Why does a star-planet pair only 12 light-years away emit radio signals?

In October, you can see the constellation of Cetus in the evening sky, visible to the naked eye, above the horizon. You would also likely be looking in the general direction of an alien world called YZ Ceti b which has suddenly become the focus of astronomers.

YZ Ceti b is a rocky Earth-sized exoplanet (a planet that orbits a star other than our sun) orbiting a small red dwarf star, YZ Ceti, just 12 light-years from Earth. Earth, a handshake distance in astronomical terms. Astronomers are excited because they have detected a repeating radio signal from this exoplanet that suggests the presence of a magnetic field – one of the prerequisites for a habitable planet – around it.

How was the discovery made?

The discovery was made by Jackie Villadsen of Bucknell University, Pennsylvania, and Sebastian Pineda of the University of Colorado, Boulder, using the Karl G. Jansky Very Large Array radio telescope in New Mexico. They published their findings in the journal natural astronomy April 3.

They had to perform several rounds of observations before they could detect radio signals from the star YZ Ceti, which appeared to match the orbital period of the planet YZ Ceti b. They deduced that the signals resulted from the interaction between the magnetic field of the planet and the star.

“What we are seeing with these radio detections is the possibility of a star magnetically interacting with its nearby exoplanet,” Dr Pineda said by email to The Hindu.

Why is the magnetic field important?

Just as surges of energy from the sun sometimes disrupt telecommunications on earth and damage orbiting satellites, the intense bursts of energy from the YZ Ceti star-exoplanet exchange produce spectacular auroral lights.

“We can see this indirectly in the form of the radio broadcast we receive,” Dr Pineda said.

These radio waves, powerful enough to be picked up on Earth, confirmed the existence of an exoplanetary magnetic field. Such signals can only be produced if the exoplanet orbits very close to its parent star and has its own magnetic field to influence the stellar wind and generate the signals.

What is the implication for YZ Ceti b?

This is confirmed by the small orbit of YZ Ceti b: astronomers have determined that the planet only takes a few Earth days to orbit its star. By comparison, Mercury, which has the smallest planetary orbit in the solar system, takes just under three Earth months to orbit the sun.

Since the mid-1990s, astronomers have found hundreds of planets orbiting stars similar to the sun, suggesting planet formation in galaxies across the universe is more common than scientists ever imagined. . Data from space science missions such as Kepler, Gaia and the James Webb Space Telescopes suggest the existence of perhaps over 300 billion planets in the Milky Way galaxy alone.

With dozens of exoplanets in the “neighborhood” of the Sun itself, almost half of all visible stars in the sky could potentially harbor rocky Earth-sized planets in habitable orbits around them. To have an atmosphere and retain water, a planet must be at a certain distance from its star (in orbits said to be in the “Goldilocks zone” of the star), otherwise it will be burned up.

Earth, for example, would have looked much more like hot and harsh Venus if it had been just a little closer to the sun – or cold and arid like Mars if it had been further away. Indeed, astronomers believe that nearly 30% of all discovered planet-star systems could potentially have such “Goldilocks Zones”.

What is the frequency of such magnetic fields?

With such overwhelming numbers, it has always made sense that strong planetary magnetic fields are common outside the solar system. Nevertheless, although many of the largest exoplanets detected so far possess magnetic fields, planetary scientists have never been able to identify such fields on smaller, rocky exoplanets – so far.

Dr Pineda stressed that if the latest findings were confirmed by further research, they would “demonstrate the capability of the methodology to lead to the magnetic characterization of exoplanets”.

This is important because the survival of a planet’s atmosphere may depend on whether or not it has a strong magnetic field, since the field protects its atmosphere from erosion by charged particles from its star. “Usually planets this close to their stars are very hot and their atmospheres have probably been eroded over the billions of years of exoplanetary system history,” Dr Pinade agreed.

What happens next?

Curiously, Mars orbiting the sun at a “safe” distance has a similar story to tell: Mars and Earth were very similar billions of years ago, with lots of water, warm oceans, rain and similar atmospheric systems. But despite this, life began on one planet while the other became dry and cold as solar winds stripped it of most of its atmosphere. So is this also the story of YZ Ceti b?

“We hope to get additional observations on this target,” Dr Pinade said. “Longer-term monitoring is important to confirm these results and further investigate the properties of radio signals.” One thing is certain though: these discoveries will help astronomers learn more about the rocky underworlds in the depths of space that run through the rings around their parent stars.

Prakash Chandra is a science writer.

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