On Some Magnetohydrodynamic Effects in Comets
General pattern of magnetic field-carrying solar wind flow past comet
Ioffe, Z. M.↗
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The visual appearance of comets under varying solar wind conditions
Three-dimensional MHD simulations have been performed for four different sets of solar wind conditions and cometary outgassing rates appropriate to the Halley encounters. Even though the simulations are single fluid calculations, it is possible to separate the solar wind and cometary ions using the divergenceless nature of the solar wind ions. The cometary ion density is then integrated along the line-of-sight from the observer through the comet to determine how the comet would look to a distant observer under these different conditions. In general, comet tails appear longer when the interplanetary magnetic field lies in the plane of the sky rather than along the line-of-sight. Also, the tail shrinks as the speed of the solar wind increases and/or the mass loading rate decreases.
Russell, C. T.↗
Cometary spectroscopy
The spectroscopic and morphological characteristics of comets over a wide range of heliocentric distances are investigated as they may suggest or constrain models of cometary formation environments and evolution. This program also contributes to the understanding of the general comet population with which spacecraft data will be compared. Long slit spectra and direct images of all observable comets (M2<18) are obtained on a monthly basis with either a UV sensitive microchannel plate or a red sensitive CCD spectrograph/camera. Scale lengths of the principal emission of OH, NH, CN, C3, C2, NH2 and OI different comets can be compared. The direct images are used for studies of dust anisotropy which can provide data on the spin vector and gross surface morphology.
Larson, S.↗
TEX-HEU: Integral Experiments with Highly Enriched Uranium and Polyethylene (IER-297 CED-3b Report)
This report documents the experimental critical configurations and measurements for IER-297, Thermal/Epithermal eXperiments (TEX) using highly enriched uranium (HEU) fuel, moderated and reflected by polyethylene. These experiments establish the baseline TEX-HEU configurations spanning thermal, intermediate, and fast fission energy regimes. The experiment campaign was completed in FY2020 at the National Critical Experiments Research Center at the Nevada National Security Site. The campaign produced six documented critical configurations (0”, ¹/₈” A, ¹/₈” B, ¹/₄”, ¹/₂”, and 1¹/₂”) and one reproducibility measurement (¹/₈” R). Table 1 summarizes these seven experiments along with their period and calculated reactivity, in order of execution. The Comet General Purpose Critical Assembly Machine was used to conduct the TEX-HEU experiments. The HEU fuel consists of U(93+) plates, collectively known as the “Jemima” plates. Each experiment consisted of an alternating stack of these HEU plates with or without polyethylene moderator plates. By varying the thicknesses of the polyethylene plates, the neutron spectrum of the experiment could be fine-tuned to a specific fission energy regime. The experiments were reflected by 1” of polyethylene consisting of a bottom and top plate and outer reflector rings to surround the HEU and polyethylene plates. The fine reactivity control of the system was provided by the thickness of the top reflector plate, which could be varied in increments of ¹/₃₂”.
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
IUE observations of the evolution of Comet Wilson (1986l) - Comparison with P/Halley
IUE observations of Comet Wilson from September 1986 to November 1987, through perihelion, allow a comparison to be conducted between this 'new' comet and the highly evolved P/Halley, at comparable heliocentric distances. The temporal decreases of both OH and dust in Comet Wilson near perihelion were monotonic and slow, by contrast to Comet Halley's rapid fluctuations. Despite these differences, relative gas abundances were similar within a factor of about 2 for comparable heliocentric and geocentric distances; this indicates that P/Halley's in situ gas measurements may be typical of comets generally.
Roettger, E. E.↗
A new activity index for comets
An activity index, AI, is derived from observational data to measure the increase of activity in magnitudes for comets when brightest near perihelion as compared to their inactive reflective brightness at great solar distances. Because the observational data are still instrumentally limited in the latter case and because many comets carry particulate clouds about them at great solar distances, the application of the activity index is still limited. A tentative application is made for the comets observed by Max Beyer over a period of nearly 40 years, providing a uniform magnitude system for the near-perihelion observations. In all, 32 determinations are made for long-period (L-P) comets and 15 for short-period (S-P). Although the correlations are scarcely definitive, the data suggest that the faintest comets are just as active as the brightest and that the S-P comets are almost as active as those with periods (P) exceeding 10(exp 4) years or those with orbital inclinations of i less than 120 deg. Comets in the range 10(exp 2) less than P less than 10(exp 4) yr. or with i greater than 120 deg appear to be somewhat more active than the others. There is no evidence to suggest aging among the L-P comets or to suggest other than a common nature for comets generally.
