Meteorite hunters thought they found an intense fireball origin in Australia, but they were wrong

On 22 August 2016, a fireball appeared in the sky over South Australia. A low, bright meteor. It was one of hundreds of space rocks that plunge into Earth’s atmosphere each year – and are large enough to escape the flames.

Earth is mostly water, so most meteors fall in the middle of the ocean without fanfare. the ones we notice Land on dry land is rare and precious to astronomers. They are fragments of the mysterious atmosphere in that vast dark space between the planets in our solar system…

Desert Fireball Network, a loose organization of Australian scientists centered at Curtin University in Perth, went in search of the August 2016 meteorite we call the meteor’s landing. Noting that the rock orbited the Earth before falling toward the desert, he even gave it a clever nickname: Minimoon.

They finally found it after two years! Festivities were in order. Astronomers can add the 1.2-ounce rock, around the size of a AA battery, to their small but growing collection of recovered meteorites, each a piece of the interplanetary puzzle.

But the party did not last. DFN’s closer inspection of a meteorite found in the orange Australian desert yielded startling findings. It was definitely a rock from space. but it was Wrong Rock from space.

The meteorite DFN, recovered from the sand, inside the projected impact zone of the 2016 fireball, was not the same meteorite that caused the fireball. How Martin Towner, a Curtin University research fellow and DFN operations manager, described the recovered rock to The Daily Beast, is “a rogue meteorite.”

Incredibly, the Australians went looking for a rare space rock and found an unrelated Rare space rock. It is difficult to judge the likelihood of this happening, but the Australian team tried. Spoiler: They are few.

The Desert Fireball Network camped in the middle of the desert while searching for Minimoon.

Martin Kapaki

Now Minimoon Audacity stands as a warning. As astronomers scour the planet for meteorites, they need to be careful to trace the origins of each rock. If they associate a meteorite with the wrong fireball—evidence of a rock’s journey through the atmosphere—they run the risk of drawing incorrect conclusions about the region of space where a meteor originated. They could corrupt the whole field of science.

“This is an important example to show that the fireball-meteorite pairing must be carefully verified,” wrote Towner and other members of the DFN team. a new study,

Calculating the trajectory of the fireball, the DFN team narrowed down the area of ​​impact to an area of ​​about 170 acres. Due to the extreme remoteness of the sphere of influence, it took a few years to organize an expedition: a two-day trip by car from Perth.

“It was nice to find it on the mud poles,” Towner told The Daily Beast, using a term for a clay-rich depression, “but there was a bit of hit and miss on the dunes, with some loose sand that buried things. And there were dense bushes under the trees.

,If they associate a meteorite with the wrong fireball—evidence of a rock’s journey through the atmosphere—they run the risk of drawing incorrect conclusions about the region of space where a meteor originated. They could corrupt the whole field of science.,

A four-person team crawls over the potential impact zone, looking for telltale signs of an extraterrestrial rock. round in shape. Deep in colour. Dense and thus heavy. When they finally found a meteorite, after six days of searching, it was only a hundred yards from where they expected to find one.

Just in case there were more fragments from the same meteor, the team searched for two more days—and found nothing. They went back to their laboratories to analyze the rock. An obvious test was to judge how smooth the meteorite was. The smoother a space rock is, the longer it has gone through a slow, steady process of polishing with wind-blown dirt or sand on Earth.

The DFN team assessed their newly recovered meteorite as only “mildly” weathered. “It could have been tempting to underestimate the degree of weather lightness by two years spent on the ground,” the team wrote in their study, (which appeared online on July 12 and has not yet been reviewed). In other words, the smoothness was consistent with the rock that had recently descended.

Thus scientists had reason to believe that they had found the minimoon. “It sat on the sand, it was roughly the right size, in roughly the right place and it looked so refreshing, and it’s not like you often find meteorites when searching,” Towner said. “So we were very happy at the time!”

Night sky over the Australian desert.

Martin Kapaki

But the next Test shattered his happiness. The DFN team cut, crushed and burned a quarter-gram piece of the meteorite. Using a technique called accelerator mass spectrometry, they bombarded the resulting gas with electrons. Different elements carried different charges, changed their weight and made it possible to separate them.

It’s all very technical, but after careful analysis, the result was that the DFN team could estimate how many rapidly decaying radioactive particles were still in the rock. Some subatomic particles called radionuclides from cobalt and manganese atoms come from space and do not survive long on Earth.

If a meteorite still has these nuclides, it is “fresh”. That is, it has landed in the last one thousand years. If it didn’t have nuclides, it impacted the Earth more than a thousand years ago.

There were no telltale nuclides in the rock. The DFN team estimated that it hit the desert at least 1,900 years ago. In other words, it was not a minimoon. it was completely different The meteorite that just landed in the same area that the minimoon probably did, depending on the latter’s trajectory.

Martin Towner and his DFN allies walk through the desert on foot.

Martin Kapaki

Scientists scrutinized previous investigations and concluded that false fireball-meteorite pairings—where scientists observe a meteor falling, look for it on the ground and find the wrong space rock—are probably rare. As in, 50 meteorite investigations involved strong fireballs even if not more than one.

These misidentifications, although rare, are a big deal. We keep getting better and better at detecting and analyzing fireballs. The US military also tracks them using various sensors and releases data from time to time. most recent releaseThis spring, data from about a thousand fireballs dating back to 1988 were included.

The data — a fireball’s speed, duration, brightness and color — hint at the meteor’s internal structure. The faster the meteor is, the further away from Earth it must have originated. The color, brightness and duration can indicate the mineral composition and size of the meteor.

Finding meteorites on the ground gives scientists a chance to confirm and add to any findings from observing the fireball. Maybe a particularly fiery fireball looks like it actually came from far away—maybe even traveling to Earth beyond the Solar System. Scientists would like to know what minerals make up such a strange, far-flung rock. The implications of planetary formation are deep.

,Scientists would like to know what minerals make up such a strange, far-flung rock. The implications of planetary formation are deep.,

But these comprehensive analyzes of fireball-meteorite pairings only work if space-rock-hunters pair the right fireballs and meteorites. Mismatched fireballs and meteorites, and they can all lead to wrong conclusions.

Because fireballs are rare, and finding an intact meteorite is even rarer, complacency can be established. Scientists look at fireballs, go looking for meteorites, find one in or near the predicted impact zone, and assume the two things are related.

As Australians found out, this is not a safe assumption. There are just so many meteorites on Earth that sometimes scientists go looking for a space rock and accidentally find a different one.

Together, the Minimoon fireball and the unrelated South Australia meteorite are “a cautionary tale”, Towner said. “Just because it looks right and is in the right place isn’t enough — you have to go through a full range of analyzes in the lab wherever possible to confirm that it’s right.”

If you don’t, you may be doing bad science.

There is a consequence in this unlikely story. The minimoon must still be there, somewhere in the Australian desert. “If it landed, it would still be hanging around,” Towner said. “However, little time has passed now, and the fall area has sand dunes and plants that can move or grow in the wind, so it’s likely buried and lost by now.”

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