Publications
164 results found
Chadney JM, Koskinen TT, Hu X, et al., 2022, Energy deposition in Saturn's equatorial upper atmosphere, Icarus, Vol: 372, Pages: 1-16, ISSN: 0019-1035
We construct Saturn equatorial neutral temperature and density profiles of H, H2, He, and CH4, between 10−12 and 1 bar using measurements from Cassini’s Ion Neutral Mass Spectrometer (INMS) taken during the spacecraft’s final plunge into Saturn’s atmosphere on 15 September 2017, combined with previous deeper atmospheric measurements from the Cassini Composite InfraRed Spectrometer (CIRS) and from the UltraViolet Imaging Spectrograph (UVIS). These neutral profiles are fed into an energy deposition model employing soft X-ray and Extreme UltraViolet (EUV) solar fluxes at a range of spectral resolutions (∆λ = 4×10−3 nm to 1 nm) assembled from TIMED/SEE, from SOHO/SUMER, and from the Whole Heliosphere Interval (WHI) quiet Sun campaign. Our energy deposition model calculates ion production rate profiles through photo-ionisation and electron-impact ionisation processes, as well as rates of photo-dissociation of CH4. The ion reaction rate profiles we determine are important to obtain accurate ion density profiles, meanwhile methane photo-dissociation is key to initiate complex organic chemical processes. We assess the importance of spectral resolution in the energy deposition model by using a high-resolution H2 photo-absorption cross section, which has the effect of producing additional ionisation peaks near 800 km altitude. We find that these peaks are still formed when using low resolution (∆λ = 1 nm) or mid-resolution (∆λ = 0.1 nm) solar spectra, as long as high-resolution cross sections are included in the model.
Matteini L, Laker R, Horbury T, et al., 2021, Solar Orbiter's encounter with the tail of comet C/2019 Y4 (ATLAS): Magnetic field draping and cometary pick-up ion waves, Astronomy and Astrophysics: a European journal, Vol: 656, ISSN: 0004-6361
ontext. Solar Orbiter is expected to have flown close to the tail of comet C/2019 Y4 (ATLAS) during the spacecraft’s first perihelion in June 2020. Models predict a possible crossing of the comet tails by the spacecraft at a distance from the Sun of approximately 0.5 AU.Aims. This study is aimed at identifying possible signatures of the interaction of the solar wind plasma with material released by comet ATLAS, including the detection of draped magnetic field as well as the presence of cometary pick-up ions and of ion-scale waves excited by associated instabilities. This encounter provides us with the first opportunity of addressing such dynamics in the inner Heliosphere and improving our understanding of the plasma interaction between comets and the solar wind.Methods. We analysed data from all in situ instruments on board Solar Orbiter and compared their independent measurements in order to identify and characterize the nature of structures and waves observed in the plasma when the encounter was predicted.Results. We identified a magnetic field structure observed at the start of 4 June, associated with a full magnetic reversal, a local deceleration of the flow and large plasma density, and enhanced dust and energetic ions events. The cross-comparison of all these observations support a possible cometary origin for this structure and suggests the presence of magnetic field draping around some low-field and high-density object. Inside and around this large scale structure, several ion-scale wave-forms are detected that are consistent with small-scale waves and structures generated by cometary pick-up ion instabilities.Conclusions. Solar Orbiter measurements are consistent with the crossing through a magnetic and plasma structure of cometary origin embedded in the ambient solar wind. We suggest that this corresponds to the magnetotail of one of the fragments of comet ATLAS or to a portion of the tail that was previously disconnected and advected past the spacec
Stephenson P, Galand M, Deca J, et al., 2021, Forming a cold electron population at a weakly outgassing comet 
