Исследованы крыловой рисунок, строение гениталий самцов и последовательности COI шашечниц группы Melitaea minerva. Обозначены лектотипы M. asteroida variegata и M. asteroida maculata, показано, что ...оба таксона относятся к M. minerva как его подвиды, а не к M. asteroida. На основании исследования ДНК (последовательность COI) делается предположение о конспецифичности таксонов M. minerva и M. pallas. Таксон M. solona не является самостоятельным видом, а представляет сборную группу фенотипов, характерных как для M. minerva, так и для M. asteroida. Для идентификации видов внутри группы M. minerva признаки гениталий самцов непригодны.
Asteroidi su najveća mala tijela Sunčeva sustava. Danas se intenzivno proučavaju iz nekoliko razloga. Kao prvo, neki asteroidi (tzv. NEA podvrsta) mogu se sudariti sa Zemljom, a posljedice takva ...sudara bile bi katastrofalne. Drugo, na njih se gleda kao na potencijalni izvor materijala koji na Zemlji postaju rijetki, a koji će ionako biti potrebni za svemirske konstrukcije budućnosti. I treće, oni čuvaju tajne postanka Sunčeva sustava i njegove evolucije do danas. Na kraju, kako je nekoliko hrvatskih znanstvenika nedavno počašćeno nazivanjem asteroida po njima, dan je i kratak opis postupka imenovanja i popis asteroida čija su imena povezana s našom zemljom i njezinim ljudima.
In order to understand the geological evolution of asteroids Eros, Itokawa and Ryugu and their collisional history, previous studies investigated boulder size distributions on their surfaces. ...However, quantitative comparison of these size distributions is hampered by numerous differences between these studies regarding the definition of a boulder's size, measuring technique and the fitting method to determine the power-index of the boulder size distributions. We provide a consistent and coherent model of boulder size distributions by remeasuring the boulders on the entire surfaces of Eros and Itokawa using the Small Body Mapping Tool (SBMT) and combining our observations with the Ryugu data of Michikami et al. (2019). We derived power-indices of the boulder size distributions of −3.25 ± 0.14 for Eros, −3.05 ± 0.14 for Itokawa and −2.65 ± 0.05 for Ryugu. The asteroid with the highest number density of boulders ≥ 5 m turns out to be Ryugu, not Itokawa, as suggested by an earlier study. We show that the appearance of the boulders tends towards more elongated shapes as the size of an asteroid decreases, which can be explained by differences in asteroid gravity and boulder friction angles. Our quantitative observational results indicate that boulder migration preferentially affects smaller boulders, and tends to occur on larger asteroids.
•First comparative survey free from observer bias of boulders on Eros, Itokawa and Ryugu.•Boulders appear to be more elongated as the size of an asteroid decreases.•Boulder migration preferentially affects smaller boulders and larger asteroids.
•Chelyabinsk meteorite source region in the main asteroid belt is the Flora family.•Shock/impact melt can explain spectral properties of Flora and Baptistina families.•Shock/impact melt presence ...could lead to ambiguous taxonomic classification.
We investigated the spectral and compositional properties of Chelyabinsk meteorite to identify its possible parent body in the main asteroid belt. Our analysis shows that the meteorite contains two spectrally distinct but compositionally indistinguishable components of LL5 chondrite and shock blackened/impact melt material. Our X-ray diffraction analysis confirms that the two lithologies of the Chelyabinsk meteorite are extremely similar in modal mineralogy. The meteorite is compositionally similar to LL chondrite and its most probable parent asteroid in the main belt is a member of the Flora family. Our work confirms previous studies (e.g., Vernazza et al. 2008. Nature 454, 858–860; de León, J., Licandro, J., Serra-Ricart, M., Pinilla-Alonso, N., Campins, H. 2010. Astron. Astrophys. 517, A23; Dunn, T.L., Burbine, T.H., Bottke, W.F., Clark, J.P. 2013. Icarus 222, 273–282), linking LL chondrites to the Flora family. Intimate mixture of LL5 chondrite and shock blackened/impact melt material from Chelyabinsk provides a spectral match with (8) Flora, the largest asteroid in the Flora family. The Baptistina family and Flora family overlap each other in dynamical space. Mineralogical analysis of (298) Baptistina and 11 small family members shows that their surface compositions are similar to LL chondrites, although their absorption bands are subdued and albedos lower when compared to typical S-type asteroids. A range of intimate mixtures of LL5 chondrite and shock blackened/impact melt material from Chelyabinsk provides spectral matches for all these BAF members. We suggest that the presence of a significant shock/impact melt component in the surface regolith of BAF members could be the cause of lower albedo and subdued absorption bands. The conceptual problem with part of this scenario is that impact melts are very rare within ordinary chondrites. Of the ∼42,000 ordinary chondrites, less than 0.5% (203) of them contain impact melts. A major reason that impact melts are rare in meteorites is that high impact velocities (V>10km/s) are needed to generate the necessary shock pressures and temperatures (e.g., Pierazzo, E., Melosh, H.J. 1998. Hydrocode modeling of oblique impacts: The fate of the projectile. In: Origin of the Earth and Moon, Proceedings of the Conference. LPI Contribution No. 957) unless the target material is highly porous. Nearly all asteroid impacts within the main belt are at ∼5km/s (Bottke, W.F., Nolan, M.C., Greenberg, R., Kolvoord, R.A. 1994. Collisional lifetimes and impact statistics of near-Earth asteroids. In: Tucson, Gehrels T. (Ed.), Hazards Due to Comets and Asteroids. The University of Arizona Press, Arizona, pp. 337–357), which prevents them from producing much impact melt unless they are highly porous. However, shock darkening is an equally efficient process that takes place at much lower impact velocities (∼2km/s) and can cause the observed spectral effects. Spectral effects of shock darkening and impact melt are identical. The parent asteroid of BAF was either a member of the Flora family or had the same basic composition as the Floras (LL Chondrite). The shock pressures produced during the impact event generated enough impact melt or shock blackening to alter the spectral properties of BAF, but keep the BAF composition largely unchanged. Collisional mixing of shock blackened/impact melt and LL5 chondritic material could have created the Baptistina Asteroid Family with composition identical to those of the Floras, but with subdued absorption bands. Shock darkening and impact melt play an important role in altering the spectral and albedo properties of ordinary chondrites and our work confirms earlier work by Britt and Pieters (Britt, D.T., Pieters, C.M. 1994. Geochimica et Cosmochimica Acta 58, 3905–3919).
