DaG 298

LL4

Found 1997
26° 58.20′ N., 16° 42.28′ E. A mass totaling 2,459 g was found on the Dar al Gani plateau in the eastern Sarir al Qattusah in central Libya, an area that covers ~12,000 km², of which ~8,000 km² are favorable for meteoriteWork in progress. A solid natural object reaching a planet’s surface from interplanetary space. Solid portion of a meteoroid that survives its fall to Earth, or some other body. Meteorites are classified as stony meteorites, iron meteorites, and stony-iron meteorites. These groups are further divided according to their mineralogy and recovery (Schlüter et al., 2002). The area of meteorite recovery lies on Tertiary limestoneA common form of calcium carbonate (CaCO3). Other common forms of CaCO3 include chalk and marble. marine sediments.

Dar al Gani 298 has a very fresh appearance with a weathering grade of W0, and it is rich in noble gasesElement occurring in the right-most column of the periodic table; also called "inert" gases. In these gases, the outer electron shell is completely filled, making them very unreactive. suggesting a very recent fallMeteorite seen to fall. Such meteorites are usually collected soon after falling and are not affected by terrestrial weathering (Weathering = 0). Beginning in 2014 (date needs confirmation), the NomComm adopted the use of the terms "probable fall" and "confirmed fall" to provide better insight into the meteorite's history. If. The meteorite has been shocked to stage S3, with a 21Ne-based CRE age of 52.6 m.y. In contrast to many LL chondritesChondrites are the most common meteorites accounting for ~84% of falls. Chondrites are comprised mostly of Fe- and Mg-bearing silicate minerals (found in both chondrules and fine grained matrix), reduced Fe/Ni metal (found in various states like large blebs, small grains and/or even chondrule rims), and various refractory inclusions (such with Ar–Ar ages reflecting late impact resetting, some events as recent as ~1 b.y. ago (Weirich et al., 2009), the gas retention age of DaG 298 was calculated to be 4.48 b.y. This age likely preserves its original crystallizationPhysical or chemical process or action that results in the formation of regularly-shaped, -sized, and -patterned solid forms known as crystals. age; a similar Ar–Ar age of 4.471 (±0.009) b.y. was measured for a sample of the LL5 chondriteChondrites are the most common meteorites accounting for ~84% of falls. Chondrites are comprised mostly of Fe- and Mg-bearing silicate minerals (found in both chondrules and fine grained matrix), reduced Fe/Ni metal (found in various states like large blebs, small grains and/or even chondrule rims), and various refractory inclusions (such Tuxtuac (Lindsay et al., 2009). The specimen of DaG 298 shown above is a 28.9 g partial slice.

