Europa Clipper has has a key Review

A NASA mission to a potentially habitable moon of Jupiter has cleared a major review despite uncertainty about when, or how, it will launch.

NASA announced Aug. 19 that it had formally confirmed the Europa Clipper mission to proceed into its next phase of development, known as Phase C. That will cover final design of the spacecraft, followed by assembly and testing.

“We are all excited about the decision that moves the Europa Clipper mission one key step closer to unlocking the mysteries of this ocean world,” Thomas Zurbuchen, NASA associate administrator for science, said in a statement announcing the milestone.

Europa Clipper will enter orbit around Jupiter and make dozens of close approaches to Europa, one of the planet’s largest moons. Europa has an icy surface, below which most scientists believe is a deep ocean of liquid water. Combined with the interior heat source that keeps the ocean from freezing, and the presence of organic compounds, Europa has the basic requirements to support life.

While the programmatic milestone Europa Clipper achieved, known in NASA parlance as Key Decision Point C, is the point where NASA sets the schedule and budget for the mission, exactly when Europa Clipper will launch is not yet clear. In the statement announcing the mission’s confirmation, NASA noted that current plans have the spacecraft ready for launch as soon as 2023. However, the mission has a formal launch readiness date of 2025.

That uncertainty is linked to how the mission will be launched. The mission’s preferred launch option is the Space Launch System, which will allow the spacecraft to travel directly to Jupiter without the need of gravity assists, arriving within three years of launch. Language in appropriations bills for fiscal year 2019 and prior years also directed NASA to use the SLS.

link.

The IG office of NASA is asking for flexibility for the launch of the Europa Clipper.  This includes which launch vehicle will be used and when.  If NASA selects any other launch vehicle, the arrival at Europa will be delayed by over 5 years, if not more.  For that reason, I'd have to say I hope Congress declines the request.

China is Planning a Jupiter Space Probe

China, which is already working to send its first probe to Mars by 2020, now says it has plans for deep-space exploration including sending a spacecraft to Jupiter.

The spacecraft will fly by Jupiter, the China National Space Administration said on Monday.

China hopes to collect rock and soil samples as well as explore Mars surface by 2020.

Last week, the Space Administration announced that it had shortlisted eight names for the first Mars probe.

China has released a short list of eight names for the country’s first Mars spacecraft, which is scheduled to launch by 2020.

“Fenghuang” (phoenix), “Tianwen” (questions for heaven), “Huoxing” (Mars), “Tenglong” (soaring dragon), “Qilin” (Kylin), “Zhuque” (rose finch), “Zhuimeng” (chasing dreams) and “Fengxiang” (flying phoenix), were shortlisted from over 35,000 name proposals sent in from different countries.

The planned space probes are in tandem with the Chinese government’s ambitions to become a space power within the next decade.

link.

Juno has Sent Back its First Images of Jupiter

link.

NASA's Juno Probe is now Orbiting Jupiter

NASA’s Juno spacecraft, on a mission to study Jupiter’s interior and its magnetic field, successfully entered orbit around the planet late July 4 after completing a critical maneuver.

Juno fired its main engine as planned at 11:18 p.m. Eastern time July 4, slowing down the spacecraft as it made a close approach to Jupiter. The engine shut down 35 minutes later, within one second of its planned duration, placing the spacecraft into a 53-day orbit around the planet.

“We have the tone for burn cutoff on delta-v,” mission control at NASA’s Jet Propulsion Laboratory announced to cheers as they received telemetry from the spacecraft that the engine had shut down at the end of its burn. “Welcome to Jupiter.”

“NASA did it again,” said Scott Bolton, Juno principal investigator from the Southwest Research Institute, at a press conference shortly after orbit insertion. “Now the fun begins with science.”

link.

