Boron has been identified for the first time on the surface of Mars, indicating the potential for long-term habitable groundwater in the ancient past. This finding and others from NASA's Curiosity rover science team will be discussed in a press conference today in San Francisco during the American Geophysical Union conference.
"No prior mission to Mars has found boron," said Patrick Gasda, a postdoctoral researcher at Los Alamos National Laboratory. "If the boron that we found in calcium sulfate mineral veins on Mars is similar to what we see on Earth, it would indicate that the groundwater of ancient Mars that formed these veins would have been 0-60 degrees Celsius [32-140 degrees Fahrenheit] and neutral-to-alkaline pH." The temperature, pH, and dissolved mineral content of the groundwater could make it habitable.
The boron was identified by the rover's laser-shooting Chemistry and Camera (ChemCam) instrument, which was developed at Los Alamos National Laboratory in conjunction with the French space agency. Los Alamos' work on discovery-driven instruments like ChemCam stems from the Laboratory's experience building and operating more than 500 spacecraft instruments for national defense.
Boron is famously associated with arid sites where much water has evaporated away--think of the borax that mule teams once hauled from Death Valley. However, environmental implications of the boron found by Curiosity are still open to debate. Scientists are considering at least two possibilities for the source of boron that groundwater left in the veins: It could be that the drying out of part of Gale lake resulted in a boron-containing deposit in an overlying layer, not yet reached by Curiosity. Some of the material from this layer could have later been carried by groundwater down into fractures in the rocks. Or perhaps changes in the chemistry of clay-bearing deposits and groundwater affected how boron was picked up and dropped off within the local sediments.
The discovery of boron is only one of several recent findings related to the composition of Martian rocks. Curiosity is climbing a layered Martian mountain and finding rock-composition evidence of how ancient lakes and wet underground environments changed, billions of years ago, in ways that affected their favorability for microbial life.
he lack of liquid water on the surface of Mars today has been demonstrated by new evidence in the form of meteorites on the Red Planet examined by an international team of planetary scientists.
In a study led by the University of Stirling, an international team of researchers has found the lack of rust on the meteorites indicates that Mars is incredibly dry, and has been that way for millions of years.
The discovery, published in Nature Communications, provides vital insight into the planet's current environment and shows how difficult it would be for life to exist on Mars today.
Mars is a primary target in the search for life outside Earth, and liquid water is the most important pre-requisite for life.
Dr Christian Schröder, Lecturer in Environmental Science and Planetary Exploration at the University of Stirling and Science Team Collaborator for the Mars Exploration Rover Opportunity mission, said:
"Evidence shows that more than 3 billion years ago Mars was wet and habitable. However, this latest research reaffirms just how dry the environment is today. For life to exist in the areas we investigated, it would need to find pockets far beneath the surface, located away from the dryness and radiation present on the ground."
A study published last year, which used data from the Curiosity Rover investigating Gale crater on Mars, suggested that very salty liquid water might be able to condense in the top layers of Martian soil overnight.
"But, as our data show, this moisture is much less than the moisture present even in the driest places on Earth," explains Dr Schröder.
Was Venus the First Habitable World of our Solar System?
Authors:
Way et al
Abstract:
Present-day Venus is an inhospitable place with surface temperatures approaching 750K and an atmosphere over 90 times as thick as present day Earth's. Billions of years ago the picture may have been very different. We have created a suite of 3D climate simulations using topographic data from the Magellan mission, solar spectral irradiance estimates for 2.9 and 0.715 billion years ago, present day Venus orbital parameters, an ocean volume consistent with current theory and measurements, and an atmospheric composition estimated for early Venus. Using these parameters we find that such a world could have had moderate temperatures if Venus had a rotation period slower than about 16 Earth days, despite an incident solar flux 46-70% higher than modern Earth receives. At its current rotation period of 243 days, Venus's climate could have remained habitable until at least 715 million years ago if it hosted a shallow primordial ocean. These results demonstrate the vital role that rotation and topography play in understanding the climatic history of exoplanetary Venus-like worlds being discovered in the present epoch.
Venus may have had a shallow liquid-water ocean and habitable surface temperatures for up to 2 billion years of its early history, according to computer modeling of the planet's ancient climate by scientists at NASA's Goddard Institute for Space Studies (GISS) in New York.
The findings, published this week in the journal Geophysical Research Letters, were obtained with a model similar to the type used to predict future climate change on Earth.
