Pre-impact Orbit Research Articles

Orbital period change of Dimorphos due to the DART kinetic impact

The Double Asteroid Redirection Test (DART) spacecraft successfully performed the first test of a kinetic impactor for asteroid deflection by impacting Dimorphos, the secondary of near-Earth binary asteroid (65803) Didymos, and changing the orbital period of Dimorphos. A change in orbital period of approximately 7 min was expected if the incident momentum from the DART spacecraft was directly transferred to the asteroid target in a perfectly inelastic collision1, but studies of the probable impact conditions and asteroid properties indicated that a considerable momentum enhancement (β) was possible2,3. In the years before impact, we used lightcurve observations to accurately determine the pre-impact orbit parameters of Dimorphos with respect to Didymos4–6. Here we report the change in the orbital period of Dimorphos as a result of the DART kinetic impact to be −33.0 ± 1.0 (3σ) min. Using new Earth-based lightcurve and radar observations, two independent approaches determined identical values for the change in the orbital period. This large orbit period change suggests that ejecta contributed a substantial amount of momentum to the asteroid beyond what the DART spacecraft carried.

Observation of metre-scale impactors by the Desert Fireball Network

The Earth is impacted by 35-40 metre-scale objects every year. These meteoroids are the low mass end of impactors that can do damage on the ground. Despite this they are very poorly surveyed and characterised, too infrequent for ground based fireball bservation efforts, and too small to be efficiently detected by NEO telescopic surveys whilst still in interplanetary space. We want to evaluate the suitability of different instruments for characterising metre-scale impactors and where they come from. We use data collected over the first 3 years of operation of the continent-scale Desert Fireball Network, and compare results with other published results as well as orbital sensors. We find that although the orbital sensors have the advantage of using the entire planet as collecting area, there are several serious problems with the accuracy of the data, notably the reported velocity vector, which is key to getting an accurate pre-impact orbit and calculating meteorite fall positions. We also outline dynamic range issues that fireball networks face when observing large meteoroid entries.

Homing in for New Year: impact parameters and pre-impact orbital evolution of meteoroid 2014 AA

On 2008 October 7, small asteroid 2008 TC3 turned itself into the parent body of the first meteor ever to be predicted before entering the Earth's atmosphere. Over five years later, the 2014 AA event became the second instance of such an occurrence. The uncertainties associated with the pre-impact orbit of 2008 TC3 are relatively small because thousands of observations were made during the hours preceding the actual meteor airburst. In sharp contrast, 2014 AA was only observed seven times before impact and consequently its trajectory is somewhat uncertain. Here, we present a recalculation of the impact parameters -location and timing- of this meteor based on infrasound recordings. The new values and their uncertainties together with Monte Carlo and N-body techniques, are applied to obtain an independent determination of the pre-impact orbit of 2014 AA. Our orbital solution is used to investigate the possible presence of known near-Earth objects (NEOs) moving in similar orbits. Prior to impact, 2014 AA was subjected to a web of overlapping secular resonances and it followed a path similar to those of 2011 GJ3, 2011 JV10, 2012 DJ54, and 2013 NJ4. NEOs in this transient group have their orbits controlled by close encounters with the Earth-Moon system at perihelion and Mars at aphelion, perhaps constituting a dynamical family. Extensive comparison with other studies is also presented.

CHASING THE CHELYABINSK ASTEROIDN-BODY STYLE

On 2013 February 15 a small asteroid rammed against the atmosphere above the region of Chelyabinsk in Russia, producing the most powerful superbolide since the Tunguska event in 1908. Lacking proper astrometric observations, the pre-impact orbit of this object has been determined using videos, satellite images, and pure geometry. Unfortunately, more than two years after the event, the published estimates vary so much that there is no clear orbital solution that could be used to investigate the origin of the impactor and the existence of dynamically, or perhaps even genetically, related asteroids. Here, we revisit this topic using a full N-body approach. A robust statistical test is applied to published solutions to discard those unable to produce a virtual impact at the observed time (03:20:20.8 s UTC). The same N-body methodology and the latest ephemerides are used to compute a new orbital solution: a=1.6247 AU, e=0.5318, i=3.9750 degrees, Omega=326.4607 degrees and omega=109.7012 degrees. This new solution --which has an impact probability > 0.99999 and uncertainties in time and space of 0.2 s and 6 km, respectively-- is utilized to explore the past orbital evolution of the impactor as well as the presence of near-Earth objects moving in similar paths. A dynamical link between asteroid 2011 EO40 and the Chelyabinsk impactor is confirmed. Alternative orbital solutions are extensively explored.

