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Before Rosetta, There Was a Space Peanut
published during a waning gibbous moon.
08/23/2016

Space Peanut

Credit: JAXA

Billions of years ago, a wee asteroid waved goodbye to its parent as it set off for the universe. It drifted toward our planet, where someone noticed it among 15,000 of its rocky brethren.

But this wasn’t just any near-Earth asteroid: This was 25143 Itokawa, more fondly referred by its surname. Its peanut shape looked oddly cobbled together. On one end, it had a smooth finish; on the other, it was bumpy and had a completely different mass.

In other words, its innards weren’t homogenous, and that meant it could contain prized blueprints. Asteroids are on the smaller end of celestial bodies, which allows them to be better preserved — and rich with clues about their (and our) formation.

Space Peanut

A schematic view of the strange peanut-shaped asteroid Itokawa. Credit: ESO/JAXA

And so in the mid-1990s, the Japanese Aerospace Exploration Agency (JAXA) initiated a mission: A small spacecraft named Hayabusa would venture toward the asteroid and nab a sample.

A decade later, the sophisticated Hayabusa gently landed on Itokawa for a half hour. There, it encountered a tense hiccup: The projectiles intended to kick up dust from the surface failed, leaving only microscopic grains from landing for gathering. It lifted off back to Earth, precious particle cargo hopefully in tow, and dropped it in an Australia desert — the first ever successful asteroid sample return mission.

Space Peanut

Credit: JAXA

But one agonizing question remained: Did it even collect anything? Initial scans showed no contents in the capsule, so scientists were forced to wait months while it was dismantled and carefully scrutinized to prevent any contamination.

Finally, joy. About 1,500 particles were confirmed to be from the asteroid.

After combing through them, scientists discovered that some of them appeared to be from Itokawa’s parent, which was about 40 times bigger than Itokawa is currently, JAXA recently revealed in a statement. Other patterns, however, hinted at wear and tear from prolonged exposure to solar wind or friction.

Space Peanut

Asteroid (25143) Itokawa seen in close-up. Credit: JAXA

Itokawa was ultimately deemed a rubble pile, which is when bits of rock cluster back together. That means that the parent was demolished in a collision and then coalesced into the small asteroid, resulting in varying densities and internal imprints.

Some of its microscopic grains are four billion years old — a verifiable fossil with a map of its own chaotic history that can also give insight into ours.

And with hundreds of thousands of other celestial forms, who knows what other family trees we’ll find.