Revealing the Mysteries of Venus: The DAVINCI Mission

The Deep Atmosphere Venus Investigation of Noble gases, Chemistry, and Imaging (DAVINCI) mission described herein has been selected for flight to Venus as part of the NASA Discovery Program. DAVINCI will be the first mission to Venus to incorporate science-driven flybys and an instrumented descent sphere into a unified architecture. The anticipated scientific outcome will be a new understanding of the atmosphere, surface, and evolutionary path of Venus as a possibly once-habitable planet and analog to hot terrestrial exoplanets. The primary mission design for DAVINCI as selected features a preferred launch in summer/fall 2029, two flybys in 2030, and descent sphere atmospheric entry by the end of 2031. The in situ atmospheric descent phase subsequently delivers definitive chemical and isotopic composition of the Venus atmosphere during a cloud-top to surface transect above Alpha Regio. These in situ investigations of the atmosphere and near infrared descent imaging of the surface will complement remote flyby observations of the dynamic atmosphere, cloud deck, and surface near infrared emissivity. The overall mission yield will be at least 60 Gbits (compressed) new data about the atmosphere and near surface, as well as first unique characterization of the deep atmosphere environment and chemistry, including trace gases, key stable isotopes, oxygen fugacity, constraints on local rock compositions, and topography of a tessera.


