Collision With a 2 Earth Mass Planet Shaped Uranus' Evolution

Uranus was hit by a massive object roughly twice the size of Earth that caused the planet to tilt and could explain its freezing temperatures, according to new research.

Astronomers at Durham University, UK, led an international team of experts to investigate how Uranus came to be tilted on its side and what consequences a giant impact would have had on the planet's evolution.

The team ran the first high-resolution computer simulations of different massive collisions with the ice giant to try to work out how the planet evolved.

The research confirms a previous study which said that Uranus' tilted position was caused by a collision with a massive object - most likely a young proto-planet made of rock and ice - during the formation of the solar system about 4 billion years ago.

The simulations also suggested that debris from the impactor could form a thin shell near the edge of the planet's ice layer and trap the heat emanating from Uranus' core. The trapping of this internal heat could in part help explain Uranus' extremely cold temperature of the planet's outer atmosphere (-216 degrees Celsius, -357 degrees Fahrenheit), the researchers said.

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Are Rings Around Saturn & Other Gas Giants From Shattered Dwarf Planets?

Ring Formation around Giant Planets by Tidal Disruption of a Single Passing Large Kuiper Belt Object

Authors:

Hyodo et al

Abstract:

The origin of rings around giant planets remains elusive. Saturn's rings are massive and made of 90-95% of water ice. In contrast, the much less massive rings of Uranus and Neptune are dark and likely to have higher rock fraction. Here we investigate, for the first time, the tidal disruption of a passing object, including the subsequent formation of planetary rings. First, we perform SPH simulations of the tidal destruction of big differentiated objects (Mbody=1021−23) that experience close encounters with Saturn or Uranus. We find that about 0.1−10% of the mass of the passing body is gravitationally captured around the planet. However, these fragments are initially big chunks and have highly eccentric orbits around the planet. Then, we perform N-body simulations including the planet's oblateness, starting with data obtained from the SPH simulations. Our N-body simulations show that the chunks are tidally destroyed during their next several orbits. Their individual orbits then start to precess incoherently around the planet's equator, which enhances their encounter velocities on longer-term evolution, resulting in more destructive impacts. These collisions would damp their eccentricities resulting in a progressive collapse of the debris cloud into a thin equatorial and low-eccentricity ring. These high energy impacts are expected to be catastrophic enough to produce small particles. Our numerical results also show that the mass of formed rings is large enough to explain current rings including inner regular satellites around Saturn and Uranus. In the case of Uranus, a body can go deeper inside the planet's Roche limit resulting in a more efficient capture of rocky material compared to Saturn's case in which mostly ice is captured. Thus, our results can naturally explain the compositional difference between the rings of Saturn, Uranus and Neptune.

The Inclination of the Gas Giants in the Solar System Constrains Planet Nine

The inclination of the planetary system relative to the solar equator may be explained by the presence of Planet 9

Authors:

Gomes et al

Abstract:

We evaluate the effects of a distant planet, commonly known as planet 9, on the dynamics of the giant planets of the Solar System. We find that, given the large distance of planet 9, the dynamics of the inner giant planets can be decomposed into a classic Lagrange-Laplace dynamics relative to their own invariant plane (the plane orthogonal to their total angular momentum vector) and a slow precession of said plane relative to the total angular momentum vector of the Solar System, including planet 9. Under some specific configurations for planet 9, this precession can explain the current tilt of approximately 6 degrees between the invariant plane of the giant planets and the solar equator. An analytical model is developed to map the evolution of the inclination of the inner giant planets' invariant plane as a function of the planet 9's mass, inclination, eccentricity and semimajor axis, and some numerical simulations of the equations of motion of the giant planets and planet 9 are performed to validate our analytical approach. The longitude of the ascending node of planet 9 is found to be linked to the longitude of the ascending node of the giant planets' invariant plane, which also constrain the longitude of the node of planet 9 on the ecliptic. Some of the planet 9 configurations that allow explaining the current solar tilt are compatible with those proposed to explain the orbital confinement of the most distant Kuiper belt objects. Thus, this work on the one hand gives an elegant explanation for the current tilt between the invariant plane of the inner giant planets and the solar equator and, on the other hand, adds new constraints to the orbital elements of planet 9.

