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Jupiter, a laboratory for studying exoplanets

The scientific journal Astrophysical Journal Letters is publishing a study, led by researchers at the Astrophysical Institute of the Canaries (IAC), which has been the subject of a report in the journal Nature. It the study Jupiter is presented as an ideal laboratory for research into exoplanets which are similar. Jupiter, the largest planet in the Solar System, has large satellites around it. The study has used the largest of the satellites, which is the biggest satellite in the Solar System, Ganymede, as a mirror to analyse the atmosphere of the planet. The observations were performed during an eclipse of Ganymede by Jupiter, and allowed the researchers to observe Jupiter as if it were a transiting exoplanet.
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Title: Effect of transient solar wind pulses on atmospheric heating at Jupiter
Authors: J. N. Yates, N. Achilleos, P. Guio (Physics and Astronomy, University College London, London, UK and Centre for Planetary Sciences, UCL/Birkbeck, UK)

Previously, we have presented the first study to investigate the response of the Jovian thermosphere to transient variations in solar wind dynamic pressure, using a coupled, azimuthally symmetric global circulation model coupled with a simple magnetosphere model. This work (Yates et al., 2013, submitted) described the response of thermospheric flows, momentum sources, and the magnetosphere-ionosphere coupling currents to transient compressions and expansions in the magnetosphere. The present study describes the response of thermospheric heating, cooling and the auroral emissions to the aforementioned transient events. We find that transient compressions and expansions, on time scales <= 3 hours, cause at least a factor of two increase in Joule heating per unit volume. Ion drag significantly changes the kinetic energy of the thermospheric neutrals depending on whether the magnetosphere is compressed or expanded. These processes lead to local temperature variations >= 25 K and a ~2000 TW increase in the total power dissipated in the thermosphere. In terms of auroral processes, transient compressions increase main oval UV emission by a factor of ~4.5 whilst transient expansions increase this main emission by a more modest 37%. Both types of transient event cause shifts in the position of the main oval, of up to 1 deg latitude.

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Title: Jupiter will become a hot Jupiter: Consequences of Post-Main-Sequence Stellar Evolution on Gas Giant Planets
Authors: David S. Spiegel, Nikku Madhusudhan

When the Sun ascends the red giant branch (RGB), its luminosity will increase and all the planets will receive much greater irradiation than they do now. Jupiter, in particular, might end up more highly irradiated than the hot Neptune GJ 436b and, hence, could appropriately be termed a "hot Jupiter." When their stars go through the RGB or asymptotic giant branch (AGB) stages, many of the currently known Jupiter-mass planets in several-AU orbits will receive levels of irradiation comparable to the hot Jupiters, which will transiently increase their atmospheric temperatures to ~1000 K or more. Furthermore, massive planets around post-main-sequence stars could accrete a non-negligible amount of material from the enhanced stellar winds, thereby significantly altering their atmospheric chemistry as well as causing a significant accretion luminosity during the epochs of most intense stellar mass loss. Future generations of infrared observatories might be able to probe the thermal and chemical structure of such hot Jupiters' atmospheres. Finally, we argue that, unlike their main-sequence analogues (whose zonal winds are thought to be organised in only a few broad, planetary-scale jets), red-giant hot Jupiters should have multiple, narrow jets of zonal winds and efficient day-night redistribution.

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Title: Forward and Inverse Modeling for Jovian Seismology
Authors: J. Jackiewicz, N. Nettelmann, M. Marley, J. Fortney

