Magnetic_storms_on_Earth_like_exoplanets_closer_to_their_host_stars.pdf
Creators: name: Donnerer, Julia
Publisher: name: figshare
Year: 2019
Subjects: subject: Astrophysics
subject: 20107 Mesospheric, Ionospheric and Magnetospheric Physics
subject: FOS: Physical sciences
subject: FOS: Physical sciences
subject: Planetary Science
subject: Solar System, Solar Physics, Planets and Exoplanets
subject: Space Science
subject: 20109 Space and Solar Physics

description: Abstract:<br>In order to ﬁnd life on planets in other stellar systems we are looking for exoplanets which are likely to have habitable conditions to enable the evolution of life. Besides the stellar radiation ﬂux, the plasma conditions around an exoplanet should be seen as an additional inﬂuence on habitability. Looking at magnetic disturbances like interplanetary coronal mass ejections (ICME’s), resulting in magnetic storms on Earth, is very important as they temporarily interact with an exoplanet’s magnetic ﬁeld and possibly its atmosphere. Due to this interaction, magnetic storms on Earth-like exoplanets may play a role in deﬁning their habitability, in addition to well-known other factors like the planet’s surface temperature, its orbit or its atmosphere. With that in mind, an ICME event sample of about 165 magnetic ﬂux ropes has been selected from the OMNI2 data set and the Heliospheric Cataloguing, Analysis and Techniques Service (HELCATS) catalogue and has been analysed in this master thesis. Therefore, the magnetic ﬁeld strength, the density, the speed and the duration of the ICMEs have been scaled to heliospheric distances from 0.3 astronomical units (AU) to 0.9 AU in steps of 0.1 AU. Thus, scale values for these diﬀerent heliospheric distances have been created. The scaled data have been used as input for modelling the disturbance storm time (Dst) index, which shows the severity of a magnetic storm. The observed and the scaled magnetic ﬁeld strength and Dst-index have been plotted for an example of a single ICME event, one representative for a solar minimum and the other for a solar maximum. Furthermore, histograms and a ﬁt for the Dst-index distribution have been created. One resulting graph of an ICME at 0.3 AU shows an increased magnetic storm strength by a factor of 8 compared to the same ICME at 1 AU. Although the duration of an ICME closer to the star is shorter, the magnetic ﬁeld strength is much higher, which overrules the eﬀect of the shorter duration and makes the magnetic storm much stronger than at 1 AU. The main motivation of the work presented in this master thesis has been to study the relative importance of these two contributions to Dst. Many exoplanets are located as close as 0.3 AU or even closer to their host stars, so they would be exposed to very severe magnetic storms every few weeks. This would make it harder for them to keep a potential atmosphere over their lifetime, which is exceedingly important for deﬁning their habitability, especially if they orbit around M- or K-type host stars with habitable zones at closer orbit locations. Therefore, the results presented in this master thesis shall help future studies to improve the deﬁnition of the habitability of exoplanets.<br>