Fracturing and flow: Investigations on the formation of shallow water sills on Europa

Fracturing and flow: Investigations on the formation of shallow water sills on Europa

Authors:

Craft et al

Abstract:

Double ridge tectonic features appear prominently and ubiquitously across the surface of Jupiter's icy moon Europa. Previous studies have interpreted flanking fractures observed along some of the ridges as indicators of stress resulting from the ridge loading and flexing of the ice shell above a shallow water body. Here, we investigate a shallow water sill emplacement process at a time when the shell is cooling and thickening and explore the conditions that would make such a system feasible on timescales of ridge formation. Results show that fracture initiation and transport of ocean water to shallow depths can realistically occur, although horizontal fracturing and sill lifetimes prove challenging. Finite element models demonstrate that mechanical layering or a fractured shell do not provide enough stress change to promote horizontal fracturing, but tidal forcing does result in a small amount of turn. Assuming it is possible for a shallow sill to form, a sill would convect internally and conduct heat out quickly, resulting in a short lifetime in comparison to an estimated flexure timeframe of 100 kyr suggested required for double ridge formation. Consideration of heat transfer and residence in the overlying ice, however, extends the flexure timeframe and multiple sill intrusions or replenishment with warm ocean water could prolong the effective sill lifetime. Though challenges still remain for sill formation at Europa, these analyses constrain the potential mechanisms for emplacement and indicate sills can act as viable options for supplying the heat needed for surface flexure. Further analyses and future missions to Europa will help to increase our understanding of these enigmatic processes.

Is the Grand Tack Model Compatible with Our Asteroid Belt?

Is the Grand Tack model compatible with the orbital distribution of main belt asteroids?

Authors:

Deienno et al

Abstract:

The Asteroid Belt is characterized by the radial mixing of bodies with different physical properties, a very low mass compared to Minimum Mass Solar Nebula expectations and has an excited orbital distribution, with eccentricities and inclinations covering the entire range of values allowed by the constraints of dynamical stability. Models of the evolution of the Asteroid Belt show that the origin of its structure is strongly linked to the process of terrestrial planet formation. The Grand Tack model presents a possible solution to the conundrum of reconciling the small mass of Mars with the properties of the Asteroid Belt, including the mass depletion, radial mixing and orbital excitation. However, while the inclination distribution produced in the Grand Tack model is in good agreement with the one observed, the eccentricity distribution is skewed towards values larger than those found today. Here, we evaluate the evolution of the orbital properties of the Asteroid Belt from the end of the Grand Tack model (at the end of the gas nebula phase when planets emerge from the dispersing gas disk), throughout the subsequent evolution of the Solar System including an instability of the Giant Planets approximately 400 Myr later. Before the instability, the terrestrial planets were modeled on dynamically cold orbits with Jupiter and Saturn locked in a 3:2 mean motion resonance. The model continues for an additional 4.1 Gyr after the giant planet instability. Our results show that the eccentricity distribution obtained in the Grand Tack model evolves towards one very similar to that currently observed, and the semimajor axis distribution does the same. The inclination distribution remains nearly unchanged with a slight preference for depletion at low inclination; this leads to the conclusion that the inclination distribution at the end of the Grand Tack is a bit over-excited. Also, we constrain the primordial eccentricities of Jupiter and Saturn, which have a major influence on the dynamical evolution of the Asteroid Belt and its final orbital structure.

NASA Seeking Ways to Avoid Using SLS for Europa Mission(s)

Faced with a congressional mandate to add a lander to a planned mission to Jupiter’s icy moon Europa, NASA is considering launching the lander separately from the main mission.

In discussions Feb. 1 at a meeting of NASA’s Outer Planets Assessment Group in San Antonio, Texas, agency officials said they are considering how to add a lander to a mission under development to make multiple flybys of Europa, even though the lander will weigh significantly more than the main “clipper” spacecraft.

Curt Niebur, outer planets program scientist at NASA Headquarters, said at the meeting that the biggest challenge of adding the lander to the Europa mission is its mass: about 8,000 kilograms, to accommodate the propellant needed to land the spacecraft softly on the surface. He added that estimate was “very rough” based on the limited studies of lander concepts to date. By comparison, the clipper spacecraft alone would have a mass of only about 5,000 kilograms.

