Using radio waves to discover and study exoplanets | Space

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Artist’s impression of a rocky planet’s atmosphere interacting with the strong magnetic field of its neighboring red dwarf star. This would create auroras in the planet’s atmosphere powerful enough for their radio waves to be detected from Earth. Image via ASTRON.

Exoplanets orbiting distant stars are difficult to detect, but there are several ways to do it. The most popular method is to monitor the dip in light from a star as an exoplanet passes in front of it. Other exoplanets are found via a small shift in a star’s motion through space, caused by the tug of an exoplanet’s gravity. Rarely, some exoplanets are found by direct imaging. There is now another novel technique that scientists are testing: finding aurora radio waves caused by the interaction between a planet and its star, red dwarf stars in particular. And now scientists using this new technique have their first candidate exoplanet.

Using the Low Frequency Array (LOFAR) radio telescope, Dutch scientists have detected unusual radio waves originating from the nearby red dwarf star GJ1151. These radio waves are exactly what you would expect from auroras on a planet, caused by the interaction of the star and a strong magnetic field around a planetary body.

The intriguing peer-reviewed results have been published in Nature on February 17, 2020.

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Harish Vedantham, the lead author of the study and scientist from the Netherlands Institute for Radio Astronomy (ASTRON), said in a statement:

The movement of the planet through the strong magnetic field of a red dwarf acts like an electric motor in the same way a bicycle dynamo works. This generates a huge current that powers auroras and radio emissions on the star.

Basically, the radio waves generated by auroras on a planet could be taken as proof that the planet exists, even if it has not yet been detected by other methods. For this study, these would be planets orbiting red dwarf stars, as they have stronger magnetic fields that could generate auroras strong enough to be detected.

Planet with colored bands and blue-violet spots at top and bottom.
Aurora borealis at the poles of Jupiter on October 2, 2011. This image is a composite of data from the Chandra X-ray Observatory and the Hubble Space Telescope. Similar auroras would be more powerful on planets orbiting close to red dwarf stars and could be detected by their radio waves. Image via NASA/ CXC/ UCL/ W. Dunn et al./ STScI/ Sci-News.

This does not work in our own solar system, because the sun’s magnetic field is weaker and the currents generated in the planets’ atmospheres are therefore not as strong. According to Joe Callingham, co-author of the study:

We have adapted knowledge from decades of radio observations of Jupiter to the case of this star. An enlarged version of Jupiter-Io has long been predicted to exist as a star-planet system, and the emission we observed fits the theory very well.

The researchers now want to examine other red dwarfs for similar emissions. Many exoplanets have already been found orbiting red dwarfs, and red dwarfs are the most common type of star in our galaxy. It therefore stands to reason that many other exoplanets are waiting to be discovered around these stars. According to Callingham:

We now know that almost all red dwarfs host terrestrial planets, so there must be other stars showing similar emission. We want to know how this impacts our search for another Earth around another star.

11 small spheres on a black background with text annotations.
Many planets orbiting near red dwarf stars would likely be uninhabitable due to strong solar radiation. But not at all. The TRAPPIST-1 system has at least seven Earth-sized rocky planets, at least three of which are considered potentially habitable. This illustration compares them (artist’s concepts) to the four rocky planets of our solar system. Image via NASA/JPL-Caltech.

To do this, the researchers will use images from the ongoing northern sky survey called LOFAR Two Meter Sky Survey (LoTSS), also known as LoTSS Wide Area Survey. Study co-author Tim Shimwell said:

With the sensitivity of LOFAR, we expect to find about 100 such systems in the solar neighborhood. LOFAR will be the best game in town for such science until the Square Kilometer Array comes online.

Not only could this be a unique new way to detect exoplanets, but it could also help to better understand the environment of these planets. According to Vedantham:

The long-term goal is to determine the impact of the star’s magnetic activity on the habitability of an exoplanet, and radio emissions are a big piece of that puzzle. Our work has shown this to be viable with the next generation of radio telescopes and sets us on an exciting path.

For many planets orbiting red dwarfs, habitability can be severely compromised. Red dwarfs, with their intense magnetic fields, generate powerful solar radiation, which can pull the atmospheres away from planets that are too close, rendering them uninhabitable, at least on the surface. But not all planets will necessarily suffer this fate, and there should still be planets far enough from their red dwarf stars to avoid this problem, while also not being too much away, possibly allowing them to have liquid water.

Smiling man in a hat with a rock behind him.
Harish Vedantham at ASTRON, lead author of the new study. Image via ASTRON.

The TRAPPIST-1 system is a good example. There are at least seven Earth-sized rocky worlds orbiting this red dwarf, and at least three of them are considered potentially habitable with the possibility of having liquid water on their surface. It will be very interesting to see what a closer study of these worlds reveals.

Detecting planetary auroras by the radio waves they emit will be an exciting new way to find and study exoplanets, including those that may be missed by other methods. Stay tuned!

Conclusion: A study from the Netherlands shows a new way for scientists to detect exoplanets from radio waves generated by auroras on these worlds.

Source: Coherent radio emission from a resting red dwarf indicating star-planet interaction

Via ASTRON

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