Cometary Origin Research Articles

Evidence for depletion of heavy silicon isotopes at comet 67P/Churyumov-Gerasimenko

Context. The Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) was designed to measure the composition of the gas in the coma of comet 67P/Churyumov-Gerasimenko, the target of the European Space Agency's Rosetta mission. In addition to the volatiles, ROSINA measured refractories sputtered off the comet by the interaction of solar wind protons with the surface of the comet. Aims. The origin of different solar system materials is still heavily debated. Isotopic ratios can be used to distinguish between different reservoirs and investigate processes occurring during the formation of the solar system. Methods. ROSINA consisted of two mass spectrometers and a pressure sensor. In the ROSINA Double Focusing Mass Spectrometer (DFMS), the neutral gas of cometary origin was ionized and then deflected in an electric and a magnetic field that separated the ions based on their mass-to-charge ratio. The DFMS had a high mass resolution, dynamic range, and sensitivity that allowed detection of rare species and the known major volatiles. Results. We measured the relative abundance of all three stable silicon isotopes with the ROSINA instrument on board the Rosetta spacecraft. Furthermore, we measured $^{13}$C/$^{12}$C in C$_2$H$_4$, C$_2$H$_5$, and CO. The DFMS in situ measurements indicate that the average silicon isotopic composition shows depletion in the heavy isotopes $^{29}$Si and $^{30}$Si with respect to $^{28}$Si and solar abundances, while $^{13}$C to $^{12}$C is analytically indistinguishable from bulk planetary and meteorite compositions. Although the origin of the deficiency of the heavy silicon isotopes cannot be explained unambiguously, we discuss mechanisms that could have contributed to the measured depletion of the isotopes $^{29}$Si and $^{30}$Si.

Effect of lighter and heavier pair ions on solitary waves

We investigate solitary waves in a multicomponent plasma of positively and negatively charged lighter and heavier ionsand electrons ofsolar and cometary origin; the electron components are modeled by kappa distributions. The solitary wave solution of the Zakharov-Kuznetsov (ZK) equation is plotted for parameters of comet Halley; physical variables like densities and temperatures of negatively charged lighter ions significantly affect the width and amplitude of the solitary waves.

Comment on “Cometary origin of atmospheric methane variations on Mars unlikely” by Roos‐Serote et al. 2016

Comment on “Cometary origin of atmospheric methane variations on Mars unlikely” by Roos‐Serote et al. 2016

Reply to comment by Fries on “Cometary origin of atmospheric methane variations on Mars unlikely”

Reply to comment by Fries on “Cometary origin of atmospheric methane variations on Mars unlikely”

Stability of the magnetosonic wave in a cometary multi-ion plasma

A generalized dispersion relation of the magnetosonic wave in a four component plasma consisting of electrons and hydrogen ions of solar origin and positively and negatively charged oxygen ions of cometary origin has been derived by using the Vlasov-Maxwell kinetic model. Parallel to the magnetic field, the hydrogen and electron components are modeled by a drifting Maxwellian distribution; perpendicular to the magnetic field, we use a loss cone type distribution obtained by the subtraction of two Maxwellian distributions having different temperatures. The effect of change in the drift velocity of streaming components and number densities and temperatures of each species in driving the instability has been analyzed both analytically and numerically. For typical parameters at comet Halley, we find that both positively and negatively charged oxygen ions can drive the wave unstable.

Spectra and physical properties of Taurid meteoroids

Taurids are an extensive stream of particles produced by comet 2P/Encke, which can be observed mainly in October and November as a series of meteor showers rich in bright fireballs. Several near-Earth asteroids have also been linked with the meteoroid complex, and recently the orbits of two carbonaceous meteorites were proposed to be related to the stream, raising interesting questions about the origin of the complex and the composition of 2P/Encke. Our aim is to investigate the nature and diversity of Taurid meteoroids by studying their spectral, orbital, and physical properties determined from video meteor observations. Here we analyze 33 Taurid meteor spectra captured during the predicted outburst in November 2015 by stations in Slovakia and Chile, including 14 multi-station observations for which the orbital elements, material strength parameters, dynamic pressures, and mineralogical densities were determined. It was found that while orbits of the 2015 Taurids show similarities with several associated asteroids, the obtained spectral and physical characteristics point towards cometary origin with highly heterogeneous content. Observed spectra exhibited large dispersion of iron content and significant Na intensity in all cases. The determined material strengths are typically cometary in the KB classification, while PE criterion is on average close to values characteristic for carbonaceous bodies. The studied meteoroids were found to break up under low dynamic pressures of 0.02–0.10MPa, and were characterized by low mineralogical densities of 1.3–2.5gcm−3. The widest spectral classification of Taurid meteors to date is presented.