Tracking Neptune's Migration History through High-Perihelion Resonant Trans-Neptunian Objects

Tracking Neptune's Migration History through High-Perihelion Resonant Trans-Neptunian Objects

Authors:

Kaib et al

Abstract:

Recently, Sheppard et al. (2016) presented the discovery of 7 new trans-Neptunian objects with perihelia beyond 40 AU with moderate eccentricities and semimajor axes over 50 AU. Like the handful of previously known bodies on similar orbits, these objects' semimajor axes are just beyond the Kuiper belt edge and clustered around mean motion resonances (MMRs) with Neptune. The objects likely obtained their observed orbits while trapped in a MMR, where the Kozai-Lidov mechanism can raise their perihelia. This mechanism generates a high-perihelion population and also weakens Neptune's dynamical influence over these objects. Here we numerically model the production of this population under a variety of different migration scenarios for Neptune, varying both migration speed and migration smoothness. We find that high-perihelion objects near Neptunian MMRs constrain the nature of Neptune's migration. In particular, the population near the 3:1 MMR (near 62 AU) is especially useful due to its large population and short dynamical evolution timescale. If Neptune reaches its modern orbit after just ~100 Myrs or less of total migration time, we predict that ~90% of the high-perihelion objects near the 3:1 MMR will all have semimajor axes within 1 AU of each other, residing very near the modern resonance's center. On the other hand, if Neptune takes ~300 Myrs of total time to migrate to its final orbit, we expect ~50% of this population to be in dynamically fossilized orbits slightly closer (>~1 AU) to the Sun than the modern resonance location. We highlight 2015 KH162 as a likely member of this fossilized 3:1 population. Under any plausible migration scenario, the vast majority of high-perihelion objects in resonances more distant than the 4:1 MMR (near 76 AU) reach their orbits well after Neptune stops migrating and represent a recently generated, dynamically active population.

Neptune's Migration was not Smooth

NEPTUNE'S ORBITAL MIGRATION WAS GRAINY, NOT SMOOTH

Authors:

Nesvorný et al

Abstract:

The Kuiper Belt is a population of icy bodies beyond the orbit of Neptune. The complex orbital structure of the Kuiper Belt, including several categories of objects inside and outside of resonances with Neptune, emerged as a result of Neptune's migration into an outer planetesimal disk. An outstanding problem with the existing migration models is that they invariably predict excessively large resonant populations, while observations show that the non-resonant orbits are in fact common (e.g., the main belt population is sime2–4 times larger than Plutinos in the 3:2 resonance). Here we show that this problem can be resolved if it is assumed that Neptune's migration was grainy, as expected from scattering encounters of Neptune with massive planetesimals. The grainy migration acts to destabilize resonant bodies with large libration amplitudes, a fraction of which ends up on stable non-resonant orbits. Thus, the non-resonant-to-resonant ratio obtained with the grainy migration is higher, up to ~10 times higher for the range of parameters investigated here, than in a model with smooth migration. In addition, the grainy migration leads to a narrower distribution of the libration amplitudes in the 3:2 resonance. The best fit to observations is obtained when it is assumed that the outer planetesimal disk below 30 au contained 1000–4000 Plutos. We estimate that the combined mass of Pluto-class objects in the original disk represented 10%–40% of the estimated disk mass (${M}_{{\rm{disk}}}\simeq 20$ ${M}_{{\rm{Earth}}}$). This constraint can be used to better understand the accretion processes in the outer solar system.

