Scientists are hard at work considering what kinds of engineering alien probes would need to reach us through interstellar space.

When you hear the phrase “alien probes,” what comes to mind?

Maybe it’s abduction stories from the 1960s, in which alien doctors poke and prod human subjects with surgical tools. Or perhaps you picture something a little more like Oumuamua: a rocky, cigar-shaped “interstellar interloper” that slingshotted around the center of our solar system roughly 15 million miles from Earth back in 2017.

It’s this second type of potential “probe” that has attracted the attention of scientists, including Harvard astronomer Avi Loeb. In addition to suggesting that Oumuamua might have been an alien spaceship, Loeb, who holds a Ph.D. in plasma physics, has also searched the bottom of the ocean for evidence of alien visitors. These ideas, however, are not widely accepted in the greater scientific community.

But that doesn’t mean scientists aren’t actively preparing for the possibility of alien probes to arrive one day—or discovering they’ve already visited. In theory, these probes could be similar to the type of space probes that Earth scientists have already sent out into space, including missions like Voyager and New Horizons. At their core, space probes (of alien or human origin) are scientific instruments sent into space with the goal of collecting information about space or other planets.

However, crossing deep space to reach Earth with a probe would require know-how that Earth scientists have not yet mastered. This is why scientists are hard at work considering what kinds of engineering alien probes would need to reach us through interstellar space, and how we might intercept their communications if or when they arrive.

“Earth has had biosignatures for 3 billion years,” says Adam Frank, Ph.D., a professor of astrophysics at the University of Rochester who has written books on the search for extraterrestrial life. Biosignatures are things like oxygen in our atmosphere or water on our planet that could support the presence of life as we know it. Some signatures can even be detected from space using methods like spectroscopy to “read” the chemistry of a planet’s atmosphere.

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