It is known that the large Flora family of asteroids, as well as the compositionally linked Baptistina asteroid family, is located near the ν₆ secular resonance at the inner edge of the asteroid beltBelt located between 2.12 and 3.3 AU from the Sun and located between the orbits of Mars and Jupiter containing the vast majority of asteroids. The asteroid belt is also termed the main asteroid belt or main belt to distinguish it from other asteroid populations in the Solar System such (2.1 AUThe astronomical unit for length is described as the "mean" distance (average of aphelion and perihelion distances) between the Earth and the Sun. Though most references state the value for 1 AU to be approximately 150 million kilometers, the currently accepted precise value for the AU is 149,597,870.66 km. The) and might be the source of LL chondrites (Bottke et al., 2009; Binzel et al., 2016). In a study of LL6 chondrite orbits, Ustinova et al. (2008) propose that the ~7 km-diameter asteroid 3628 Božněmcová, which has a reflectance spectrum almost identical to the LL-group, is a good match to this chondrite group. In their study they determined a probable orbitThe elliptical path of one body around another, typically the path of a small body around a much larger body. However, depending on the mass distribution of the objects, they may rotate around an empty spot in space • The Moon orbits around the Earth. • The Earth orbits around for two 2002 LL6 falls, Bensour and Kilabo, which fell within five months of each other in northern Africa and which show striking similarities to each other. Based on their measured content of cosmogenic 26Al, the calculated orbits for these meteorites coincidentally intersect that of 3628 Božněmcová at the same point near the inner asteroid belt. They proposed that Bensour and Kilabo were ejected in a common event 19 m.y. ago, and that any differences in their CRE ages reflect differences in their shielding depth while on the parent asteroid. Spectral and compositional studies of the LL5 Chelyabinsk meteorite by Reddy et al. (2014) have led them to conclude that the Baptistina asteroid family is also consistent with the Flora asteroid family, the LL chondrites, and the asteroid Itokawa. They determined that the spectral variations observed in members of the Baptistina family are consistent with incorporation of an impact melt component (associated with the presence of fine-grained opaques) similar to that observed in portions of the Chelyabinsk meteorite.
Diagram credit: Binzel et al., 47th LPSC, #1352 (2016) In their near-IR spectrographic study of asteroids located near the 3:1 orbital resonanceDynamic relationship between bodies in heliocentric orbits in which a small body has an orbital period that is a simple fraction of a nearby larger body such as Asteroid Belt objects and Jupiter. The periodic gravitational tug of the large body induces changes in the orbit of the smaller body (a Kirkwood gapLack of asteroids in regions within the asteroid belt (between Mars and Jupiter) coinciding with orbital periods that are simple fractions of Jupiter’s own orbital period. The absence of asteroids in these gaps is due to resonance with Jupiter’s gravitational influence.         associated with Jupiter), Fieber-Beyer et al. (2009) found that close similarities exist in the absorptionTransfer of energy to a medium as a particle or electromagnetic radiation passes through it. Absorption of electromagnetic radiation is the combined result of Compton scattering, σ, and photoelectric absorption, τ. It may be quantified: where, t = thickness, ρ = density, and μ = mass absorption coefficient, which combines Compton and photoelectric effects (μ = σ + τ). spectra of the S(IV) asteroid 974 Lioba and that of LL chondrites. Importantly, the recent touchdown of the Hayabusa spacecraft onto the surface of the sub-km-sized, S-type asteroid Itokawa has provided a wealth of knowledge about this most abundant type of asteroid. Itokawa’s reflectance spectrum reveals an olivineGroup of silicate minerals, (Mg,Fe)2SiO4, with the compositional endpoints of forsterite (Mg2SiO4) and fayalite (Fe2SiO4). Olivine is commonly found in all chondrites within both the matrix and chondrules, achondrites including most primitive achondrites and some evolved achondrites, in pallasites as large yellow-green crystals (brown when terrestrialized), in the silicate portion and pyroxeneA class of silicate (SiO3) minerals that form a solid solution between iron and magnesium and can contain up to 50% calcium. Pyroxenes are important rock forming minerals and critical to understanding igneous processes. For more detailed information, please read the Pyroxene Group article found in the Meteoritics & Classification category. composition very similar to that of known LL chondriteOrdinary chondrites ("low Fe" / "low metal") with only 1 to 3% free metal. Their olivine is more Fe-rich than in the other ordinary chondrites (Fa27-32), implying that the LL types must have formed under more oxidizing conditions than their H or L cousins. Orthopyroxene compositions are also Fe-the rich meteorites, such as DaG 298 (Abe et al., 2006). The mean Δ17O for the mineralogy of 25143 Itokawa is the same as that for LL or L chondrites (Yurimoto et al., 2011). The photo shown above is a view of the southern hemisphere of asteroid Itokawa taken by the Japanese Space Agency (JAXA) Hayabusa spacecraft. It shows a surface largely strewn with angular boulders, many too large to have originated from impact craters present on Itokawa (e.g., the boulder ‘Yoshinodai’ measures 50 × 30 × 20 m in size; Demura et al., 2006) (see top photo below). By contrast, the lowest topographic areas, such as the touchdown/sample collection location in Muses Sea, are smoothly surfaced with cm-sized gravel (see bottom photo below), probably produced by grain-size sorting due to seismically-driven gravitational settling (Zolensky et al., 2013). The unusual double-lobed shape of Itokawa (~540 m in largest dimension), which is characterized by a constricted neck 20 m deep and up to 120 m wide, demonstrates that it is a low-density (1.90 ±0.13 g/cm³) contact binary formed by gravitational coalescence of separate portions of an impact-disrupted parent body—its structure is a rubble-pile with a macro-porosity of ~40%. New geothermometry results for LL meteorite samples obtained by Dygert et al. (2018) show that rapid cooling/quenching (≥1°C/yr) occurred near peak temperatures, which is consistent with a catastrophic breakup event. Other temperature data indicate that LL chondrites cooled much slower at lower temperatures (≤500°C), which is consistent with conditions at some depth in a reassembled rubble-pile.

Sub-mm-sized particles of Itokawa returned by the Hayabusa spacecraft have been analyzed, and the mineralogy is consistent with that of an LL5–6 chondrite (Busemann et al., 2013). Evidence of space weathering is present in the form of nano-sized Fe and S phases. Noble gasElement occurring in the right-most column of the periodic table; also called "inert" gases. In these gases, the outer electron shell is completely filled, making them very unreactive. studies based on 21Ne indicate a CRE age of 3–8 m.y., based on a sample residence either on the surface or buried half a meter deep, respectively (Nagao et al., University of Tokyo). No melting was observed on any of the returned particles, which is consistent with low impact velocities on the parent asteroid of ~5 km per second (Tsuchiyama et al., 2011), but it is estimated by Busemann et al. (2013) that the rate of loss from the asteroid is relatively high. Continued analyses of the returned particles is ongoing.

Images presented courtesy of JAXA—Japan Aerospace Exploration Agency.

Particles from asteroid Itokawa have compositions similar to LL-group ordinary chondrites that have experienced space weathering. Coarsened particles of plagioclaseAlso referred to as the plagioclase feldspar series. Plagioclase is a common rock-forming series of feldspar minerals containing a continuous solid solution of calcium and sodium: (Na1-x,Cax)(Alx+1,Si1-x)Si2O8 where x = 0 to 1. The Ca-rich end-member is called anorthite (pure anorthite has formula: CaAl2Si2O8) and the Na-rich end-member is albite and diopside are indicative of a high-temperature metamorphicRocks that have recrystallized in a solid state due to changes in temperature, pressure, and chemical environment. period (~800°C) that established a petrologic typeMeasure of the degree of aqueous alteration (Types 1 and 2) and thermal metamorphism (Types 3-6) experienced by a chondritic meteorite. Type 3 chondrites are further subdivided into 3.0 through 3.9 subtypes. of 5 to 6 (Nakamura et al., 2011). See also the article from PSRD ‘Samples from Asteroid Itokawa’, by G. J. Taylor and L. M. V. Martel, August, 2011.