<p>You usually look for electronic <a href="https://en.wikipedia.org/wiki/Synchrotron_radiation" rel="nofollow noreferrer">synchrotron emission</a> in the radio, which corresponds to the magnetic field strength expected for giant planets. There has been a single detection claimed with LOFAR by <a href="https://www.aanda.org/component/article?access=doi&amp;doi=10.1051/0004-6361/201937201" rel="nofollow noreferrer">Turner et al., (2020)</a> around <span class="math-container">$\tau$</span> Bootes, but it's very noisy and hence disputed.</p>
<p>Other effects like <a href="https://en.wikipedia.org/wiki/Zeeman_splitting" rel="nofollow noreferrer">Zeeman-splitting</a> have been considered for detection, but require clean, high-resolution signals from planets. So far this is too difficult to perform due to stellar contamination.</p>
<p>Magnetic field searches around brown dwarves have been more successful, but those are not planets, of course.</p>

CC BY-SA 4.0
2021-03-12T09:46:54.180Z
2021-03-12T09:46:54.180Z
AtmosphericPrisonEscape
<p>Magnetic fields can be measured via the <a href="https://en.wikipedia.org/wiki/Zeeman_effect" rel="nofollow noreferrer">Zeeman effect</a>, thus a change of absorption and emission lines in spectra - a shift which depends on the direction and the strength of the magnetic field. This is a <a href="https://interestingengineering.com/the-zeeman-effect-that-helps-measure-the-magnetic-field-of-the-sun" rel="nofollow noreferrer">method</a> commonly employed to measure and map the <a href="https://www.aanda.org/articles/aa/pdf/2011/07/aa16767-11.pdf" rel="nofollow noreferrer">magnetic field of the Sun</a> (<a href="https://ui.adsabs.harvard.edu/abs/1997SPD....28.0127H/abstract" rel="nofollow noreferrer">also here</a>).</p>
<p>The difficulty in doing so is the necessary precision in the spectral data of the source and the ambiguity if you sample over a broad area where this effect is also convoluted with the doppler broadening due to mapping areas with different relative speed towards the observer. Generally, getting high-resolution spectral data requires much light or long exposure, both of which can be difficult to obtain for exoplanet atmospheres. I'm not aware of magnetic field measurements on exoplanets so far, yet it might become viable in the future. It is done for stars.</p>

CC BY-SA 4.0
2021-03-12T09:48:48.597Z
2021-03-12T09:48:48.597Z
planetmaker
<p>Of course, we can't fly a magnetometer next to an exoplanet to measure the magnetic field, but might it be possible to find indirect evidence (e.g. polar auroras) of a magnetic field generated by an exoplanet? Has this already been done?</p>

<observational-astronomy><exoplanet><magnetic-field>
Would it be possible to detect a magnetic field around an exoplanet?
usernumber
# Would it be possible to detect a magnetic field around an exoplanet?

(Asked by: username_0 on 2021-03-12)

Of course, we can't fly a magnetometer next to an exoplanet to measure the magnetic field, but might it be possible to find indirect evidence (e.g. polar auroras) of a magnetic field generated by an exoplanet? Has this already been done?

**Tags:** observational-astronomy, exoplanet, magnetic-field

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## 2 answers

### Answer by username_1 on 2021-03-12. Score: 3

You usually look for electronic [synchrotron emission](https://en.wikipedia.org/wiki/Synchrotron_radiation) in the radio, which corresponds to the magnetic field strength expected for giant planets. There has been a single detection claimed with LOFAR by [Turner et al., (2020)](https://www.aanda.org/component/article?access=doi&doi=10.1051/0004-6361/201937201) around $\tau$ Bootes, but it's very noisy and hence disputed.

Other effects like [Zeeman-splitting](https://en.wikipedia.org/wiki/Zeeman_splitting) have been considered for detection, but require clean, high-resolution signals from planets. So far this is too difficult to perform due to stellar contamination.

Magnetic field searches around brown dwarves have been more successful, but those are not planets, of course.


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### Answer by username_2 on 2021-03-12. Score: 2

Magnetic fields can be measured via the [Zeeman effect](https://en.wikipedia.org/wiki/Zeeman_effect), thus a change of absorption and emission lines in spectra - a shift which depends on the direction and the strength of the magnetic field. This is a [method](https://interestingengineering.com/the-zeeman-effect-that-helps-measure-the-magnetic-field-of-the-sun) commonly employed to measure and map the [magnetic field of the Sun](https://www.aanda.org/articles/aa/pdf/2011/07/aa16767-11.pdf) ([also here](https://ui.adsabs.harvard.edu/abs/1997SPD....28.0127H/abstract)).

The difficulty in doing so is the necessary precision in the spectral data of the source and the ambiguity if you sample over a broad area where this effect is also convoluted with the doppler broadening due to mapping areas with different relative speed towards the observer. Generally, getting high-resolution spectral data requires much light or long exposure, both of which can be difficult to obtain for exoplanet atmospheres. I'm not aware of magnetic field measurements on exoplanets so far, yet it might become viable in the future. It is done for stars.


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