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Register a new userTaurid stream #628: a reservoir of large cometary impactors
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Added by
Hadrien Devillepoix
Publication date
2021
fields
Physics
and research's language is
English
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The Desert Fireball Network observed a significant outburst of fireballs belonging to the Southern Taurid Complex of meteor showers between October 27 and November 17, 2015. At the same time, the Cameras for Allsky Meteor Surveillance project detected a distinct population of smaller meteors belonging to the irregular IAU shower #628, the s-Taurids. While this returning outburst was predicted and observed in previous work, the reason for this stream is not yet understood. 2015 was the first year that the stream was precisely observed, providing an opportunity to better understand its nature. We analyse the orbital elements of stream members, and establish a size frequency distribution from millimetre to metre size range. The stream is highly stratified with a large change of entry speed along Earths orbit. We confirm that the meteoroids have orbital periods near the 7:2 mean-motion resonance with Jupiter. The mass distribution of this population is dominated by larger meteoroids, unlike that for the regular Southern Taurid shower. The distribution index is consistent with a gentle collisional fragmentation of weak material. A population of metre-sized objects is identified from satellite observations at a rate consistent with a continuation of the size-frequency distribution established at centimetre size. The observed change of longitude of perihelion among the s-Taurids points to recent (a few centuries ago) activity from fragmentation involving surviving asteroid 2015TX24. This supports a model for the Taurid Complex showers that involves an ongoing fragmentation cascade of comet 2P/Encke siblings following a breakup some 20,000 years ago.
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The measured nitrogen-to-carbon ratio in comets is lower than for the Sun, a discrepancy which could be alleviated if there is an unknown reservoir of nitrogen in comets. The nucleus of comet 67P/Churyumov-Gerasimenko exhibits an unidentified broad spectral reflectance feature around 3.2 micrometers, which is ubiquitous across its surface. On the basis of laboratory experiments, we attribute this absorption band to ammonium salts mixed with dust on the surface. The depth of the band indicates that semivolatile ammonium salts are a substantial reservoir of nitrogen in the comet, potentially dominating over refractory organic matter and more volatile species. Similar absorption features appear in the spectra of some asteroids, implying a compositional link between asteroids, comets, and the parent interstellar cloud.
The TRAPPIST-1 system is unique in that it has a chain of seven terrestrial Earth-like planets located close to or in its habitable zone. In this paper, we study the effect of potential cometary impacts on the TRAPPIST-1 planets and how they would affect the primordial atmospheres of these planets. We consider both atmospheric mass loss and volatile delivery with a view to assessing whether any sort of life has a chance to develop. We ran N-body simulations to investigate the orbital evolution of potential impacting comets, to determine which planets are more likely to be impacted and the distributions of impact velocities. We consider three scenarios that could potentially throw comets into the inner region (i.e within 0.1au where the seven planets are located) from an (as yet undetected) outer belt similar to the Kuiper belt or an Oort cloud: Planet scattering, the Kozai-Lidov mechanism and Galactic tides. For the different scenarios, we quantify, for each planet, how much atmospheric mass is lost and what mass of volatiles can be delivered over the age of the system depending on the mass scattered out of the outer belt. We find that the resulting high velocity impacts can easily destroy the primordial atmospheres of all seven planets, even if the mass scattered from the outer belt is as low as that of the Kuiper belt. However, we find that the atmospheres of the outermost planets f, g and h can also easily be replenished with cometary volatiles (e.g. $sim$ an Earth ocean mass of water could be delivered). These scenarios would thus imply that the atmospheres of these outermost planets could be more massive than those of the innermost planets, and have volatiles-enriched composition.
The Martian Moons Exploration (MMX) spacecraft is a JAXA mission to Mars and its moons Phobos and Deimos. MMX will carry the Circum-Martian Dust Monitor (CMDM) which is a newly developed light-weight ($mathrm{650,g}$) large area ($mathrm{1,m^2}$) dust impact detector. Cometary meteoroid streams (also referred to as trails) exist along the orbits of comets, forming fine structures of the interplanetary dust cloud. The streams consist predominantly of the largest cometary particles (with sizes of approximately $mathrm{100,mu m}$ to 1~cm) which are ejected at low speeds and remain very close to the comet orbit for several revolutions around the Sun. The Interplanetary Meteoroid Environment for eXploration (IMEX) dust streams in space model is a new and recently published universal model for cometary meteoroid streams in the inner Solar System. We use IMEX to study the detection conditions of cometary dust stream particles with CMDM during the MMX mission in the time period 2024 to 2028. The model predicts traverses of 12 cometary meteoroid streams with fluxes of $mathrm{100,mu m}$ and bigger particles of at least $mathrm{10^{-3},m^{-2},day^{-1}}$ during a total time period of approximately 90~days. The highest flux of $mathrm{0.15,m^{-2},day^{-1}}$ is predicted for comet 114P/Wiseman-Skiff in October 2026. With its large detection area and high sensitivity CMDM will be able to detect cometary meteoroid streams en route to Phobos. Our simulation results for the Mars orbital phase of MMX also predict the occurrence of meteor showers in the Martian atmosphere which may be observable from the Martian surface with cameras on board landers or rovers. Finally, the IMEX model can be used to study the impact hazards imposed by meteoroid impacts on to large-area spacecraft structures that will be particularly necessary for crewed deep space missions.
The Earth is impacted by 35-40 metre-scale objects every year. These meteoroids are the low mass end of impactors that can do damage on the ground. Despite this they are very poorly surveyed and characterised, too infrequent for ground based fireball bservation efforts, and too small to be efficiently detected by NEO telescopic surveys whilst still in interplanetary space. We want to evaluate the suitability of different instruments for characterising metre-scale impactors and where they come from. We use data collected over the first 3 years of operation of the continent-scale Desert Fireball Network, and compare results with other published results as well as orbital sensors. We find that although the orbital sensors have the advantage of using the entire planet as collecting area, there are several serious problems with the accuracy of the data, notably the reported velocity vector, which is key to getting an accurate pre-impact orbit and calculating meteorite fall positions. We also outline dynamic range issues that fireball networks face when observing large meteoroid entries.
Context. During their journey to perihelion, comets may appear in the field-of-view of space-borne optical instruments, showing in some cases a nicely developed plasma tail extending from their coma and exhibiting an oscillatory behaviour. Aims. The oscillations of cometary tails may be explained in terms of vortex shedding because of the interaction of the comet with the solar wind streams. Therefore, it is possible to exploit these oscillations in order to infer the value of the Strouhal number $St$, which quantifies the vortex shedding phenomenon, and the physical properties of the local medium. Methods. We used the Heliospheric Imager (HI) data of the Solar TErrestrial Relations Observatory (STEREO) mission to study the oscillations of the tails of the comets 2P/Encke and C/2012 S1 (ISON) during their perihelion in Nov 2013, determining the Strouhal numbers from the estimates of the halo size, the relative speed of the solar wind flow and the period of the oscillations. Results. We found that the estimated Strouhal numbers are very small, and the typical value of $Stsim0.2$ would be extrapolated for size of the halo larger than $sim10^6$ km. Conclusions. Despite the vortex shedding phenomenon has not been unambiguously revealed, the findings suggest that some MHD instability process is responsible for the observed behaviour of cometary tails, which can be exploited for probing the physical conditions of the near-Sun region.
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