The Interstellar “Gardener” Comet That May Seed Life

While the world debated elections, artificial intelligence, and coffee prices for the majority of last winter, a tiny object was stealthily passing through the inner solar system at speeds that no machine created by humans could match. It originated somewhere else. Not just another part of our system, but somewhere completely different. A different chemistry, a different planetary nursery, a different star. Then it started to glow in December.

The comet, designated 3I/ATLAS, is just the third interstellar object that has ever been observed passing through our region. The location was ideal for NASA’s SPHEREx telescope, a tiny infrared observatory that was launched in March of last year and wasn’t even designed with comet-chasing in mind. When the device was aimed at the visitor in early December, it detected methanol, methane, cyanide, water vapor, and carbon dioxide, which caused even cautious astronomers to lean forward. With characteristic restraint, scientists refer to these molecules as “the building blocks of life.”

The SPHEREx results could be interpreted as simply a comet acting like a comet. The coma expands into something visible as the sun warms the icy body, the ice sublimates, and gas escapes into space. According to Carey Lisse of Johns Hopkins APL, the measurements fall within the “usual range of early Solar System materials.” Most of his coworkers feel that this is an ordinary, if infrequent, chemistry lesson from a celebrity.

Then there’s Avi Loeb. The Harvard astrophysicist sees something different after years of annoying his colleagues by posing queries they believe to be settled. He suggested that 3I/ATLAS might be the product of what he refers to as a “interstellar gardener”—an advanced civilization purposefully dispersing microbial life throughout the galaxy, much like a person might toss wildflower seeds across a meadow—in a Medium essay published in early December. Panspermia in a technological guise. Loeb is aware that it’s an odd notion. Saying the odd thing first has become a small part of his career.

He wrote that the methane was what made him hesitate. Even though methane evaporates more readily than carbon dioxide, it was still leaking out after the comet had completed its closest dance with the Sun. Perhaps the gas was buried deep and is only now coming to the surface. Or perhaps, and this is where Loeb’s writing becomes cautious, almost playful, it was created by something living, awakening in the sun. He doesn’t assert it. He lifts it. Though it is frequently obscured by headlines, there is a difference.

It makes sense that the majority of astronomers I’ve read about this are not persuaded. There are many non-biological sources of methane. Without the assistance of microbes, cosmic rays bombarding a comet for a billion years can do a great deal of bizarre chemistry. In fact, that’s exactly what Carey Lisse’s team proposes: a radiation-processed crust that fractures under solar heat, releasing chemicals that haven’t seen daylight in eons. That’s also a lovely tale. Simply put, it doesn’t become popular on social media.

Observing the conversation from a distance, I’m struck by how much people want this to have significance. The NASA paper, with its subdued language about sublimation curves and dust grain temperatures, stands awkwardly next to the Reddit threads, the Facebook comments that quote Salvador Dalí, and the channelers who claim to receive transmissions from the rock. Half provocateur, half scientist, Loeb sits between those two worlds, answering emails from strangers who claim the night sky has always called to them. It’s difficult to avoid thinking of the comet as a sort of mirror.

3I/ATLAS is already on its way out by the time you read this. No second pass will be granted. It will continue to move, unconcerned, whether it is a frozen remnant of the birth of another sun, a chemistry experiment that took four billion years to complete, or something completely different. There will be years of debate over the data it left behind. Perhaps longer. Whether or not life intentionally travels between stars is a persistent question. It only ever seems to get deeper.