A space rock came hurtling into Earth鈥檚 atmosphere 鈥� and then flew straight back out again. Astronomers say this is a rare example of a 鈥済razing fireball鈥�.
Patrick Shober at Curtin University in Australia and his colleagues observed the event in July 2017 with the Desert Fireball Network, a suite of cameras that searches Australian skies for bright meteors known as fireballs. They saw an intense trail 1300 kilometres long as the rock flew overhead at nearly 16 kilometres per second.
鈥淭he meteoroid transited the atmosphere for over 90 seconds and reached a minimum height of 58.5 km before returning to interplanetary space,鈥� the researchers write in their paper. They estimate the rock was 30 centimetres across and weighed at least 60 kilograms.
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A handful of such events have been seen before, with the first , as picture above. But the 2017 event was notable for its low altitude, and because the encounter dramatically changed the rock鈥檚 orbit in the solar system.
Although the rock slowed by about 1.5 kilometres per second as it passed through our atmosphere, it received a gravitational slingshot from Earth as it left 鈥� space probes use a similar technique to get a speed boost. This means that, having originated in the asteroid belt between Mars and Jupiter, the rock will now travel out as far as Jupiter.
Shober and his team predict it will remain in this new orbit for 200,000 years, before probably being pushed further out, towards Neptune, or ejected from the solar system. 鈥淭his one really was quite unusual,鈥� says Peter Brown at Western University in Canada.
While interesting, these events have scientific value too. By studying such space rocks before and after, we can observe how they withstand the pressures of our atmosphere. 鈥淚t鈥檚 an exquisite experiment in seeing how strong these objects are,鈥� says Brown.
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