Aqueously altered igneous rocks sampled on the floor of Jezero crater, Mars.

The Perseverance rover landed in Jezero crater, Mars, to investigate ancient lake and river deposits. We report observations of the crater floor, below the crater's sedimentary delta, finding that the floor consists of igneous rocks altered by water. The lowest exposed unit, informally named Séítah, is a coarsely crystalline olivine-rich rock, which accumulated at the base of a magma body. Magnesium-iron carbonates along grain boundaries indicate reactions with carbon dioxide-rich water under water-poor conditions. Overlying Séítah is a unit informally named Máaz, which we interpret as lava flows or the chemical complement to Séítah in a layered igneous body. Voids in these rocks contain sulfates and perchlorates, likely introduced by later near-surface brine evaporation. Core samples of these rocks have been stored aboard Perseverance for potential return to Earth.

Assessment of Mars Exploration Rover landing site predictions.

Comprehensive analyses of remote sensing data during the three-year effort to select the Mars Exploration Rover landing sites at Gusev crater and at Meridiani Planum correctly predicted the atmospheric density profile during entry and descent and the safe and trafficable surfaces explored by the two rovers. The Gusev crater site was correctly predicted to be a low-relief surface that was less rocky than the Viking landing sites but comparably dusty. A dark, low-albedo, flat plain composed of basaltic sand and haematite with very few rocks was expected and found at Meridiani Planum. These results argue that future efforts to select safe landing sites based on existing and acquired remote sensing data will be successful. In contrast, geological interpretations of the sites based on remote sensing data were less certain and less successful, which emphasizes the inherent ambiguities in understanding surface geology from remotely sensed data and the uncertainty in predicting exactly what materials will be available for study at a landing site.

Evidence for divergent plate-boundary characteristics and crustal spreading on venus.

Detailed examination of the topography and morphology of western Aphrodite Terra reveals numerous features that are similar to terrestrial divergent plate-boundary characteristics. Individual domains between fracturezone-like discontinuities contain a variety of bilaterally symmetrical topographic elements that suggest that topographic features have been created at rise crests, rifted and separated, and moved laterally to their present symmetrical positions. The topographic and morphologic similarities, together with strikingly similar mirror-image map patterns on both sides of the rise axis, suggest that western Aphrodite Terra shares the characteristics of oceanic divergent plate boundaries, and is the site of crustal spreading on Venus. Topographic profiles are consistent with spreading rates of the order of several centimeters per year.

Relation of major volcanic center concentration on venus to global tectonic patterns.

Global analysis of NASA Magellan image data indicates that a major concentration of volcanic centers covering approximately 40 percent of the surface of Venus occurs between the Beta, Atla, and Themis regiones. Associated with this enhanced concentration are geological characteristics commonly interpreted as rifting and mantle upwelling. Interconnected low plains in an annulus around this concentration are characterized by crustal shortening and infrequent volcanic centers that may represent sites of mantle return flow and net down-welling. Together, these observations suggest the existence of relatively simple, largescale patterns of mantle circulation similar to those associated with concentrations of intraplate volcanism on Earth.

Ancient aqueous environments at Endeavour crater, Mars.

Opportunity has investigated in detail rocks on the rim of the Noachian age Endeavour crater, where orbital spectral reflectance signatures indicate the presence of Fe(+3)-rich smectites. The signatures are associated with fine-grained, layered rocks containing spherules of diagenetic or impact origin. The layered rocks are overlain by breccias, and both units are cut by calcium sulfate veins precipitated from fluids that circulated after the Endeavour impact. Compositional data for fractures in the layered rocks suggest formation of Al-rich smectites by aqueous leaching. Evidence is thus preserved for water-rock interactions before and after the impact, with aqueous environments of slightly acidic to circum-neutral pH that would have been more favorable for prebiotic chemistry and microorganisms than those recorded by younger sulfate-rich rocks at Meridiani Planum.

5-Fluorouracil neurotoxicity.

Two cases of 5-fluorouracil-induced neurotoxicity from the University of North Carolina are presented. 5-Fluorouracil metabolism is briefly discussed with reference to possible mechanisms for the neurotoxicity. A possible role for thiamine supplementation in the prevention of this unusual complication is supported by our experience.

Hexamethylmelamine chemotherapy for persistent or recurrent epithelial ovarian cancer.

The purpose of this study was to determine the activity and toxicity of hexamethylmelamine chemotherapy in patients with persistent or recurrent epithelial ovarian cancer. Forty-nine women received hexamethylmelamine 100 to 150 mg/day for 14 days, repeated at 4-week intervals. All patients had previously received at least one chemotherapy regimen, and 46 (94%) had received cisplatin. Among 25 patients with clinically measurable disease there were three complete and two partial responses, for an objective response rate of 20%. The mean progression-free interval for responders was 38.6 months versus 9.6 months for nonresponders or patients with nonmeasurable disease (p less than 0.001). Thirteen patients are alive, eight with no clinical evidence for disease. Only four patients discontinued therapy because of toxic reactions. Hexamethylmelamine appears to be a well-tolerated drug with activity against ovarian cancer previously treated with cisplatin.

Hexamethylmelamine/altretamine as second-line therapy for epithelial ovarian carcinoma.

The purpose of this report was to review second-line hexamethylmelamine (HMM) chemotherapy of epithelial ovarian cancer to determine if HMM was active in cisplatin-resistant disease. Forty-four women with measurable disease received 100-300 mg/day HMM for 14 days, courses repeated every 4 weeks. There were 6 complete and 3 partial responses for an objective response rate of 20%. Among responding patients disease-free survival was 55% and overall survival was 88% at 3 years. Five of the 6 patients with a complete response remained disease-free at 10-117 months. Only 7/35 (20%) nonresponding patients were alive with mean follow-up of 16 months, and all had persistent cancer. Five women manifesting disease progression during cisplatin or carboplatin were subsequently treated with HMM, and none responded. Seventeen patients developing progressive cancer while receiving HMM were subsequently treated with cisplatin or carboplatin and objective responses occurred in 5 (29%). HMM was an active drug against epithelial ovarian cancer previously treated with cisplatin, but further study is needed to determine its activity against cisplatin-resistant ovarian cancer.

Basaltic rocks analyzed by the Spirit Rover in Gusev Crater.

The Spirit landing site in Gusev Crater on Mars contains dark, fine-grained, vesicular rocks interpreted as lavas. Pancam and Mini-Thermal Emission Spectrometer (Mini-TES) spectra suggest that all of these rocks are similar but have variable coatings and dust mantles. Magnified images of brushed and abraded rock surfaces show alteration rinds and veins. Rock interiors contain