That additional mass would drive the selection of the launch vehicle, requiring the use of the Space Launch System. “If we co-manifest the lander and clipper, we’re only on SLS,” he said. “It’s still a slow boat, so to speak: you’d still do inner solar system gravity assists.”

link.

Could you Catch a Cell Flying Through Europa's Plumes?

Europa ocean sampling by plume flythrough: Astrobiological expectations

Author:

Lorenz

Abstract:

The anticipated material captured from a flythrough of Europa’s putative plumes is investigated using a simple model. With parameters appropriate to observed constraints (plume height 100–200 km, column mass 1E20 H2O molecules/m2, originating in a liquid water exposure), bacterial cells of ∼10 μm could be lofted even to the plume tops, but no particles larger than 2 mm will be lofted above ∼2 km, a likely lower limit on feasible altitude. Intercepted mass densities of 1E−5 to 1E−3 kg/m2 are calculated. With a small in-situ sampler at the lowest altitudes a few hundred cells might be captured if the liquid is as abundant in biota as the richest environments on Earth, but statistically less than 1 cell for Vostok waters, a Europa analog. The imperative for a large collection area is noted. The likelihood of capturing at least a single cell, with a log-uniform prior of cell abundances, is proposed as a science value metric for different flyby altitudes.

ESA Wants to Give Half Billion Euro Contribution to NASA Europa Mission

As NASA quietly works on a lander that could accompany a $2 billion flyby probe to Jupiter’s icy moon Europa, the head of the European Space Agency’s science program tells Spaceflight Now that Europe is ready to play a significant role in the project.

The goals of the ESA contribution would be decided by European scientists, but the agency has the funding for a piggyback probe costing up to 500 million euros, or nearly $550 million, according to Alvaro Gimenez, ESA’s director of science and robotic exploration.

NASA asked the European Space Agency last year whether it was interested in contributing to the Europa mission, and Gimenez said in an interview with Spaceflight Now that the answer is yes.

“We will participate with no cost to NASA by us contributing something equivalent to a half-billion euros in cost to ESA,” Gimenez said. “Now, where it goes depends on the cooperation.

“This is a NASA mission, and we are happy to be a junior partner with NASA,” Gimenez told Spaceflight Now in December. “It’s our natural partnership with the U.S., and we will be very happy to do it. Now, they have to tell us the profile of the mission, what they want to do, and where do we have a role. But certainly we would appreciate the opportunity.”

link.

Future Planetary Exploration on the Europa Mission Lander

While there’s at least eight years until it launches, this has been a pivotal year for developing NASA’s Europa mission. Last spring, NASA selected a rich and highly capable instrument set. This summer, following a design concept review, the mission moved from concept studies to an official mission. And just last week, Congress directed NASA to expand the mission by adding a small lander as well as launch the mission by 2022 and use the Space Launch System. These latter aren’t just suggestions: they are the law.

link.

ESA, Airbus Sign $374 Million Contract for Jupiter Icy Moons Mission (JUICE)

The European Space Agency on Dec. 9 signed a contract with Airbus Defence and Space for the construction of ESA’s Juice – Jupiter Icy Moons – orbiter, scheduled for launch in 2022 aboard a European Ariane 5 rocket.

The contract had been expected since ESA’s July decision to approve a contract valued at 350.8 million euros ($374 million) with Airbus after a competition with Thales Alenia Space of France and Italy and OHB SE of Germany, which had submitted a joint bid.

Francois Auque, head of Airbus Space Systems, said Juice hardware will be produced as early as mid-2016, with the full contracting team from 60 companies lined up by 2017. Some 150 people will be working on the prime contractor’s project team at the program’s peak in 2017-2018, he said.

link.

