A rock grazed the Earth's atmosphere and just kept going
Updated: Aug 21, 2020
In 2017 the Desert Fireball Network observed a meteoroid travel over 1300 km through the atmosphere before making its way back to space.
A grazing fireball occurs when the impact angle is really shallow. In some cases when the meteoroid is durable enough, it can pass through the atmosphere and return back to interplanetary space. These grazing fireballs have been talked about throughout history.
In 1783, the "Great Meteor" was estimated to have traveled >1600 km through the atmosphere over western Europe. The "Great Comet of 1860" was also very likely a grazing fireball over the eastern United States. It was depicted a painting by American landscape artist Frederic Church and by American poet Walt Whitman in his poem "Year of Meteors". The "1913 Great Meteor Procession" reported sightings across Canada, the north-eastern United States, Bermuda, and many ships in the Atlantic as far south as Brazil!!! This event was initially hypothesized to have been formed by a natural Earth satellite (aka 'minimoon') that had a grazing encounter with the atmosphere.
The first precisely measured grazing fireball occurred in 1972, 'The Great Daylight Fireball', as seen below (Credit & Copyright: James M. Baker). This fireball lasted ~100 s, covered over 1500 km, and reached a minimum height of 58 km.
This is what occurred again in July 2017 over southern Australia. The fireball observed traveled over 1300 km and reached a minimum height of about 58 km. This is the most spectacular grazing fireball observed since 1972.
As these rocks have close encounters with the Earth, their orbit around the Sun is also altered. This is because they can gain or lose energy from the Earth. The Australian grazing fireball was super interesting because it net gained energy from the encounter, despite slowing down while going the atmosphere.
This energy gained from encountering the Earth sent the rock on an orbit more characteristic of a comet. This is really cool because originally it was definitely asteroidal debris on an asteroidal orbit. However, given its current trajectory it will likely encounter Jupiter in 2025. This close encounter with the gas-giant will send this burnt space boulder on a chaotic journey eventually resulting in it likely being ejected from our solar system!
Below is an animation made by David Clark at UWO showing the grazing encounter and how the orbit was altered.
If you are interested, check out the paper this post is based on here in the Astronomical Journal!
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