Posts Tagged ‘ganymede’
[LINK] “ESA, Airbus Formalize Jupiter Icy Moons Contract”
The Dragon’s Tales linked to Space News’ report showing that the ESA is set to join NASA in the ranks of deep-space explorers.
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.
Juice will spend 7.5 years after launch making its way to the Jupiter system, where it will investigate the Europa, Ganymede and Callisto moons. Its mission is expected to last 3.5 years.
[LINK] On why the Galilean moons, unlike Titan, lack atmospheres
The Dragon’s Tales links to a paper, “The formation of the Galilean moons and Titan in the Grand Tack scenario”, that provides an explanation for why Galilean moons like Ganymede and Callisto lack atmospheres despite being as massive as densely-shrouded Titan. Migration in the early solar system explains this.
In the “Grand Tack” (GT) scenario for the young solar system, Jupiter formed beyond 3.5 AU from the Sun and migrated as close as 1.5 AU until it encountered an orbital resonance with Saturn. Both planets then supposedly migrated outward for several 105 yr, with Jupiter ending up at ~5 AU. The initial conditions of the GT and the timing between Jupiter’s migration and the formation of the Galilean satellites remain unexplored. We study the formation of Ganymede and Callisto, both of which consist of ~50% water and rock, respectively, in the GT scenario. We examine why they lack dense atmospheres, while Titan is surrounded by a thick nitrogen envelope. We model an axially symmetric circumplanetary disk (CPD) in hydrostatic equilibrium around Jupiter. The CPD is warmed by viscous heating, Jupiter’s luminosity, accretional heating, and the Sun. The position of the water ice line in the CPD, which is crucial for the formation of massive moons, is computed at various solar distances. We assess the loss of Galilean atmospheres due to high-energy radiation from the young Sun. Ganymede and Callisto cannot have accreted their water during Jupiter’s supposed GT, because its CPD (if still active) was too warm to host ices and much smaller than Ganymede’s contemporary orbit. From a thermal perspective, the Galilean moons might have had significant atmospheres, but these would probably have been eroded during the GT in < 105 yr by solar XUV radiation. Jupiter and the Galilean moons formed beyond 4.5 (+/-0.5) AU and prior to the proposed GT. Thereafter, Jupiter's CPD would have been dry, and delayed accretion of planetesimals should have created water-rich Io and Europa. While Galilean atmospheres would have been lost during the GT, Titan would have formed after Saturn's own tack, because Saturn still accreted substantially for ~106 yr after its closest solar approach, ending up at about 7 AU.