"Many of the same tools we use to model climate change on Earth can be adapted to study climates on other planets, both past and present," said Michael Way, a researcher at GISS and the paper's lead author. "These results show ancient Venus may have been a very different place than it is today."
Venus today is a hellish world. It has a crushing carbon dioxide atmosphere 90 times as thick as Earth's. There is almost no water vapor. Temperatures reach 864 degrees Fahrenheit (462 degrees Celsius) at its surface.
Scientists long have theorized that Venus formed out of ingredients similar to Earth's, but followed a different evolutionary path. Measurements by NASA's Pioneer mission to Venus in the 1980s first suggested Venus originally may have had an ocean. However, Venus is closer to the sun than Earth and receives far more sunlight. As a result, the planet's early ocean evaporated, water-vapor molecules were broken apart by ultraviolet radiation, and hydrogen escaped to space. With no water left on the surface, carbon dioxide built up in the atmosphere, leading to a so-called runaway greenhouse effect that created present conditions.
Previous studies have shown that how fast a planet spins on its axis affects whether it has a habitable climate. A day on Venus is 117 Earth days. Until recently, it was assumed that a thick atmosphere like that of modern Venus was required for the planet to have today's slow rotation rate. However, newer research has shown that a thin atmosphere like that of modern Earth could have produced the same result. That means an ancient Venus with an Earth-like atmosphere could have had the same rotation rate it has today.
If conditions had been just a little different an eon ago, there might be plentiful life on Venus and none on Earth.
The idea isn't so far-fetched, according to a hypothesis by Rice University scientists and their colleagues who published their thoughts on life-sustaining planets, the planets' histories and the possibility of finding more in Astrobiology this month.
The researchers maintain that minor evolutionary changes could have altered the fates of both Earth and Venus in ways that scientists may soon be able to model through observation of other solar systems, particularly ones in the process of forming, according to Rice Earth scientist Adrian Lenardic.
Obliquity Variability of a Potentially Habitable Early Venus
Authors:
Barnes et al
Abstract:
Venus currently rotates slowly, with its spin controlled by solid-body and atmospheric thermal tides. However, conditions may have been far different 4 billion years ago, when the Sun was fainter and most of the carbon within Venus could have been in solid form, implying a low-mass atmosphere. We investigate how the obliquity would have varied for a hypothetical rapidly rotating Early Venus. The obliquity variation structure of an ensemble of hypothetical Early Venuses is simpler than that Earth would have if it lacked its large moon (Lissauer et al., 2012), having just one primary chaotic regime at high prograde obliquities. We note an unexpected long-term variability of up to ±7° for retrograde Venuses.
Venus has an "electric wind" strong enough to remove the components of water from its upper atmosphere, which may have played a significant role in stripping Earth's twin planet of its oceans, according to new results from ESA's (European Space Agency) Venus Express mission by NASA-funded researchers.
"It's amazing, shocking," said Glyn Collinson, a scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "We never dreamt an electric wind could be so powerful that it can suck oxygen right out of an atmosphere into space. This is something that has to be on the checklist when we go looking for habitable planets around other stars." Collinson is lead author of a paper about this research published June 20, 2016, in the journal Geophysical Research Letters.
Ionic Strength Is a Barrier to the Habitability of Mars
Authors:
Fox-Powell et al
Abstract:
The thermodynamic availability of water (water activity) strictly limits microbial propagation on Earth, particularly in hypersaline environments. A considerable body of evidence indicates the existence of hypersaline surface waters throughout the history of Mars; therefore it is assumed that, as on Earth, water activity is a major limiting factor for martian habitability. However, the differing geological histories of Earth and Mars have driven variations in their respective aqueous geochemistry, with as-yet-unknown implications for habitability. Using a microbial community enrichment approach, we investigated microbial habitability for a suite of simulated martian brines. While the habitability of some martian brines was consistent with predictions made from water activity, others were uninhabitable even when the water activity was biologically permissive. We demonstrate experimentally that high ionic strength, driven to extremes on Mars by the ubiquitous occurrence of multivalent ions, renders these environments uninhabitable despite the presence of biologically available water. These findings show how the respective geological histories of Earth and Mars, which have produced differences in the planets' dominant water chemistries, have resulted in different physicochemical extremes which define the boundary space for microbial habitability.