Uranus evolution models with simple thermal boundary layers

Uranus evolution models with simple thermal boundary layers

Authors:

Nettelman et al

Abstract:

The strikingly low luminosity of Uranus (Teff ≃ Teq) constitutes a long-standing challenge to our understanding of Ice Giant planets. Here we present the first Uranus structure and evolution models that are constructed to agree with both the observed low luminosity and the gravity field data. Our models make use of modern ab initio equations of state at high pressures for the icy components water, methane, and ammonia. Proceeding step by step, we confirm that adiabatic models yield cooling times that are too long, even when uncertainties in the ice:rock ratio (I:R) are taken into account. We then argue that the transition between the ice/rock-rich interior and the H/He-rich outer envelope should be stably stratified. Therefore, we introduce a simple thermal boundary and adjust it to reproduce the low luminosity. Due to this thermal boundary, the deep interior of the Uranus models are up to 2–3 warmer than adiabatic models, necessitating the presence of rocks in the deep interior with a possible I:R of 1 × solar. Finally, we allow for an equilibrium evolution (Teff ≃ Teq) that begun prior to the present day, which would therefore no longer require the current era to be a ”special time” in Uranus’ evolution. In this scenario, the thermal boundary leads to more rapid cooling of the outer envelope. When Teff ≃ Teq is reached, a shallow, subadiabatic zone in the atmosphere begins to develop. Its depth is adjusted to meet the luminosity constraint. This work provides a simple foundation for future Ice Giant structure and evolution models, that can be improved by properly treating the heat and particle fluxes in the diffusive zones.

Are Saturns Moons, Rings Less Than 100 Million Years Old?

New research suggests that some of Saturn's icy moons, as well as itsfamous rings, might be modern adornments. Their dramatic birth may have taken place a mere hundred million years ago, more recent than the reign of many dinosaurs.

"Moons are always changing their orbits. That's inevitable," says Matija Cuk, principal investigator at the SETI Institute. "But that fact allows us to use computer simulations to tease out the history of Saturn's inner moons. Doing so, we find that they were most likely born during the most recent two percent of the planet's history.

"While Saturn's rings have been known since the 1600s, there's still debate about their age. The straightforward assumption is that they are primordial – as old as the planet itself, which is more than four billion years. However, in 2012, French astronomers found that tidal effects – the gravitational interaction of the inner moons with fluids deep in Saturn's interior – are causing them to spiral to larger orbital radii comparatively quickly. The implication, given their present positions, is that these moons, and presumably the rings, are recent phenomena.

Cuk, together with Luke Dones and David Nesvorny of the Southwest Research Institute, used computer modeling to infer the past dynamic behavior of Saturn's icy inner moons. While our own moon has its orbit around Earth to itself, Saturn's many satellites have to share space with each other. All of their orbits slowly grow due to tidal effects, but at different rates. This results in pairs of moons occasionally entering so-called orbital resonances. These occur when one moon's orbital period is a simple fraction (for example, one-half or two-thirds) of another moon's period. In these special configurations, even small moons with weak gravity can strongly affect each other's orbits, making them more elongated and tilting them out of their original orbital plane.

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A Second Paper Stating Planet Nine is at Aphelion

Finding Planet Nine: a Monte Carlo approach

Authors:

de la Fuente Marcos et al

Abstract:

Planet Nine is a hypothetical planet located well beyond Pluto that has been proposed in an attempt to explain the observed clustering in physical space of the perihelia of six extreme trans-Neptunian objects or ETNOs. The predicted approximate values of its orbital elements include a semimajor axis of 700 au, an eccentricity of 0.6, an inclination of 30 degrees, and an argument of perihelion of 150 degrees. Searching for this putative planet is already under way. Here, we use a Monte Carlo approach to create a synthetic population of Planet Nine orbits and study its visibility statistically in terms of various parameters and focusing on the aphelion configuration. Our analysis shows that, if Planet Nine exists and is at aphelion, it might be found projected against one out of four specific areas in the sky. Each area is linked to a particular value of the longitude of the ascending node and two of them are compatible with an apsidal antialignment scenario. In addition and after studying the current statistics of ETNOs, a cautionary note on the robustness of the perihelia clustering is presented.

Neptune's Internal Temperature NOT Caused by Centaur Impacts

Assessing the contribution of centaur impacts to ice giant luminosities

Author:

Dodson-Robinson et al

Abstract:

Voyager 2 observations revealed that Neptune’s internal luminosity is an order of magnitude higher than that of Uranus. If the two planets have similar interior structures and cooling histories, Neptune’s luminosity can only be explained by invoking some energy source beyond gravitational contraction. This paper investigates whether centaur impacts could provide the energy necessary to produce Neptune’s luminosity. The major findings are (1) that impacts on both Uranus and Neptune are too infrequent to provide luminosities of order Neptune’s observed value, even for optimistic impact-rate estimates and (2) that Uranus and Neptune rarely have significantly different impact-generated luminosities at any given time. Uranus and Neptune most likely have structural differences that force them to cool and contract at different rates.

