Possible magnetic field detected on a nearby exoplanet

Astrophysicists have detected a repeating burst of radio waves from a nearby red dwarf, signals that rise and fall in step with a tiny planet named YZ Ceti b orbiting just 12 light-years away.

The pattern points to something scientists have long hoped to find beyond the solar system: evidence of a magnetic field around a rocky exoplanet.

Researchers at the University of Colorado say YZ Ceti b may be interacting with its star in a way that only a magnetic shield can explain. This finding opens a new path for identifying which distant planets can hold on to their atmospheres.

Magnetic fields on YZ Ceti b

Earth is wrapped in a magnetosphere, a bubble of magnetic fields surrounding the exoplanet. This shield steers much of the solar wind away from the atmosphere and limits erosion by charged particles.

Scientists think magnetic cocoons can help rocky planets keep their air, although the details are more complex than one simple rule. Modeling shows solar wind can drive atmospheric loss even when a planet still has a magnetic field.

Planets without strong fields, including Mars, show how harsh star-driven erosion can be. Yet the full picture depends on atmosphere and gravity.

For exoplanets, planets that orbit stars other than the Sun, measuring the field strength is one more missing piece in that complicated puzzle.

Small and tight planetary system

YZ Ceti is a red dwarf, a small, cool star with about one-eighth the Sun’s mass and a much dimmer glow. It burns fuel slowly and can shine for trillions of years, yet it still unleashes frequent flares that blast nearby planets.

Astronomers have found at least three small planets circling YZ Ceti, all packed closer to the star than Mercury is to the Sun. YZ Ceti b is the innermost of the trio and the one now drawing attention because of the radio signal.

Based on subtle wobbles in the star’s motion, YZ Ceti b appears to be a rocky planet about 70 percent of Earth’s mass. It skims so close to the star that its orbit lies at about 0.016 astronomical units.

Magnetism and radio waves

To search for a magnetic field, the team pointed the Karl G. Jansky Very Large Array – a network of 27 linked antennas spread across the New Mexico desert – toward YZ Ceti b over five long observing sessions. 

During those observations, they spotted several short bursts of strongly polarized radio light at frequencies between about 2 and 4 gigahertz. The timing of two bursts lined up closely with YZ Ceti b’s two-day orbit. 

When the first signal appeared in the data, the team noted that the initial burst looked especially clear and striking compared with the surrounding noise.

The team interprets the bursts as possible signs of star-planet interaction, energy released when a planet moves through its star’s magnetic field.

Charged plasma flowing off the star can strike the planet’s magnetic field. That impact can channel energy back, creating radio emission and an aurora on the star.

Extrasolar space weather

The team notes that YZ Ceti offers a window into extrasolar space weather, the storms of radiation and particles that sweep through other planetary systems.

Understanding this harsh environment matters because energetic blasts from small active stars can erode atmospheres and change the chemistry on any nearby worlds.

The bursts seen so far make YZ Ceti b a candidate for a planet with a magnetic field, though the case is not closed. The discovery team notes that similar radio flashes might come from the star’s activity. More data is needed to separate the two possibilities.

Some models suggest that YZ Ceti b orbits in a sub-Alfvenic region, a zone where the stellar wind moves slower than magnetic waves.

In that regime, work finds that magnetic reconnection between planet and star can create radio signals detectable from Earth.

YZ Ceti b is baked by radiation

Even with a strong field, YZ Ceti b’s tight orbit would leave its surface extremely hot and bathed in intense radiation.

A widely read overview concludes that the planet is probably far too hot to be habitable, despite its Earth-like size.

The real promise lies in applying this radio technique to cooler worlds at distances where liquid water and stable climates might be possible.

If astronomers can link similar radio bursts to planets in those regions, they can judge which worlds are shielded from their stars.

For the first time, researchers are measuring the magnetic lives of distant rocky planets instead of guessing them.

That shift turns magnetic fields from a detail into part of understanding which planets keep their air and how they handle stellar storms.

As more sensitive arrays come online, astronomers plan to scan nearby stars for similar signals and build a catalog of planets with measurable fields.

YZ Ceti b is likely the first of many rocky worlds whose invisible magnetic armor may soon show up in radio surveys.

The study is published in Nature.

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