Earth scientists from Rice University, Yale University and the University of Tokyo are offering a new answer to the long-standing question of how our planet acquired its oxygenated atmosphere.
Based on a new model that draws from research in diverse fields including petrology, geodynamics, volcanology and geochemistry, the team's findings were published online this week in Nature Geoscience. They suggest that the rise of oxygen in Earth's atmosphere was an inevitable consequence of the formation of continents in the presence of life and plate tectonics.
"It's really a very simple idea, but fully understanding it requires a good bit of background about how the Earth works," said study lead author Cin-Ty Lee, professor of Earth science at Rice. "The analogy I most often use is the leaky bathtub. The level of water in a bathtub is controlled by the rate of water flowing in through the faucet and the efficiency by which water leaks out through the drain. Plants and certain types of bacteria produce oxygen as a byproduct of photosynthesis. This oxygen production is balanced by the sink: reaction of oxygen with iron and sulfur in the Earth's crust and by back-reaction with organic carbon. For example, we breathe in oxygen and exhale carbon dioxide, essentially removing oxygen from the atmosphere. In short, the story of oxygen in our atmosphere comes down to understanding the sources and sinks, but the 3-billion-year narrative of how this actually unfolded is more complex."
Lee co-authored the study with Laurence Yeung and Adrian Lenardic, both of Rice, and with Yale's Ryan McKenzie and the University of Tokyo's Yusuke Yokoyama. The authors' explanations are based on a new model that suggests how atmospheric oxygen was added to Earth's atmosphere at two key times: one about 2 billion years ago and another about 600 million years ago.
THEO Concept Mission: Testing the Habitability of Enceladus's Ocean
Authors:
MacKenzie et al
Abstract:
Saturn's moon Enceladus offers a unique opportunity in the search for life and habitable environments beyond Earth, a key theme of the National Research Council's 2013-2022 Decadal Survey. A plume of water vapor and ice spews from Enceladus's south polar region. Cassini data suggest that this plume, sourced by a liquid reservoir beneath the moon's icy crust, contain organics, salts, and water-rock interaction derivatives. Thus, the ingredients for life as we know it-- liquid water, chemistry, and energy sources-- are available in Enceladus's subsurface ocean. We have only to sample the plumes to investigate this hidden ocean environment. We present a New Frontiers class, solar-powered Enceladus orbiter that would take advantage of this opportunity, Testing the Habitability of Enceladus's Ocean (THEO). Developed by the 2015 Jet Propulsion Laboratory Planetary Science Summer School student participants under the guidance of TeamX, this mission concept includes remote sensing and in situ analyses with a mass spectrometer, a sub-mm radiometer-spectrometer, a camera, and two magnetometers. These instruments were selected to address four key questions for ascertaining the habitability of Enceladus's ocean within the context of the moon's geological activity: (1) How are the plumes and ocean connected? (2) Are the abiotic conditions of the ocean suitable for habitability? (3) How stable is the ocean environment? (4) Is there evidence of biological processes? By taking advantage of the opportunity Enceladus's plumes offer, THEO represents a viable, solar-powered option for exploring a potentially habitable ocean world of the outer solar system.
Weathering Profiles in Phosphorus-Rich Rocks at Gusev Crater, Mars, Suggest Dissolution of Phosphate Minerals into Potentially Habitable Near-Neutral Waters
Authors:
Adcock et al
Abstract:
Abundant evidence indicates that significant surface and near-surface liquid water has existed on Mars in the past. Evaluating the potential for habitable environments on Mars requires an understanding of the chemical and physical conditions that prevailed in such aqueous environments. Among the geological features that may hold evidence of past environmental conditions on Mars are weathering profiles, such as those in the phosphorus-rich Wishstone-class rocks in Gusev Crater. The weathering profiles in these rocks indicate that a Ca-phosphate mineral has been lost during past aqueous interactions. The high phosphorus content of these rocks and potential release of phosphorus during aqueous interactions also make them of astrobiological interest, as phosphorus is among the elements required for all known life. In this work, we used Mars mission data, laboratory-derived kinetic and thermodynamic data, and data from terrestrial analogues, including phosphorus-rich basalts from Idaho, to model a conceptualized Wishstone-class rock using the reactive transport code CrunchFlow. Modeling results most consistent with the weathering profiles in Wishstone-class rocks suggest a combination of chemical and physical erosion and past aqueous interactions with near-neutral waters. The modeling results also indicate that multiple Ca-phosphate minerals are likely in Wishstone-class rocks, consistent with observations of martian meteorites. These findings suggest that Gusev Crater experienced a near-neutral phosphate-bearing aqueous environment that may have been conducive to life on Mars in the past.
