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Direct measurement of decimetre-sized rocky material in the Oort cloud

Abstract

The Oort cloud is thought to be a reservoir of icy planetesimals and the source of long-period comets (LPCs) implanted from the outer Solar System during the time of giant-planet formation. The abundance of rocky ice-free bodies is a key diagnostic of Solar System formation models as it can distinguish between ‘massive’ and ‘depleted’ proto-asteroid-belt scenarios and thus disentangle competing planet formation models. Here we report a direct observation of a decimetre-sized (~2 kg) rocky meteoroid on a retrograde LPC orbit (eccentricity ~1.0, inclination 121°). During its flight, it fragmented at dynamic pressures similar to fireballs dropping ordinary chondrite meteorites. A numerical ablation model fit produces bulk density and ablation properties also consistent with asteroidal meteoroids. We estimate the flux of rocky objects impacting Earth from the Oort cloud to be \(1.0{8}_{-0.95}^{+2.81}\) meteoroids per 106 km2 yr−1 to a mass limit of 10 g. This corresponds to an abundance of rocky meteoroids of \(\sim {6}_{-5}^{+13}\)% of all objects originating in the Oort cloud and impacting Earth to these masses. Our result gives support to migration-based dynamical models of the formation of the Solar System, which predict that significant rocky material is implanted in the Oort cloud, a result not explained by traditional Solar System formation models.

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Fig. 1: The fireball as seen from the two GFO stations.
Fig. 2: Observed and simulated light curve and deceleration profile.
Fig. 3: Observed fragmentations of the Alberta meteoroid compared with previously observed fragmentation behaviour of OC fireballs.
Fig. 4: All published fireball data showing PE as a function of TJ for TJ < 2 fireballs in the MORP dataset.

Data availability

The trajectory data are included with this article as Supplementary Data files. The raw images and Supplementary Information are available on Zenodo at https://doi.org/10.5281/zenodo.7225827. Source data are provided with this paper.

Code availability

The optical data were calibrated using the open source SkyFit2 software available in the RMS library at https://github.com/CroatianMeteorNetwork/RMS. The WesternMeteorPyLib (wmpl) library was used to compute the trajectory and fit the meteoroid ablation model to the observations. It is available at https://github.com/wmpg/WesternMeteorPyLib/.

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Acknowledgements

We thank R. Howell for first bringing this fireball to our attention and A. DesLauriers for providing raw footage from his security camera in Cochrane, AB. Funding for this work was provided in part through NASA co-operative agreement 80NSSC21M0073 (D.V., P.G.B.), by the Natural Sciences and Engineering Research Council of Canada Discovery Grants programme (grant numbers RGPIN-2016-04433 and RGPIN-2018-05659; D.V., P.G.B.), the Canada Research Chairs programme (P.G.B.), the Slovak Research and Development Agency grant APVV-16-0148 and the Slovak Grant Agency for Science grant VEGA 1/0218/22 (P.M., J.T.).

Author information

Authors and Affiliations

Authors

Contributions

D.V. coordinated the effort, performed the analysis, implemented the software and wrote the manuscript. P.G.B. initially coordinated the effort and provided scientific insight. H.A.R.D. computed an initial trajectory and provided the raw GFO data. P.W. made valuable scientific interpretations of the results and added a connection to recent comet discoveries, and performed the orbital integrations. D.E.M. helped digitize the MORP data, systematically collected and organized all casual recordings of the fireball, provided the GLM observations, and identified fireballs for GLM calibration. P.M. and J.T. provided observations of a fireball jointly observed with the AMOS system and the GLM. C.D.K.H. and P.J.A.H. provided the GFO data from the Miquelon Lake and Vermilion cameras and helped contact the local people who observed the fireball. E.K.S. and M.C.T. analysed the global GFO dataset to locate other fireballs of interest and provided data access. W.J.C. provided initial coordination. D.W.H. provided the GoPro video and took DSLR images for its photometric calibration.

Corresponding author

Correspondence to Denis Vida.

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The authors declare no competing interests.

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Nature Astronomy thanks Petr Pokorny, Karen Meech and Peter Jenniskens for their contribution to the peer review of this work.

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Extended data

Extended Data Fig. 1 Map showing the fireball track and the camera locations.

Map showing the location of the fireball trajectory (red line), cameras, and major population centres in Calgary and Edmonton. The GoPro camera was located in Calgary.

Extended Data Fig. 2 Miquelon Lake camera astrometric calibration.

Astrometric calibration fit using a 7th order polynomial (odd terms only) radial distortion model for the Miquelon Lake camera. Forward mapping (image to sky) errors.

Extended Data Fig. 3 Vermillion camera astrometric calibration.

Astrometric calibration fit for the Vermillion camera. Forward mapping (image to sky) errors.

Extended Data Fig. 4 Cochrane security camera astrometric calibration.

Composite of frames from the Cochrane security camera video showing the fireball and the calibration stars (marked with a white letter C), four of which were in Cassiopeia. An equatorial grid is laid over the video with catalogue stars shown as yellow crosshairs. Credit: Airell DesLauriers.

Extended Data Fig. 5 Comparison between optical light curves and GLM-derived light curves of calibration fireballs.

The optical light curves (dotted curves) were derived from ground-based sensors, and the GLM light curves (red curves) were derived from the GOES-16 and 17 satellites.

Extended Data Fig. 6 Trajectory fit errors and dynamics.

a) Spatial trajectory fit residuals versus height. b) The observed lag (the distance that the meteoroid falls behind an object with a constant velocity that is equal to the initial meteoroid velocity).

Extended Data Fig. 7 Change in orbital elements between 60 and 365 days before impact.

Each clone is colour-coded individually and represents one sample within the orbital covariance matrix. Time is not shown on any axis, but the clones that start at t - 60 days are clustered at zero and spread out as we go further back in time, as the distance from Mars decreases and then increases again.

Extended Data Fig. 8 Change in orbital elements over the last 2000 years.

Backwards integration with all planets included. Each clone is colour-coded individually. Planetary perturbations produce small nearly-stochastic changes in the orbital elements.

Extended Data Fig. 9 Details of the modelled individual fragmentations of the meteoroid marked on the simulated light curve.

Solid black line is the total light production, the dashed black line is the magnitude of the main body from which fragments are released, green dashed lines are magnitudes of the eroding fragments, and purple lines are magnitudes of the grains ejected either from the main body or the eroding fragments. Arrows indicate where the fragmentations occurred with which parameters, and stars indicate the beginning of individual fragment/grain light curves.

Extended Data Fig. 10 Modelled mass loss as a function of increasing dynamic pressure.

Model fragmentation points and masses of major fragments are marked with red circles. η marks the change in the erosion coefficient, and σ the change in the ablation coefficient of the main body.

Supplementary information

Supplementary Information

Supplementary Tables 1–6.

Source data

Source Data Fig. 1

Raw fireball images in the Nikon NEF format.

Source Data Fig. 2

Calibrated light curve and trajectory data.

Source Data Fig. 3

Strength versus mass loss from Borovicka et al. (2020).

Source Data Fig. 4

A selection of MORP data used in the paper.

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Vida, D., Brown, P.G., Devillepoix, H.A.R. et al. Direct measurement of decimetre-sized rocky material in the Oort cloud. Nat Astron (2022). https://doi.org/10.1038/s41550-022-01844-3

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