If intelligent aliens are out there, why aren’t we hearing from them? Are they silently observing us like zoo animals, or staying quiet out of fear that they’d catch the attention of a bloodthirsty civilization?
Those are spooky Fermi paradox solutions to contemplate indeed. But if they’re a little too sci-fi for your taste, new research funded by NASA from the SETI Institute provides a physics-based solution to this famous conundrum: bad “space weather.”
The study, published in the The Astrophysical Journal, focuses on how potential extraterrestrial signals being beamed into the cosmos could be scrambled by common astronomical phenomena, like solar storms and plasma turbulence near an alien home world. These volatile events could broaden the narrow frequency of the potential alien signals, spreading them thin across multiple frequencies and making them nearly undetectable to most SETI searches, which focus on narrow bands.
“If a signal gets broadened by its own star’s environment, it can slip below our detection thresholds, even if it’s there, potentially helping explain some of the radio silence we’ve seen in technosignature searches,” study lead author and SETI astronomer Vishal Gajjar said in a statement about the work.
SETI efforts typically focus on narrowbands, which appear as spikes, because these signals aren’t produced by natural phenomena. If a hypothetical alien civilization wanted to be noticed, the thinking went, they’d broadcast a message this way.
But once a signal is sent, it’s at the mercy of the cosmos. It may have to travel thousands if not millions of light years before falling on intelligent ears, during which it could run into countless obstacles. This research, however, focused on the likelihood of aliens encountering uncooperative “space weather” near their planet.
As such, the astronomers studied how radio transmissions between our own spacecraft and Earth are jumbled by solar activity, including the solar wind and the star’s violent outbursts like coronal mass ejections. After quantifying its effects, they extrapolated how it might affect signals coming from systems containing either a Sun-like star or a red dwarf star, the most common type of star in the Milky Way. In simulations, the team found that 70 percent of stars can cause broadening of more than 1 Hz, and 30 percent of stars can broaden signals more than 10 Hz. If in the unlikely possibility that the Sun decides to have a coronal mass ejection during a techosignature observation, the researchers also found, it could broaden signals by more than 1,000 Hz.
The upshot, the researchers say, is that SETI researchers should consider broadening their horizons a little bit, and observe at higher radio frequencies where the broadening is less powerful.
“By quantifying how stellar activity can reshape narrowband signals, we can design searches that are better matched to what actually arrives at Earth, not just what might be transmitted,” said coauthor Grayce C. Brown, a research assistant at the SETI institute, in the statement.
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