Where Did They Come From, Where Did They Go: Grazing Fireballs

Abstract

For centuries extremely-long grazing fireball displays have fascinated observers and inspired people to ponder about their origins. The Desert Fireball Network (DFN) is the largest single fireball network in the world, covering about one third of Australian skies. This expansive size has enabled us to capture a majority of the atmospheric trajectory of a spectacular grazing event that lasted over 90 seconds, penetrated as deep as ∼ 58.5 km, and traveled over 1,300 km through the atmosphere before exiting back into interplanetary space. Based on our triangulation and dynamic analyses of the event, we have estimated the initial mass to be at least 60 kg, which would correspond to a 30 cm object given a chondritic density (3500 kg m −3 ). However, this initial mass estimate is likely a lower bound, considering the minimal deceleration observed in the luminous phase. The most intriguing quality of this close encounter is that the meteoroid originated from an Apollo-type orbit and was inserted into a Jupiter-family comet (JFC) orbit due to the net energy gained during the close encounter with the Earth. Based on numerical simulations, the meteoroid will likely spend ∼ 200 kyrs on a JFC orbit and have numerous encounters with Jupiter, the first of which will occur in January-March 2025. Eventually the meteoroid will likely be ejected from the Solar System or be flung into a trans-Neptunian orbit.

Possible Transfer of Life by Earth-Grazing Objects to Exoplanetary Systems

“…The DFN uses ∼ 50 cameras to cover ∼ 2.5 × 10 6 km 2 of the sky, or ∼ 5 × 10 −3 of the Earth's surface (Devillepoix et al 2016). While the DFN only had 4 cameras in 2007, we conservatively estimate the relevant observation parameters for the Shober et al (2019) detection to be the result of a survey that lasted ∼ 10 years and covered ∼ 5 × 10 −3 of the Earth's surface. This leads to a rate estimate of ∼ 20 yr −1 of 30 cm objects penetrating the Earth's atmosphere and eventually likely being ejected from the Solar System, with 95% Poisson bounds of 6 × 10 −1 − 1.1 × 10 2 yr −1 .…”

“…to estimate the yield strength Y i of the Shober et al (2019) meteor to be ∼ 6 × 10 5 Pa, given its density estimate of ρ obj ∼ 3500 kg m −3 . We then use equation (10) from Collins et al (2010),…”

“…where ρ air (z) is the density of air at altitude z, and the known speed of v = 15.5 km s −1 to estimate that the altitude of breakup, z ∼ 48 km, which is ∼ 10 km below the observed minimum altitude of the Shober et al (2019) meteor. Breakup is therefore not considered to be a significant factor in this analysis for typical rocky compositions, although it is noted that the Shober et al…”

“…Recently, Shober et al (2019) reported a detection by the Desert Fireball Network (DFN) 1 of a ∼ 30 cm object that reached a minimum altitude ∼ 58.5 km in the Earth's atmosphere during a 90 s grazing event, and was transferred from an Apollo-type orbit into a Jupiter-family comet orbit, making it likely to be ejected from the Solar System during a future gravitational encounter with Jupiter. This detection represents a new class of objects that can pick up life in the Earth's atmosphere before being ejected from the Solar System: rocky, inner-Solar System bodies that are scattered into Jupiter-crossing orbits after their grazing interactions with Earth and are subsequently ejected.…”

“…First, we discuss the collection of microbial life during the transporting body's passage through the atmosphere as well as the survival lifetime in space. Next, we use the Shober et al (2019) detection to calibrate the number of similar objects that could have picked up life in the Earth's atmosphere and were likely ejected from the Solar System. We then use a Monte Carlo simulation to estimate the total number of such objects that were captured by stellar binary systems over the lifetime of the Solar System, as well as the number of these objects that likely harbor living microbes at the time of capture.…”