Description: On November 5–8, 2019, the “Mars Extant Life: What's Next?” conference was convened in Carlsbad, New Mexico. The conference gathered a community of actively publishing experts in disciplines related to habitability and astrobiology. Primary conclusions are as follows: A significant subset of conference attendees concluded that there is a realistic possibility that Mars hosts indigenous microbial life. A powerful theme that permeated the conference is that the key to the search for martian extant life lies in identifying and exploring refugia (“oases”), where conditions are either permanently or episodically significantly more hospitable than average. Based on our existing knowledge of Mars, conference participants highlighted four potential martian refugium (not listed in priority order): Caves, Deep Subsurface, Ices, and Salts. The conference group did not attempt to reach a consensus prioritization of these candidate environments, but instead felt that a defensible prioritization would require a future competitive process. Within the context of these candidate environments, we identified a variety of geological search strategies that could narrow the search space. Additionally, we summarized a number of measurement techniques that could be used to detect evidence of extant life (if present). Again, it was not within the scope of the conference to prioritize these measurement techniques—that is best left for the competitive process. We specifically note that the number and sensitivity of detection methods that could be implemented if samples were returned to Earth greatly exceed the methodologies that could be used at Mars. Finally, important lessons to guide extant life search processes can be derived both from experiments carried out in terrestrial laboratories and analog field sites and from theoretical modeling.

Description: Heat flow measurements collected throughout the Auka and JaichMaa ja' ag' hydrothermal vent fields in the central graben of the Southern Pescadero Basin, southern Gulf of California, indicate upflow of hydrothermal fluids associated with rifting dissipate heat in excess of 10 W/m〈sup〉2〈/sup〉 around faults that have a few kilometers in length. Paradoxically, longer faults do not show signs of venting. Heat flow anomalies slowly decay to background values of ~2 W/m〈sup〉2〈/sup〉 at distances of ~1 km from these faults following an inverse square-root distance law. We develop a near-fault model of heat transport in steady state for the Auka vent field based on the fundamental Green’s function solution of the heat equation. The model includes the effects of circulation in fracture networks, and the lateral seepage of geothermal brines to surrounding hemipelagic sediments. We use an optimal fitting method to estimate the reservoir depth, permeability, and circulation rate. Independently derived constraints for the model, indicate the heat source is at a depth of ~5.7 km; from the model, permeability and flow rates in the fracture system are ~10〈sup〉-14〈/sup〉 m〈sup〉2〈/sup〉 and 10〈sup〉-6〈/sup〉 m/s, respectively, and ~10〈sup〉-16〈/sup〉 m〈sup〉2〈/sup〉 and 10〈sup〉-8〈/sup〉 m/s in the basin aquitards, respectively. Model results point to the importance of fault scaling laws in controlling sediment-hosted vent fields and slow circulation throughout low permeability sediments in controlling the brine's chemistry. Although the fault model seems appropriate and straightforward for the Pescadero vents, it does seem to be the exception to the other known sediment-hosted vent fields in the Pacific.

Description: Since 1963, the International Heat Flow Commission has been fostering the compilation of the Global Heat Flow Database to provide reliable heat-flow data. Over time, techniques and methodologies evolved, calling for a reorganization of the database structure and for a reassessment of stored heat-flow data. Here, we provide the results of a collaborative, community-driven approach to set-up a new, quality-approved global heat-flow database. We present background information on how heat-flow is determined and how this important thermal parameter could be systematically evaluated. The latter requires appropriate documentation of metadata to allow the application of a consistent evaluation scheme. The knowledge of basic data (name and coordinates of the site, depth range of temperature measurements, etc.), details on temperature and thermal-conductivity data and possible perturbing effects need to be given. The proposed heat-flow quality evaluation scheme can discriminate between different quality aspects affecting heat flow: numerical uncertainties, methodological uncertainties, and environmental effects. The resulting quality codes allow the evaluation of every stored heat-flow data entry. If mandatory basic data are missing, the entry is marked accordingly. In cases where more than one heat-flow determination is presented for one specific site, and all of them are considered for the site, the poorest evaluation score is inherited to the site level. The required data and the proposed scheme are presented in this paper. Due to the requirements of the newly developed evaluation scheme, the database structure as presented in 2021 has been updated and is available in the appendix of this paper. The new quality scheme will allow a comprehensible evaluation of the stored heat-flow data for the first time.

Description: Heat flow is reported at eight sites drilled into the Guaymas Basin, Gulf of California, during the International Ocean Discovery Program Expedition 385. This expedition seeks to understand the thermal regime of the basin and heat transfer between off-axis sills intruding the organic-rich sediments of the Guaymas Basin, and the basin floor. The relatively high sedimentation rates combined with active tectonism and voluminous shallow off-axis magmatism characterizes this basin. Our results bridge a data deficiency allowing basin-wide interpretations shading light on this young rift basin. Results show sedimentation corrected heat flow values range between 119 and 221 mW/m〈sup〉2〈/sup〉 in the basin and between 257 and 1003 mW/m〈sup〉2〈/sup〉 at the site of a young sill intrusion, termed Ringvent. Thermal analysis shows that heat in the Guaymas Basin is being dissipated by conduction for plate ages 〉0.2 Ma, whereas younger plate ages are also dissipating heat by advection. Drilling data show that an active ring of hydrothermal vent root to a shallow sill fueling low-temperature hydrothermal fluids with discharge velocities of 10–200 mm/yr. Possible recharge sites are located ~1 km away from the sill's border. Modeling of the heat output and assuming supplied by a cooling sill, we estimate a sill thickness at Ringvent of ~240 m. A simple order-of-magnitude model predicts that relatively small amounts of magma are needed to account for the elevated heat flow in non-volcanic, sediment-filled rifts like the central and northern Gulf of California where heating of the upper crust is achieved via advection by sill emplacement and hydrothermal circulation. Multiple timescales of cooling control the crustal, chemical and biological evolution of the Guaymas Basin. Here we recognize at least four timescales: the time interval between intrusions (~10〈sup〉3〈/sup〉 yr), the thermal relaxation time of sills (~10〈sup〉4〈/sup〉 yr), the characteristic warming time of the sediments (~10〈sup〉5〈/sup〉 yr), and the cooling of the entire crust at geologic timescales.

Description: The data publication contains the compilation of global heat-flow data by the International Heat Flow Commission (IHFC; www.ihfc-iugg.org) of the International Association of Seismology and Physics of the Earth's Interior (IASPEI). The presented data update 2023 contains data generated between 1939 and 2022 and constitutes the first intermediate update benefiting from the global collaborative assessment and quality control of the Global Heat Flow Database running since May 2021 (http://assessment.ihfc-iugg.org).