THE PATH OF REDUCED NITROGEN TOWARD EARLY EARTH: THE COSMIC TRAIL AND ITS SOLAR SHORTCUTS
Authors:
Pizzarello et al
Abstract:
Large isotopic anomalies are found in meteoritic insoluble organic materials (IOMs) and, for nitrogen, show 15N-excesses up to ${\delta }^{15}$N ~ 5000‰. These 15N-enrichments are commonly ascribed to presolar origins, but the attribution seems contradicted by available data on N-isotopes' cosmic distribution. We report here that 15N hotspots in several IOMs are reduced by hydrothermal treatment and their loss correlates with 15N values of ammonia released upon treatment. Because released ammonia's 15N-enrichments also relate with meteorites' mineralogy, i.e., asteroidal processes, and no current models offer plausible explanations for the finding, we account for our data with a novel scenario whereby 15N-enriched ammonia produced in the solar nebula is incorporated by carbonaceous materials and delivered to early Earth by comets and meteorites. The proposal also implies that abundant reduced nitrogen, a required element in origins of life theories, could reach our nascent planet and other planetary systems affecting their habitability.
Within this century, parts of the Persian Gulf region could be hit with unprecedented events of deadly heat as a result of climate change, according to a study of high-resolution climate models.
The research reveals details of a business-as-usual scenario for greenhouse gas emissions, but also shows that curbing emissions could forestall these deadly temperature extremes.
The study, published today in the journal Nature Climate Change, was carried out by Elfatih Eltahir, a professor of civil and environmental engineering at MIT, and Jeremy Pal PhD '01 at Loyola Marymount University. They conclude that conditions in the Persian Gulf region, including its shallow water and intense sun, make it "a specific regional hotspot where climate change, in absence of significant mitigation, is likely to severely impact human habitability in the future."
Running high-resolution versions of standard climate models, Eltahir and Pal found that many major cities in the region could exceed a tipping point for human survival, even in shaded and well-ventilated spaces. Eltahir says this threshold "has, as far as we know ... never been reported for any location on Earth."
That tipping point involves a measurement called the "wet-bulb temperature" that combines temperature and humidity, reflecting conditions the human body could maintain without artificial cooling. That threshold for survival for more than six unprotected hours is 35 degrees Celsius, or about 95 degrees Fahrenheit, according to recently published research. (The equivalent number in the National Weather Service's more commonly used "heat index" would be about 165 F.)
This limit was almost reached this summer, at the end of an extreme, weeklong heat wave in the region: On July 31, the wet-bulb temperature in Bandahr Mashrahr, Iran, hit 34.6 C -- just a fraction below the threshold, for an hour or less.
But the severe danger to human health and life occurs when such temperatures are sustained for several hours, Eltahir says -- which the models show would occur several times in a 30-year period toward the end of the century under the business-as-usual scenario used as a benchmark by the Intergovernmental Panel on Climate Change.
The Persian Gulf region is especially vulnerable, the researchers say, because of a combination of low elevations, clear sky, water body that increases heat absorption, and the shallowness of the Persian Gulf itself, which produces high water temperatures that lead to strong evaporation and very high humidity.
Strong water isotopic anomalies in the martian atmosphere: Probing current and ancient reservoirs
Authors:
Villanueva et al
Abstract:
We measured maps of atmospheric water (H2O) and its deuterated form (HDO) across the martian globe, showing strong isotopic anomalies and a significant high D/H enrichment indicative of great water loss. The maps sample the evolution of sublimation from the north polar cap, revealing that the released water has a representative D/H value enriched by a factor of about 7 relative to Earth’s ocean (VSMOW). Certain basins and orographic depressions show even higher enrichment, while high altitude regions show much lower values (1 to 3 VSMOW). Our atmospheric maps indicate that water ice in the polar reservoirs is enriched in deuterium to at least 8 VSMOW, which would mean that early Mars (4.5 billion years ago) had a global equivalent water layer at least 137 meters deep.
