Papers by Kathrin Altwegg
<p>Vincent et al. (2016) studied a 3-month period surrounding comet 67P&#82... more <p>Vincent et al. (2016) studied a 3-month period surrounding comet 67P’s perihelion passage in August 2015. They detected and characterized 34 different dust outbursts with the Rosetta cameras. The sudden and brief release of dust of such transient events is characterized by a short lifetime. In their study, Vincent et al. (2016) estimated the source location of the observed outbursts. They were almost entirely on the Southern hemisphere and mostly located close to morphological boundaries of 67P. Thus, a link between morphology and the outbursts is assumed. In addition, these authors also approximated the local time since sunrise on the surface for each outburst event. Their result suggests that outbursts either appeared when the local surface is at its maximum daily temperature and subsurface volatiles produce an outburst, or when the Sun just began to shine onto the surface, thus inducing large temperature gradients and thermal cracking of the surface. In addition, Vincent et al. (2016) proposed that collapsing cliffs are the third mechanism triggering such events. However, the in-situ composition of the dust or gas released by the outbursts has not been studied yet, even though this might largely improve the knowledge about the underlying mechanisms generating such events.</p> <p>In this work, knowing the source locations of the outbursts observed in Vincent et al. (2016), the gas composition in the coma after such events is studied by analysing ROSINA/DFMS mass spectrometry data and possible release mechanisms are discussed. A correlation in terms of angular separation of the sub-spacecraft latitude and longitude and the source location of the dust outburst is needed, as the gas speed is much faster than the observed dust outburst. Furthermore, Rosetta was mostly not directly above the source region during the actual camera observations. Only later or before, as the comet rotated, did Rosetta overfly the source location. Due to this time difference between the observation and the measurement of these dust events and thus the spread of the ejected gas, a distinct field of view needs to be defined in order decide whether the measured gas originated from the outburst source location or not. Consequently, it is possible that several outburst locations overlap with the same peaks in the gas ratios, making it difficult to differentiate a detection. In addition, as the outbursts were very short-lived appearances and thus mostly only detected in one image, the flow direction could not be determined making it impossible to partly decrease the field of view. Thus, a careful evaluation of each peak and its measurement configuration is necessary.</p> <p>Figure 1 shows gas abundance ratios for CO<sub>2</sub>, CO, CH<sub>4</sub>, C<sub>2</sub>H<sub>6</sub>, CH<sub>3</sub>OH, and C<sub>3</sub>H<sub>8</sub> compared to H<sub>2</sub>O for the outburst from 2015-07-26 20:22:42. For all depicted ratios, several peaks were measured at the time Rosetta flew over the outburst source location. This indicates that a larger amount of CO<sub>2</sub>, CO, and different organic species compared to H<sub>2</sub>O has been released by the outburst. It is possible that pockets of these species were buried just below the comet’s surface. Our findings show, that some features are already seen before the observed outburst itself, indicating a possible leakage of such gases creating such an event. Still, it is yet unknown whether these gases were responsible for the outbursts to appear or whether they were just released by the outburst as a by-product.</p> <p><img src="" alt="" width="958" height="675" /></p> <p><strong>References</strong>:</p> <p>Vincent, J.-B. et al., 2016, MNRAS, 462, S184–S194, https://doi.org/10.1093/mnras/stw2409</p>
The Outer Heliosphere: The Next Frontiers, Proceedings of the COSPAR Colloquium, 2001
Astronomy & Astrophysics, 2022
Context. Isotopic abundances in comets are key to understanding and reconstructing the history an... more Context. Isotopic abundances in comets are key to understanding and reconstructing the history and origin of material in the Solar System. Data for deuterium-to-hydrogen (D/H) ratios in water are available for several comets. However, no long-term studies of the D/H ratio in water of a comet during its passage around the Sun have been reported thus far. Linear alkanes are important organic molecules that have been found on several Solar System bodies, including comets. To date, the processes of their deuteration are still poorly understood, only the upper limits of isotopic ratios for D/H and 13C/12C in linear alkanes are currently available. Aims. The aim of this work is to carry out a detailed analysis of the D/H ratio in water as a function of cometary activity and spacecraft location above the nucleus. In addition, a first determination of the D/H and 13C/12C ratios in the first four linear alkanes, namely, methane (CH4), ethane (C2H6), propane (C3H8), and butane (C4H10) in the ...