Introduction
The atmosphere of Venus atmosphere holds clues to its origin, evolution, and dynamics and may reflect the history of putative past oceans and active volcanism (Bougher et al. 1997;Crisp et al. 2002;Treiman 2007;Baines et al. 2013;Glaze et al. 2017;2018;Garvin et al. 2020a;2020b;D'Inecco et al. 2021). The selected DAVINCI mission ( Figure 1 spacecraft and a descent sphere that will be dropped into the atmosphere above Alpha Regio, an enigmatic tessera (i.e. mountainous, strongly tectonically deformed highland) terrain whose composition may reflect remnants of ancient continental crust (Hashimoto et al. 2008;Gilmore et al. 2015). connections to questions leftover from past missions, and with new connections to contemporary and future missions and the era of exoplanet science. DAVINCI is viewed as a gateway for Venus as a future astrobiology target in the context of how habitability is both established and lost in our solar system and beyond (e.g. Limaye et al. 2021).
Previous Venus exploration has led to significant advancements in our understanding of the bulk atmospheric composition of the planet, its geological history, and its geodynamics (Grinspoon & Bullock 2007;Taylor and Grinspoon 2009;Way & Del Genio 2019;Lammer et al. 2020). Yet Venus remains the least understood of the inner planets.
With the recent selection of multiple Venus missions, this may soon change. The DAVINCI mission will complement contemporary Venus missions, as shown in Figure 1, which feature next-generation radar and night-side near infrared (NIR) emission spectrometers for mapping the surface at scales from tens of meters (synthetic aperture radar; SAR) to ~100 km (NIR spectroscopy). These payloads will fly on missions in the late 2020s (NASA's VERITAS) and mid-2030s (ESA's EnVision) to determine compositional patterns at regional to global scale for advancing models of Venus's crustal and thermal evolution (Ghail et al. 2018;2021). In turn, the DAVINCI mission will provide in situ context for these global remote sensing missions by capturing definitive measurements of atmospheric composition, key atmospheric isotope ratios, multi-band descent imaging, and Venus flyby imaging at ultraviolet (UV) and NIR wavelengths to establish new knowledge about the vertically resolved atmosphere and currently poorly understood regions of the surface.
Venus's thick cloud cover and harsh surface environment in the present day obscure the possibility, supported by recent modeling efforts (e.g. Way & Del Genio 2020), that Venus could have been more Earth-like in the past, possibly even for an extended time period ( Figure 2). The hypothesis of a past habitable Venus is supported by accretion models which suggest that Venus and Earth would have had similar initial water inventories (Elkins-Tanton, 2011), by evolutionary climate models (Way et al., 2016), and by the surprisingly elevated ratio of deuterium to hydrogen (D/H) in water in its atmosphere, which is at least 120 times that on Earth. This elevated D/H ratio could result from H2O photolysis following ocean evaporation, with preferential loss of hydrogen to space compared to the twice-heavier deuterium (e.g. Donahue et al. 1982;Kasting 1988;Donahue et al. 1997). However, other models suggest that Venus never condensed oceans (Hamano et al. 2013;Turbet at al. 2021) and that preferential H loss occurred directly from photolysis of a steam atmosphere.
Other possible explanations for the elevated D/H ratio include outgassed water within the past 0.5-1 billion years followed by fractionating escape (Grinspoon 1993). An improved understanding of the history of possible past Venusian water requires improved measurements of the D/H ratio: the Pioneer Venus mass spectrometer measured D/H (~0.016, ~100 × the terrestrial value) after its instrument inlet became clogged with droplets of sulfuric acid (Donahue et al., 1982), and did not survey this key parameter from the top of the atmosphere to the near surface. Ground-based measurements have estimated Venus D/H at 0.019 ± 0.006 or 120 ± 40 × the terrestrial value (De Bergh et al. 1991). More recent Venus Express measurements may be inconsistent with Pioneer Venus and Earthbased observations and imply that the D/H ratio may increase markedly with altitude: Bertaux et al. 2007 measured the bulk lower atmosphere HDO/H2O at ~0.05, while at 70-95 km, the measured value reached ~0.12, implying imply D/H values of ~0.025 in the bulk atmosphere and up to ~0.06 at 70-95 km.
DAVINCI will provide D/H measurements with high precision (~1% in 10 ppmv; 0.2% in 100 ppmv) to resolve the question of altitude distribution and discriminate between different histories of water loss. D/H measurements in the bulk of the troposphere are missing, making DAVINCI's altitude-resolved measurements particularly important. Additionally, D/H precision of 0.2% is sufficient to resolve between D/H evolution scenarios modeled in Grinspoon (1993). At least one D/H sample will be obtained above the clouds to help resolve between competing hypotheses for the surprising vertical gradient measured by Venus Express (e.g. Liang and Yung 2009), and at least 5 samples will be obtained below 50 km, including at least one below 15 km. In addition to these measurements, hundreds of moderate resolution (20%) mass spectrometer measurements of H2O and HDO will be obtained from below the clouds to surface touchdown.