Estimating precipitation on early Mars using a radiative-convective model of the atmosphere and comparison with inferred runoff from geomorphology
Authors:
von Paris et al
Abstract:
We compare estimates of atmospheric precipitation during the Martian Noachian-Hesperian boundary 3.8 Gyr ago as calculated in a radiative-convective column model of the atmosphere with runoff values estimated from a geomorphological analysis of dendritic valley network discharge rates. In the atmospheric model, we assume CO2-H2O-N2 atmospheres with surface pressures varying from 20 mb to 3 bar with input solar luminosity reduced to 75% the modern value.
Results from the valley network analysis are of the order of a few mm d-1 liquid water precipitation (1.5-10.6 mm d-1, with a median of 3.1 mm d-1). Atmospheric model results are much lower, from about 0.001-1 mm d-1 of snowfall (depending on CO2 partial pressure). Hence, the atmospheric model predicts a significantly lower amount of precipitated water than estimated from the geomorphological analysis. Furthermore, global mean surface temperatures are below freezing, i.e. runoff is most likely not directly linked to precipitation. Therefore, our results strongly favor a cold early Mars with episodic snowmelt as a source for runoff.
Our approach is challenged by mostly unconstrained parameters, e.g. greenhouse gas abundance, global meteorology (for example, clouds) and planetary parameters such as obliquity- which affect the atmospheric result - as as well as by inherent problems in estimating discharge and runoff on ancient Mars, such as a lack of knowledge on infiltration and evaporation rates and on flooding timescales, which affect the geomorphological data. Nevertheless, our work represents a first step in combining and interpreting quantitative tools applied in early Mars atmospheric and geomorphological studies.
Atmospheric mass loss during planet formation: The importance of planetesimal impacts
Authors:
Schlichting et al
Abstract:
Quantifying
the atmospheric mass loss during planet formation is crucial for
understanding the origin and evolution of planetary atmospheres. We
examine the contributions to atmospheric loss from both giant impacts
and planetesimal accretion. Giant impacts cause global motion of the
ground. Using analytic self-similar solutions and full numerical
integrations we find (for isothermal atmospheres with adiabatic index
γ=5/3γ=5/3) that the local atmospheric mass loss fraction for ground
velocities vg≲0.25vescvg≲0.25vesc is given by
χloss=(1.71vg/vesc)4.9χloss=(1.71vg/vesc)4.9, where vescvesc is the
escape velocity from the target. Yet, the global atmospheric mass loss
is a weaker function of the impactor velocity vImpvImp and mass mImpmImp
and given by Xloss≃0.4x+1.4x2-0.8x3Xloss≃0.4x+1.4x2-0.8x3 (isothermal
atmosphere) and Xloss≃0.4x+1.8x2-1.2x3Xloss≃0.4x+1.8x2-1.2x3 (adiabatic
atmosphere), where x=(vImpm/vescM)x=(vImpm/vescM). Atmospheric mass loss
due to planetesimal impacts proceeds in two different regimes: (1)
large enough impactors View the MathML sourcem≳2ρ0(πhR)3/2 (25 km for
the current Earth), are able to eject all the atmosphere above the
tangent plane of the impact site, which is h/2Rh/2R of the whole
atmosphere, where View the MathML sourceh,R and ρ0ρ0 are the atmospheric
scale height, radius of the target, and its atmospheric density at the
ground. (2) Smaller impactors, but above m greater than 4πρ0h3m greater
than 4πρ0h3 (1 km for the current Earth) are only able to eject a
fraction of the atmospheric mass above the tangent plane. We find that
the most efficient impactors (per unit impactor mass) for atmospheric
loss are planetesimals just above that lower limit (2 km for the current
Earth). For impactor flux size distributions parametrized by a single
power law, N( greater than r)∝r-q+1N( greater than r)∝r-q+1, with
differential power law index q , we find that for 1 less than q less
than 31 less than q less than 3 the atmospheric mass loss proceeds in
regime (1) whereas for q grater than 3q greater than 3 the mass loss is
dominated by regime (2). Impactors with m≲4πρ0h3m≲4πρ0h3 are not able to
eject any atmosphere. Despite being bombarded by the same planetesimal
population, we find that the current differences in Earth’s and Venus’
atmospheric masses can be explained by modest differences in their
initial atmospheric masses and that the current atmosphere of the Earth
could have resulted from an equilibrium between atmospheric erosion and
volatile delivery to the atmosphere from planetesimal impacts. We
conclude that planetesimal impacts are likely to have played a major
role in atmospheric mass loss over the formation history of the
terrestrial planets.