Reply to Comment on “A cometary origin for atmospheric martian methane” by Crismani et al., 2017

Reply to Comment on “A cometary origin for atmospheric martian methane” by Crismani et al., 2017

Comment on “A cometary origin for atmospheric martian methane” by Fries et al., 2016

Comment on “A cometary origin for atmospheric martian methane” by Fries et al., 2016

Fast and Slow Mode Solitary Waves in a Five-Component Plasma

We have investigated fast- and slow-mode solitary profiles in a five-component plasma consisting of positively and negatively charged pair ions, hydrogen ions, and hotter and colder electrons. Of these, the heavier ions and colder photoelectrons are of cometary origin while the other components are of solar origin; the electrons are described by kappa distributions. The Zakharov-Kuznetsov (ZK) equation is derived, and solutions for fast- and slow-mode solitary structures are plotted for parameters relevant to comet Halley. We found that the presence of hydrogen ions determines the polarity of the fast- and slow-mode solitary structures. Also, variations of equilibrium number density of hydrogen ions and charge numbers on the heavier pair ions act differently on the fast- and slow-mode solitary structures. The addition of hydrogen ions significantly affects the amplitude of the solitary structures for the fast mode. Further, the cyclotron frequency of the lighter and heavier ions has a noticeable effect on the width of the solitary waves.

Geologic mapping of the Comet 67P/Churyumov–Gerasimenko's Northern hemisphere

OSIRIS, the Scientific Imaging System onboard the Rosetta mission, has been acquiring images of the nucleus of the comet 67P/Churyumov-Gerasimenko since August 2014 with a resolution that allows a detailed analysis of its surface. Indeed, data reveal a complex surface morphology that is likely the expression of different processes that occurred at different times on the cometary nucleus. In order to characterize these different morphologies and better understand their distribution, we performed a geologic mapping of comet's 67P northern hemisphere in which features have been distinguished based on their morphological, textural and stratigraphic characteristics. For this purpose we used NAC images acquired on August and September 2014 with a spatial scale ranging from 1.2 to 2.4 m/pixel. Several different geologic units have been identified on the basis of their different surface textures, granulometry, and morphology. Some of these units are distinctive and localised, whereas others are more common and distributed all over the northern hemisphere. Moreover, different types of linear features have been distinguished on the basis of their morphology. Some of these lineaments have never been observed before on a comet and can offer important clues on the internal structures of the nucleus itself. The geologic mapping results presented here will allow us to better understand the processes that affected the nucleus’ surface and thus the origin and evolutionary history of comet 67P/Churyumov-Gerasimenko.

Variations in cometary dust composition fromGiottotoRosetta, clues to their formation mechanisms

This paper reviews the current knowledge on the composition of cometary dust (ice, minerals and organics) in order to constrain their origin and formation mechanisms. Comets have been investigated by astronomical observations, space missions (Giotto to Rosetta), and by the analysis of cometary dust particles collected on Earth, chondritic porous interplanetary dust particles (CP-IDPs) and ultracarbonaceous Antarctic micrometeorites (UCAMMs). Most ices detected in the dense phases of the interstellar medium (ISM) have been identified in cometary volatiles. However, differences also suggest that cometary ices cannot be completely inherited from the ISM. Cometary minerals are dominated by crystalline Mg-rich silicates, Fe sulphides and glassy phases including GEMS (glass with embedded metals and sulphides). The crystalline nature and refractory composition of a significant fraction of the minerals in comets imply a high temperature formation/processing close to the proto-Sun, resetting a possible presolar signature of these phases. These minerals were further transported up to the external regions of the disc and incorporated in comet nuclei. Cometary matter contains a low abundance of isotopically anomalous minerals directly inherited from the presolar cloud. At least two different kinds of organic matter are found in dust of cometary origin, with low or high nitrogen content. N-poor organic matter is also observed in primitive interplanetary materials (like carbonaceous chondrites) and its origin is debated. The N-rich organic matter is only observed in CP-IDPs and UCAMMs and can be formed by Galactic cosmic ray irradiation of N2- and CH4-rich icy surface at large heliocentric distance beyond a ‘nitrogen snow line’.