Estimates of surface composition from DAVINCI may provide additional corroborating evidence for past oceans. On Earth, silica-enriched felsic rocks (specifically granites and granitoids) form from interior continent-building processes with involvement of water (as opposed to mafic magmas and rocks, e.g. basalt, which form more commonly in water-poor mantle regions) (e.g. Campbell & Taylor 1983;Filiberto 2014). On Venus, emissivity signatures consistent with felsic rocks have been reported in certain highland regions (e.g. Hashimoto et al. 2008;Weller & Kiefer 2020), including the DAVINCI descent site, the Alpha Regio tessera region (Gilmore et al. 2015 The evolution of Venus's climate is the result of the interplay between the conditions of formation, the history of solar insolation, the role of exogenous sources of volatiles, and the effects of volcanism over time. DAVINCI measurements of noble gases will provide new insights into all of these processes because, being non-reactive, once released to the atmosphere, they do not react with other material sinks or readily return to the planet's interior. A comparison of noble gases on Venus, Earth, and Mars can provide insights into differences or similarities in the materials that formed each of these planets (e.g., Pepin 2006;Baines et al. 2013;Avice & Marty 2020). The late-1970s measurements from Pioneer Venus Large Probe (PVLP) were incomplete and did not offer the precision required to sufficiently measure the noble gases, especially xenon and helium (Lammer et al. 2020). To date, only Ne and Ar have been robustly measured on Venus, rendering it difficult to definitively compare the formation of Venus to Earth and Mars. Neon and argon are both much more abundant on Venus than on Earth ---by factors of 30 and 70, respectively ---and are roughly as abundant as they are in chondritic meteorites ( Figure 3). Krypton was measured, but the two reported Kr abundances differ by a factor of fifteen (von Zahn et al. 1983). Only upper limits exist for xenon ( Figure 3). The chondritic Ne and Ar abundances suggest a meteoritic source and little subsequent escape. The higher Kr abundance is consistent with this, but the smaller Kr abundance instead suggests a solar nebular source.
The noble gas isotope structures should be more telling. Argon can indicate atmospheric loss through the 36 Ar/ 38 Ar ratio. Source 36 Ar/ 38 Ar ratios range from 5.3 (chondritic) to 5.50 (solar), but the 36 Ar/ 38 Ar is only 4.1±0.1 on Mars , reflecting a history of atmospheric escape since formation. Neon isotopes can distinguish between nebular and meteoritic sources of the atmosphere. Earth's atmospheric 20 Ne/ 22 Ne is 9.8 (chondritic), but its interior ratio is 12.5, and rarely greater, possibly reflecting the solar nebula (Williams and Mukhopadhyay 2019). Venus's 20 Ne/ 22 Ne ratio was reported as 11.8±1.7 or 14±3 by two different missions (von Zahn et al. 1983), which together suggest a protoplanetary nebular source for Ne (with solar ratio is 13.9±0. 1;Meshik et al. 2012) rather than a chondritic source with ratio ~10. Confirmation of a solar ratio would be telling. Note, however, that Viking reported Mars's 36 Ar/ 38 Ar ratio as 5.5±1.5, which although correct is also misleading, because the actual ratio hit the bottom of the error bar at 4.1±0.1 ). It is difficult for Kr to escape from Venus by any process other than impact erosion; hence, it is expected that Kr isotopes should preserve the fingerprints of the source (chondritic for Earth, solar for Mars). Any deviation from this (e.g., a strong mass fractionation) would be revolutionary. Xenon isotopes are the most numerous and have the most potential to see deep into Venus's history. Xenon on Earth and Mars is depleted (i.e., the Kr/Xe ratios are high) and mass fractionated (i.e, the heavy isotopes are relatively more abundant), the latter in particular indicating that, despite its great weight, Xe has escaped.
Chemically active gases could react with surface minerals and glasses leading to formation of newly formed solids such ferrous compounds that undergo oxidation by atmospheric CO2 and in sulfates and sulfides that trap S-bearing gases (e.g., Fegley et al., 1997a;Zolotov, 2018). In addition to compositional changes, these interactions influence such physical properties of surface materials as grain size, density, electrical conductivity, and reflectance that all affect detectability of altered materials by remote sensing methods (Gilmore et al., 2017). Better understanding of these gas-solid type interactions will require chemical and physical knowledge of the lowest 12 km of the Venus atmosphere. DAVINCI measurements of H2O, SO2, OCS, CO, H2S, sulfur allotropes (Sn), and HCl together with temperature-pressure conditions in the deep atmosphere will constrain the stability of primary and secondary solids and inform the directions of gas-solid type reactions. In particular, redox conditions at the atmosphere-surface interface remain uncertain, with fugacity (f) of O2 uncertain within almost two orders of magnitude (log10fO2 = 10 -21.7 to 10 -20.0 bars, Fegley et al., 1997b). In the deepest atmosphere, the redox state will be constrained with DAVINCI measurements of major chemically active gases (CO2, SO2, CO, OCS) and fO2 itself will be directly measured with a DAVINCI student collaboration experiment. These measurements will also help determine whether the atmosphere is close to the conditions conducive to varied gas-mineral equilibria (e.g. magnetite-hematite, magnetite-hematitepyrite), which could assess potential control (buffering) of concentrations of some atmospheric oxidants by surface mineralogy (Figure 4). DAVINCI will conduct definitive in situ analyses of near-surface gases to reveal chemical exchange between the surface and deep atmosphere, and link these in situ investigations to new observations of the topography and near infrared reflectivity of a representative tessera to test hypotheses of water-rock interactions that could have led to aqueous minerals, layered water-deposited sediments, and light-colored felsic igneous rocks. Furthermore, the instruments can provide critical compositional context for potential newly discovered species (e.g. PH3; Greaves et al. 2020) that may be linked to the history of habitability on Venus even today (e.g. Limaye et al. 2021), or possibly to ongoing volcanic activity (Truong & Lunine 2021). DAVINCI will also provide a detailed survey of compounds bearing elements critical to life on Earth (e.g., those containing such elements as carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur). DAVINCI has been designed to provide flexibility and responsiveness to new discoveries about the Venus atmosphere and will provide vital constraints on key chemical cycles such as those involving sulfur as an example ( Figure 6).
Because Venus-like exoplanets may represent the most readily observable class of terrestrial worlds for the James Webb Space Telescope ( Arney & Kane 2020).