Whipple, Fred L.↗
Dynamics of the Trans-Neptune Region: Apsidal Waves in the Kuiper Belt
The role of apsidal density waves propagating in a primordial trans-Neptune disk (i.e., Kuiper belt) is investigated. It is shown that Neptune launches apsidal waves at its secular resonance near 40 AU that propagate radially outward, deeper into the particle disk. The wavelength of apsidal waves is considerably longer than waves that might be launched at Lindblad resonances, because the pattern speed, g(sub s), resulting from the apsis precession of Neptune is much slower than its mean motion, Omega(sub s). If the early Kuiper belt had a sufficient surface density, sigma, the disk's wave response to Neptune's secular perturbation would have spread the disturbing torque radially over a collective scale lambda(sub *) approx. = r(2(mu)(sub d)Omega/ absolute value of r dg/dr)(sup 1/2), where mu(sub d)equivalent pi(sigma)r(exp 2)/(1 solar mass) and Omega(r) and g(r) are respectively the mean motion and precession frequency of the disk particles. This results in considerably smaller eccentricities at resonance than had the disk particles been treated as noninteracting test particles. Consequently, particles are less apt to be excited into planet-crossing orbits, implying that the erosion timescales reported by earlier test-particle simulations of the Kuiper belt may be underestimated. It is also shown that the torque the disk exerts upon the planet (due to its gravitational attraction for the disk's spiral wave pattern) damps the planet's eccentricity and further inhibits the planet's ability to erode the disk. Key words: celestial mechanics, stellar dynamics - comets: general minor planets, asteroids
Ward, William R.↗
Catastrophic Disruption of Comet ISON
We report submillimeter 450 and 850 microns dust continuum observations for comet C/2012 S1 (ISON) obtained at heliocentric distances 0.31-0.08 au prior to perihelion on 2013 November 28 (rh=0.0125 au). These observations reveal a rapidly varying dust environment in which the dust emission was initially point-like. As ISON approached perihelion, the continuum emission became an elongated dust column spread out over as much as 60″ (greater than 10(exp 5) km in the anti-solar direction. Deconvolution of the November 28.04 850 microns image reveals numerous distinct clumps consistent with the catastrophic disruption of comet ISON, producing approximately 5.2×10(exp 10) kg of submillimeter-sized dust. Orbital computations suggest that the SCUBA-2 emission peak coincides with the cometʼs residual nucleus.
comets: individual↗
Electron plasma environment at comet Grigg-Skjellerup: General observations and comparison with the environment at comet Halley
The three-dimensional electron spectrometer of the Reme plasma analyzer-complete positive ion, electron and ram negative ion measurements near comet Halley (RPA-COPERNIC) experiment aboard the Giotto spacecraft, although damaged during the comet Halley encounter in March 1986, has provided very new results during the encounter on July 10, 1992, with the weakly active comet Grigg-Skjellerup (G-S). The main characteristic features of the highly structured interaction region extending from approximately 26,500 km inbound to approximately 37,200 km outbound are presented. These results are compared to the results obtained by the same instrument during the Giotto comet Halley fly-by. Despite the large difference in the size of the interaction regions (approximately 60,000 km for G-S, approximately 2000,000 km for Halley) due to 2 orders of magnitude difference in cometary neutral gas production rate, there are striking similarities in the solar wind interactions with the two comets.
Reme, H.↗
Radio observations of comets
Three general techniques of radio science used to attempt to observe comets are discussed: spectral line, continum and radar observations. Of these, only radio spectral line observations achieved a degree of success but, more often than not, the results was negative. Cometary excitation and reasons why radio searches can fail were examined.
Snyder, L. E.↗
Carbonate in Comets: A Comparison of Comets 1P/Halley, 9P/Temple 1, and 81P/Wild 2
Comets are generally believed to have formed in a cold region, trapping in the cometary ices the original low-temperature condensate grains of our Solar System. These grains would have been preserved in cold-storage, at a temperature below the freezing point of CO2, for the last 4.5+ billion years. Carbonates are common in hydrous meteorites and hydrous interplanetary dust particles (IDPs), where they are believed to have formed by parent-body aqueous processing. Since simple models of cometary evolution involve no aqueous processing, carbonates were generally presumed not to occur in comets. However, Toppani et al. [1] have performed experiments that indicate carbonate can be formed by non-equilibrium condensation in circumstellar environments where water is present as a vapor, not as a liquid. This suggests carbonate might have condensed in cold regions of the Solar Nebula, and might be present in comets.