The Solar System Probably did NOT Have Another Gas Giant

TILTING SATURN WITHOUT TILTING JUPITER: CONSTRAINTS ON GIANT PLANET MIGRATION

Authors:

Brasser et al

Abstract:

The migration and encounter histories of the giant planets in our solar system can be constrained by the obliquities of Jupiter and Saturn. We have performed secular simulations with imposed migration and N-body simulations with planetesimals to study the expected obliquity distribution of migrating planets with initial conditions resembling those of the smooth migration model, the resonant Nice model and two models with five giant planets initially in resonance (one compact and one loose configuration). For smooth migration, the secular spin–orbit resonance mechanism can tilt Saturn's spin axis to the current obliquity if the product of the migration timescale and the orbital inclinations is sufficiently large (exceeding 30 Myr deg). For the resonant Nice model with imposed migration, it is difficult to reproduce today's obliquity values, because the compactness of the initial system raises the frequency that tilts Saturn above the spin precession frequency of Jupiter, causing a Jupiter spin–orbit resonance crossing. Migration timescales sufficiently long to tilt Saturn generally suffice to tilt Jupiter more than is observed. The full N-body simulations tell a somewhat different story, with Jupiter generally being tilted as often as Saturn, but on average having a higher obliquity. The main obstacle is the final orbital spacing of the giant planets, coupled with the tail of Neptune's migration. The resonant Nice case is barely able to simultaneously reproduce the orbital and spin properties of the giant planets, with a probability $\sim 0.15\%.$ The loose five planet model is unable to match all our constraints (probability less than 0.08%). The compact five planet model has the highest chance of matching the orbital and obliquity constraints simultaneously (probability ~0.3%).

The Bright Storm of Uranus in 2014

Spectral analysis of Uranus' 2014 bright storm with VLT/SINFONI

Authors:

Irwin et al

Abstract:

An extremely bright storm system observed in Uranus' atmosphere by amateur observers in September 2014 triggered an international campaign to observe this feature with many telescopes across the world. Observations of the storm system in the near infrared were acquired in October and November 2014 with SINFONI on ESO's Very Large Telescope (VLT) in Chile. SINFONI is an Integral Field Unit spectrometer returning 64x64 pixel images with 2048 wavelengths. Image cubes in the H-band (1.43 - 1.87 microns) were obtained at spatial resolutions of ~0.1". The observations show that the centre of the storm feature shifts markedly with increasing altitude, moving in the retrograde direction and slightly poleward with increasing altitude. We also see a faint 'tail' of more reflective material to the immediate south of the storm, which again trails in the retrograde direction. The observed spectra were analysed with the radiative transfer and retrieval code, NEMESIS. We find that the storm is well-modelled using either two main cloud layers of a 5-layer aerosol model based on Sromovsky et al. (2011) or by the simpler two-cloud-layer model of Tice et al. (2013). The deep component appears to be due to an increase in reflectivity and altitude of the main tropospheric cloud deck at 2 - 3 bars for both models, while the upper component of the feature was modelled as being due to either a thickening of the tropospheric haze of the 2-layer model or a vertical extension of the upper tropospheric cloud of the 5-layer model, assumed to be composed of methane ice and based at the methane condensation level at 1.23 bar. During the twelve days between our sets of observations the higher-altitude component of the feature was observed to have brightened significantly and extended to even higher altitudes, while the deeper component

Could Jupiter or Saturn Have Ejected a Fifth Giant Planet?

Could Jupiter or Saturn Have Ejected a Fifth Giant Planet?

