Mysterious radio signal coming from planet outside Solar System for first time

Astronomers detected radio emission from Beta Pictoris b using South Africa's MeerKAT array. The finding gives scientists a direct way to estimate an exoplanet's magnetic field.

In Short

• MeerKAT recorded repeating bursts and steady emission between 0.85 and 3.5 GHz
• Scientists link the emissions to electron cyclotron maser instability in action
• The bursts are interpreted as signs of auroral activity on the planet

Astronomers have detected a mysterious radio signal coming directly from a planet outside our Solar System for the first time, offering scientists a new way to measure the magnetic field of a distant world.

The signal was detected from Beta Pictoris b, a giant exoplanet located about 63 light-years from Earth, using the MeerKAT radio telescope array in South Africa.

Researchers identified rapidly repeating bursts as well as persistent radio emission at frequencies ranging from 0.85 to 3.5 gigahertz.

The study, which reports the first direct detection of auroral radio emission from an exoplanet, provides the first direct measurement of an exoplanetary magnetic field.

The researchers believe the radio emission is produced by a process known as electron cyclotron maser instability, or ECMI. It occurs when energetic electrons interact with a planet's magnetic field and generate intense, organised radio waves.

On Earth and other planets in the Solar System, similar processes are associated with auroras. The researchers therefore interpret the radio bursts from Beta Pictoris b as evidence of an auroral process occurring on the distant planet.

The frequency of the radio emission also provides a crucial clue about the strength of the magnetic field. Based on the highest-frequency emission detected, the researchers estimate that Beta Pictoris b has a magnetic field of at least 1.25 kilogauss, or about 1,250 gauss.

A planet's magnetic field is generated by processes deep inside it and can influence how its atmosphere interacts with radiation and charged particles from its host star. Measuring the field can therefore provide clues about the planet's interior, evolution and interaction with stellar winds.

Auroral radio emissions have previously been observed from planets in our Solar System and from some ultracool dwarfs. However, astronomers had not previously been able to unambiguously localise such emission to an exoplanet rather than its host star.

That localisation is what makes the new observation significant.

The researchers say the detection opens a new avenue for studying magnetic fields on worlds beyond the Solar System. Rather than observing an exoplanet's magnetic field directly, astronomers can potentially use its radio aurora as a natural signal revealing the field's strength.

For Beta Pictoris b, the detection effectively allows astronomers to “listen” to its magnetic environment from 63 light-years away, providing a new window into the physics of distant planetary systems.

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