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Meenakshi Wadhwa

Publications and source records attributed to Meenakshi Wadhwa.

13 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2025

Diverse and Highly Differentiated Lava Suite in Jezero Crater, Mars: Constraints on Intracrustal Magmatism Revealed By Mars 2020 PIXL

The Jezero crater floor features a suite of related, iron-rich lavas that were examined and sampled by the Mars 2020 rover Perseverance , and whose textures, minerals, and compositions were characterized by the Planetary Instrument for X-ray Lithochemistry (PIXL). This suite, known as the Máaz formation (fm), includes dark-toned basaltic/trachy-basaltic rocks with intergrown pyroxene, plagioclase feldspar, and altered olivine and overlying trachy-andesitic lava with reversely zoned plagioclase phenocrysts in a K-rich groundmass. Feldspar thermal disequilibrium textures indicate that they were carried from their crustal staging area. Bulk and mafic minerals have very high FeO and low MgO to FeO total ratios, which are partially reproduced by thermodynamic models involving high-degree fractional crystallization of a gabbroic assemblage and possibly also assimilation of iron-rich basement. Together, these in situ constraints on petrogenesis provide a uniquely detailed record of intracrustal processes beneath Jezero crater during a time period not represented by Mars samples to date.

Jezero Crater floor↗
NASA NTRS2023

The Magnesium Isotope Composition of Samples Returned From Asteroid Ryugu

The nucleosynthetic isotope composition of planetary materials provides a record of the heterogeneous distribution of stardust within the early solar system. In 2020 December, the Japan Aerospace Exploration Agency Hayabusa2 spacecraft returned to Earth the first samples of a primitive asteroid, namely, the Cb-type asteroid Ryugu. This provides a unique opportunity to explore the kinship between primitive asteroids and carbonaceous chondrites. We report high-precision μ 26 Mg* and μ 25 Mg values of Ryugu samples together with those of CI, CM, CV, and ungrouped carbonaceous chondrites. The stable Mg isotope composition of Ryugu aliquots defines μ 25 Mg values ranging from –160 ± 20 ppm to –272 ± 30 ppm, which extends to lighter compositions relative to Ivuna-type (CI) and other carbonaceous chondrite groups. We interpret the μ 25 Mg variability as reflecting heterogeneous sampling of a carbonate phase hosting isotopically light Mg (μ 25 Mg ∼ –1400 ppm) formed by low temperature equilibrium processes. After correcting for this effect, Ryugu samples return homogeneous μ 26 Mg* values corresponding to a weighted mean of 7.1 ± 0.8 ppm. Thus, Ryugu defines a μ 26 Mg* excess relative to the CI and CR chondrite reservoirs corresponding to 3.8 ± 1.1 and 11.9 ± 0.8 ppm, respectively. These variations cannot be accounted for by in situ decay of 26 Al given their respective 27 Al/ 24 Mg ratios. Instead, it requires that Ryugu and the CI and CR parent bodies formed from material with a different initial 26 Al/ 27 Al ratio or that they are sourced from material with distinct Mg isotope compositions. Thus, our new Mg isotope data challenge the notion that Ryugu and CI chondrites share a common nucleosynthetic heritage.

Solar system evolution↗
NASA NTRS2023

Pervasive aqueous alteration in the early Solar System revealed by potassium isotopic variations in Ryugu samples and carbonaceous chondrites

C-type asteroids are the presumed home to carbonaceous chondrites, some of which contain abundant life-forming volatiles and organics. For the first time, samples from a C-type asteroid (162173 Ryugu) were successfully returned to Earth by JAXA’s Hayabusa2 mission. These pristine samples, uncontaminated by the terrestrial environment, allow a direct comparison with carbonaceous chondrites. This study reports the stable K isotopic compositions (expressed as δ 41 K) of Ryugu samples and seven carbonaceous chondrites to constrain the origin of K isotopic variations in the early Solar System. Three aliquots of Ryugu particles collected at two touchdown sites have identical δ 41 K values, averaged at -0.194 ± 0.038‰ (2SD). The K isotopic composition of Ryugu falls within the range of δ 41 K values measured on representative CI chondrites, and together, they define an average δ 41 K value of -0.185 ± 0.078‰ (2SE), which provides the current best estimate of the K isotopic composition of the bulk Solar System. Samples of CI chondrites with δ 41 K values that deviate from this range likely reflect terrestrial contaminations or compositional heterogeneities at sampled sizes. In addition to CI chondrites, substantial K isotopic variability is observed in other carbonaceous chondrites and within individual chondritic groups, with δ 41 K values inversely correlated with K abundances in many cases. These observations indicate widespread fluid activity occurred in chondrite parent bodies, which significantly altered the original K abundances and isotopic compositions of chondrules and matrices established at their accretion.

