When you buy through links on our articles, Future and its syndication partners may earn a commission.The SETI Institute’s Allen Telescope Array in Northern California searches for radio signals that could have been generated by intelligent alien life. | Credit: SETI InstituteSETI might not have succeeded in finding alien life yet because space weather around other stars could be disrupting aliens’ attempts to send radio messages out, according to a new study that tries to make sense of why the universe seems so quiet.”Space weather” describes the electromagnetic disturbances produced by gusts of radiation in a stellar wind or coronal mass ejections (CMEs) from a star. These events spew a lot of plasma and electrons into interplanetary space around a star, and plasma and electrons are like kryptonite to coherent radio signals.AdvertisementAdvertisementVarious deleterious effects occur when radio waves interact with a dense patch of charged particles. For example, scientists working in SETI, the search for extraterrestrial intelligence, already factor in the consequences of electron dispersion in the interstellar medium between stars. When a radio wave encounters an electron in interstellar space, lower radio frequencies interact more strongly than higher frequencies, causing the lower frequencies to be delayed and arrive at their destination later than higher frequencies. A broadband signal stuffed with many frequencies would be seriously affected by this dispersion, which is why SETI scientists expect that aliens would be transmitting narrowband signals of fewer frequencies instead.The other reason why SETI looks for narrowband signals, with bandwidths of just a few hertz, is that nothing known in nature produces such a tightly constrained radio signal. So, if we detected one, we’d know it was more than likely artificial.However, until now no one had quantified the effects of plasma and electrons spewed out by activity on stars. If a technological species on a distant exoplanet wanted to beam a message into deep space, the space weather in its home system could negatively affect the characteristics of that signal.”SETI searches are often optimized for extremely narrow signals,” Vishal Gajjar, of the SETI Institute in Mountain View, California, said in a statement. “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.”AdvertisementAdvertisementThe most likely impact of space weather on narrowband radio signals is something called diffractive scintillation. This can cause a signal to become smeared across a much wider range of frequencies when it interacts with plasma from a star. Whereas the initial narrowband signal might have a strong power across just a few frequencies, the smearing spreads that power across more frequencies, reducing the strength of the signal.However, identifying the problem was only the first step. Gajjar and his SETI Institute colleague Grayce Brown wanted to take it one step further and quantify the effect of space weather so that it can become easier to mitigate during SETI searches.To do so, the duo first had to quantify the effect in our own neighborhood, analyzing radio signals between Earth and space missions exploring our solar system. Gajjar and Brown calibrated how fluctuations in the solar wind and bursts from CMEs can affect narrowband signals, and averaged that over time. They then used the example of our sun as a basis for ca …