NASA's Juno to Arrive at Jupiter on July 4th, 2016

When Galileo Galilei turned his telescope to Jupiter in 1610, he uncovered the planet’s four large moons, as well as a new vision of the cosmos. Not everything had to orbit Earth.

NASA’s first dedicated mission to Jupiter, named in honor of the great astronomer, was intended to bring about a similar revolution. And it mostly did. Much of what astronomers know about the gas giant and its satellites still comes from Galileo’s dataset.

But that’s poised to change July 4, 2016. NASA’s Juno spacecraft will beam breathtaking views of the gas giant and its atmosphere back to Earth. Every two weeks, the solar-powered spacecraft will plunge past Jupiter at a distance as close as 3,100 miles (5,000 kilometers) above the cloudtops. An array of scientific instruments will also help Juno peer into the heart of the largest planet in the solar system, uncovering the planet’s structure, atmosphere, and magnetosphere. Another visit to the system, the Europa Multiple Flyby Mission, is also in the works.

link.

Attempting to Explain the Formation of the Galilean Moons

A semi-analytical model for exploring Galilean satellites formation from a massive disk

Authors:

Miguel et al

Abstract:

A better knowledge of Jovian satellites' origins will bring light on the environment that surrounded Jupiter during its formation and can help us to understand the characteristics of this unique satellite system. We developed a semi-analytical model to investigate Jupiter's regular satellite formation and present the results of our population synthesis calculations. We performed simulations adopting a massive, static, low-viscosity circumplanetary disk model, in agreement with a current study of magnetorotational instability in a circum-planetary disk. We find that the high gas density leads to very rapid migration of satellitesimals due to gas drag and type II migration of satellites in a faster disk-dominated mode. A large concentration of solids, large building blocks and longer type II migration time-scales favor formation and survival of large satellites. However, bodies as massive as Ganymede and those located far away from Jupiter, such as Callisto, are difficult to form with this scenario.

Eruptions of Galilean Moon Io's Pillan Volcanoes From 1996 to 2015

Io: Eruptions at Pillan, and the time evolution of Pele and Pillan from 1996 to 2015

Authors:

de Pater et al

Abstract:

Observations obtained with the near-infrared camera NIRC2, coupled to the adaptive optics system on the 10-m W.M. Keck II telescope on Mauna Kea, Hawaii, on 14 August 2007 revealed an active and highly-energetic eruption at Pillan at 245.2 ± 0.7°W and 8.5 ± 0.5°S. A one-temperature blackbody fit to the data revealed a (blackbody) temperature of 840 ± 40 K over an area of 17 km2, with a total power output of ∼500 GW. Using Davies’ (Davies, A.G. [1996]. Icarus 124(1), 45–61) Io Flow Model, we find that the oldest lava present is less than 1-2 h old, having cooled down from the eruption temperature of greater than 1400 K to ∼710 K; this young hot lava suggests that an episode of lava fountaining was underway. In addition to an examination of this eruption, we present data of the Pele and Pillan volcanoes obtained with the same instrument and telescope from 2002 through 2015. These data reveal another eruption at Pillan on UT 28 June 2010. Model fits to this eruption yield a blackbody temperature of 600–700 K over an area of ∼60 km2, radiating over 600 GW. On UT 18 February 2015 an energetic eruption was captured by the InfraRed Telescope Facility (IRTF) via mutual event occultations. The eruption took place at 242.7 ± 1°W and 12.4 ± 1°S, i.e., in the eastern part of Pillan Patera. Subsequent observations showed a gradual decrease in the intensity of the eruption. Images obtained with the Keck telescope on 31 March and 5 May 2015 revealed that the locations of the eruption had shifted by 120–160 km to the NW.

In contrast to the episodicity of Pillan, Pele has been persistent, observed in every appropriate 4.7 μm observation. Pele was remarkably consistent in its thermal emission from the Galileo era through February 2002, when a blackbody temperature of 940 ± 40 K and an area of 6.5 km2 was measured. Since that time, however, the radiant flux from what is likely a apparently large, overturning lava lake has gradually subsided over the next decade by a factor of ∼4, while the location of the thermal source was moving back and forth between areas roughly ∼100 km to the W of the 2002 location and an area roughly ∼100 km to the SE of the 2002 location.