Jupiter is expected to pulsate in a spectrum of acoustic modes and recent re-analysis of a spectroscopic time series has identified a regular pattern in the spacing of the frequencies {gaulme2011}. This exciting result can provide constraints on gross Jovian properties and warrants a more in-depth theoretical study of the seismic structure of Jupiter. With current instrumentation, such as the SYMPA instrument {schmider2007} used for the {gaulme2011} analysis, we assume that, at minimum, a set of global frequencies extending up to angular degree \ell=25 could be observed. In order to identify which modes would best constrain models of Jupiter's interior and thus help motivate the next generation of observations, we explore the sensitivity of derived parameters to this mode set. Three different models of the Jovian interior are computed and the theoretical pulsation spectrum from these models for \ell\leq 25 is obtained. We compute sensitivity kernels and perform linear inversions to infer details of the expected discontinuities in the profiles in the Jovian interior. We find that the amplitude of the sound-speed jump of a few percent in the inner/outer envelope boundary seen in two of the applied models should be reasonably inferred with these particular modes. Near the core boundary where models predict large density discontinuities, the location of such features can be accurately measured, while their amplitudes have more uncertainty. These results suggest that this mode set would be sufficient to infer the radial location and strength of expected discontinuities in Jupiter's interior, and place strong constraints on the core size and mass. We encourage new observations to detect these Jovian oscillations.

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Title: Jupiter models with improved ab initio hydrogen EOS (H-REOS.2)
Authors: Nadine Nettelmann, Andreas Becker, Bastian Holst, Ronald Redmer

The amount and distribution of heavy elements in Jupiter gives indications on the process of its formation and evolution. Core mass and metallicity predictions however depend on the equations of state used, and on model assumptions. We present an improved ab initio hydrogen equation of state, H-REOS.2 and compute the internal structure and thermal evolution of Jupiter within the standard three-layer approach. The advance over comparable previous Jupiter models (Nettelmann et al. 2008, ApJ 683, 1217) is that the new models are also consistent with the observed \gtrsim 2 times solar heavy element abundances in Jupiter's atmosphere. Such models have a rock core mass Mcore=0-8 ME, total mass of heavy elements MZ=28-31 ME, a deep internal layer boundary at \geq 4 Mbar, and a cooling time of 4.7 Gyrs when assuming homogeneous evolution. We also calculate two-layer models in the manner of Militzer et al. (2008), ApJ 688, L45, and find a comparable core mass but significantly higher envelope metallicity of 4.5 times solar. According to our three-layer models, neither the equidistance (156 microHz) nor the moment of inertia (0.276) are sensitive to the core mass but accurate measurements could well help to rule out some classes of models.

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Jupiter has a long list of oddities. For one thing, it's enormous, containing 70% of our solar system's planetary material, yet it is not like the rocky world beneath our feet. Jupiter is so gassy, it seems more like a star. Jupiters atmosphere brews hurricanes twice as wide as Earth itself, monsters that generate 400 mph winds and lightning 100 times brighter than terrestrial bolts. The giant planet also emits a brand of radiation lethal to unprotected humans.
Jupiter's strangest feature, however, may be a 25,000 mile deep soup of exotic fluid sloshing around its interior. It's called liquid metallic hydrogen.

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What Lies Inside Jupiter



For four long centuries the gas giant's vast interior has remained hidden from view. NASA's Juno probe, scheduled to launch on August 5th, could change all that.



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Jupiter reaches perihelion (closest approach to he Sun) on the 17th March, 2011.
The last planetary perihelion was in 1999 - Jupiter takes 12 years to orbit the sun.

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Observations of Jupiter reveal rare signatures of weather

One of Jupiter's dark brown stripes that faded out last spring is regaining its colour, providing an unprecedented opportunity for astronomers to observe a rare and mysterious phenomenon caused by the planet's winds and cloud chemistry.
Earlier this year, amateur astronomers noticed that the long-standing stripe, known as the South Equatorial Belt (SEB), just south of Jupiter's equator, had turned white. In early November, amateur astronomer Christopher Go of Cebu City in the Philippines observed a prominent bright spot in the unusually whitened belt, piquing the interest of professional and amateur astronomers around the world.

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Jupiter's brown stripe is returning, say astronomers

One of the "stripes" on Jupiter that faded away earlier this year is making a comeback, astronomers have said.
The South Equatorial Belt had blended into surrounding white clouds but an "outbreak" spotted by an amateur astronomer heralds the stripe's return.

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