Astronomers have cocked their ears hoping to hear signals from an alien civilization ever since Cornell University astronomer Frank Drake pointed a radio telescope at the stars Tau Ceti and Epsilon Eridani back in 1960. Named Project Ozma after the queen of L. Frank Baum’s fictional land of Oz, a place “very far away, difficult to reach, and populated by strange and exotic beings,” it was the first modern SETI (Search for Extraterrestrial Intelligence) attempt.
Drake trained the 85-foot NRAO radio telescope on the stars for six hours a day from April to July 1960 tuned to 1,420 megahertz (MHz), the frequency of the radio energy given off by cold hydrogen gas floating between the stars. To give you an idea of where that energy is on the radio band, the upper end of commercial FM radio is 108 MHz or 13 times lower in frequency. Astronomers figured that aliens might choose to broadcast a strong signal at and around that frequency, since it penetrates interstellar dust, and would be universally known to technological species throughout the universe as significant.
Fast forward now to August 1977, when radio astronomer Jerry Ehman was looking through data gathered on August 15 from the now-defunct Big Ear radio telescope at Ohio State. Ehman saw mostly static on the printouts until he spotted an unusually strong signal transmitted at 1,420 MHz that lasted all of 72 seconds. Amazed, he whipped out a red pen and scrawled a big “Wow!” on the readout. The burst emanated from near the 5th magnitude star Chi-1 Sagittarii in eastern Sagittarius not far from the globular cluster M55.
Since that time, scientists have been trying to figure out the signal’s origin. All the usual suspects — stars, asteroids and human-caused interference from aircraft or satellites — have been ruled out. A few non-scientists saw it as proof it might possibly be the real thing, a proverbial message in a bottle tossed into the void by extraterrestrials. But as with any fringy proposal, we mustn’t be too hasty.
Last year, a team at the Center of Planetary Science (CPS) suggested that it might originate in the cloud of hydrogen gas that swaddles some comets. Energetic solar UV light breaks down comet water molecules into H2 and O. The H2 forms a huge, distended halo that can expand to many times the size of the Sun (photo below). CPS pointed out that two yet-to-be-discovered comets were in the same part of the sky where the signal was spotted: 335P/Gibbs and 266P/Christensen. Since comets are always on the move, it jived with the fact that the signal was never found again.
From November 2016 through February 2017, the team made 200 observations of the comets to test their hypothesis and found it was correct! The investigation discovered that comet 266/P Christensen emitted a radio signal at 1420.25 MHz while passing through the neighborhood of the “Wow!” signal on its return. No other radio emissions were found within a degree of the comet. To verify their observations, they observed three other comets and got similar results — 40-year-old mystery solved!
Even though Comet Christensen gave off the right frequency in the same general area, the researchers aren’t saying with 100% certainty that this particular comet was the cause, but they’re nearly certain the signal was generated by a comet.
Are you disappointed? Sure, I would have preferred aliens, too, but a natural explanation is always the more likely one … until the day we finally happen on the “unnatural” one. Better to eliminate false positives than live in the land of Oz.