A Map of Io's Volcanic Heat Flow

Map of Io’s volcanic heat flow

Authors:

Gerard Davies et al

Abstract:

We present a map of Io’s volcanic heat flow. Io’s high heat flow is a result of intense tidal heating, which generates widespread volcanic activity. The surface expression of ongoing volcanic activity constrains the location and magnitude of tidal dissipation within Io. Tidal heating models place heating either at relatively shallow (aesthenosphere) levels, or deep in the mantle. It was thought that actual tidal heating could be approximated using a combination of these end-member models. Io’s volcanic heat flow has now been mapped in sufficient detail to compare with the models. Our maps show that the distribution of heat flow is not matched by current models of deep nor shallow tidal heating, nor by any combination of these two models. We find relatively low heat flow at sub-jovian (0°W) and anti-jovian (180°W) longitudes, at odds with the pure aesthenospheric heating model. Furthermore, there are large swaths of Io’s surface where there is poor correlation between the number of hot spots in an area and the power emitted. We have previously accounted for ≈54% of Io’s observed heat flow. We now show that Io’s anomalously warm poles, possibly the result of heat flow from deep-mantle heating, would yield the “missing” energy (48 TW) if the polar surfaces are at temperatures of ∼90 K to ∼95 K and cover latitudes above ∼43° to ∼48° respectively. This possibility implies a ratio of deep to shallow heating of about 1:1. However, explaining regional variations in surface volcanic activity requires more detailed modeling of the location and magnitude of the internal tidal dissipation and the consequences of mantle convection and advection within Io. Future model predictions can be compared to our heat flow map.

Europa's Plumes Have a Complicated Mechanism

Linking Europa’s plume activity to tides, tectonics, and liquid water

Authors:

Rhoden et al

Abstract:

Much of the geologic activity preserved on Europa’s icy surface has been attributed to tidal deformation, mainly due to Europa’s eccentric orbit. Although the surface is geologically young (30–80 Myr), there is little information as to whether tidally-driven surface processes are ongoing. However, a recent detection of water vapor near Europa’s south pole suggests that it may be geologically active. Initial observations indicated that Europa’s plume eruptions are time-variable and may be linked to its tidal cycle. Saturn’s moon, Enceladus, which shares many similar traits with Europa, displays tidally-modulated plume eruptions, which bolstered this interpretation. However, additional observations of Europa at the same time in its orbit failed to yield a plume detection, casting doubt on the tidal control hypothesis. The purpose of this study is to analyze the timing of plume eruptions within the context of Europa’s tidal cycle to determine whether such a link exists and examine the inferred similarities and differences between plume activity on Europa and Enceladus. To do this, we determine the locations and orientations of hypothetical tidally-driven fractures that best match the temporal variability of the plumes observed at Europa. Specifically, we identify model faults that are in tension at the time in Europa’s orbit when a plume was detected and in compression at times when the plume was not detected. We find that tidal stress driven solely by eccentricity is incompatible with the observations unless additional mechanisms are controlling the eruption timing or restricting the longevity of the plumes. The addition of obliquity tides, and corresponding precession of the spin pole, can generate a number of model faults that are consistent with the pattern of plume detections. The locations and orientations of these hypothetical source fractures are robust across a broad range of precession rates and spin pole directions. Analysis of the stress variations across the fractures suggests that the plumes would be best observed earlier in the orbit (true anomaly ∼120°). Our results indicate that Europa’s plumes, if confirmed, differ in many respects from the Enceladean plumes and that either active fractures or volatile sources are rare.