Orbit determination based on meteor observations using numerical integration of equations of motion

Recently, there has been a worldwide proliferation of instruments and networks dedicated to observing meteors, including airborne and future space-based monitoring systems . There has been a corresponding rapid rise in high quality data accumulating annually. In this paper, we present a method embodied in the open-source software program "Meteor Toolkit", which can effectively and accurately process these data in an automated mode and discover the pre-impact orbit and possibly the origin or parent body of a meteoroid or asteroid. The required input parameters are the topocentric pre-atmospheric velocity vector and the coordinates of the atmospheric entry point of the meteoroid, i.e. the beginning point of visual path of a meteor, in an Earth centered-Earth fixed coordinate system, the International Terrestrial Reference Frame (ITRF). Our method is based on strict coordinate transformation from the ITRF to an inertial reference frame and on numerical integration of the equations of motion for a perturbed two-body problem. Basic accelerations perturbing a meteoroid's orbit and their influence on the orbital elements are also studied and demonstrated. Our method is then compared with several published studies that utilized variations of a traditional analytical technique, the zenith attraction method, which corrects for the direction of the meteor׳s trajectory and its apparent velocity due to Earth's gravity. We then demonstrate the proposed technique on new observational data obtained from the Finnish Fireball Network (FFN) as well as on simulated data. In addition, we propose a method of analysis of error propagation, based on general rule of covariance transformation.

Reconstructing the Chelyabinsk event: pre-impact orbital evolution

Abstract The Chelyabinsk superbolide was the largest known natural object to enter the Earth's atmosphere since the Tunguska event in 1908 and it has become a template to understand, manage and mitigate future impacts. Although the event has been documented in great detail, the actual pre-impact orbit of the parent body is still controversial. Here, we revisit this topic using an improved Monte Carlo approach that includes the coordinates of the impact point to compute the most probable solution for the pre-impact orbit (a = 1.62 au, e = 0.53, i = 3 $_{.}^{\circ}$97, Ω = 326 $_{.}^{\circ}$45 and ω = 109 $_{.}^{\circ}$71). We also check all the published solutions using a simple yet robust statistical test to show that many of them have problems to cause an impact at the right time. We use the improved orbit and N-body simulations to revisit the dynamical status of a putative Chelyabinsk asteroid family and confirm that it could be linked to resonant asteroids 2007 BD7 and 2011 EO40. In addition, and as the classification of Chelyabinsk meteorites is well established, a search for meteorite falls of the same chondrite group and petrologic type gives some evidence for the existence of an associated LL5 chondrite cluster.

The Chelyabinsk superbolide: a fragment of asteroid 2011 EO40?

Abstract Bright fireballs or bolides are caused by meteoroids entering the Earth's atmosphere at high speed. Some have a cometary origin, a few may have originated within the Venus–Earth–Mars region as a result of massive impacts in the remote past but a relevant fraction is likely the result of the break-up of asteroids. Disrupted asteroids produce clusters of fragments or asteroid families and meteoroid streams. Linking a bolide to a certain asteroid family may help to understand its origin and pre-impact dynamical evolution. On 2013 February 15, a superbolide was observed in the skies near Chelyabinsk, Russia. Such a meteor could be the result of the decay of an asteroid and here we explore this possibility applying a multistep approach. First, we use available data and Monte Carlo optimization (validated using 2008 TC3 as template) to obtain a robust solution for the pre-impact orbit of the Chelyabinsk impactor (a = 1.62 au, e = 0.53, i = 3 $_{.}^{\circ}$82, Ω = 326 $_{.}^{\circ}$41 and ω = 109 $_{.}^{\circ}$44). Then, we use this most probable orbit and numerical analysis to single out candidates for membership in, what we call, the Chelyabinsk asteroid family. Finally, we perform N-body simulations to either confirm or reject any dynamical connection between candidates and impactor. We find reliable statistical evidence on the existence of the Chelyabinsk cluster. It appears to include multiple small asteroids and two relatively large members: 2007 BD7 and 2011 EO40. The most probable parent body for the Chelyabinsk superbolide is 2011 EO40. The orbits of these objects are quite perturbed as they experience close encounters not only with the Earth–Moon system but also with Venus, Mars and Ceres. Under such conditions, the cluster cannot be older than about 20–40 kyr.

The Košice meteorite fall: Atmospheric trajectory, fragmentation, and orbit

AbstractThe Košice meteorite fall occurred in eastern Slovakia on February 28, 2010, 22:25 UT. The very bright bolide was imaged by three security video cameras from Hungary. Detailed bolide light curves were obtained through clouds by radiometers on seven cameras of the European Fireball Network. Records of sonic waves were found on six seismic and four infrasonic stations. An atmospheric dust cloud was observed the next morning before sunrise. After careful calibration, the video records were used to compute the bolide trajectory and velocity. The meteoroid, of estimated mass of 3500 kg, entered the atmosphere with a velocity of 15 km s−1 on a trajectory with a slope of 60° to the horizontal. The largest fragment ceased to be visible at a height of 17 km, where it was decelerated to 4.5 km s−1. A maximum brightness of absolute stellar magnitude about −18 was reached at a height of 36 km. We developed a detailed model of meteoroid atmospheric fragmentation to fit the observed light curve and deceleration. We found that Košice was a weak meteoroid, which started to fragment under the dynamic pressure of only 0.1 MPa and fragmented heavily under 1 MPa. In total, 78 meteorites were recovered in the predicted fall area during official searches. Other meteorites were found by private collectors. Known meteorite masses ranged from 0.56 g to 2.37 kg. The meteorites were classified as ordinary chondrites of type H5 and shock stage S3. The heliocentric orbit had a relatively large semimajor axis of 2.7 AU and aphelion distance of 4.5 ± 0.5 AU. Backward numerical integration of the preimpact orbit indicates possible large variations of the orbital elements in the past due to resonances with Jupiter.

