-gravitational acceleration in the motion of 'Oumuamua. We analyse imaging data from extensive observations by ground-based and orbiting facilities. This analysis rules out systematic biases and shows that all astrometric data can be described once a non-gravitational component representing a heliocentric radial acceleration proportional to r
or r
(where r is the heliocentric distance) is included in the model. After ruling out solar-radiation pressure, drag- and friction-like forces, interaction with solar wind for a highly magnetized object, and geometric effects originating from 'Oumuamua potentially being composed of several spatially separated bodies or having a pronounced offset between its photocentre and centre of mass, we find comet-like outgassing to be a physically viable explanation, provided that 'Oumuamua has thermal properties similar to comets.
Abstract The Gaia mission has provided astrometric observations of unprecedented accuracy for more than 156,000 asteroids. The reported astrometric uncertainties are of the order of milliarcseconds, ...about 2 orders of magnitude smaller than that of traditional ground-based observations. The accuracy of Gaia data requires a high-fidelity orbit determination process, especially in the observation modeling. We present a statistical analysis of Gaia Focused Product Release to test the accuracy of the reported positions and associated uncertainties. We find that center-of-light offsets due to phase variations need to be modeled to properly fit the observational data. Prediction tests show that the uncertainty in the fitted orbits can be optimistic unless the observational uncertainty is inflated to account for errors in finding the center-of-mass of the body. Moreover, errors in the masses of small-body perturbers can cause differences in the orbital solution that exceed formal uncertainties of the best constrained orbits. As an example, we provide an update of the impact hazard analysis of 1950 DA, one of the asteroids observed by Gaia, and find that the impact probability in the year 2880 increases to 3.8 × 10 −4 .
Abstract We characterize asteroid (16) Psyche using high-precision astrometry, including the recent Gaia Focused Product Release. The gravitational perturbations of Psyche on other asteroids can be ...observable in the case of mutual encounters. Using a least squares approach, we estimate the mass of Psyche by fitting astrometric data of asteroids that come within 0.05 au of Psyche. Combining the resulting individual estimates, we find GM = 1.601 ± 0.017 km 3 s −2 . This result is robust against variations in the orbit determination setup and specific data set used. The volume and equivalent radius of Psyche are currently constrained by occultations and radar and optical imaging to (5.75 ± 0.19) × 10 6 km 3 and 111 − 0.5 + 2 km, respectively. Given the volume of Psyche, our mass estimate corresponds to a bulk density of 4172 ± 145 kg m −3 , which is compatible with an M-type taxonomic classification. Finally, the phase-dependent photocenter offset is visible in the residuals of Gaia astrometric observations of Psyche. This effect is consistent with the size of Psyche.
•Asteroid Bennu has a well-determined orbit due primarily to 12years of radar ranging.•The Yarkovsky effect on Bennu causes a semimajor axis drift of 284±1.5m/year.•We estimate Bennu’s bulk density ...at 1260±70kg/m3 and macroporosity 40±10%.•Bennu has a 1 in 2700 chance of an Earth impact late in the 22nd century.
The target asteroid of the OSIRIS-REx asteroid sample return mission, (101955) Bennu (formerly 1999 RQ36), is a half-kilometer near-Earth asteroid with an extraordinarily well constrained orbit. An extensive data set of optical astrometry from 1999 to 2013 and high-quality radar delay measurements to Bennu in 1999, 2005, and 2011 reveal the action of the Yarkovsky effect, with a mean semimajor axis drift rate da/dt=(-19.0±0.1)×10-4au/Myr or 284±1.5m/year. The accuracy of this result depends critically on the fidelity of the observational and dynamical model. As an example, neglecting the relativistic perturbations of the Earth during close approaches affects the orbit with 3σ significance in da/dt.
The orbital deviations from purely gravitational dynamics allow us to deduce the acceleration of the Yarkovsky effect, while the known physical characterization of Bennu allows us to independently model the force due to thermal emissions. The combination of these two analyses yields a bulk density of ρ=1260±70kg/m3, which indicates a macroporosity in the range 40±10% for the bulk densities of likely analog meteorites, suggesting a rubble-pile internal structure. The associated mass estimate is (7.8±0.9)×1010kg and GM=5.2±0.6m3/s2.
Bennu’s Earth close approaches are deterministic over the interval 1654–2135, beyond which the predictions are statistical in nature. In particular, the 2135 close approach is likely within the lunar distance and leads to strong scattering and numerous potential impacts in subsequent years, from 2175 to 2196. The highest individual impact probability is 9.5×10-5 in 2196, and the cumulative impact probability is 3.7×10-4, leading to a cumulative Palermo Scale of −1.70.
Abstract
The catalog of km-sized near-Earth objects (NEOs) is nearly complete. Typical impact monitoring analyses search for possible impacts over the next 100 yr and none of the km-sized objects ...represent an impact threat over that time interval. Assessing the impact risk over longer timescales is a challenge since orbital uncertainties grow. To overcome this limitation we analyze the evolution of the minimum orbit intersection distance (MOID), which bounds the closest possible encounters between the asteroid and the Earth. The evolution of the MOID highlights NEOs that are in the vicinity of the Earth for longer periods of time, and we propose a method to estimate the probability of a deep Earth encounter during these periods. This metric is used to rank the km-sized catalog in terms of their long-term impact hazard to identify targets of potential interest for additional observation and exploration.
