Fireball networks: from sky to orbit

When a fireball is filmed from several places at once, scientists can find where its meteorites landed and trace where they came from in space.

Triangulating a fireball

A single camera shows a fireball's path across the sky but not how far away it is. Two or more cameras, at different locations, see the same fireball against different background stars. By combining their views, a process called triangulation, scientists can calculate the fireball's true path in three dimensions.

If the cameras also record precise timing, the speed and deceleration of the meteoroid can be measured along its path. Many modern systems use a rapid shutter or electronic chopping of the light, which breaks the trail into dashes at known intervals.

From the speed at the top of the atmosphere and the direction of travel, the meteoroid's orbit around the Sun before it met Earth can be calculated. This links each meteorite to a region of the Solar System.

A short history

The first meteorite fall with a photographically measured orbit was Příbram, which fell in what is now the Czech Republic in 1959. It was recorded by cameras at the Ondřejov Observatory, and the orbit reached out into the asteroid belt.

Dedicated camera networks followed. The Prairie Network in the USA recovered the Lost City meteorite in 1970, and the Canadian Meteorite Observation and Recovery Project recovered Innisfree in 1977. The European Fireball Network has operated for decades, and in Australia the Desert Fireball Network has recovered several meteorites from remote areas.

Today, networks around the world share data, and dash cameras, security cameras and doorbell cameras also contribute. Several dozen meteorites now have well-determined orbits, and the number is growing quickly.

Finding the stones

Once the bright part of the trajectory is known, scientists model the dark flight. They estimate the masses of surviving fragments from the deceleration, then use wind measurements at different heights to calculate where each mass would land. The result is a predicted strewn field, often a narrow strip a few kilometres long.

Search teams then walk carefully in lines across the area, with landowner permission. Local people who report unusual stones are often vital.

In the UK, the Winchcombe fall of 28 February 2021 was recorded by cameras of several networks working together under the UK Fireball Alliance. Its orbit was traced back to the outer asteroid belt, and the first piece was found on a driveway within days. Searchers recovered about 0.6 kilograms of this rare carbonaceous chondrite.

Asteroids seen before impact

A few meteorites have been predicted before they arrived. In October 2008, the small asteroid 2008 TC3 was discovered by a telescope survey about 20 hours before it hit Earth's atmosphere over Sudan. A search led by Peter Jenniskens and Muawia Shaddad found hundreds of fragments, named Almahata Sitta. They included ureilites and several kinds of chondrite, showing that a single small asteroid could be a mixture of different rock types.

Since then, a handful of other asteroids have been spotted shortly before impact and their meteorites recovered, including 2018 LA over Botswana, 2023 CX1 over northern France and 2024 BX1 over Germany.

These events let scientists compare the telescopic view of an asteroid in space directly with the rocks in their hands.

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