Flynn, G. J.↗
Monitoring of asteroids in cometary orbits and activated asteroids through archival images and new observations
Transitional objects are minor bodies that share some characteristics with asteroids and others with comets. These objects include asteroids in cometary orbits (ACOs), which behave dynamically like comets, but lack observed activity, while activated asteroids (AAs) follow typical asteroidal orbits, but have shown dust ejections. The monitoring of a set of these objects carried out in 2015 and 2016 is continued using archival images from various observatories and new data from the IMPACTON telescope in Brazil. Two techniques were applied to detect activity: (i) surface brightness profiles were compared with those of field stars to identify widening, and (ii) the magnitudes reported in the Minor Planet Center, combined with our observations, were reduced and analyzed to identify abrupt brightness increases as a function of heliocentric distance. We analyzed the surface brightness profiles of 133 ACOs and 7 AAs. To study the reduced magnitude, we obtained data from the 705 ACOs that were known at the time of the analysis. Together with the data from our previous work, our analysis covered 23% of the total known ACOs; 8 deviated slightly in the surface brightness profile, 6 brightened in the reduced magnitude, and one object is in common in both samples. A very low percentage of objects might show activity (4% of the sample with brightness profiles and <1% in the reduced magnitudes). These results would rule out a slow transition from active to inert. Regarding AAs, 4 showed activity, and 3 of them matched previously reported periods, while the data we analyzed for P/2015 X 6 were obtained 19 days before the first existing activity report. The activity episodes of these objects are very restricted in time and do not always occur in the same region of the orbit.
asteroids: general↗
General features of the Comet Halley-solar wind interaction from plasma measurements
The Giotto Complete Positive ion, Electron and Ram Negative Ion measurements near Comet Halley plasma experiment identified regions in which the solar wind interaction with the cometary plasma displayed characteristic features. Beginning 4.6 million km from the comet there is an upstream region with sporadic connection to the comet. An electron foreshock is present up to 250,000 km away from the bow shock. A bow shock is detected at 1.15 million km. Between the bow shock and the cometopause the outer regions can be divided into three parts. A cometopause is found at 135,000 km, and a density decrease is detected at 45,000 km from the comet. The detailed plasma features associated with these regions are described.
Reme, H.↗
Combined Mesonet and Tracker
Title: Combined Mesonet and Trackers (UNL Mobile Mesonets) Authors University of Nebraska PI: Adam Houston, UNL Professor (ahouston2@unl.edu) Mailing Address: 126 Bessey Hall P.O. Box 880340 Lincoln, NE 68588-0340 CoMeT Overview The University of Nebraska-Lincoln operates three Combined Mesonet and Tracker (CoMeTs). CoMeTs are Ford Explorers (model years 2015, 2017, and 2019) with forward-mounted suites of meteorological sensors and dual moonroofs, combining the capability of a mobile mesonet to collect near-surface observations with the capability of an unmanned aircraft systems (UAS) tracker vehicle, which enables an observer in the second row of seats to see the aircraft and maintain compliance with Federal Aviation Administration policies on UAS operation. The CoMeTs collect observations of slow temperature and humidity at ~2 m above ground level (AGL) using a Vaisala HMP155A, fast temperature at ~2 m AGL using a Campbell Scientific 109SS-L thermistor, pressure at ~2.5 m AGL using a Vaisala PTB210, wind speed and direction at ~3.25 m AGL using an R.M. Young 05103 propeller anemometer, and vehicle heading using a KVH Industries C-100 fluxgate compass (Barbieri et al. 2019). The HMP155A and 109SS-L thermistor are shielded and aspirated within a U-tube (Waugh and Frederickson 2010; Houston et al. 2016). This list of sensors is also included in the CoMeT data file metadata. Manufacturer specifications for these instruments are given in Table 1 of Hanft and Houston (2018). The reported measured quantities