The mystery of the super-asteroids.

What you are looking at here is an asteroid—specifically, the asteroid Donald Johanson—and it is absolutely massive. It is 8 kilometers long; imagine Mount Everest, but floating in space. The thing is, this asteroid is actually the remnant of something much larger.

NASA released these images on June 18; they were captured by the Lucy probe. These are real images—not AI-generated. The Lucy probe is designed specifically to study and investigate asteroids, and this was the first one it observed. It measures 8 kilometers in length and holds a fascinating mystery regarding its origins. It consists of fragments that fused together following a violent collision—a cosmic cataclysm—that occurred 155 million years ago. This brings us to a key detail: we aren't talking about the origin of the solar system or events from billions of years ago; we are talking about 155 million years ago. While that is certainly a long time, life already existed on Earth by then. Furthermore, this asteroid isn't located at the fringes of the solar system—it is relatively close by, situated in the main asteroid belt, making it the first one Lucy visited.

The object that was destroyed was much larger, and—here is a second interesting detail—it contained liquid water, at least temporarily. There was enough water to create an environment conducive to the formation of complex organic molecules. While complex organic molecules have been discovered on other asteroids, none have yet been found on this one.

Nor was it the same large object that was destroyed—leaving behind the remnants that formed these two other asteroids, Ryugu and Bennu. Bennu was visited by a NASA spacecraft, while Ryugu was visited by a spacecraft from JAXA, the Japanese space agency. The "giant peanut" must have originally belonged to a massive asteroid—estimated to be between 80 and 100 km in diameter—that contained liquid water at some point, for a period of at least a few thousand years.

As for these two, that is a different story—one involving another very curious cataclysm—because they are the remnants of a much larger object where liquid water existed for at least several million years. How do we know this? Through clues; in these instances, it was because probes landed—the Japanese and American ones—and collected samples that could be analyzed. However, in the case of the "peanut" asteroid—the one named Johanson—the discovery came from analyzing the images taken and conducting a surface analysis that revealed a chemical clue.

It turns out that on this giant body, although clays were present, the iron within them had not been replaced by magnesium. For a chemist, this is a significant clue because it indicates that the process of replacing iron with magnesium in clays requires millions of years in a liquid aqueous environment; the clay must remain wet for that long for the substitution to occur. In this case, however, it was found that while iron and clays were present—and there was plenty of iron—the substitution hadn't happened. This implies that liquid water was indeed present, but only for a short time—a few thousand years at most.

The object that was destroyed to form Ryugu and Bennu is believed to have been at least a protoplanet—an object the size of Ceres, roughly 1,000 km in diameter. It might have resembled Enceladus or Europa, featuring an icy crust with water inside; that is the most straightforward scenario for the early solar system. However, it could also have been a mature, Mars-sized planet. Still, the prevailing theory—following the principle of seeking the simplest explanation—favors the Enceladus-like model: an object 500 to 1,000 km in diameter with an icy crust and an interior containing water.

It seems that during the first few hundred million years of the solar system's existence, there must have been many worlds of that type—a great many. So, the story told by the "giant peanut"—while different, and originating from a distinct source (a smaller object that nevertheless held liquid water)—reveals something curious: these remnants are only 155 million years old. In other words, while the event that gave rise to the other two bodies must have occurred long ago, this particular event happened relatively recently on the solar system's timescale. And consider a cataclysm capable of hurling rocks 8 kilometers in diameter; just imagine—one of those wayward asteroids might well end up striking Earth.

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