A Conspicuous Clay Ovoid in Nakhla: Evidence for Subsurface Hydrothermal Alteration on Mars with Implications for Astrobiology
Authors:
Chatzitheodoridis et al
Abstract:
A conspicuous biomorphic ovoid structure has been discovered in the Nakhla martian meteorite, made of nanocrystalline iron-rich saponitic clay and amorphous material. The ovoid is indigenous to Nakhla and occurs within a late-formed amorphous mesostasis region of rhyolitic composition that is interstitial to two clinopyroxene grains with Al-rich rims, and contains acicular apatite crystals, olivine, sulfides, Ti-rich magnetite, and a new mineral of the rhoenite group. To infer the origin of the ovoid, a large set of analytical tools was employed, including scanning electron microscopy and backscattered electron imaging, wavelength-dispersive X-ray analysis, X-ray mapping, Raman spectroscopy, time-of-flight secondary ion mass spectrometry analysis, high-resolution transmission electron microscope imaging, and atomic force microscope topographic mapping. The concentric wall of the ovoid surrounds an originally hollow volume and exhibits internal layering of contrasting nanotextures but uniform chemical composition, and likely inherited its overall shape from a preexisting vesicle in the mesostasis glass. A final fibrous layer of Fe-rich phases blankets the interior surfaces of the ovoid wall structure. There is evidence that the parent rock of Nakhla has undergone a shock event from a nearby bolide impact that melted the rims of pyroxene and the interstitial matter and initiated an igneous hydrothermal system of rapidly cooling fluids, which were progressively mixed with fluids from the melted permafrost. Sharp temperature gradients were responsible for the crystallization of Al-rich clinopyroxene rims, rhoenite, acicular apatites, and the quenching of the mesostasis glass and the vesicle. During the formation of the ovoid structure, episodic fluid infiltration events resulted in the precipitation of saponite rinds around the vesicle walls, altered pyrrhotite to marcasite, and then isolated the ovoid wall structure from the rest of the system by depositing a layer of iron oxides/hydroxides. Carbonates, halite, and sulfates were deposited last within interstitial spaces and along fractures. Among three plausible competing hypotheses here, this particular abiotic scenario is considered to be the most reasonable explanation for the formation of the ovoid structure in Nakhla, and although compelling evidence for a biotic origin is lacking, it is evident that the martian subsurface contains niche environments where life could develop
On the Spin-axis Dynamics of a Moonless Earth
Authors:
Li et al
Abstract:
The
variation of a planet's obliquity is influenced by the existence of
satellites with a high mass ratio. For instance, the Earth's obliquity
is stabilized by the Moon, and would undergo chaotic variations in the
Moon's absence. In turn, such variations can lead to large-scale changes
in the atmospheric circulation, rendering spin-axis dynamics a central
issue for understanding climate. The relevant quantity for
dynamically-forced climate change is the rate of chaotic diffusion.
Accordingly, here we reexamine the spin-axis evolution of a Moonless
Earth within the context of a simplified perturbative framework. We
present analytical estimates of the characteristic Lyapunov coefficient
as well as the chaotic diffusion rate and demonstrate that even in
absence of the Moon, the stochastic change in the Earth's obliquity is
sufficiently slow to not preclude long-term habitability. Our
calculations are consistent with published numerical experiments and
illustrate the putative system's underlying dynamical structure in a
simple and intuitive manner.
Follow the Plume: The Habitability of Enceladus
Authors:
McKay et al
Abstract:
The astrobiological exploration of other worlds in our Solar System is moving from initial exploration to more focused astrobiology missions. In this context, we present the case that the plume of Enceladus currently represents the best astrobiology target in the Solar System. Analysis of the plume by the Cassini mission indicates that the steady plume derives from a subsurface liquid water reservoir that contains organic carbon, biologically available nitrogen, redox energy sources, and inorganic salts. Furthermore, samples from the plume jetting out into space are accessible to a low-cost flyby mission. No other world has such well-studied indications of habitable conditions. Thus, the science goals that would motivate an Enceladus mission are more advanced than for any other Solar System body. The goals of such a mission must go beyond further geophysical characterization, extending to the search for biomolecular evidence of life in the organic-rich plume. This will require improved in situ investigations and a sample return.