are summarized below.CoMeT-3 was funded through an equipment allocation included in the NSF TORUS award (AGS-1824649). Instrument Description The specific sensors included on each CoMeT are summarized in the table at the end of this section. In general each CoMeT collects observations of slow temperature and humidity at ~2 m above ground level (AGL) using a Vaisala HMP155, fast temperature at ~2 m AGL using a Campbell Scientific 109SS-L thermistor, pressure at ~2.5 m AGL using a Vaisala PTB210 barometer with a Gill pressure port, wind speed and direction at ~3.25 m AGL using an R.M. Young 05103 propeller anemometer, position using a Garmin 19x HVS receiver, and vehicle heading using a KVH Industries C-100 fluxgate compass. The HMP155 and 109SS are shielded and aspirated within a U-tube (Waugh and Frederickson 2010; Houston et al. 2016). Fast temperature and corrected RH measurements (using sensors housed within the U-tube) have a time constant of 10-12 s based on data collected across a temperature and RH shock during the CLOUD-MAP 2017 calibration/validation tests on June 26, 2017. Vehicle speed was < 10 kts for this test. CoMeT-1 CoMeT-2 CoMeT-3 Slow Temperature Slow RH Vaisala HMP155A-L20-PT Part #: 22280-7 Vaisala HMP155E Part #: E1AA11A0B1A1A0A Vaisala HMP155E Part #: E1AA11A0B1A1A0A Fast temperature Campbell Scientific 109SS-L20-PT Part #: 21448-3 Campbell Scientific 109SS-L12-PW Part #: 21448-109 Campbell Scientific 109SS-L12-PW Part #: 21448-150 Pressure Vaisala PTB-210 Part #: A1A1B Gill Pressure Port Part #: 61002 Vaisala PTB-210 Part #: A1A1B Gill Pressure Port Part #: 61002 Vaisala PTB-210 Part #: A1A1B Gill Pressure Port Part #: 61002 Wind RM Young 05103-L20-PT Part #: 18435-310 RM Young 05103-L20-PW Part #: 18435-244 RM Young 05103-L20-PW Part #: 18435-244 GPS Garmin GPS 19x HVS (NMEA 0183) Part #: 010-01010-00 Garmin GPS 19x HVS (NMEA 0183) Part #: 010-01010-00 Garmin GPS 19x HVS (NMEA 0183) Part #: 010-01010-00 Compass KVH C-100 Part #: 01-0177-15 KVH C-100 Part #: 01-0177-15 KVH C-100 Part #: 01-0177-15 Logger Campbell Scientific CR6-NA-XT-SW Part #: 28385-9 Campbell Scientific CR6-WIFI-XT-SW Part #: 28385-6 Campbell Scientific CR6-WIFI-XT-SW Part #: 28385-6 Data Collection and Real-Time Processing The reported measured quantities are summarized in the table below. Quantity Units Source Epoch time Seconds GPS Latitude and longitude Degrees GPS Altitude m GPS Pressure hPa PTB210 Temperature (fast) deg C 109SS-L Temperature (slow) deg C HMP155 RH (slow) % HMP155 Vehicle speed m/s GPS Vehicle heading deg C-100 and GPS In addition to the measured variables, several derived variables are calculated. Corrected/fast relative humidity (%) Relative humidity is adjusted to the fast temperature following Richardson et al. (1998) and Houston et al. (2016). Water vapor mixing ratio (g/kg) Dew point temperature (°C) Potential temperature (Kelvin) Virtual potential temperature (Kelvin) Equivalent potential temperature (Kelvin) Regular intercomparisons between all three CoMeTs were performed during TORUS 2019. Comparisons were also conducted between CoMeT-1 and CoMeT-2 during LAPSE-RATE (2018) on 14 July. In these intercomparisons, the vehicles were parked adjacent to each other aligned perpendicular to (and facing into) the wind. To minimize engine heating effects, intercomparisons were only conducted when the wind speed was >10 kts. Data Format Original data files for each deployment are saved as text files and then converted to NetCDF. NetCDF versions have units that are CF compliant and may not match the original units in the txt files. The naming convention for the NetCDF files is as follows: UNL.CoMeT3.{deployment date YYYYMMDD}.{start time of observation collection in UTC HHMM}.L2.