DAVINCI Mission Science Objectives
In summary, through its comprehensive suite of measurements, DAVINCI will provide answers to the many scientific questions of our neighboring planet via measurements to be completed during the late 2020s and early 2030s:

Mission Design tied to Science Drivers
DAVINCI is a multi-element mission concept that delivers both a deep atmosphere descent sphere (DS) (i.e., a "probe") and a flyby remote sensing Carrier-Relay-Imaging-Spacecraft (CRIS) to Venus, each carrying sophisticated instruments tailored to the prioritized scientific goals and objectives of the mission. As selected by NASA in June 2021, the primary mission design for DAVINCI features two flybys and an in situ descent phase that would deliver definitive chemical and isotopic composition of the Venus atmosphere during a 59-minute transect from ~ 70 km to the surface ( Figure 5). This in situ investigation is preceded by remote observations of the dynamic atmosphere, cloud deck, and surface properties during the flybys, prior to the entry-descent-science in situ phase involving the DS. As described in Section 1, this "flyby-probe" mission architecture is optimized to produce a set of focused measurements to improve models of Venus's current and past state, its atmospheric and interior evolution, and questions about habitability (e.g. Way & Del Genio 2020; Limaye et al. 2021;Turbet et al. 2021).

Overall Mission Architecture
As selected, DAVINCI would nominally launch in June 2029 as shown in Figure 7, and after a ~six-month cruise, the spacecraft would fly by Venus for unique remote sensing science that includes dayside UV cloud motion videos, hyperspectral UV imaging spectroscopy, and night side NIR surface emissivity mapping. As currently planned, the trajectory returns nine months later for a second flyby in November 2030 with additional dayside UV observations and nightside surface measurements of key highlands (e.g., tesserae and Maat Mons). The flight system returns to Venus seven months later and delivers the in situ descent sphere to Alpha Regio on June 21, 2031 with favorable solar illumination for descent high-sensitivity NIR imaging under the clouds. DAVINCI's targeted entry-descent-imaging site within Alpha twice the size of Texas) such that a precisely controlled descent is not necessary. DAVINCI's touchdown ellipse comfortably fits within this area with large margin, and enables highresolution descent images to map the local composition-related infrared emissivity and local topography of this unique region. Figure 8 highlights the descent sphere imaging corridor and its landing error ellipse within Alpha Regio using the Arecibo radio-telescope-based pseudo-topography of this tessera region at sub-km scales.  being the 3-sigma error ellipse that constitutes the imaging descent corridor. The color scaling represents pseudo-topography from low blue (0 km at the mean planetary radius, MPR, of 6051.84 km) to dark brown (over 2.5 km above MPR, AMPR). At right is a perspective view of the entry corridor (red ellipse is ~ 310 km in its long-axis) atop the ridged mountains of Alpha Regio with over 900m of local relief. Arecibo data analysis and processing by the DAVINCI team.
In June 2031, two days before arrival at Venus, the Probe Flight System (PFS) is released.
The spacecraft observes its release, and then conducts a divert maneuver to fly by Venus   Table 2 for instrument details for the in situ descent sphere in comparison with previous in situ missions (PVLP).