Cracking Comet: A Window to the Past

An unusual feature on comet 67P/Churyumov-Gerasimenko offers insights into cometary origins.

Comparison of the structures of meteor streams of cometary and possible asteroidal origin

The structures of the meteor streams of cometary origin—Draconids, Ursids, Perseids, and Lyrids—and the streams presumably connected with asteroids—Taurids and α-Capricornids—are compared. The comparative analysis was performed by the mass distribution of meteoroids in the stream and the activity profile for the meteors with the maximum recorded stellar magnitude +3 m and brighter. Visual observations of 1987–2008 from the database of the International Meteor Organization (IMO) and earlier sources were considered. It has been shown that the structures of the meteor streams of cometary and, presumably, asteroidal origin differ somewhat by the activity profile and the mass distribution of meteoroids in the cross-section of a stream along the Earth’s orbit.

On a possible cometary origin of the object 2015TB145

The Earth-crossing asteroid 2015TB145 was discovered on 10 October 2015 and on 31 October 2015 it already approached close to the Earth at the minimal distance. On the base of obtained radio images of the asteroid, the value of an albedo has estimated as p=0.06. Coming from the albedo value and the comet-like orbit, it was suggested, that the object is a dead comet. In order to verify the supposition, the orbital evolution of 2015TB145 was investigated under the perturbing action of major planets for the time interval of 50 kyrs. As a result, it was found that one cycle of variations of the argument of perihelion is equal to nearly 40 kyrs and during this period the object intersects the Earth's orbit eight times, i.e. it is the octuple crosser. Consequently, if the object has a cometary origin, then it can be associated with a meteoroid stream producing eight meteor showers which should be observable on the Earth. Features of the predicted meteor showers, theoretically associated with 2015TB145, were calculated and a search for observable showers identical to predicted ones was realized using all published catalogues. It turned out, that seven of eight predicted showers were identified with the active observable meteor showers. So, comet-like orbit, low value of an albedo and association with the meteoroid stream producing identified showers are strong evidences pointing that 2015TB145 is really inactive comet. A conclusion was made that the potentially hazardous object 2015TB145 is very likely extinct nucleus of a parent comet of the found meteoroid stream.

Cometary origin of atmospheric methane variations on Mars unlikely

AbstractThe detection of methane in the atmosphere of Mars was first reported in 2004. Since then a number of independent observations of methane have been reported, all showing temporal variability. Up until recently, the origin of methane was attributed to sources either indigenous to Mars or exogenous, where methane is a UV degradation byproduct of organics falling on to the surface. Most recently, a new hypothesis has been proposed that argues that the appearance and variation of methane are correlated with specific meteor events at Mars. Indeed, extraplanetary material can be brought to a planet when it passes through a meteoroid stream left behind by cometary bodies orbiting the Sun. This occurs repeatedly at specific times in a planet's year as streams tend to be fairly stable in space. In this paper, we revisit this latest hypothesis by carrying out a complete analysis of all available data on Mars atmospheric methane, including the very recent data not previously published, together with all published predicted meteor events for Mars. Whether we consider the collection of individual data points and predicted meteor events, whether we apply statistical analysis, or whether we consider different time spans between high methane measurements and the occurrence of meteor events, we find no compelling evidence for any correlation between atmospheric methane and predicted meteor events.

Planetary science: Cometary dust under the microscope.

The Rosetta spacecraft made history by successfully orbiting a comet. Data from the craft now reveal the structure of the comet's dust particles, shedding light on the processes that form planetary systems. See Letter p.73 Mark Bentley et al. report in situ measurements of dust particles at comet 67P/Churyumov–Gerasimenko, obtained using the MIDAS instrument on the Rosetta spacecraft, the first atomic force microscope to be launched into space. The particles are revealed to be aggregates of smaller, elongated grains, with structures at distinct sizes indicating hierarchical aggregation. The dust particles show a variety of morphologies, from compact single grains to large porous aggregate particles, similar to chondritic porous interplanetary dust particles, supporting the suggestion that the latter are of cometary origin.

