The First Radio Signal From An Exoplanet May Have Just Been Detected

An artist's impression of the magnetic field around Tau Boötis b, under the impact of Tau Boötis A's stellar wind. Jack Madden/Cornell University

Of the thousands of planets beyond our Solar System (exoplanets) found since 1992, only a handful have been directly observed. In the rare cases where this has occurred, it has been in visible, or near-visible, wavelengths. Now, however, astronomers have picked up what appear to be radio waves coming from an exoplanet. Before you make an interplanetary-sized jump to conclusions, no this isn't a sign of extraterrestrial intelligence. Still, it could be a significant milestone in the quest to find life beyond the Earth.

To the naked eye, Tau Boötis looks like a very ordinary star one needs to get away from city lights to even see. However, at 51 light-years away and a spectral classification of F, the larger component of this two-star system is one of our nearer neighbors with a strong resemblance to the Sun, although somewhat on the brighter and more massive size. Besides a red dwarf, the system also includes one of the first exoplanets to be discovered, Tau Boötis b, located in 1996.

It is from the direction of this system that Dr Jake Turner of Cornell University helped detect a 14-21 megahertz radio signal using the Low-Frequency Array in the Netherlands. “We make the case for an emission by the planet itself. From the strength and polarization of the radio signal and the planet's magnetic field, it is compatible with theoretical predictions." Turner said in a statement

Turner and co-authors present their findings, and the reasons they think the signal is from Tau Boötis b, in Astronomy and Astrophysics. They argue the circularly polarized nature of the signal, the lack of flare events on Tau Boötis A, and the known nature of the planet all make it much more likely the signal came from the planet rather than the star. If so, it indicates a very strong magnetic field being bombarded by Tau Boötis A's strong stellar wind.

Turner studied Jupiter's radio emissions and scaled what he saw for a planet 40-100 light-years away, in the hope of knowing what to look for. A brief signal was detected from the Upsilon Andromedae system, and nothing at all from 55 Cancri, both potential candidates studied at the same time.

We can be very confident Tau Boötis b does not host life. It's a classic “hot Jupiter” – gas giant exoplanets similar to Jupiter that orbit much closer to their star – six times as massive as our Solar System's largest planet, with a temperature estimated at 1,400ºC (2,600ºF). However, the Earth's magnetic field is very important for life on Earth, having enabled our planet to hold onto its atmosphere by shielding against the solar wind. Without a magnetic field life might not be impossible, but would certainly be constrained. If Turner's work is the introduction to detecting magnetic fields around planets more promising than Tau Boötis b, it could be a big step towards identifying habitable worlds.

The SETI Institute wants to make quite sure you're not misinterpreting this.

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Turner and his supervisor Professor Ray Jayawardhana stress the weakness of the signal means confirmation is required. If this succeeds, however, “This observation opens up a new window on exoplanets, giving us a novel way to examine alien worlds that are tens of light-years away,” Jayawardhana said.

Researchers have, by the way, used radio waves to detect an exoplanet before, but that was very different. GJ1151, a red dwarf 26 light-years away, has a strong magnetic field, which gets disturbed by a planet passing through it, producing radio waves as a result. We know the exoplanet is there because the radio waves can't really be explained any other way, they don't come from the exoplanet itself.

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