{post-processing codes}.cdf example: UNL.CoMeT3.20190627.1931.L2.g1.f1.cdf Post-processing codes are included to track modifications to the raw data. These codes are closely connected to error flags associated with each record. Each letter corresponds to a particular instrument: g: GPS p: Barometer tf: Fast temperature ts: Slow temperature rh: Relative humidity f: Compass w: Wind monitor a: All instruments Each number corresponds to a particular post-processing action described more below. Measured and derived variables are included in the following table. Variable Heading Standard Name Units time Time seconds since 00:00:00, 01-01-1970 Alt Altitude meters lat Latitude degrees north lon Longitude degrees east fast_temp Air Temperature kelvin slow_temp Air Temperature kelvin pressure Air Pressure pascals logger_RH Relative Humidity percent calc_corr_RH Relative Humidity percent wind_speed Wind Speed meters per second wind_dir Wind From Direction degrees vehicle_dir Vehicle Direction degrees dewpoint Dew Point Temperature kelvin mixing_ratio Humidity Mixing Ratio g/g theta Air Potential Temperature kelvin theta_v Virtual Potential Temperature kelvin theta_e Equivalent Potential Temperature Kelvin error_flag The error_flag variable is a string that matches the post-processing codes listed above. All instruments will have an associated code, but will have a “0” if the datum is unchanged from the initial processed value. Error Codes The following table summarizes the error codes for data collected before 2020: Error Code Relevant CoMeT Description g1 1,2,3 Exact correction. GPS position and time reprocessed from raw data g2 1 As far as we can tell this is an exact correction to an error in the GPS time. During the correct time periods the time suddenly went backwards ~250s and stayed at this offset for 750s when it corrected itself. The offset was applied to the “time warp” period. p1 2 Approximate correction. Hole in the pressure tube connecting the pressure port to the barometer. Resulted in erroneously low air pressure measurements when the vehicle was in motion. Derived variables recalculated (dew point temperature [e depends on qv and p], water vapor mixing ratio, potential temperature, virtual potential temperature, equivalent potential temperature) a1 3 Exact correction. Missing data reprocessed from raw data a2 1 Bug fix to bias correction for ts1, ts2, and rh1: water vapor mixing ratio was off by a factor of 10 and virtual potential temperature was wrong because of this. f1 3 No correction, missing data. Fluxgate compass inoperable. Wind speed and direction calculated using GPS-derived vehicle heading instead. rh1 1 Approximate correction. Constant bias of +1.7% removed from relative humidity. Derived variables recalculated (corrected/fast relative humidity, dew point temperature, water vapor mixing ratio, virtual potential temperature, equivalent potential temperature) ts1 1 Approximate correction. Constant bias of +0.6 K removed from slow temperature. Derived variables recalculated (corrected/fast relative humidity, dew point temperature, water vapor mixing ratio, virtual potential temperature, equivalent potential temperature) ts2 1 Approximate correction. Constant bias of +1.0 K removed. Derived variables recalculated (corrected/fast relative humidity, dew point temperature, water vapor mixing ratio, virtual potential temperature, equivalent potential temperature) References Bolton, D., 1980: The Computation of Equivalent Potential Temperature. Mon. Wea. Rev., 108, 1046–1053, https://doi.org/10.1175/1520-0493(1980)108<1046:TCOEPT>2.0.CO;2. Hanft, W., and A. L. Houston, 2018: An Observational and Modeling Study of Mesoscale Air Masses with High Theta-E. Mon. Wea. Rev., 146, 2503–2524, https://doi.org/10.1175/MWR-D-17-0389.1.Wexler Houston, A. L., R. J. Laurence III, T. W. Nichols, S. Waugh, B. Argrow, and C. L. Ziegler, 2016: Intercomparison of unmanned aircraft-borne and mobile mesonet atmospheric sensors. Journal of Atmospheric and Oceanic Technology. 33, 1569-1582, doi: 10.1175/JTECH-D-15-0178.1. Lowe, P. R., 1977: An Approximating Polynomial for the Computation of Saturation Vapor Pressure. J. Applied Meteorology, 16, 100–103. Richardson, S. J., S. E. Frederickson, F. V. Brock, and J. A. Brotzge, 1998: Combination temperature and relative humidity probes: Avoiding large air temperature errors and associated relative humidity errors. Preprints, 10th Symp. On Meteorological Observations and Instrumentation, Phoenix, AZ, Amer. Meteor. Soc., 278–283. Waugh, S., and S. E. Frederickson, 2010: An improved aspirated temperature system for mobile meteorological observations, especially in severe weather. 25th Conf. on Severe Local Storms, Denver, CO, Amer. Meteor. Soc., P5.2. [Available online at https://ams.confex.com/ams/25SLS/techprogram/paper_176205.htm.]
