Magnetic moment and plasma environment of HD 209458b as determined from Lyα observations

• DOI: 10.1126/science.1257829
• Publication Date: 2014-11-20T19:23:03Z
• Authors: Kristina G. Kisly...; Mats Holmström; Helmut Lammer; Petra Odert; Maxim L. Khodachenko
• Keywords: Exosphere; Line (geometry); Outflow; Radiation Pressure

Transit observations of HD 209458b in the stellar Lyman-α(Lyα) line revealed strong absorption both blue and red wings interpreted as hydrogen atoms escaping from planet's exosphere at high velocities. The following sources for were suggested: acceleration by radiation pressure, natural spectral broadening, or charge exchange with wind. We reproduced observation means modeling that includes all aforementioned processes. Our results support a wind velocity ≈400 kilometers per second time planetary magnetic moment ≈1.6 × 10(26) amperes square meter.