Astronomy & Astrophysics, 2021
Context. Gas-phase sodium, silicon, potassium, and calcium were previously identified in mass spe... more Context. Gas-phase sodium, silicon, potassium, and calcium were previously identified in mass spectra recorded in the coma of comet 67P/Churyumov-Gerasimenko, the target of the European Space Agency’s Rosetta mission. The major release process for these atoms was identified as sputtering by the solar wind. More recently, remote observations of numerous comets over a range in heliocentric distances revealed the presence of metal atoms of iron and nickel that had been released either from the nucleus or from a distributed source with a short scale length. Sputtering, however, has been dismissed as a major release process due to the attenuation of the solar wind in the comae of some of the observed targets. Aims. We investigated the presence of refractory species in the gas phase of the coma of 67P/Churyumov-Gerasimenko. This investigation includes a period close to perihelion when the solar wind was likely absent from the near-nucleus region due to the increased cometary activity. Add...
<jats:p>&amp;lt;p&amp;gt;Small and volatile molecules are the most abundant constit... more <jats:p>&amp;lt;p&amp;gt;Small and volatile molecules are the most abundant constituents of a comet&amp;amp;#8217;s neutral coma. Thanks to ESA&amp;amp;#8217;s Rosetta mission, the neutral coma of comet 67P/Churyumov-Gerasimenko (67P hereafter) has been analyzed in great spatial and temporal detail, e.g., by Rubin et al. (2019) or by L&amp;amp;#228;uter et al. (2020). However, the Double Focusing Mass Spectrometer (DFMS) &amp;amp;#8211; part of the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA; Balsiger et al. 2007) &amp;amp;#8211; delivered data which contains information about the transition region between volatiles and macromolecular matter. Manual fitting of individual spectra allows to resolve pure hydrocarbon from heteroatom-bearing species also in the higher mass-range of the instrument, up to mass-to-charge (m/z) ratios of 140.&amp;lt;/p&amp;gt; &amp;lt;p&amp;gt;While Altwegg et al. (2019) have reported tentative detections of some heavier species like benzoic acid or naphthalene, spectra of m/z&amp;gt;70 have not been investigated systematically. Here, we will present preliminary results from the first comprehensive analysis of a full data set (from m/z=12 to m/z=140) collected on August 3, 2015. On this day, the comet was close to its perihelion and the dust activity, as seen by the OSIRIS camera (Vincent et al. 2016), was high. Probably due to sublimation of molecules from ejected and heated-up dust grains, ROSINA/DFMS registered many signals above m/z=70. Due to the problem of isomerism and the lack of reference data, we chose to follow a statistical approach for our analysis. Larger species tend to expose a lower degree of saturation and the H/C ratio seems to approach that of highly unsaturated insoluble organic matter (IOM), cf., e.g., Sandford 2008. Although we cannot identify individual molecules in the complex gas mixture that makes up for the cometary coma, we are able to characterize for the first time the larger organic species that bridge the small volatiles and the macromolecular matter observed in 67P&amp;amp;#8217;s dust by the Rosetta secondary ion mass spectrometer COSIMA (Fray et al. 2016).&amp;lt;/p&amp;gt; &amp;lt;p&amp;gt;&amp;amp;#160;&amp;lt;/p&amp;gt; &amp;lt;p&amp;gt;&amp;amp;#160;&amp;lt;/p&amp;gt; &amp;lt;p&amp;gt;&amp;amp;#160;&amp;lt;/p&amp;gt; &amp;lt;p&amp;gt;Altwegg et al., 2019, Annu. Rev. Astron. Astrophys., 57, 113-55.&amp;lt;/p&amp;gt; &amp;lt;p&amp;gt;Balsiger H. et al., 2007, Space Sci. Rev., 128, 745-801.&amp;lt;/p&amp;gt; &amp;lt;p&amp;gt;Fray et al., 2016, Nature, 538, 72-74.&amp;lt;/p&amp;gt; &amp;lt;p&amp;gt;L&amp;amp;#228;uter et al., 2020, MNRAS, 498, 3, 3995-4004.&amp;lt;/p&amp;gt; &amp;lt;p&amp;gt;Rubin et al., 2019, MNRAS, 489, 594-607.&amp;lt;/p&amp;gt; &amp;lt;p&amp;gt;Sandford, 2008, Annu. Rev. Anal. Chem. 1, 549&amp;amp;#8211;78.&amp;lt;/p&amp;gt; &amp;lt;p&amp;gt;Vincent et al., 2016, MNRAS, 462 (Suppl_1), 184-194.&amp;lt;/p&amp;gt;</jats:p>
