Last Wednesday, at 3:45 pm, scientists from the Breakthrough Listen project trained the Green Bank Telescope in West Virginia on 'Oumuamua—the mysterious, oblong space-rock which last month became the first known object to enter our solar system from elsewhere in the universe—and scanned it for signs of intelligent life.

For six hours, astronomers interrogated the interstellar asteroid. Green Bank swept across four radio bands and billions of individual channels, searching for transmissions as weak as the signal from your cell phone. Signals that could indicate 'Oumuamua is not just a rock but a spacecraft, with aliens—or alien technology—aboard.

By Thursday, astronomers had reported that their initial observations had turned up nothing. (Surprise!) If 'Oumuamua is harboring extraterrestrial stowaways, they're not producing a continuous signal across the frequencies Breakthrough Listen's researchers have monitored thus far. But Listen's scientists may have been onto something: Whether there's life aboard or not, 'Oumuamua kind of has the makings of an interstellar space vehicle.

Today in the journal Nature Astronomy, astronomers report observations that suggest 'Oumuamua is encased in a dry, carbon-rich crust that could have protected a water-ice core from being vaporized as it made a close pass of our sun earlier this year. You can almost think of it as the hull of a spaceship.

Or, if you prefer another analogy: "Basically you have a really nice baked Alaska," says Queen's University astronomer Alan Fitzsimmons, who led the investigation. "A flaming baked Alaska of an object with a rather warm exterior, but with a gooey, icy mixture in the middle."

Now, the researchers can't say definitively that there is ice in 'Oumuamua's middle (let alone extraterrestrial life), but spectral observations performed by Fitzsimmons' team suggest the object could have been icy long, long ago.

Different materials reflect light in different ways. By analyzing the spectrum that an object reflects, astronomers can see how the relative amount of light changes, and search for signatures of certain materials, like metals, rock, and ice.

Fitzsimmons’ team found that 'Oumuamua’s material composition seems to resemble that of objects at the outer edges of our own solar system. Astronomers hypothesize that beyond Jupiter, objects are far enough from the sun to contain a lot of ice—including on their surfaces. Billions of years ago, when the biggest, outer planets were forming, many of those objects were flung outward. Some still orbit our sun at the fringes of our solar system, in a thick bubble of icy debris called the Oort Cloud. Others were probably ejected from our solar system entirely.

If other solar systems formed like ours, it stands to reason that any object flung from such a system would be icy, too. "That's why we think it's more likely to see an interstellar object formed from ice, not rock," Fitzsimmons says. But when ‘Oumuamua passed by our sun, it didn’t behave like an object made of ice.