THE IMPACT OF A LARGE OBJECT ON JUPITER IN 2009 JULY

On 2009 July 19, we observed a single, large impact on Jupiter at a planetocentric latitude of 55^{\circ}S. This and the Shoemaker-Levy 9 (SL9) impacts on Jupiter in 1994 are the only planetary-scale impacts ever observed. The 2009 impact had an entry trajectory opposite and with a lower incidence angle than that of SL9. Comparison of the initial aerosol cloud debris properties, spanning 4,800 km east-west and 2,500 km north-south, with those produced by the SL9 fragments, and dynamical calculations of pre-impact orbit, indicate that the impactor was most probably an icy body with a size of 0.5-1 km. The collision rate of events of this magnitude may be five to ten times more frequent than previously thought. The search for unpredicted impacts, such as the current one, could be best performed in 890-nm and K (2.03-2.36 {\mu}m) filters in strong gaseous absorption, where the high-altitude aerosols are more reflective than Jupiter's primary cloud.

Detection of Earth-impacting asteroids with the next generation all-sky surveys

We have performed a simulation of a next generation sky survey’s (Pan-STARRS 1) efficiency for detecting Earth-impacting asteroids. The steady-state sky-plane distribution of the impactors long before impact is concentrated towards small solar elongations (Chesley, S.R., Spahr T.B., 2004. In: Belton, M.J.S., Morgan, T.H., Samarashinha, N.H., Yeomans, D.K. (Eds.), Mitigation of Hazardous Comets and Asteroids. Cambridge University Press, Cambridge, pp. 22–37) but we find that there is interesting and potentially exploitable behavior in the sky-plane distribution in the months leading up to impact. The next generation surveys will find most of the dangerous impactors (>140 m diameter) during their decade-long survey missions though there is the potential to miss difficult objects with long synodic periods appearing in the direction of the Sun, as well as objects with long orbital periods that spend much of their time far from the Sun and Earth. A space-based platform that can observe close to the Sun may be needed to identify many of the potential impactors that spend much of their time interior to the Earth’s orbit. The next generation surveys have a good chance of imaging a bolide like 2008 TC 3 before it enters the atmosphere but the difficulty will lie in obtaining enough images in advance of impact to allow an accurate pre-impact orbit to be computed.

Comparison of the trace element composition of Tagish Lake with other primitive carbonaceous chondrites

Abstract— A meteorite fall on 2000 January 18 was detected by U.S. Defense Department satellites which established its pre‐impact orbit. Fresh samples were collected from frozen Tagish Lake in British Columbia a week later and some properties of these samples reveal it to be a unique meteorite. We characterized Tagish Lake and 8 other samples using inductively‐coupled plasma mass spectrometry and radiochemical neutron activation analysis: data for 47 elements reveal that each of 9 carbonaceous chondrites of different type exhibit the Orgueil‐normalized plateaus expected for members of such types. Trends evident in Tagish Lake differ from all other carbonaceous chondrites, including CI and CM. Samples of Tagish Lake collected later show similar patterns affected by weathering.

The orbital motion and impact circumstances of Comet Shoemaker-Levy 9

Two months after the discovery of comet Shoemaker-Levy 9 came the astonishing announcement that the comet would impact Jupiter in July 1994. Computing the orbital motion of this remarkable comet presented several unusual challenges. We review the pre-impact orbit computations and impact predictions for SL9, from the preliminary orbit solutions shortly after discovery to the final set of predictions before the impacts. The final set of predicted impact times were systematically early by an average of 7 minutes, probably due to systematic errors in the reference star catalogs used in the reduction of the fragments' astrometric positions. The actual impact times were inferred from the times of observed phenomena for 16 of the impacts. Orbit solutions for the fragments were refined by using the actual impact times as additional data, and by estimating and removing measurement biases from the astrometric observations. The final orbit solutions for 21 fragments are tabulated, along with final estimates of the impact times and locations. The pre-breakup orbital history of the comet was investigated statistically, via a Monte Carlo analysis. The progenitor nucleus of SL9 was most likely captured by Jupiter around 1929 ± 9 years. Prior to capture, the comet was in a low-eccentricity, low-inclination heliocentric orbit entirely inside Jupiter's orbit, or, less likely, entirely outside. The ensemble of possible pre-capture orbits is consistent with a group of Jupiter family comets known as the quasi-Hildas.