<jats:p>&lt;p&gt;The Rosetta Mission rendezvoused with comet 67P/Churyumov-Gerasimenko in August 2014 and escorted it for two years along its orbit. The Rosetta Plasma Consortium (RPC) was a suite of instruments, which observed the plasma environment at the spacecraft throughout the escort phase. The Mutual Impedance Probe (RPC/MIP; Wattieaux et al, 2020; Gilet et al., 2020) and Langmuir Probe (RPC/LAP; Engelhardt et al., 2018), both part of RPC, measured the presence of a cold electron population within the coma.&lt;/p&gt;&lt;p&gt;Newly born electrons, generated by ionisation of the neutral gas, form a warm population within the coma at ~10eV. Ionisation is either through absorption of extreme ultraviolet photons or through collisions of energetic electrons with the neutral molecules. The cold electron population is formed by cooling the newly born, warm electrons via electron-neutral collisions. Assuming the radial outflow of electrons, the cold population was only expected at comet 67P close to perihelion, where outgassing rate from the nucleus was at its highest (Q &gt; 10&lt;sup&gt;28&lt;/sup&gt; s&lt;sup&gt;-1&lt;/sup&gt;). However, cold electrons were observed until the end of the Rosetta mission at 3.8au when the outgassing was weak (Q&lt;10&lt;sup&gt;26&lt;/sup&gt; s&lt;sup&gt;-1&lt;/sup&gt;). Under the radial outflow assumption, there should not have been sufficient neutral gas to efficiently degrade the electron energies.&lt;/p&gt;&lt;p&gt;We have developed the first 3D collision model of electrons at a comet. Self-consistently calculated electric and magnetic fields from a collisionless and fully-kinetic Particle-in-Cell model (Deca et al., 2017; 2019) are used as a stationary input for the test particle simulations. We model th
Rothkaehl H, Andre N, Auster U, et al., 2021, Dust, Field and Plasma instrument onboard ESA&#8217;s Comet Interceptor &#160;mission&#160;
<jats:p>&lt;p&gt;The main goal of ESA&amp;#8217;s F-1 class Comet Interceptor mission is to characterise, for the first time, a long period comet; preferably a dynamically-new or an interstellar object. The main spacecraft, will have its trajectory outside of the inner coma, whereas two sub-spacecrafts will be targeted inside the inner coma, closer to the nucleus. The flyby of such a comet &amp;#160;will offer unique multipoint measurement opportunity to study the comet's dusty and ionised environment in ways exceeding that of the previous cometary missions, including Rosetta.&lt;br /&gt;&amp;#160;&lt;br /&gt;The Dust Field and Plasma (DFP) instruments located on both the main spacecraft A and on the sub-spacecraft B2, is a combined experiment dedicated to the in situ, multi-point study of the multi-phased ionized and dusty environment in the coma of the target and &amp;#160;its interaction with the surrounding space environment and the Sun.&lt;br /&gt;&amp;#160;&lt;br /&gt;The DFP instruments will be present in different configurations on the Comet Interceptor spacecraft A and B2. To enable the measurements on spacecraft A, the DFP is composed of 5 sensors; Fluxgate magnetometer DFP-FGM-A, Plasma instrument with nanodust and E-field measurements capabilities DFP-COMPLIMENT, Electron spectrometer DFP-LEES, Ion and energetic neutrals spectrometer DFP-SCIENA &amp;#160;and Dust detector DFP-DISC. On board of spacecraft B2 the DFP is composed of 2 sensors: Fluxgate magnetometer DFP-FGM-B2 and Cometary dust detector DFP-DISC.&lt;br /&gt;&amp;#160;&lt;br /&gt;The DFP instrument will measure magnetic field, the electric field, plasma parameters (density, temperature, speed), the distribution functions of electrons, ions and energetic neutrals, spacecraft potential, mass, number and spatial density of c
Galand M, Feldman PD, Bockelee-Morvan D, et al., 2021, Far-ultraviolet aurora identified at comet 67P/Churyumov-Gerasimenko (vol 4, pg 1084, 2020), NATURE ASTRONOMY, ISSN: 2397-3366
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