This October, you can see the constellation of Cetus in the evening sky, visible to the unaided eye, high above the horizon. You would also probably be looking in the general direction of an alien world called YZ Ceti b that has suddenly become the cynosure of astronomers.
YZ Ceti b is a rocky, earth-sized exoplanet (a planet that orbits a star other than our sun) rotating around a small red dwarf star, YZ Ceti, barely 12 light-years from 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 from Bucknell University, Pennsylvania, and Sebastian Pineda from 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 Nature Astronomy on April 3.
They had to make multiple rounds of observations before they could detect the radio signals from the star YZ Ceti, which seemed to match the orbital period of the planet YZ Ceti b. From this, they deduced that the signals were a result of the interaction between the planet’s magnetic field and the star.
“What we are seeing with these radio detections is the possibility of a star interacting magnetically with its close-in exoplanet,” Dr. Pineda said via email to The Hindu.
Why does the magnetic field matter?
Just as energy surges from the sun sometimes disrupt telecommunications on earth and damage orbiting satellites, intense bursts of energy from the YZ Ceti star-exoplanet exchange produce spectacular auroral lights.
“We get to see this indirectly in the form of the radio emission we receive,” Dr. Pineda said.
These radio waves, strong 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’s the implication for YZ Ceti b?
This is borne out by the small orbit of YZ Ceti b: the astronomers determined that the planet takes just a couple of earth days to circle its star. To compare, Mercury, which has the smallest planetary orbit in the solar system, takes a little under three earth-months to go around the sun.
Since the mid-1990s, astronomers have found hundreds of planets orbiting stars similar to the sun, suggesting that planet formation in the universe’s galaxies is more common than scientists ever reckoned. Data from space-science missions such as Kepler, Gaia, and the James Webb space telescopes suggest the existence of possibly more than 300 billion planets in the Milky Way Galaxy alone.
With scores of exoplanets in the Sun’s ‘neighbourhood’ itself, nearly half of all the stars visible in the sky could potentially harbour rocky, earth-sized planets in the habitable orbits around them. To have an atmosphere and sustain water, a planet has to be at a certain distance from its star (in orbits said to be in the star’s “Goldilocks zone”), or it will get burnt.
Earth, for example, would have been a lot more like hot, harsh Venus if it had been just a little closer to the sun – or cold and barren like Mars if it had been any farther. Indeed, astronomers believe nearly 30% of all star-planet systems discovered could potentially have such “Goldilocks zones”.
How common are such magnetic fields?
With such overwhelming numbers, it always stood to reason that strong planetary magnetic fields should be common outside the solar system. Nevertheless, despite many of the larger exoplanets detected thus far being found to possess magnetic fields, planetary scientists have never been able to identify such fields on smaller, rocky exoplanets – until now.
Dr. Pineda pointed out that if the latest findings are confirmed by further research, they “would demonstrate the ability of the methodology to lead towards the magnetic characterisation of exoplanets.”
This is important because the survival of a planet’s atmosphere may well depend on its having, or not having, a strong magnetic field, since the field protects its atmosphere from being eroded by the charged particles blowing in from its star. “Usually, planets this close to their stars are very hot and have likely had their atmospheres eroded away across the billions of years of history of the exoplanetary system,” Dr. Pinade agreed.
What happens next?
Curiously, Mars orbiting the sun at a ‘safe’ distance has a similar story to tell: both Mars and Earth were very much alike billions of years ago, with a lot of water, warm oceans, rain and similar atmospheric systems. But in spite of this, life started on one planet while the other became dry and cold as the solar winds stripped it of most of its atmosphere. So is this the story of YZ Ceti b as well?
“We are hoping 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 the radio signals.” One thing is certain though: these findings will help astronomers learn more about the rocky netherworlds in the deepest reaches of space that run rings around their parent stars.
Prakash Chandra is a science writer.
- Astronomers are excited because they have detected a repeating radio signal from YZ Ceti b – a rocky, earth-sized exoplanet that suggests the presence of a magnetic field – one of the prerequisites for a habitable planet – around it.
- The discovery was made by Jackie Villadsen from Bucknell University, Pennsylvania, and Sebastian Pineda from 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 Nature Astronomy on April 3 .
- This is important because the survival of a planet’s atmosphere may well depend on its having, or not having, a strong magnetic field, since the field protects its atmosphere from being eroded by the charged particles blowing in from its star.