<p>Rosetta was a mission developed by the European Space Agency aimed at the prolonged stud... more <p>Rosetta was a mission developed by the European Space Agency aimed at the prolonged study of a remnant of the Solar System formation: the Jupiter-family comet 67P/Churyumov-Gerasimenko (hereafter, 67P). After ten years of travel, on 6 August 2014 the Rosetta spacecraft arrived at its target and an observation campaign of almost two years started.</p> <p>The spacecraft was equipped with various instruments designed to analyze cometary dust in 67P's coma, such as the Micro-Imaging Dust Analysis System (MIDAS; Riedler et al. 2007), the Grain Impact Analyzer and Dust Accumulator (GIADA; Colangeli et al. 2007), and the COmetary Secondary Ion Mass Analyser (COSIMA; Kissel et al. 2007). In Pestoni et al. (2021), we demonstrated that, although not designed for this purpose, also the ram gauge (RG) of the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis COmet Pressure Sensor (ROSINA-COPS; Balsiger et al. 2007) may be used to obtain information on the cometary dust, namely its volatile content. This was possible as the RG reported abruptly density increases generated by the sublimation of the ice fraction of cometary particles impacting the instrument.</p> <p>We show that also the second gauge of ROSINA-COPS, the nude gauge (NG, see Figure 1), can obtain information about 67P dust particles (Pestoni et al. 2021, accepted for publication on A&A).</p> <p><img src="data:image/png;base64,…
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The European Space Agency’s Rosetta spacecraft is now close to the comet 67P/Churyumov-Gerasimenk... more The European Space Agency’s Rosetta spacecraft is now close to the comet 67P/Churyumov-Gerasimenko (67P/C-G). On board is the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) instrument suite. ROSINA consists of two mass spectrometers, the Double Focusing Mass Spectrometer (DFMS) and the Reflectron-type Time-Of-Flight (RTOF), as well as the COmet Pressure Sensor (COPS). The first signal with ROSINA/RTOF of the gaseous environment of the comet was a significant increase in water density observed on DOY 218.1 of 2014 (at 3.5 AU) by RTOF above the gaseous envelope of the Rosetta spacecraft. A similar density increase is observed by COPS at the same time. A preliminary analysis shows that the water density is nH2O ≈ 1012 m–3 at 100 km distance from the comet (located at 3.5 AU from the Sun). This gives a density at the surface of nH2O ≈ 6.4·1015 m–3 and a vertical column density of water of NCH2O ≈ 6.5·1018 m–2. Assuming an active area of 4% we arrive at a production r...
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The European Space Agency's Rosetta spacecraft, with the Rosetta Orbiter Spectrometer for Ion and... more The European Space Agency's Rosetta spacecraft, with the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) onboard [1], has been following and observing comet 67P/Churyumov-Gerasimenko (67P/C-G) since August 2014. ROSINA has provided new information on the molecular, elemental, and isotopic composition of 67P/C-G's coma [2,3]. ROSINA consists of a pressure sensor (COPS) and two mass spectrometers, the Double Focusing Mass Spectrometer (DFMS) and the Reflectron Time Of Flight mass spectrometer (RTOF). DFMS has a high mass resolution (ca. 3'000 at 1%) and a high sensitivity, whereas RTOF has a wide mass range (from 1 amu/e to >300 amu/e) and a high temporal resolution. Both mass spectrometers are designed to measure cometary neutral gas as well as cometary ions. In this work, we present the first results and discuss the evolution of the composition of the coma measured by ROSINA from November 2014 until the end of March 2015. During this period, Rosetta delivered the lander, then stayed in bound orbits at distances of 20-30 km away from the comet center, and finally performed comet flybys from 10 km up to 250 km away from 67P/C-G.
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Papers by Kathrin Altwegg