Solar system X-rays from charge exchange processes

Summary of the spectral results obtained with Chandrafor all the comets (denoted by A–H) which were observed from2000 to 2006: a ) the 0.3–1.0 keV pulse height distributions, b )theecliptic latitudes and c ) phases in the solar cycle of the observedcomets,and d )thededuced informationaboutthesolarwindheavyion content. Fig.3a,c,d were adapted from Bodewits et al. (2007). rienced a spectacular outburst, which increased its dust andgasoutflowandopticalbrightnessbyalmostamilliontimeswithin hours,from under17 magto 3 mag, makingit by farthe optically brightest comet observable by Chandra sinceits launch. At the time, comet 17P/Holmes was located at asufficiently high heliographic latitude (19 ◦ ) to be exposedto the polar wind at solar minimum. It was thus expectedthat this comet would exhibit considerably different X-rayproperties, and in fact this was observed: 17P/Holmes be-came the first comet where Chandra did not detect any sig-nificant X-ray emission at all (Christian et al. 2010). Themost likely explanation for this dramatic X-ray faintness isthat the polar wind was so diluted and its ionization so lowthat only very little X-ray flux was generated by charge ex-change at energies above∼300eV. An instrumental effect,i.e., a loss of sensitivity, can definitively be ruled out, be-cause only two months later, another comet, 8P/Tuttle, wasobservedwith Chandra,andthiscomet,at lowlatitude (3