Authors:

Cloutier et al

Abstract:

Models of the dynamical evolution of the early solar system following the dispersal of the gaseous protoplanetary disk have been widely successful in reconstructing the current orbital configuration of the giant planets. Statistically, some of the most successful dynamical evolution simulations have initially included a hypothetical fifth giant planet, of ice giant mass, which gets ejected by a gas giant during the early solar system's proposed instability phase. We investigate the likelihood of an ice giant ejection event by either Jupiter or Saturn through constraints imposed by the current orbits of their wide-separation regular satellites Callisto and Iapetus respectively. We show that planetary encounters that are sufficient to eject an ice giant, often provide excessive perturbations to the orbits of Callisto and Iapetus making it difficult to reconcile a planet ejection event with the current orbit of either satellite. Quantitatively, we compute the likelihood of reconciling a regular Jovian satellite orbit with the current orbit of Callisto following an ice giant ejection by Jupiter of ~ 42% and conclude that such a large likelihood supports the hypothesis of a fifth giant planet's existence. A similar calculation for Iapetus reveals that it is much more difficult for Saturn to have ejected an ice giant and reconcile a Kronian satellite orbit with that of Iapetus (likelihood ~ 1%), although uncertainties regarding the formation of Iapetus, on its unusual orbit, complicates the interpretation of this result.

Theia Wasn't Alone: Uranus Formed From Two Protoplanets Colliding

Stimulated Radiative Molecular Association in the Early Solar System. II. Orbital Radii of the Planets and Other Satellites of the Sun

Author:

Lombardi

Abstract:

In a previous investigation, the orbital radii of regular satellites of Uranus, Jupiter, Neptune, and Saturn are shown to be directly related to photon energies in the spectra of atomic and molecular hydrogen. To explain these observations a model was developed involving stimulated radiative molecular association (SRMA) reactions among photons and atoms in the protosatellite disks of the planets. In the present investigation, the previously developed model is applied to the planets and important satellites of the Sun. A key component of the model involves resonance associated with SRMA. Through this resonance, thermal energy is extracted from the protosun's protoplanetary disk at specific distances from the protosun wherever there is a match between the local thermal energy of the disk and the energy of photons impinging on the disk. Orbital radii of the planets and satellites are related to photon energies (EP values) in the spectrum of atomic hydrogen. An expression determined previously is used to relate EP values to temperatures in the disk. Results indicate the surface temperature of the protosun at the time when the evolution of the planets begins is higher than the surface temperature of a typical T Tauri star. The present investigation offers an explanation for the existence of the asteroid and classical Kuiper belts and predicts that a primordial belt once existed in the vicinity of Neptune. It also indicates that Uranus is formed from two protoplanets and is thus consistent with the theory that the large tilt of Uranus's axis of rotation was created by the collision of two bodies.

The Hera Saturn Entry Probe Mission

The hera saturn entry probe mission

Authors:

Mousis et al

Abstract:

The Hera Saturn entry probe mission is proposed as an M–class mission led by ESA with a contribution from NASA. It consists of one atmospheric probe to be sent into the atmosphere of Saturn, and a Carrier–Relay spacecraft. In this concept, the Hera probe is composed of ESA and NASA elements, and the Carrier–Relay Spacecraft is delivered by ESA. The probe is powered by batteries, and the Carrier–Relay Spacecraft is powered by solar panels and batteries. We anticipate two major subsystems to be supplied by the United States, either by direct procurement by ESA or by contribution from NASA: the solar electric power system (including solar arrays and the power management and distribution system), and the probe entry system (including the thermal protection shield and aeroshell). Hera is designed to perform in situ measurements of the chemical and isotopic compositions as well as the dynamics of Saturn's atmosphere using a single probe, with the goal of improving our understanding of the origin, formation, and evolution of Saturn, the giant planets and their satellite systems, with extrapolation to extrasolar planets. Hera's aim is to probe well into the cloud-forming region of the troposphere, below the region accessible to remote sensing, to the locations where certain cosmogenically abundant species are expected to be well mixed. By leading to an improved understanding of the processes by which giant planets formed, including the composition and properties of the local solar nebula at the time and location of giant planet formation, Hera will extend the legacy of the Galileo and Cassini missions by further addressing the creation, formation, and chemical, dynamical, and thermal evolution of the giant planets, the entire solar system including Earth and the other terrestrial planets, and formation of other planetary systems.