Descent Sphere Design
The DAVINCI DS is a hermetically sealed titanium pressure vessel with dimensions (  All of the science instruments are mounted on the forward deck. Plumbing connects each atmospheric sensor to its respective port. The VMS and VTLS inlet ports, totaling four inlets, are fitted with break-off caps that are ejected at the appropriate times to allow atmospheric gas ingestion at different altitudes. The aft deck accommodates battery to power the DS after separation from the spacecraft; an adaptive transponder; avionics to execute the descent timeline activities, collect, store and forward science data; internal pressure and acceleration sensors; and a small gas re-pressurization system used in the event of pressure decay during cruise.
To protect against external temperatures that increase during descent and reach up to 460°C at the surface, the temperatures of the internal components of the DS are maintained within their operational limits during the descent through the Venus atmosphere using several passive thermal control techniques refined during GSFC design and test efforts. The DS benefits from over ten years of investment and engineering refinement at GSFC including testing in representative Venus environments ( Figure 11; The ~1 hour descent sequence is shown in summary in Figure 5 and in detail in Figure   12. Monte Carlo simulations of the sequence have been performed over the past five years using current Venus atmosphere reference models, with results that were independently checked against performance requirements throughout the mission proposal review process.

2.3Descent Sphere Payload
The DAVINCI mission will explore Venus and its atmosphere through a carefully architected in situ mission rich in comprehensive measurements. The DAVINCI DS utilizes five instruments to bring a highly capable analytical chemistry laboratory (   (Donahue 1982), with specific details listed in right-most column (Bougher et al. 1997, Crisp et al. 2002).  To avoid this on DAVINCI, VMS incorporates heated inlet tubes to vaporize trapped droplets, filters of passivated/sintered metal spheres to capture particles large enough to cause clogs in capillary leaks used for pressure reduction, and the aforementioned second inlet for sampling below the sulfuric acid cloud and haze. Table 3 Figure 13 and described in Table 3.  situ environmental measurements during the descent. VASI aims to determine the temperature profile to better than 1 K to constrain models and to permit improved calibration of emissivity retrievals, which depend on knowing the temperature of the Venus surface. In addition to their high quality, atmospheric structure data will be obtained with much higher vertical resolution (<50 m) than previous missions.

Venus Descent Imager (VenDI):
VenDI is a NIR descent imaging system with a nadir orientation and 1024x1024 pixel full-frame CCD detector permitting high SNR imaging from under the clouds and sub-cloud haze (~38 km) to the surface of Venus at spatial scales from 1-200 m. The VenDI camera head is based on the heritage design from MSL/MastCam, MSL/MAHLI, and MSL/MARDI (e.g. Malin et al. 2017). Its broadband (740-1040 nm) and narrow-band filters (980-1030 nm) will provide images at spatial scales (< 200 m down to 2 m/pixel) not possible from orbit. These data will be used to constrain surface composition (i.e., distinguish rocks that are felsic from ones that are mafic) by utilizing band ratios, a technique used effectively with data from various sensors and platforms on many planetary surfaces (e.g., Robinson et al., 2007;Delamere et al., 2010;Gilmore et al., 2008). VenDI will acquire bundles of images from which topography can be derived using machine vision algorithms via Structure-from-Motion (SfM), a method that employs multiple overlapping images to infer three-dimensional texture (Garvin et al. 2018). Topography with meter-scale vertical precision can be computed from bundles of VenDI descent images acquired in the lower-most 5 km of descent, with horizontal (spatial) resolution of 10m and finer. Images from ~1.5 km to the surface will feature spatial resolution less than 1-meter allowing erosional studies relating to the environmental history of Venus. Final VenDI imaging resolutions is expected to be < 50 cm/pixel and as fine as 10 cm/pixel depending on twoway data links between the DS and the overhead CRIS in the last moments before touchdown in June 2031. Figure 14 shows an example digital elevation map (DEM) and overlaid band ratio map of the Zagros Mountains on Earth, a terrain with comparable topography to Alpha Regio.

