For the first time, astronomers have detected radio signals coming directly from a planet outside our solar system, according to a new preprint study. Spoiler alert: It's not aliens. But astrophysicists are still very excited about this discovery.
"Astronomers have been looking for radio signals from exoplanets for some time," Suzanne Aigrain, a professor of astrophysics at the University of Oxford who was not involved in the study, told Live Science in an email. "There have been tentative, indirect detections before, but this is the first truly convincing direct detection, and it hopefully paves the way for many more."
Artificial radio signals are a key focus in the search for extraterrestrial intelligence (SETI), which involves scanning the cosmos for signs of alien life. Such "technosignatures" could suggest advanced technologies built by intelligent extraterrestrial civilizations. However, radio signals can be emitted by natural sources, too.
"There are two natural processes that can produce radio emission in exoplanets," Aigrain said. "One is magnetic reconnection, when the planet orbits really close to the star and its magnetic field interacts directly with that of the star. The other is aurorae (like those we have on Earth and on other solar system planets like Saturn, but much stronger), when energetic charged particles streaming from the star interact with the upper atmosphere of the planet."
"This second effect is what the authors of the paper believe they have detected," Aigrain added.
In the study, a research group led by Kevin Ortiz Ceballos, a graduate student at the Harvard and Smithsonian Center for Astrophysics, turned MeerKAT, a radio telescope array in South Africa, toward a massive gas giant called Beta Pictoris b, an exoplanet that's 64 light-years from Earth and has a mass roughly 10 times that of Jupiter, according to NASA. They picked up rapid, repeating bursts of radio signals coming from the planet.
At first, it wasn't clear whether the signal was coming from the planet or the star it orbits (named simply Beta Pictoris). However, after comparing the radio images of both the planet and the star with the positions of distant background quasars (bright, active galaxies that act as fixed reference points), the team confirmed that the radio bursts were indeed emanating from the gas giant.
"No radio detection has previously been unambiguously localized to an extrasolar planet rather than its host star," they wrote in the study, which has not been peer-reviewed yet.
Aigrain emphasized that "this is definitely not aliens!" The signals are consistent with what would be expected from auroras, and this finding offers insight into the planet itself. From these measurements, the team calculated the planet's magnetic-field strength, which they estimated to be roughly 1,250 gauss. For comparison, Jupiter's magnetic-field strength is only about 4.3 gauss and Earth's is a measly 0.5 gauss, according to Live Science's sister site Space.com.
Magnetic-field measurements like these are important because we don't fully understand how planets' magnetospheres are generated and what controls how strong they are, Aigrain said. The ability to measure a planet's magnetic field could also help in our search for potentially habitable exoplanets.
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"[A] planet's magnetic field shields its atmosphere from the 'wind' of charged particles from [its] star, which might otherwise carry material away from the atmosphere," Aigrain said. "On Earth, for example, the magnetic field has played a key role in retaining the atmosphere and shielding life on the planet from harmful high-energy radiation.
"The planet in this paper is quite massive and has a thick atmosphere, so even without a strong magnetic field it could probably hold on to its atmosphere, and it is not expected to host life," Aigrain added. "But in the future we might be able to make similar measurements for smaller planets, for which this shielding effect would be more important."
MeerKAT is a pathfinder instrument for a new large telescope called the Square Kilometre Array, which is expected to come online in the next few years. This observatory "will be significantly more powerful," Aigrain said, "so there will be many more systems where we can look for this type of signal."
