Meteoroids that never reach Earth may hold clues to life's origins

A major new study may help solve a long-standing puzzle in planetary science: why the meteoroids that are most likely to carry the building blocks of life so rarely make it to Earth.

Although carbon-rich asteroids are widespread in our solar system, meteorites containing carbonaceous material represent only a tiny fraction of what we find on the ground.

After analyzing nearly 8,500 fireball events from 39 countries, researchers now believe the Sun and Earth’s atmosphere destroy or weaken meteoroids before scientists can collect and study them.

Meteoroids with life-bearing ingredients

For decades, scientists have puzzled over why fewer carbonaceous meteoroids reach Earth than predicted. Models estimate that over half of all meteoroids are carbon-rich, but only about 4% of meteorites ever recovered on Earth fit that category.

These carbonaceous meteorites are of great scientific interest because they may hold clues to life’s early ingredients.

“Carbon-rich meteorites are some of the most chemically primitive materials we can study – they contain water, organic molecules, and even amino acids,” explained lead author Patrick Shober, an astronomer at the Paris Observatory.

“However, we have so few of them in our meteorite collections that we risk having an incomplete picture of what’s actually out there in space and how the building blocks of life arrived on Earth.”

Only the strongest survive

A two-step filtering process likely causes the scarcity of carbonaceous meteorites on Earth, the new study reveals.

First, many of these meteoroids are exposed to extreme thermal stress as their orbits bring them close to the Sun. Repeated heating and cooling weakens the material, causing it to break apart long before it reaches Earth.

“We’ve long suspected weak, carbonaceous material doesn’t survive atmospheric entry,” said co-author Hadrien Devillepoix, an astronomer at Curtin University. “What this research shows is that many of these meteoroids don’t even make it that far. They break apart from being heated repeatedly as they pass close to the Sun.”

The second layer of filtering happens when meteoroids enter Earth’s atmosphere. Those already weakened by solar heating are far less likely to survive the intense forces of atmospheric entry.

Data show compact, high-strength meteoroids “baked” in orbit are more likely to survive and land intact on Earth. That means what we recover on Earth is not representative of what’s actually out there in space.

Some meteoroids are especially fragile

In addition to the dangers posed by the Sun’s heat and Earth’s atmosphere, the study also found that certain kinds of meteoroids are especially fragile due to gravitational interactions.

When large asteroids pass close to planets, they can be torn apart by tidal forces. The fragments from these disruptions, while potentially abundant, rarely survive the trip to the ground.

The researchers used data from 19 fireball camera networks around the world, spanning continents and hemispheres, to track incoming meteoroids and assess their physical characteristics. In total, they examined 7,982 impacts and 540 likely meteorite falls, making this the most comprehensive study of its kind.

Meteoroids and life on Earth

The implications of these findings go beyond statistics. Carbonaceous meteoroids may have carried water, volatiles, and amino acids – key ingredients for life on early Earth. If most of these are being destroyed before reaching the ground, it means we may be missing a huge part of the story.

“Understanding what gets filtered out, and why, is key to reconstructing our solar system’s history and the conditions that made life possible,” noted Shober.

Their scarcity suggests we may have underestimated their impact simply because we haven’t been able to study them properly.

Shaping future space missions

The study’s conclusions could have far-reaching effects. Future space missions targeting asteroids – especially those involving sample return – may need to reconsider which types to explore.

The findings are also relevant to planetary defense, since understanding how fragile different types of meteoroids are helps to refine models for assessing potential threats from space.

“This finding could influence future asteroid missions, impact hazard assessments and even theories on how Earth got its water and organic compounds to allow life to begin,” said Shober.

This research urges scientists to rethink meteorite interpretations and be cautious about conclusions that are based only on existing collections. The rocks that reach Earth may tell only part of the story.

Now, thanks to fireball networks and large-scale observational data, researchers are beginning to fill in the gaps – revealing how cosmic forces shape not just our skies, but perhaps even the very origins of life itself.

The study was published in the journal Nature Astronomy.

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