Dynamics of dm-sized Particles in the Coma of Comet 67P/Churyumov&#8211;Gerasimenko
Authors: Pfeifer Marius , Agarwal Jessica , Marschall Raphael 
Published: September 2022

&lt;p&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;During the visit of the European Space Agency&amp;#8217;s &lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;Rosetta&lt;/span&gt; &lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;mission&lt;/span&gt; &lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;to&lt;/span&gt; &lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;comet&lt;/span&gt; &lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;67P/Churyumov-&lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;Gerasimenko,&lt;/span&gt; &lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;the&lt;/span&gt; &lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;Optical,&lt;/span&gt; &lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;Spectroscopic,&lt;/span&gt; &lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;and &lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;Infrared Remote Imaging System (OSIRIS) on the &lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;spacecraft took several image sequences of 67P&amp;#8217;s&lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt; nucleus that highlight its activity against the dark &lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;backdrop of space. Especially during the later phase&lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt; of the mission when 67P was outbound from peri&lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;helion and its activity ceasing, Rosetta was able to &lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;record sequences from less than 100 km away, which &lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;resulted in m-sized resolutions at the distance of the &lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;nucleus. At this distance, thousands of point-source-&lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;like particles can be distinguished from the diffuse &lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;coma.&lt;br /&gt;&lt;/span&gt;&lt;br role=&quot;presentation&quot; /&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;Following Agarwal et al. (2016), who successfully &lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;tracked such particles manually, we developed a fully &lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;automated tracking algorithm (Pfeifer et al. 2021) &lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;which we have now applied to several datasets and per&lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;formed an in-depth analysis of the results.&lt;/span&gt;&lt;/p&gt;
&lt;p&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;We for example selected sub-sets of particles and &lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;extrapolated their 2D-trajectories in the image plane &lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;back in time to relatively confined areas on the nu&lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;cleus. Assuming that the particles originated from the &lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;identified location and that they have not moved too &lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;far away from it, we can estimate their distance to the &lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;spacecraft and thus their (projected) dynamics and size &lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;distributions. &lt;br /&gt;&lt;br /&gt;&lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;In particular, we can compare the measured acceler&lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;ations to a (simplified) version of the particle&amp;#8217;s equa&lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;tion of motion:&lt;/span&gt;&lt;/p&gt;
&lt;p&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;&lt;img src=&quot;https://pad.gwdg.de/uploads/1efe89c62a34c072ef266dcfe.png&quot; width=&quot;1000&quot; height=&quot;&quot; /&gt;&lt;/span&gt;&lt;/p&gt;
&lt;p&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;where &amp;#8407;&lt;em&gt;a&lt;/em&gt; is the particle acceleration, &lt;em&gt;m&lt;/em&gt;&lt;sub&gt;p&lt;/sub&gt;, the particle mass, &amp;#8407; &lt;em&gt;F&lt;/em&gt;&lt;sub&gt;G&lt;/sub&gt; the nucleus gravity, &amp;#8407; &lt;em&gt;F&lt;/em&gt;&lt;sub&gt;D&lt;/sub&gt; the gas drag, &lt;em&gt;G &lt;/em&gt;the gravitational constant, &lt;em&gt;M &lt;/em&gt;the nucleus mass, &lt;em&gt;d &lt;/em&gt;the particle-nucleus distance, &amp;#8407;&lt;em&gt;n&lt;/em&gt;&lt;sub&gt;G&lt;/sub&gt; the gravity unit vector, &lt;em&gt;C&lt;/em&gt;&lt;sub&gt;D&lt;/sub&gt; the drag coefficient, &lt;em&gt;m&lt;/em&gt;&lt;sub&gt;g&lt;/sub&gt; the mass of a water molecule,&lt;em&gt; n&lt;/em&gt;&lt;sub&gt;g&lt;/sub&gt; the gas number density, &lt;em&gt;&amp;#961;&lt;/em&gt;&lt;sub&gt;p&lt;/sub&gt; the particle density, &amp;#8407;&lt;em&gt;v&lt;/em&gt;&lt;sub&gt;g&lt;/sub&gt; the gas and &amp;#8407;&lt;em&gt;v&lt;/em&gt;&lt;sub&gt;p&lt;/sub&gt; the particle velocity, and &lt;em&gt;r&lt;/em&gt; the particle radius. By fitting this equation to our data we try to constrain the parameters that go into it.&lt;br /&gt;&lt;br role=&quot;presentation&quot; /&gt;We present our latest results from tracking mostly dm-sized particles that were recorded by OSIRIS near the surface of comet 67P in December 2015 and January 2016. While the particle dynamics themselves already present new information, the properties that we can derive from them also help us to better understand the gas flow and other circumstances at the time of the observed activity.&lt;br /&gt;&lt;/span&gt;&lt;/p&gt;
&lt;p&gt;&amp;#160;&lt;/p&gt;
&lt;p&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;&lt;br /&gt;&lt;strong&gt;Acknowledgements&lt;/strong&gt;&lt;/span&gt;&lt;/p&gt;
&lt;p&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;&lt;br role=&quot;presentation&quot; /&gt;We acknowledge the operation and calibration team at MPS and the Principal Investigator Holger Sierks on behalf of the OSIRIS Team for providing the OSIRIS images and related datasets. OSIRIS was built by a consortium of the Max-Planck-Institut f&amp;#252;r Sonnensystemforschung, G&amp;#246;ttingen, Germany; the CISAS University of Padova, Italy; the Laboratoire d&amp;#8217;Astrophysique de Marseille, France; the Instituto de Astrof&amp;#237;sica de Andalucia, CSIC, Granada, Spain; the Research and Scientific Support Department of the European Space Agency, Noordwijk, The Nether- lands; the Instituto Nacional de T&amp;#233;cnica Aeroespacial, Madrid, Spain; the Universidad Polit&amp;#233;chnica de Madrid, Spain; the Department of Physics and Astronomy of Uppsala University, Sweden; and the Institut f&amp;#252;r Datentechnik und Kommunikationsnetze der Technischen Universit&amp;#228;t Braunschweig, Germany. The support of the national funding agencies of Germany (DLR), France (CNES), Italy (ASI), Spain (MEC), Sweden (SNSB), and the ESA Technical Directorate is gratefully acknowledged. We thank the Rosetta Sci&lt;/span&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;ence Ground Segment at ESAC, the Rosetta Missions Operations Centre at ESOC and the Rosetta Project at ESTEC for their outstanding work enabling the science return of the Rosetta Mission.&lt;br role=&quot;presentation&quot; /&gt;MP and JA acknowledge funding by the ERC Starting Grant No. 757390 Comet and Asteroid Re-Shaping through Activity (CAstRA). JA acknowledges funding by the Volkswagen Foundation.&lt;/span&gt;&lt;/p&gt;
&lt;p&gt;&amp;#160;&lt;/p&gt;
&lt;p&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;&lt;strong&gt;References&lt;/strong&gt;&lt;/span&gt;&lt;/p&gt;
&lt;p&gt;&lt;span dir=&quot;ltr&quot; role=&quot;presentation&quot;&gt;&lt;br role=&quot;presentation&quot; /&gt;Agarwal, J., A&amp;#8217;Hearn, M. F., Vincent, J.-B., et al. 2016, MNRAS, 462, S78&lt;br role=&quot;presentation&quot; /&gt;Pfeifer, Marius, Agarwal, Jessica, &amp; Schr&amp;#246;ter, Matthias. 2022, A&amp;A, 659, A171&lt;br /&gt;&lt;/span&gt;&lt;/p&gt;