Asteroid Ryugu↗
NASA NTRS2022

Oxygen Isotopes of Anhydrous Primary Minerals Show Kinship Between Asteroid Ryugu and Comet 81P/Wild2

The extraterrestrial materials returned from asteroid (162173) Ryugu consist predominantly of low-temperature aqueously formed secondary minerals and are chemically and mineralogically similar to CI (Ivuna-type) carbonaceous chondrites. Here we show that high-temperature anhydrous primary minerals in Ryugu and CI chondrites exhibit a bimodal distribution of oxygen isotopic compositions: 16 O-rich (associated with refractory inclusions) and 16 O-poor (associated with chondrules). Both the 16 O-rich and 16 O-poor minerals probably formed in the inner solar protoplanetary disk and were subsequently transported outwards. The abundance ratios of the 16 O-rich to 16 O-poor minerals in Ryugu and CI chondrites are higher than in other carbonaceous chondrite groups, but are similar to that of comet 81P/Wild2, suggesting that Ryugu and CI chondrites accreted in the outer Solar System closer to the accretion region of comets.

Noriyuki Kawasaki↗
NASA NTRS2022

The Scientific Importance of Returning Airfall Dust as a Part of Mars Sample Return (MSR)

Dust transported in the martian atmosphere is of intrinsic scientific interest and has relevance for the planning of human missions in the future. The MSR Campaign, as currently designed, presents an important opportunity to return serendipitous, airfall dust. The tubes containing samples collected by the Perseverance rover would be placed in cache depots on the martian surface perhaps as early as 2023–24 for recovery by a subsequent mission no earlier than 2028–29, and possibly as late as 2030–31. Thus, the sample tube surfaces could passively collect dust for multiple years. This dust is deemed to be exceptionally valuable as it would inform our knowledge and understanding of Mars' global mineralogy, surface processes, surface-atmosphere interactions, and atmospheric circulation. Preliminary calculations suggest that the total mass of such dust on a full set of tubes could be as much as 100 mg and, therefore, sufficient for many types of laboratory analyses. Two planning steps would optimize our ability to take advantage of this opportunity: (1) the dust-covered sample tubes should be loaded into the Orbiting Sample container (OS) with minimal cleaning and (2) the capability to recover this dust early in the workflow within an MSR Sample Receiving Facility (SRF) would need to be established. A further opportunity to advance dust/atmospheric science using MSR, depending upon the design of the MSR Campaign elements, may lie with direct sampling and the return of airborne dust.

Monica M. Grady↗
NASA NTRSDate not supplied

Mars 2020's First Sample: The Fractured Rough Rock Unit on the Floor of Jezero Crater

A central goal of the Mars 2020 mission is to select and cache samples for future return to Earth. The first samples targeted for collection are from the crater-retaining, Crater Floor Fractured Rough (CF-Fr) unit of Stack et al., 2020.The CF-Fr unit is a topographically low unit in the current Jezero setting, likely overlain by morphologically discrete units, including possible Jezero delta deposits and eolian features. CF-Fr is an aerially extensive unit with lobate margins. Two distinct morphologies are observed: a locally-exposed lower expression, with flat relatively horizontal light-toned surfaces and polygonal fracturing, and an upper expression consisting of up to ~5vertical meters of massive, sometimes boulder-producing, material. The locally-exposed lower expression appears to represent a local ground level in which the upper material has been removed. Near the Octavia E. Butler landing site, the lower morphology is exposed as polygonally-fractured, light-toned bedrock that appears to grade continuously into higher-standing massive outcrops, often with no clearly exposed contact. Further south, a darker upper expression of the CF-Fr unit is more distinct and the unit exhibits some horizontal layering. The Perseverance rover will initially sample the flat-lying expression of this unit. Hypotheses for the origin of CF-Fr include fluvial, aeolian, or lacustrine sediment likely derived from the Jezero watershed, and/or pyroclastic material resulting from regional volcanism. Geochronology of the returned sample could be used to help constrain the timing of geological events in Jezero. It may also help constrain stratigraphic relationships with crater-retaining units outside of Jezero within the Nili Planum, which could be used to calibrate the cratering chronology of Mars. Paleomagnetic analyses of an oriented sample could establish the history of the martian dynamo and whether it persisted into the Hesperian. Finally, if present, secondary phases within the primary deposit would help constrain diagenetic conditions and inform post-depositional aqueous and potentially habitable environmental conditions.

Justin I Simon↗
NASA NTRSDate not supplied

Collecting Samples from the Máaz Formation of Jezero Crater with the Mars 2020 Perseverance Rover

Collection of samples that could be returned to Earth from the floor of Jezero,a Noachian crater characterized by a delta–lake system with high potential for habitability, is a major goal of the Mars 2020 mission. The Mars 2020 Perseverancerover iscurrently exploringthe Máaz and Séítahformationsto the southeastof the delta. Here wefocus on thecrater-retainingMáaz formation, a widespread, rough and fractured terrain with lobatemarginsmapped in orbital images, e.g.[1]. Outcrop morphology and texture, as well as the appearance, composition and mineralogy of abraded rock surfaces observed by Perseverance suggest that theMáazformation consists of asequence of maficigneous units, likely lavas flows. These rocks have experienced variable interaction with aqueous fluids. Type localities of the lower Roubion and the more resistant Rochette members of the Máazformation have been targeted and their abraded surfaces characterized prior to sample collection. In thispresentation we will summarize these sampling activities and potential future sampling of theheavily crateredupperCh’ałmember that is indicative of the Máazformationfrom orbit.

Justin Ibrahim Simon↗