Salt key to Understanding Neptune and Uranus' Interiors?

The interiors of several of our Solar System's planets and moons are icy, and ice has been found on distant extrasolar planets, as well. But these bodies aren't filled with the regular kind of water ice that you avoid on the sidewalk in winter. The ice that's found inside these objects must exist under extreme pressures and high-temperatures, and potentially contains salty impurities, too.

New research from a team including Carnegie's Alexander Goncharov focuses on the physics underlying the formation of the types of ice that are stable under the paradoxical-seeming conditions likely to be found in planetary interiors. Their work, published by Proceedings of the National Academy of Sciences, could challenge current ideas about the physical properties found inside icy planetary bodies.

When water (H2O) freezes into ice, the molecules are bound together in a crystalline lattice held together by hydrogen bonds. Due to the versatility of these hydrogen bonds, ice reveals a striking diversity of at least 16 different crystalline structures. But most of these structures could not exist in the interiors of frozen planets and moons.

Under high pressures, the variety of possible ice structures shrinks, just as the space between its hydrogen-bonded oxygen atoms does as the ice grows denser. When pressure is increased to more than about 20,000 times Earth's atmosphere (2 gigapascals), this number of possible ice structures is reduced to just two -- ice VII and ice VIII. Ordinary ice has a hexagonal structure. Ice VII has a cubic structure. Ice VIII has a tetragonal structure.

As the pressure increases further, both forms of ice transform to another phase called ice X. This happens at pressures around 600,000 times Earth's atmosphere (60 gigapascals), which would be comparable to the pressure conditions found in the interior of an icy-cored planet, like Neptune or Uranus. Ice X has a whole new kind of symmetrical lattice structure. It's called non-molecular ice, because the water molecule is broken apart and the hydrogen atoms are shared between neighboring oxygens.

Under similar pressures but higher temperatures, it has been suggested that ice X could possibly transform into a phase of ice that can conduct electricity as hydrogen atoms move freely around the oxygen lattice. But how such ice would be formed at the temperatures found in planetary interiors has remained mysterious.

Because the interiors of icy planetary bodies might also be salty, due to interactions between the ice and the surrounding rocks or a liquid ocean, lead author Livia Eleonora Bove of the CNRS & Université Pierre et Marie Curie in France and the Ecole Polytechnique Federal de Lausanne in Switzerland and the rest of the team studied the effects of salts on the formation of the ice X from ice VII.

They found that the inclusion of salts in ice VII -- both ordinary sodium chloride (NaCl) that you have on your table and the similarly structured lithium chloride (LiCl) -- pushes the formation of ice X to occur at higher and higher pressures. Such salts could easily have been incorporated as impurities when matter accreted during the planetary formation process and be present in rocks or liquid water with which the core ice interacts.

'These findings could challenge our current thinking on the physics occurring in the interiors of icy planetary bodies,' Goncharov said. 'All of our current assumptions are based on the behavior of ice without any impurities.'

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Record-breaking Storm Activity on Uranus or did Uranus get Whacked?

Record-breaking storm activity on Uranus in 2014

Authors:

de Pater et al

Abstract:

In spite of an expected decline in convective activity following the 2007 equinox of Uranus, eight sizable storms were detected on the planet with the near-infrared camera NIRC2, coupled to the adaptive optics system, on the 10-m W.M. Keck telescope on UT 5 and 6 August 2014. All storms were on Uranus’ northern hemisphere, including the brightest storm ever seen in this planet at 2.2 μm, reflecting 30% as much light as the rest of the planet at this wavelength. The storm was at a planetocentric latitude of ∼15°N and reached altitudes of ∼330 mbar, well above the regular uppermost cloud layer (methane-ice) in the atmosphere. A cloud feature at a latitude of 32°N, that was deeper in the atmosphere (near ∼2 bar), was later seen by amateur astronomers. We also present images returned from our HST ToO program, that shows both of these cloud features. We further report the first detection of a long-awaited haze over the north polar region.