Venus Oxygen Fugacity Student Collaboration Experiment (VfOx):
VƒOx is a solid-state nernstian ceramic oxygen sensor that relies on a reference material with known oxygen fugacity, ƒO2 (e.g., a gas mixture or solid oxide). The ƒO2 differential between the known and unknown sample causes a diffusion of oxygen through the electrolyte, resulting in a small, measurable voltage. VƒOx will measure oxygen composition of the lower atmosphere of Venus, with a particular emphasis on informing the oxidation state of surface rocks at our descent location and providing constraints on surface-atmosphere exchange chemistry.

Payload
The DAVINCI CRIS flyby remote sensing payload consists of two instrument packages: (1) Venus Imaging System for Observational Reconnaissance (VISOR); and (2) (Goodfellow et al. 2014) will be employed for atmospheric parameter retrievals. This will demonstrate how complex tasks can be performed by an AI-enabled device in the on-board data handling system to analyze data on-board in near real time, generate a reduced dataset to be returned in full, and to help flag and prioritize full resolution data to return.
With these new capabilities, CUVIS will obtain spectra that are far better for diagnosing upper cloud composition than has been previously possible. CUVIS will provide new spectral clues to the UV absorber(s) located in the upper cloud deck that are responsible for absorbing half of the solar radiation received by Venus. With its hyperspectral imaging capability, CUVIS enables correlation between cloud features, structure, and chemistry in the upper cloud deck. CUVIS will image Venus in full sun during each of the two DAVINCI mission flybys.
The DAVINCI payload instruments will work together to comprehensively investigate the Venus environment. Table 4 summarizes how the DAVINCI instruments will address the mission's Key Questions introduced in Section 1. Table 4. DAVINCI measurements taken with its suite of seven instruments will address key DAVINCI objectives introduced in Section 1.

DAVINCI Key Questions DAVINCI Measurements
What is the origin of Venus's atmosphere,