ESA's JUICE at Europa

Late in 2030, Europe’s Jupiter Icy moon Explorer (JUICE) spacecraft will twice zoom past Europa, a world that has all the ingredients to harbor life. During the minutes of each closest flyby, it will study an areas identified from images taken in the 1990s by the Galileo spacecraft as locations of recent geological activity. Then after those two encounters, the spacecraft will move on to study Jupiter and the moons Ganymede and Callisto. Unless another space agency commits to another mission that will visit Europa, this will be our only chance to explore Europa in the next several decades. (But see the note at the end of this post.)

link.

Extreme Shrimp as a Guide to Potential Europan Life?

link.

Tides on Europa

Tides on Europa: The membrane paradigm

Author:

Beuthe

Abstract:

Jupiter’s moon Europa has a thin icy crust which is decoupled from the mantle by a subsurface ocean. The crust thus responds to tidal forcing as a deformed membrane, cold at the top and near melting point at the bottom. In this paper I develop the membrane theory of viscoelastic shells with depth-dependent rheology with the dual goal of predicting tidal tectonics and computing tidal dissipation. Two parameters characterize the tidal response of the membrane: the effective Poisson’s ratio View the MathML sourceν¯ and the membrane spring constant Λ , the latter being proportional to the crust thickness and effective shear modulus. I solve membrane theory in terms of tidal Love numbers, for which I derive analytical formulas depending on View the MathML sourceΛ,ν¯, the ocean-to-bulk density ratio and the number View the MathML sourcek2∘ representing the influence of the deep interior. Membrane formulas predict h2h2 and k2k2 with an accuracy of a few tenths of percent if the crust thickness is less than one hundred kilometers, whereas the error on l2l2 is a few percents. Benchmarking with the thick-shell software SatStress leads to the discovery of an error in the original, uncorrected version of the code that changes stress components by up to 40%. Regarding tectonics, I show that different stress-free states account for the conflicting predictions of thin and thick shell models about the magnitude of tensile stresses due to nonsynchronous rotation. Regarding dissipation, I prove that tidal heating in the crust is proportional to Im(Λ)Im(Λ) and that it is equal to the global heat flow (proportional to Im(k2)Im(k2)) minus the core-mantle heat flow (proportional to View the MathML sourceIm(k2∘)). As an illustration, I compute the equilibrium thickness of a convecting crust. More generally, membrane formulas are useful in any application involving tidal Love numbers such as crust thickness estimates, despinning tectonics or true polar wander.

Forming Ganymede’s Grooves

Forming Ganymede’s grooves at smaller strain: Toward a self-consistent local and global strain history for Ganymede

Authors:

Bland et al

Abstract:

The ubiquity of tectonic features formed in extension, and the apparent absence of ones formed in contraction, has led to the hypothesis that Ganymede has undergone global expansion in its past. Determining the magnitude of such expansion is challenging however, and extrapolation of locally or regionally inferred strains to global scales often results in strain estimates that exceed those based on global constraints. Here we use numerical simulations of groove terrain formation to develop a strain history for Ganymede that is generally consistent at local, regional, and global scales. These simulations reproduce groove-like amplitudes, wavelengths, and average slopes at modest regional extensions (10–15%). The modest strains are more consistent with global constraints on Ganymede’s expansion. Yet locally, we also find that surface strains can be much larger (30–60%) in the same simulations, consistent with observations of highly-extended impact craters. Thus our simulations satisfy both the smallest-scale and largest-scale inferences of strain on Ganymede. The growth rate of the topography is consistent with (or exceeds) predictions of analytical models, and results from the use of a non-associated plastic rheology that naturally permits localization of brittle failure (plastic strain) into linear fault-like shear zones. These fault-like zones are organized into periodically-spaced graben-like structures with stepped, steeply-dipping faults. As in previous work, groove amplitudes and wavelengths depend on both the imposed heat flux and surface temperature, but because our brittle strength increases with depth, we find (for the parameters explored) that the growth rate of topography is initially faster for lower heat flows. We observe a transition to narrow rifting for higher heat flows and larger strains, which is a potential pathway for breakaway margin or band formation.