What Kind of Extraterrestrial Life Should We Be Searching For? - The Atlantichttps://www.theatlantic.com/science/archive/2022/09/search-for-extraterrestrial-life-aliens/671410/The Case for Technosignatures: Why They May Be Abundant, Long-lived, Highly Detectable, and Unambiguous - IOPsciencehttps://iopscience.iop.org/article/10.3847/2041-8213/ac5824A new study, led by Jason Wright of Penn State University and to which I contributed as part of a NASA-funded technosignature-research group, has laid out the argument that astronomy is overlooking the value of technosignatures. The problem with biosignatures is that they’re forever tied to their biospheres—their planets. Biosignatures have no way to leave their biosphere of origin. And, for that matter, if all life were to disappear from Earth tomorrow, most of Earth’s biosignatures would disappear quickly too. For example, the oxygen in our atmosphere comes from the planet’s life. If that life went extinct, atmospheric oxygen would react back into rocks and disappear quickly on the scale of deep time.
To detect a biosignature, in other words, we have to find a fully functional biosphere. But we don’t really know how long biospheres generally last. Ours has, thankfully, persisted for more than 3 billion years. But there are many ways a biosphere might die, including the loss of the planet’s atmosphere from solar winds or a really big asteroid impact. Once the biosphere goes, the biosignatures likely go with it.
Technosignatures have no such constraint. Consider the fact that the solar system is already full of Earth’s technosignatures. More than 10 spacecraft are orbiting Mars or on its surface right now. And that’s just one planet. Hundreds of other spacecraft are out there traversing the sun’s spaceways. We have even blasted five craft entirely out of the solar system and into the interstellar domain. Every one of these machines we’ve sent into space constitutes a material technosignature—an artifact—in its own right. More important, all of the active ones are sending radio signals into space. These signals are weak, but each still constitutes a technosignature that some other species conceivably could detect.