In recent days, two spectacular fireballs have decorated Australia's skies.
The first flashed across the Northern Territory in the early hours of May 20, and was seen by both Tennant Creek and Alice Springs, more than 500 km apart.
The second occurred over South Australia and Victoria two days later.
Such fireballs are not uncommon events and serve as further reminder that the earth is in a heavenly shooting range. In addition to their spectacle, they possess the key to understanding the origin and history of the solar system.
Crash, bang, boom!
If you look up into the sky long enough on a clear night, you'll see meteors. These flashes of light are the result of objects that affect the atmosphere of our planet.
Harmless debris stains evaporate in the atmosphere, 80-1
The larger the object, the more spectacular the flash. Where a typical meteor is caused by an object the size of a speck of dust (or, for a particularly light one, a grain of rice), fireballs like those seen this week are caused by much larger bodies – the size of a grapefruit, a melon or even a Automobile.
Such impacts are rarer than their small siblings because there are many more small objects in the solar system than larger bodies.
Moving to even larger objects will yield truly spectacular but rare events such as the incredible Chelyabinsk fireball in February 2013.
This was probably the largest impact on Earth for 100 years and caused many damage and injuries , It was the result of the explosion of an object with a mass of 10,000 tons and a diameter of around 20 meters.
On longer time scales, the biggest impact is huge. 66 million years ago, a comet or asteroid with a diameter of about 10 km plowed into today's Mexican Yucatan Peninsula. The result? A crater with a diameter of 200 km and a mass extinction that included the dinosaurs.
That, too, is not the biggest influence Earth has experienced. When our planet was still young, it had fallen victim to a truly catastrophic event when it collided with an object the size of Mars.
When dust and debris broke up, our former lonely planet was accompanied by the moon.
Fortunately, impacts that could threaten life on Earth are very rare. While scientists are actively trying to ensure there is no impact on extinction in the near future, we should not lose too much sleep.
Minor effects seen earlier this week are much more common. In fact, footage from another fireball was reported earlier this month over Illinois in the United States.
In other words, it's not uncommon to have two bright fireballs over a country like Australia within days.
Original Relics of Planetary Formation
These bright fireballs can be an incredible blessing to our understanding of the formation and evolution of the solar system. When an object is large enough, fragments (or the whole) can invade the atmosphere undamaged and bring a new meteorite to the surface of our planet.
Meteorites are incredibly valuable to scientists. They are celestial time capsules – relatively flawless fragments of asteroids and comets that formed when the solar system was still young.
Most of the meteorites we find have lain on Earth long before their discovery. These findings, called "discoveries", are still valuable but are often degraded and weathered and chemically altered by the humid and warm environment of our planet.
In contrast, "falls" (meteorites whose fall was observed and recovered within hours or days of the event) are far more precious. When we study their composition, we can be sure that we are studying something ancient and primitive, rather than worrying about the Earth's influence.
Tracking the Fireballs
Because of this, the Australian Desert Fireball Network has set up a huge network of cameras on our huge continent. These cameras are designed to roam the skies every night, watching for fireballs as they were seen earlier this week.
If we can observe such a fireball from multiple directions, we can triangulate its path and calculate its motion through the sky atmosphere, and see if it has probably fallen a meteorite. With this data we can even find out where to look.
In addition to these cameras, the project can use all data provided by people who saw the event. That's why the Fireballs team developed a free app, Fireballs in the Sky.
It contains great information about fireballs and meteor showers and links to experiments that are included in the national curriculum. More importantly, users can submit their own fireball reports.
As for the fireball this week over South Australia, NASA claims it was probably caused by an object the size of a small car. As far as finding remnants is concerned, they are now likely to be lost in the waters of the Great Australian Bay.
The search for meteorites begins
This article was re-published in The Conversation under a Creative Commons license. Read the original article.
What caused the fireballs that lit up the sky over Australia? (2019, May 24)
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