Connecting Venus to Exploration beyond the Solar System
Venus is important to study not only as a deeply mysterious and compelling world of our solar system, but also as an example of a larger class of exo-Venus worlds that will likely be observed beyond the solar system in the upcoming era of the James Webb Space Telescope (JWST). Almost 5,000 exoplanets have been detected over the past several decades through a multitude of efforts. Some of these worlds will soon be observed by JWST, successfully launched in December 2021 with an anticipated mission lifetime greater than 10 years. If DAVINCI launches in 2029 and arrives at Venus in June 2031, there may be of overlap between these two missions, potentially permitting an interplay between DAVINCI in situ measurements and JWST targeted observations of exoplanets.
Exoplanets that receive Venus-like insolation levels likely represent the most observable class of terrestrial exoplanets to JWST (Kane et al. 2014). Yet these worlds will be challenging targets to interpret: most of the mass of the Venus atmosphere resides beneath its thick cloud and haze layers, but the transit transmission observations available to JWST cannot penetrate below cloud and haze and will therefore be limited to skimming the rarefied upper atmospheres of these worlds if they are enshrouded like Venus.
Consequently, it has been suggested that a planet with a high altitude cloud layer could appear spectrally similar to a very different kind of planet with a thin, clear sky atmosphere (Lustig-Yaeger et al. 2019). Statistical trends in observations of such worlds could produce a "mirage" of the cosmic shoreline, the empirical dividing line in insolation-escape velocity space that separates planets with and without atmospheres (Zahnle & Catling 2017 (Jessup et al. 2020).
In a more general sense, given the challenges inherent to exoplanet observations, which will typically have large error bars in even the best case scenarios for near-term observations, the worlds of the solar system including Venus provide valuable "ground truth" to improve our models and interpretations of these distant worlds. Given the particular challenges associated with observing cloudy Venus-like worlds (e.g. Barstow et al. 2016), and given that multiple potential exo-Venus planets at varied ages and stages of evolution are some of the highest priority targets for JWST (e.g., Ostberg & Kane 2019; Lustig-Yaeger et al. 2019), DAVINCI offers an opportunity for definitive "atmosphere truth" to inform and constrain studies of Venus-like exoplanets. For instance, planets of the TRAPPIST-1 system will represent a core community observation initiative with JWST (Gillon et al. 2020), and more than one of these worlds may be Venus-like (e.g., Lincowski at al. 2018; Moran et al. 2018). Furthermore, if Venus was habitable in the past, some exo-Venus planets may likewise host habitable conditions, so understanding the mechanisms and processes that governed and enabled past Venus habitability may help us to better understand the parameter space in which habitable worlds may be found beyond the solar system, allowing refinement of the habitable zone. Indeed, the inner edge of the classical habitable zone is typically used as a barometer of terrestrial planet habitability limits, as applied to other solar systems, based on our limited knowledge of Venus's evolutionary history (e.g. Kasting et al. 1993;Kopparapu et al. 2013). Thus, improvement in our understanding of the current and past chemical and physical states of Venus represents arguably the highest priority synergistic target between the solar system and exoplanet communities for the coming years (Kane et al. 2021).
Venus may even help us to better understand how to search for and interpret oxygen as a biosignature (i.e. a remotely observable sign of life) in certain exoplanet atmospheres (e.g. Meadows 2017). Venus currently generates abiotic oxygen through CO2 photolysis, which can be observed through airglow of excited (a 1 Δg) oxygen on the Venusian nightside at 1.27 mm (Crisp et al. 1996), but the abundance of ground-state oxygen in the Venus atmosphere is highly unconstrained, suggesting rapid removal through chemical processes that can be better understood through DAVINCI measurements of oxygen-bearing species.
Additionally, if Venus lost oceans of water to space the past, oxygen would have been generated through the processes of H2O photolysis, but this oxygen is not observed in the Venus atmosphere today. Exoplanets that lose multiple Earth oceans-worth of water could generate 100s to even 1000s of bars of abiotic O2 through this process (e.g. Luger& Barnes 2015). Understanding the fate of oxygen due to possible past water loss on Venus may help to evaluate the plausibility of such models. These so-called oxygen "false positives" may be particularly relevant to JWST targets because the high activity levels and particular evolutionary histories of the low mass stars JWST will target make them especially vulnerable to generating abiotic oxygen through these processes (e.g. Meadows 2017; Meadows et al. 2018).
Beyond JWST, the Astronomy and Astrophysics 2020 decadal survey (NAS 2021) recently recommended a large infrared/optical/ultraviolet flagship observatory capable of observing exoplanets directly in reflected light around sun-like stars. Such a telescope would be capable of observing Venus-like planets in solar systems with evolutionary histories that may be similar to our own. Pathways to Discovery in Astronomy and Astrophysics for the 2020s discusses that observations of young Venus analog planets orbiting sun-like stars could help us understand how Venus evolved in our solar system.

Conclusions
The DAVINCI mission concept builds upon the flyby, landed, and orbital mapping missions of the past (e.g., PVLP, Venera, Vega, Magellan, Venus Express, and Akatsuki) to take the next critical step in Venus exploration: a sophisticated descent sphere-flyby combination ( Figure 1). DAVINCI will deliver a chemical laboratory capable of revealing the atmospheric chemistry, a descent imager surpassing previous similar instruments on Mars (e.g., with composition and topography), an environmental package to establish context, and flyby imaging (and communications) to connect remote sensing to in situ exploration. The discoveries to be made by DAVINCI will close long-standing gaps in models of atmospheric evolution, Venus's water loss, and surface-atmosphere interactions. There are multiple competing models for the state of early Venus (e.g. Way et al. 2016;Turbet et al. 2021), and a precise measurement of the bulk atmosphere D/H is essential for quantifying the timing and quantity of possible water loss on Venus. Additional information will come from DAVINCI's measurements of the rock types of the tesserae and precise measurements of noble gases, which will provide multiple lines of evidence for interpreting our neighboring planet's ancient history. The resulting model inputs and constraints would benefit a broad community of next-generation scientists to understand how planetary habitability may evolve (Seager at al. 2021;Sousa-Silva et al. 2020;Greaves at al. 2020;Encrenaz et al. 2020) and to pave the way for exoplanetary modeling, observations, and exploration of Venus-like worlds beyond our solar system.