Apophis source population and Earth encounter frequency of Apophis-like bodies

Abstract

We provide context for Apophis' 2029 Earth passage by analyzing its possible source populations, in particular, the Flora family, which has a similar composition, corresponding to LL chondrite meteorites. Out of $\sim 3380$ NEOs larger or equal than Apophis ($\ge 420\mathrm{m}$), $610\pm 140$ are LL-like NEOs from Flora. Their mean encounter probability is $p=86\times 10^{-18}{\mathrm{km}}^{-2}{\mathrm{y}}^{-1}$, corresponding to once per 13000 y frequency of encounters closer than 38000 km. However, this does not apply to Apophis alone, for which the specific encounter probability is higher, $p^{\prime }=1603\times 10^{-18}{\mathrm{km}}^{-2}{\mathrm{y}}^{-1}$, but the frequency is lower, only once per 430000 y, when we consider it as a single object. Our simulation of the Flora family over $\sim$1 billion years indicates that Apophis-like bodies have orbits that are particularly persistent in near-Earth space. The temporal distribution of encounter probabilities exhibits peaks (up to $>10^4$ in the same units) and the specific value for Apophis is not unusual (occurring $\sim 70\%$ of time). In other words, there is always at least one Apophis-like body among NEOs. We find that such persistence also creates favorable opportunities for temporary capture as Earth coorbitals. Apophis-like bodies are ultimately removed from the inner solar system by approaching the Sun or by impact into one of the terrestrial planets, where the relative split between these outcomes is $(45\pm 2)\%$ and $(50\pm 2)\%$. While our current knowledge of Apophis' orbit guarantees no threat from Apophis in the next few centuries, we cannot predict any specific outcome for Apophis in the coming thousands or millions of years. Evaluating this statistically over the long term, we find that objects in Apophis-like orbits have a $(19\pm 2)\%$ chance of Earth impact over their lifetime of $\sim 30\mathrm{My}$.

A&A, accepted

References in corpus (11)

• Compositional distributions and evolutionary processes for the near-Earth object population: Results from the MIT-Hawaii Near-Earth Object Spectroscopic Survey (MITHNEOS
• Combining asteroid models derived by lightcurve inversion with asteroidal occultation silhouettes
• Source regions of carbonaceous meteorites and NEOs
• Tidal distortion and disruption of rubble-pile bodies revisited -- Soft-sphere discrete element analyses
• Asteroid Kamo`oalewa's journey from the lunar Giordano Bruno crater to Earth 1:1 resonance
• Thermal Infrared Observations of Asteroid (99942) Apophis with Herschel
• The debiased compositional distribution of MITHNEOS: Global match between the near-Earth and main-belt asteroid populations and excess of D-type Near-Earth Objects
• Horseshoe Co-orbitals of Earth: Current Population and New Candidates
• JWST sighting of decameter main-belt asteroids and view on meteorite sources
• Refinement of the convex shape model and tumbling spin state of (99942) Apophis using the 2020-2021 apparition data
• The young Hobson family: Possible binary parent body and low-velocity dispersal

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