Europa and Life 5 October 2016

The Galilean Satellites of Jupiter In 1609, Galileo used his recently invented telescope to look at Jupiter He saw 4 small ‘stars’ moving with the planet He concluded that they were moons orbiting Jupiter, like planets circling the Sun Although he called them the ‘Medician’ stars in honor of his patron, Duke Cosimo of Medici, we know them as the Galilean satellites

If we remove water density increases Io 3.57 g/cc Ganymede 1.94 g/cc Europa 2.97 g/cc Callisto 1.86 g/cc If we remove water density increases Orbital Resonance Io Europa Ganymede Callisto Tidal Heating

Europa: general characteristics Size: R = 1560.8±0.5 km Composition: silicate rock and H2O ice Interior: water-ice crust and probably, subsurface ocean, and an iron–nickel core Surface: temperature averages about 110 K (−160 °C) at the equator and only 50 K (−220 °C) at the poles -> water ice acts like rock Atmosphere: Tenuous, O2 Size: R = 1560.8±0.5 km Composition: silicate rock and H2O ice Interior: water-ice crust and probably, subsurface ocean, and an iron–nickel core Surface: temperature averages about 110 K (−160 °C) at the equator and only 50 K (−220 °C) at the poles -> water ice acts like rock Atmosphere: Tenuous, O2 Slightly smaller than the Moon, Europa is primarily made of silicate rock and has a water-ice crust and probably an iron–nickel core. tenuous atmosphere composed primarily of oxygen

Warm ice..or..liquid water? Europa: interior Warm ice..or..liquid water? or some combination?

Europa: surface hypothesis proposes that heat from tidal flexing causes the ocean to remain liquid and drives geological activity similar to plate tectonics the smoothest surface of any known solid object in the Solar System Europa's most striking surface features are a series of dark streaks crisscrossing the entire globe, called lineae

Conamara Chaos mysterious “brown gunk” is probably sea salt baked by radiation -> means underlying ocean is in direct contact with rock and enriched with potentially life-nurturing amounts of minerals produced by the disruption of the icy crust of Europa

Compare to California’s San Andreas Fault Europa Astypalaea Linea San Andreas Fault

“cycloid” ridges daily fracturing? (120 miles across)

Lenticulae – “freckles” – convective upwelling of warm buoyant ice

Icebergs? (25 miles across)

Tilted ice blocks look like the Arctic Ocean too…

Europa’s surface shows few craters

Tyre multi-ring impact structure Few large impact craters: -> Suggests 60 Myr surface age. A couple of multi-ringed impacts: -> Penetrated 20 km thick ice!

Few large impact craters: -> Suggests 60 Myr surface age. A couple of multi-ringed impacts: -> Penetrated 20 km thick ice!

Europa: ocean and atmosphere surface pressure of Europa's atmosphere is 10−12 atm tenuous ionosphere H2, O2, O that escapes Europa's gravity form a gas torus in the vicinity of Europa's orbit around Jupiter -> feeds Jupiter’s magnetospheric plasma A lot of water periodically occurring plumes of water 200 km high ionosphere (an upper-atmospheric layer of charged particles) around Europa created by solar radiation and energetic particles from Jupiter's magnetosphere

Europa: potential habitability one of the top locations in the Solar System in terms of potential habitability and the possibility of hosting life Life could exist in its under-ice ocean, perhaps subsisting in an environment similar to Earth's deep-ocean hydrothermal vents.[

Discussion Topics What experiments would you take to Europa to find the water and search for life? Talk with those near you and make a short list. Would you land on Europa? Why or why not? Where would you land?

Summary Many of the icy bodies in the outer Solar System are internally differentiated Thanks to tidal heating, Europa and Enceladus may have a liquid ocean between the icy crust and the rocky core Warm rock in contact with water heats it: this starts convection. Hot water can emerge from cracks in the surface: this provides chemical energy for possible life If Earth life arose at hydrothermal vents, it could happen there, too. Also light can reach into the cracks, possibly allowing temporary photosynthesis