WASP-39b. How to learn more about exoplanet

The planet WASP-39b is a “hot Jupiter”, which has already been studied quite well by researchers. However, the nature of the star’s luminosity does not allow us to accurately determine its parameters, and scientists are already guessing how to overcome this problem. 

Exoplanet WASP-39b. Source: nyuad.nyu.edu

Exoplanet WASP-39b

Recently, scientists from a number of American and European universities conducted a study that would significantly improve the accuracy of assessing conditions on exoplanets. It concerns the famous gas giant WASP-39b, but the results can be used for other similar worlds.

WASP-39b is a “hot Jupiter”, a gas giant with an orbit much closer to its star than Earth or even Mercury is to the Sun. The year there lasts only 4 earth days. The planet is located 700 light years away from us in the constellation Virgo. It is in transit, that is, it passes between us and its luminary.

The latter fact is extremely important, since the passages allow us to accurately determine not only the period of its rotation, but also the diameter and composition of the atmosphere. Scientists already know that there is water vapor, methane and carbon dioxide.

However, it is expected that much more can be learned about this world. That is why the James Webb Space Telescope has been peering into the atmosphere of WASP-39b since the very beginning of its work, that is, for two years now. However, scientists have stumbled upon a problem that hinders these studies.

Star’s light curve and atmosphere of WASP-39b

The basis for determining the physical characteristics of the planet during transit is the study of the light curve of its star. When WASP-39b or any other transit planet passes between us and its luminary, the brightness of the latter decreases according to a certain law, from which it is possible to deduce the characteristics of the solid surface and the atmosphere of what covers it. 

The only problem is that the light curve of the star WASP-39 does not correspond to theoretical models of how this should happen. This is a problem not only for this exoplanet and not only for the James Webb Telescope. The problem is that the limb of the star looks dimmer during an eclipse than it should be.

The limb is the very edge of the stellar disk. In fact, it emits no less energy than the rest of the surface of the sun. However, during the transit of the planet, we see it at a greater angle and therefore observe deeper and colder layers. Because of this, the light curve looks more inclined than it should be and this introduces a large error in all calculations.

Magnetic fields of a star

So far, all attempts to build a theory of the interaction of the star’s limb radiation with the planet’s atmosphere during transit have failed. Therefore, in a new study, scientists decided to deal with this issue in more detail. They assumed that magnetic fields were still an unaccounted element.

They are an integral part of any luminary and permeate its entire plasma. At the same time, they have different intensities for different stars. And this, according to the researchers, determines how much dimmer the limb looks during transit.

The more powerful the magnetic fields of a star, the weaker its limb dims during transit. Scientists have already tested the assumption on data from the Kepler telescope. From 2009 to 2018, it examined thousands of luminaries and these data confirm the correctness of the ideas expressed regarding magnetic fields. Now scientists want to apply the results to the WASP-39 research using the James Webb Telescope.

According to phys.org

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