Characterizing cometary electrons with kappa distributions

AbstractThe Rosetta spacecraft has escorted comet 67P/Churyumov‐Gerasimenko since 6 August 2014 and has offered an unprecedented opportunity to study plasma physics in the coma. We have used this opportunity to make the first characterization of cometary electrons with kappa distributions. Two three‐dimensional kappa functions were fit to the observations, which we interpret as two populations of dense and warm (density = 10 cm−3, temperature = 2 × 105 K, invariant kappa index = 10−>1000), and rarefied and hot (density = 0.005 cm−3, temperature = 5 × 105 K, invariant kappa index = 1–10) electrons. We fit the observations on 30 October 2014 when Rosetta was 20 km from 67P, and 3 AU from the Sun. We repeated the analysis on 15 August 2015 when Rosetta was 300 km from the comet and 1.3 AU from the Sun. Comparing the measurements on both days gives the first comparison of the cometary electron environment between a nearly inactive comet far from the Sun and an active comet near perihelion. We find that the warm population density increased by a factor of 3, while the temperature cooled by a factor of 2, and the invariant kappa index was unaffected. We find that the hot population density increased by a factor of 10, while the temperature and invariant kappa index were unchanged. We conclude that the hot population is likely the solar wind halo electrons in the coma. The warm population is likely of cometary origin, but its mechanism for production is not known.

Weird astronomical theories of the solar system and beyond

After addressing strange cosmological hypotheses in Weird Universe, David Seargent tackles the no-lessbizarre theories closer to home.Alternate views on the Solar System's formation, comet composition, andthe evolution of life on Earth are only some of the topics he addresses in this new work.Although these ideasexist onthe fringe of mainstream astronomy, they can still shed light on the origins of life and the evolution of the planets. Continuing the author's series of bookspopularizingstrange astronomy facts and knowledge, Weird Astronomical Theoriespresents an approachable exploration ofthe still mysterious questions about the origin of comets, the pattern of mass extinctions onEarth, and more.The alternative theories discussed here do not come from untrained amateurs. The scientists whose work iscovered includes the mid-20th century Russian S. K. Vsekhsvyatskii, cosmologist Max Tegmark, Britishastronomers Victor Clube and William Napier, and American Tom Van Flandern, a specialist in celestial mechanics who held a variety of unusual beliefs about the possibility of intelligent life having come from elsewhere. Despite being outliers, their work reveals how much astronomical understanding is still evolving.Unconventional approaches have also pushed our scientific understanding for the better, as with R.W. Mandl's approaching Einstein with regard to gravitational lensing. Even without full substantiation (and some theories are hardly credible), their hypotheses allow for a new perspective onhow the Solar System became what it is today

The end states of long-period comets and the origin of Halley-type comets

We analyze a sample of 73 old long-period comets (LPCs) (orbital periods $200 < P < 1000$ yr) with perihelion distances $q < 2.5$ au, discovered in the period 1850-2014. We cloned the observed comets and also added fictitious LPCs with perihelia in the Jupiter's zone. We consider both a purely dynamical evolution and a physico-dynamical one with different physical lifetimes. We can fit the computed energy distribution of comets with $q < 1.3$ au to the observed one only within the energy range $0.01 < x < 0.04$ au$^{-1}$ (or periods $125 < P < 1000$ yr), where the "energy" is taken as the inverse of the semimajor axis $a$, namely $x \equiv 1/a$. The best results are obtained for physical lifetimes of about 200-300 revolutions (for a comet with a standard $q = 1$ au). We find that neither a purely dynamical evolution, nor a physico-dynamical one can reproduce the long tail of larger binding energies ($x \gsim 0.04$ au$^{-1}$) that correspond to most Halley-type comets (HTCs) and Jupiter-family comets. We conclude that most HTCs are not the end states of the evolution of LPCs, but come from a different source, a flattened one that we identify with the Centaurs that are scattered to the inner planetary region from the trans-Neptunian belt. These results also show that the boundary between LPCs and HTCs should be located at an energy $x \sim 0.04$ au$^{-1}$ ($P \sim 125$ yr), rather than the conventional classical boundary at $P = 200$ yr.

Dawn of small worlds: dwarf planets, asteroids, comets

This book gives a detailed introduction to the thousands and thousands of smaller bodies in the solar system. Written for interested laymen, amateur astronomers and students it describes the nature and origin of asteroids, dwarf planets and comets, and gives detailed information about their role in the solar system. The author nicely reviews the history of small-world-exploration and describes past, current and future space craft missions studying small worlds, and presents their results. Readers will learn that small solar system worlds have a dramatically different nature and appearance than the planets. Even though research activity on small worlds has increased in the recent past many of their properties are still in the dark and need further research