The Science Case for an Uranus Orbiter

The science case for an orbital mission to Uranus: Exploring the origins and evolution of ice giant planets

Authors:

Arridge et al

Abstract:

Giant planets helped to shape the conditions we see in the Solar System today and they account for more than 99% of the mass of the Sun's planetary system. They can be subdivided into the Ice Giants (Uranus and Neptune) and the Gas Giants (Jupiter and Saturn), which differ from each other in a number of fundamental ways. Uranus, in particular is the most challenging to our understanding of planetary formation and evolution, with its large obliquity, low self-luminosity, highly asymmetrical internal field, and puzzling internal structure. Uranus also has a rich planetary system consisting of a system of inner natural satellites and complex ring system, five major natural icy satellites, a system of irregular moons with varied dynamical histories, and a highly asymmetrical magnetosphere. Voyager 2 is the only spacecraft to have explored Uranus, with a flyby in 1986, and no mission is currently planned to this enigmatic system. However, a mission to the uranian system would open a new window on the origin and evolution of the Solar System and would provide crucial information on a wide variety of physicochemical processes in our Solar System. These have clear implications for understanding exoplanetary systems. In this paper we describe the science case for an orbital mission to Uranus with an atmospheric entry probe to sample the composition and atmospheric physics in Uranus’ atmosphere. The characteristics of such an orbiter and a strawman scientific payload are described and we discuss the technical challenges for such a mission. This paper is based on a white paper submitted to the European Space Agency's call for science themes for its large-class mission programme in 2013.

LLNL's National Ignition Facility Used to Compress Diamond, Simulate Interior of Jupiter

Lawrence Livermore scientists for the first time have experimentally re-created the conditions that exist deep inside giant planets, such as Jupiter, Uranus and many of the planets recently discovered outside our solar system.

Researchers can now re-create and accurately measure material properties that control how these planets evolve over time, information essential for understanding how these massive objects form. This study focused on carbon, the fourth most abundant element in the cosmos (after hydrogen, helium and oxygen), which has an important role in many types of planets within and outside our solar system. The research appears in the June 17 edition of the journal, Nature.

Using the largest laser in the world, the National Ignition Facility at Lawrence Livermore National Laboratory, teams from the Laboratory, University of California, Berkeley and Princeton University squeezed samples to 50 million times Earth's atmospheric pressure, which is comparable to the pressures at the center of Jupiter and Saturn. Of the 192 lasers at NIF, the team used 176 with exquisitely shaped energy versus time to produce a pressure wave that compressed the material for a short period of time. The sample – diamond – is vaporized in less than 10 billionths of a second.

Though diamond is the least compressible material known, the researchers were able to compress it to an unprecedented density greater than lead at ambient conditions.

"The experimental techniques developed here provide a new capability to experimentally reproduce pressure–temperature conditions deep in planetary interiors," said Ray Smith, LLNL physicist and lead author of the paper.

Such pressures have been reached before, but only with shock waves that also create high temperatures – hundreds of thousands of degrees or more – that are not realistic for planetary interiors. The technical challenge was keeping temperatures low enough to be relevant to planets. The problem is similar to moving a plow slowly enough to push sand forward without building it up in height. This was accomplished by carefully tuning the rate at which the laser intensity changes with time.

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Measuring Jupiter's Water Abundance by Juno

Measuring Jupiter's water abundance by Juno: the link between interior and formation models

Authors:

Helled et al

Abstract:

The Juno mission to Jupiter is planned to measure the water abundance in Jupiter's atmosphere below the cloud layer. This measurement is important because it can be used to reveal valuable information on Jupiter's origin and its composition. In this paper, we discuss the importance of this measurement, the challenges in its interpretation, and address how it can be connected to interior and formation models of Jupiter.

Using Juno to see how wet Jupiter is

Measuring Jupiter's water abundance by Juno: the link between interior and formation models

Authors:

Helled et al

Abstract:

The JUNO mission to Jupiter is planned to measure the water abundance in Jupiter's atmosphere below the cloud layer. This measurement is important because it can be used to reveal valuable information on Jupiter's origin and its composition. In this paper we discuss the importance of this measurement, the challenges in its interpretation, and address how it can be connected to interior and formation models of Jupiter.