On July 31, 2013, a constellation of US defense satellites saw a streak of light over South Australia as a rock from outer space burned through Earth’s atmosphere and crashed into the ground. The impact caused an explosion equivalent to about 220 tons of TNT. More than 1,500 kilometers away, in Tasmania, the explosion was heard by detectors normally used to detect extremely low-frequency sounds from illegal nuclear weapons tests.

These were two excellent indications that there must be a meteorite landmass somewhere north of Port Augusta. But how can we follow them? My colleagues and I at the Desert Fireball Network (DFN), which monitors incoming asteroids and meteorites, had a few ideas: weather radar and drones.

eyes in space

Finding meteorites is not an easy task. There is a network of high-quality ground-based sensors called the Global Fireball Observatory, but it only covers about 1% of the planet. US satellite data released by NASA covers a much larger area than ground-based detectors, but only picks up the largest fireballs. At most, they don’t always give an accurate picture of the meteor’s trajectory. So, to have any chance of finding a meteorite using this data, you need some outside help.

meteorological radars

In 2019, the Australian Bureau of Meteorology began making weather radar data available to researchers and the public. I saw this as an opportunity to complete the puzzle. The Woomera weather station recorded reflections from falling meteorites. I’ve read the Desert Fireball Network and NASA event logs and cross-referenced with the closest weather radars. Next, I looked for unusual radar signs that might indicate the presence of falling meteorites.

And bingo, the 2013 event took place not far from the Woomera radar station. The weather was clear and the radar showed several small signals in the right place at the right time. Next, I had to use weather data to figure out how the wind would push meteors toward Earth. If I had made the correct calculations, I would have a treasure map showing the location of many meteorites. If I misunderstood them, I would have sent my team to the desert for two weeks to no avail.

Call

I gave my colleague Andy Tomkins at Monash University exactly the treasure map I was hoping for. He happened to pass by Nullarbor on his way back from an expedition in September of this year. Luckily, Andy found the first meteorite within 10 minutes of searching. In the next two hours, his team found nine more.

The technique of searching for meteorites using meteorological radars was introduced in the USA by my colleague Mark Fries. However, this is the first time it has been done outside of the US NEXRAD radar network. (When it comes to airspace monitoring, the US has more powerful and more intense technology than anyone else.)

This initial search confirmed a large number of meteorites on Earth. But how would we find them all?

This is where drones come to the rescue. We used a method developed by my colleague Seamus Anderson to automatically detect meteors from drone images. A machine learning algorithm detected meteors from photographs taken by the drone. Credits: Curtin Uni, courtesy of the author We finally collected 44 meteorites with a total weight of just over 4 kg. Together they form what we call a “seed field.” Fields tell us a lot about how an asteroid decays in our atmosphere.

This is very important to know because the energy of these things is comparable to the energy of a nuclear weapon. For example, the 17-meter asteroid that exploded over the Russian city of Chelyabinsk in 2013 exploded 30 times faster than the bomb dropped on Hiroshima in 1945. Therefore, as the next major hurricane is about to strike, it may be useful to predict how it will project its energy into our atmosphere.

Thanks to new telescopes and better technology, we’re starting to see some asteroids before they hit Earth. We’ll see even more when projects like the Vera Rubin Observatory and the Asteroid Impact Alert System (ATLAS) launch. These systems can tell us that an asteroid is heading towards Earth in a matter of days. It will be too late to make any effort to deflect it, but there will be plenty of time to prepare and control the damage on the ground.

Value of open data

This discovery was only possible thanks to free access to important data and the people who made it available. US satellites that detect the fireball are believed to be designed to detect rocket and missile launches. However, someone (I don’t know who) must have figured out how to broadcast some satellite data without revealing too much about its capabilities, and then lobbied hard to publish the data.

Additionally, the reconnaissance would not have been possible without the work of Joshua Soderholm of the Australian Bureau of Meteorology, who is trying to make low-level weather radar data openly usable for other purposes. Söderholm went far beyond the vague phrases found at the end of scientific articles, such as “data available upon reasonable request”, to make radar data readily available and easy to use. There is no shortage of fireballs to watch. We are currently searching for a meteorite that was detected in space last weekend before it blasted into the sky over Ontario, Canada. Source