Recent theoretical work in celestial mechanics has revealed that an asteroid may orbit stably in the same region as a planet, despite revolving around the Sun in the sense opposite to that of the ...planet itself. Asteroid 2015 BZ
was discovered in 2015, but with too much uncertainty in its measured orbit to establish whether it was such a retrograde co-orbital body. Here we report observations and analysis that demonstrates that asteroid 2015 BZ
is indeed a retrograde co-orbital asteroid of the planet Jupiter. We find that 2015 BZ
has long-term stability, having been in its current, resonant state for around a million years. This is long enough to preclude precise calculation of the time or mechanism of its injection to its present state, but it may be a Halley-family comet that entered the resonance through an interaction with Saturn. Retrograde co-orbital asteroids of Jupiter and other planets may be more common than previously expected.
•The geopotential on a rapidly spinning spheroidal body is studied.•Estimates for the rate of shedding surface material are given for rapidly spinning spheroids.•Predictions are made on the shapes ...and exposed sub-surface regions on rapidly spinning spheroidal asteroids.
Conditions for regolith landslides to occur on spinning, gravitating spheroidal asteroids and their aftermath are studied. These conditions are developed by application of classical granular mechanics stability analysis to the asteroid environment. As part of our study we determine how slopes evolve across the surface of these bodies as a function of spin rate, the dynamical fate of material that exceeds the angle of repose, and an analysis of how the shape of the body may be modified based on these results. We find specific characteristics for body surfaces and shapes when spun near the surface disruption limit and develop what their observable implications are. The small, oblate and rapidly spinning asteroids such as 1999 KW4 Alpha and 2008 EV5 exhibit some of these observable traits. The detailed mechanisms outlined here can also provide insight and constraints on the recently observed active asteroids such as P/2013 P5, and the creation of asteroidal meteor streams.
•We mapped 2 quadrangles of Vesta in detail.•We identified and analyzed different mass wasting features.•We explain how spur-and-gully morphologies and slumping blocks were be formed on an airless ...body like Vesta.
The Quadrangles Av-11 and Av-12 on Vesta are located at the northern rim of the giant Rheasilvia south polar impact basin. The primary geologic units in Av-11 and Av-12 include material from the Rheasilvia impact basin formation, smooth material and different types of impact crater structures (such as bimodal craters, dark and bright crater ray material and dark ejecta material). Av-11 and Av-12 exhibit almost the full range of mass wasting features observed on Vesta, such as slump blocks, spur-and-gully morphologies and landslides within craters. Processes of collapse, slope instability and seismically triggered events force material to slump down crater walls or scarps and produce landslides or rotational slump blocks. The spur-and-gully morphology that is known to form on Mars is also observed on Vesta; however, on Vesta this morphology formed under dry conditions.
Examining the albedo distribution of the near-Earth object (NEO) population allows for a better understanding of the relationship between absolute (H) magnitude and size, which impacts calculations ...of the size frequency distribution and impact hazards. Examining NEO albedos also sheds light on the differences between the NEO and Main Belt populations. We combine albedo results from the ExploreNEOs Warm Spitzer Exploration Science program with taxonomic classifications from the literature, publicly available data sets, and new observations from our concurrent spectral survey to derive the average albedos for C-, D-, Q-, S-, V-, and X-complex NEOs. Using a sample size of 118 NEOs, we calculate average albedos of 0.29+0.05 --0.04, 0.26+0.04 --0.03, and 0.42+0.13 --0.11 for the Q-, S-, and V-complexes, respectively. The averages for the C- and D-complexes are 0.13+0.06 --0.05 and 0.02+0.02 --0.01, but these averages are based on a small number of objects (five and two, respectively) and will improve with additional observations. We use albedos to assign X-complex asteroids to one of the E-, M-, or P-types. Our results demonstrate that the average albedos for the C-, S-, V-, and X-complexes are higher for NEOs than the corresponding averages observed in the Main Belt.
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