54 ENVIRONMENTAL SCIENCES↗
The reality of comet groups and pairs
Although the common genetic origin of the Kreutz family of sun-grazing comets has generally been accepted, there remains uncertainty with regard to genetic identity among other groups of comets whose orbital elements are nearly alike. Porter (1952) has listed a number of such groups, and Opik (1971) has made a statistical study of the orbits of 472 comets with aphelion distances beyond Saturn. Opik lists 97 groups that show similarities among their three angular elements, calculates an overall probability of some 10 to the -39th power that these similarities could have occurred by chance, and thus concludes that 60% or more of such comets fall into genetic groups containing from two to seven members. This paper explores the statistical reality of Opik's groups utilizing the Monte Carlo method of statistics as well as ordinary probability theory. The conclusion is reached that except for a few pairs, the similarity among orbital elements within the groups is no greater than random expectation.
Whipple, F. L.↗
A generalized behavioral model for rotating short period comets with spectral orbital elements and axial orientation
A generalized model for short period comets is developed which integrates in a fairly rigorous manner the isolation history of regions on rotating comets with specified axial orientation and the complex feedback processes involving heat, gas and dust transport, dust mantle development and coma opacity. Attention is focused on development, reconfiguration and partial or complete launching of dust mantles and the reciprocal effects of these three processes on ice surface temperature and gas and dust production. The dust mantle controls the H2O flux not only by its effect on the temperature at the ice interface but (dominantly) by its dynamic stability which strongly influences vapor diffusivity. The model includes the effects of latitude, rotation and spin axis orientation are included and applied to an initially homogeneous sphere of H2O ice and silicate using the orbital parameters of comet Encke. Numerous variations of the model, using combinations of grain size distribution, dust-to-ice ratio, latitude and spin axis orientation, are presented and discussed. Resulted for a similar nonrotating, constant Sun orientation models are also included.
Fanale, F. P.↗
Laboratory simulation of the surface of Halley's Comet
In the past year we have developed a model for the dissociation of icy grains in comets. In general, this model does not predict the radical yield that is observed in the jets of comets. To reproduce these yields, the concentration of the radical's precursors will have to be too high to be consistent with the abundance that we expect in comets. We have also constructed a theoretical model for the formation of ions on icy cometary grains. That model shows that only a small number of the cometary ions could be produced as ions in icy grains if the particle has only positively charged ions. If it contains both positive and negative ions then it could have a higher concentration of ions without violating charge neutrality. When such a particle evaporates, it can release ions with both charges into the gas phase. These ions could produce radicals via dissociative recombination with electrons if they are positive ions or by photoattachment of electrons if they are negative electrons. Finally, an avalanche process involving the acceleration of electrons towards charged particles is evaluated. It is shown that this will not lead directly to gas phase ions, but it might lead to additional ionization and dissociation on the grain.
Jackson, William M.↗
Understanding Olivine and Pyroxene in Chondritic IDPs
There is a widespread depletion of Cr from the FeO-rich olivine in Wild-2, relative to type IIA chondrules(Frank et al., 2014)-the degree of this depletion is akin to that in unequilibrated chondrites such as Krymka (LL3.2) or Rainbow (CO3.2).Since Cr is highly mobile under even mild thermal metamorphism(as low as 200ºC), it is a sensitive indicator of such an event, showing greater depletion in smaller grains (i.e., matrix vs. chondrules) (Grossman and Brearley, 2005). Grossman and Brearley (2005) found that the distribution of Cr in FeO-rich olivine systematically changes as metamorphism increases between type 3.0 and type 3.2. Thus, Wild-2 olivine appears to carry evidence of mild thermal metamorphism. It is critical to determine whether there is any evidence for this from samples of other comets. For this we can examine an hydrous chondritic IDPs. Unfortunately, the data for olivine and pyroxene in IDPs is sparse, mainly decades old and lacks useful information on minor elements. We have begun to collect new compositional data for olivine and pyroxene in chondritic interplanetary dust particles (filling a major gap in our knowledge, as approximately half of these grains derive from comets), to determine whether the results obtained for Wild-2 are typical for comets in general, or whether Wild-2 (or its accretion components) has experienced an atypical geological history. A determination that a comet, or its accretion components, had experienced significant thermal metamorphism would greatly alter models of early solar system history.
Michael Zolensky↗