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 observation 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.

We describe the fall of the Dingle Dell (L/LL 5) meteorite near Morawa in Western Australia on October 31, 2016. The fireball was observed by six observatories of the Desert Fireball Network (DFN), a continental‐scale facility optimized to recover meteorites and calculate their pre‐entry orbits. The 30 cm meteoroid entered at 15.44 km s−1, followed a moderately steep trajectory of 51° to the horizon from 81 km down to 19 km altitude, where the luminous flight ended at a speed of 3.2 km s−1. Deceleration data indicated one large fragment had made it to the ground. The four person search team recovered a 1.15 kg meteorite within 130 m of the predicted fall line, after 8 h of searching, 6 days after the fall. Dingle Dell is the fourth meteorite recovered by the DFN in Australia, but the first before any rain had contaminated the sample. By numerical integration over 1 Ma, we show that Dingle Dell was most likely ejected from the Main Belt by the 3:1 mean motion resonance with Jupiter, with only a marginal chance that it came from the ν6 resonance. This makes the connection of Dingle Dell to the Flora family (currently thought to be the origin of LL chondrites) unlikely.

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The isotopic composition of water in Earth's oceans is challenging to recreate using a plausible mixture of known extraterrestrial sources such as asteroids -an additional isotopically light reservoir is required. The Sun's solar wind could provide an answer to balancing Earth's water budget. We used atom probe tomography to directly observe an average ~1 molecular percent enrichment in water and hydroxyls in the solar wind irradiated rim of an olivine grain from the S-type asteroid Itokawa. We also experimentally confirm that H irradiation of silicate mineral surfaces produces water molecules. These results suggest that the Itokawa regolith could contain ~20 litres per m 3 of solar wind derived water and that such water reservoirs are likely ubiquitous on airless worlds throughout our galaxy. The production of this isotopically light water reservoir by solar wind implantation into fine grained silicates may have been a particularly important process in the early Solar System, potentially providing a means to recreate Earth's current, water-isotope ratios. Main Text:The origin of Earth's water and volatile budget is a topic of considerable debate in planetary science [1][2][3][4][5][6][7][8][9][10] . Most current dynamical models of Earth's formation assume that the majority of Earth's water and other volatiles was added later from an exogenous source 1-4 . That volatile source shared a common parent population with C-type asteroids, that is likely located in the Jupiter-Saturn region and beyond [11][12][13][14] . C-Type asteroids are thought to be the parent bodies of carbonaceous (C) chondrite meteorites as they exhibit similar reflectance spectra, in particular the CRs, CMs and CIs 15 , which can contain up to 10 weight percent (wt. %) H 2 O (Table 1) 9 . Although the D/H isotope ratios of C-chondrite meteorites are a closer fit to the Earth than to comets or other meteorite types, with CMs being a particularly close match (Table 1) 2,16 , the Earth's mantle and Standard Mean Ocean Water (SMOW) are lighter in D/H 17 than the average of CI-, CR-and CM-chondrite groups [e.g., 1,16,18 Table 1]. Given the diversity of water rich C-chondrites in the meteorite record, it is unlikely that CM-like asteroids alone delivered all of Earth's water. Thus, as they are the most water-rich meteorites 9 , the CIs, CRs and CMs are believed to represent the majority of Earth's chondritic water component. Although recent studies of nominally anhydrous minerals from enstatite chondrites 10 and Itokawa particles 19 suggests that these materials may be more water-rich than previously thought, they only contain sufficient water for the lowest estimate of Earth's water budget (Table 1). D/H ratios of the Earth's deep mantle are even lighter than SMOW (Table 1) 2 ; recent analysis of volcanically exhumed material indicate that a component of 4 isotopically-light, solar-like D/H may be extant in the primitive mantle (Table 1) 6 . In addition, the bulk D/H ratio of the Earth may have increased from its initial value over the last 4.5...

Meteoroid modelling of fireball data typically uses a one dimensional model along a straight line triangulated trajectory. The assumption of a straight line trajectory has been considered an acceptable simplification for fireballs, but it has not been rigorously tested. The unique capability of the Desert Fireball Network (DFN) to triangulate discrete observation times gives the opportunity to investigate the deviation of a meteoroid's position to different model fits. Here we assess the viability of a straight line assumption for fireball data in two meteorite-dropping test cases observed by the Desert Fireball Network (DFN) in Australia -one over 21 seconds (DN151212 03 ), one under 5 seconds (DN160410 03 ). We show that a straight line is not valid for these two meteorite dropping events and propose a three dimensional particle filter to model meteoroid positions without any straight line constraints. The single body equations in three dimensions, along with the luminosity equation, are applied to the particle filter methodology described by . Modelling fireball camera network data in three dimensions has not previously been attempted. This allows the raw astrometric, line-of-sight observations to be incorporated directly. In analysing these two DFN events, the triangulated positions based on a straight line assumption result in the modelled meteoroid positions diverging up to 3.09 km from the calculated observed point (for DN151212 03 ). Even for the more typical fireball event, DN160410 03, we see a divergence of up to 360 m. As DFN observations are typically precise to < 100 m, it is apparent that the assumption of a straight line is an oversimplification that will affect orbit calculations and meteorite search regions for a significant fraction of events.