1I/'Oumuamua is the first confirmed interstellar body in our solar system. Here we report on observations of 'Oumuamua made with the Spitzer Space Telescope on 2017 November 21-22 (UT). We integrated ...for 30.2 hr at 4.5 m (IRAC channel 2). We did not detect the object and place an upper limit on the flux of 0.3 Jy (3 ). This implies an effective spherical diameter less than 98, 140, 440 m and albedo greater than 0.2, 0.1, 0.01 under the assumption of low, middle, or high thermal beaming parameter , respectively. With an aspect ratio for 'Oumuamua of 6:1, these results correspond to dimensions of 240:40, 341:57, 1080:180 m, respectively. We place upper limits on the amount of dust, CO, and CO2 coming from this object that are lower than previous results; we are unable to constrain the production of other gas species. Both our size and outgassing limits are important because 'Oumuamua's trajectory shows non-gravitational accelerations that are sensitive to size and mass and presumably caused by gas emission. We suggest that 'Oumuamua may have experienced low-level post-perihelion volatile emission that produced a fresh, bright, icy mantle. This model is consistent with the expected value and implied high-albedo value for this solution, but, given our strict limits on CO and CO2, requires another gas species-probably H2O-to explain the observed non-gravitational acceleration. Our results extend the mystery of 'Oumuamua's origin and evolution.
Abstract
We attempt to detect a signal of Yarkovsky-related acceleration in the orbits of 134 main belt asteroids (MBAs) we observed with the University of Hawai’i 88 inch telescope, supplemented ...with observations publicly available from the Minor Planet Center and Gaia Data Release 3. We estimated the expected Yarkovsky acceleration values based on parameters derived through thermophysical modeling, but we were not able to find any reliable detections of Yarkovsky in our sample. Through tests with synthetic observations, however, we estimated the minimum observational arc length needed to detect the Yarkovsky effect for all of our sample MBAs, which in nearly every case exceeded the current arc length of the existing observations. We find that the Yarkovsky effect could be detectable within a couple of decades of discovery for a 100 m MBA assuming 0.″1 astrometric accuracy, which is at the size range detectable by the upcoming Vera Rubin Observatory Legacy Survey of Space and Time.
The Pan-STARRS Moving Object Processing System Denneau, Larry; Jedicke, Robert; Grav, Tommy ...
Publications of the Astronomical Society of the Pacific,
04/2013, Letnik:
125, Številka:
926
Journal Article
Recenzirano
Odprti dostop
ABSTRACT We describe the Pan-STARRS Moving Object Processing System (MOPS), a modern software package that produces automatic asteroid discoveries and identifications from catalogs of transient ...detections from next-generation astronomical survey telescopes. MOPS achieves >99.5% efficiency in producing orbits from a synthetic but realistic population of asteroids whose measurements were simulated for a Pan-STARRS4-class telescope. Additionally, using a nonphysical grid population, we demonstrate that MOPS can detect populations of currently unknown objects such as interstellar asteroids. MOPS has been adapted successfully to the prototype Pan-STARRS1 telescope despite differences in expected false detection rates, fill-factor loss, and relatively sparse observing cadence compared to a hypothetical Pan-STARRS4 telescope and survey. MOPS remains highly efficient at detecting objects but drops to 80% efficiency at producing orbits. This loss is primarily due to configurable MOPS processing limits that are not yet tuned for the Pan-STARRS1 mission. The core MOPS software package is the product of more than 15 person-years of software development and incorporates countless additional years of effort in third-party software to perform lower-level functions such as spatial searching or orbit determination. We describe the high-level design of MOPS and essential subcomponents, the suitability of MOPS for other survey programs, and suggest a road map for future MOPS development.
We present an approach to estimate an upper bound for the impact probability of a potentially hazardous asteroid when part of the force model depends on unknown parameters whose statistical ...distribution needs to be assumed. As case study, we consider Apophis’ risk assessment for the 2036 and 2068 keyholes based on information available as of 2013. Within the framework of epistemic uncertainties, under the independence and non-correlation assumption, we assign parametric families of distributions to the physical properties of Apophis that define the Yarkovsky perturbation and in turn the future orbital evolution of the asteroid. We find
IP
≤
5
×
10
-
5
for the 2036 keyhole and
IP
≤
1.6
×
10
-
5
for the 2068 keyhole. These upper bounds are largely conservative choices due to the rather wide range of statistical distributions that we explored.
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 H
2
O sublimation model allows for brightening due to activity consistent with the scatter of the data. We estimate the production rate required for H
2
O outgassing to power the acceleration and find that, assuming a diameter of 300 m, 2003 RM would require Q(H
2
O) ∼ 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 (∼86% probability) as opposed to from the Jupiter-family comet region (∼11% probability). Further observations, especially in the infrared, could shed light on the nature of this anomalous acceleration.
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