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Nilsson, Hans
Publications (2 of 2) Show all publications
Gunell, H., Maggiolo, R., Nilsson, H., Stenberg Wieser, G., Slapak, R., Lindkvist, J., . . . De Keyser, J. (2018). Why an intrinsic magnetic field does not protect a planet against atmospheric escape [Letter to the editor]. Astronomy and Astrophysics, 614, Article ID L3.
Open this publication in new window or tab >>Why an intrinsic magnetic field does not protect a planet against atmospheric escape
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2018 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 614, article id L3Article in journal, Letter (Refereed) Published
Abstract [en]

The presence or absence of a magnetic field determines the nature of how a planet interacts with the solar wind and what paths are available for atmospheric escape. Magnetospheres form both around magnetised planets, such as Earth, and unmagnetised planets, like Mars and Venus, but it has been suggested that magnetised planets are better protected against atmospheric loss. However, the observed mass escape rates from these three planets are similar (in the approximate (0.5–2) kg s−1 range), putting this latter hypothesis into question. Modelling the effects of a planetary magnetic field on the major atmospheric escape processes, we show that the escape rate can be higher for magnetised planets over a wide range of magnetisations due to escape of ions through the polar caps and cusps. Therefore, contrary to what has previously been believed, magnetisation is not a sufficient condition for protecting a planet from atmospheric loss. Estimates of the atmospheric escape rates from exoplanets must therefore address all escape processes and their dependence on the planet’s magnetisation.

Keywords
Planets and satellites: magnetic fields, Planets and satellites: atmospheres, plasmas
National Category
Fusion, Plasma and Space Physics
Research subject
Space and Plasma Physics; Space Physics
Identifiers
urn:nbn:se:umu:diva-148205 (URN)10.1051/0004-6361/201832934 (DOI)000435753000001 ()2-s2.0-85049562755 (Scopus ID)
Available from: 2018-05-30 Created: 2018-05-30 Last updated: 2018-11-26Bibliographically approved
Giang, T., Hamrin, M., Yamauchi, M., Lundin, R., Nilsson, H., Ebihara, Y., . . . McCarthy, M. (2009). Outflowing protons and heavy ions as a source for the sub-keV ringcurrent. Annales Geophysicae, 27(2), 839-849
Open this publication in new window or tab >>Outflowing protons and heavy ions as a source for the sub-keV ringcurrent
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2009 (English)In: Annales Geophysicae, ISSN 0992-7689, E-ISSN 1432-0576, Vol. 27, no 2, p. 839-849Article in journal (Refereed) Published
Abstract [en]

Data from the Cluster CIS instrument have been used for studying proton and heavy ion (O+ and He+ ) char- acteristics of the sub-keV ring current. Thirteen events with dispersed heavy ions (O+ and He+ ) were identified out of two years (2001 and 2002) of Cluster data. Allevents took place during rather geomagnetically quiet periods. Three of those events have been investigated in detail: 21 August 2001, 26 November 2001 and 20 February 2002. These events were chosen from varying magnetic local times (MLT), and they showed different characteristics. In this article, we discuss the potential source for sub-keV ring current ions. We show that: (1) outflows of terrestrialsub-keV ions are supplied to the ring current also during quiet geomagnetic conditions; (2) the composition of the out-flow implies an origin that covers an altitude interval from the low-altitude ionosphere to the plasmasphere, and (3) terrestrial ions are moving upward along magnetic field lines, at times forming narrow collimated beams, but  frequently also as broad beams. Over time, the ion beams are expected to gradually become isotropised as a result of wave-particleinteraction, eventually taking the form of isotropic drifting sub-keV ion signatures. We argue that the sub-keV energy-time dispersed signatures originate from field-aligned terrestrial ion energising and outflow, which may occur at all local times and persist also during quiet times.

Keywords
Magnetospheric physics (Magnetosphere- ionosphere interactions; Magnetospheric configuration and dynamics; Plasma convection)
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:umu:diva-19228 (URN)10.5194/angeo-27-839-2009 (DOI)
Available from: 2009-03-05 Created: 2009-03-05 Last updated: 2018-06-09Bibliographically approved
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