Jupiter: Giant of the Solar System

Transcription

1 Jupiter: Giant of the Solar System Jupiter s Red spot : A huge storm that has raged for over 300 years that is ~2x size of the Earth. Gas Giant is really a Liquid Giant! Pictures over ~7 years from Hubble

2 Jupiter Third brightest object in the sky (Moon and Venus) Largest size is: ~50 arc-seconds. Has 63 moons; 16 have size >10 km, 4 largest are Galilean Moons.

3 Property Earth Jupiter Radius 6378km 71492km (11.21 R E ) Mass 5.97x10 24 kg 1.90x10 27 kg = M E Average Density 5520kg/m kg/m 3 (0.241) Gravity Earth s Escape Speed 11.2km/s 59.5km/s Average Temperature = 1 M E 290K / 17C 124K / -149C (at Cloud tops) Eccentricity

4 More Properties of Jupiter Mass is ~1/1000 Mass of the Sun Sidereal orbital period years. Synodic orbital period days. Surface magnetic field 13.89x that of Earth Sidereal rotation period ~0.41 days, ~9h 55m Axial Tilt 3.08 Orbital inclination to the ecliptic 1.31

5 Differential Rotation Jupiter has no Solid Surface! Internal structure is mainly H 2 and He. Rotation rate varies with latitude. Faster at Equator by ~5mins. Rotation Bulge ~6.5% R Eq = 71,500km R Po = 66,900km

6 Jupiter s Atmosphere Ever-changing, multicoloured bands, parallel to the equator. Reds Yellows White Greens Tans Blues Browns

7 Atmospheric Composition Spectroscopic studies in UV, IR H 2 : 86.1% Helium: 13.8% Smaller amounts of: methane, ammonia, water vapour. Galileo Probe found traces of ethane and phosphine: PH 3, Xe, Ar, Kr, and elements C, N, S Note: Escape speed so high that light gases cannot escape Jupiter s gravity.

8 Atmospheric Bands Divided into Bright Zones and Dark Belts. Vary in both latitude and intensity. Left: Infra- Red image. Bright = Hot, Dark = Cold

9 Atmospheric Bands II No Seasons Dynamic patterns Light Zones warm rising gas will then cool. Dark belts Cool sinking gas will warm up. Convection Cycles

10 Zone / Belt Differences Different Pressures (Zones higher) Different Temperatures Different Colours due to different rates ons chemical reactions in clouds. Different Speeds (Faster near Equator) Different flow Directions (bit simplistic)

11 Zonal Flow Very stable underlying eastward and westward wind flow. Near Poles both zonal flow and bands disappear. Wind speed and direction relative to the Planet s internal rotation rate

12 Atmospheric Structure Colour due to complex chemical and photochemical reactions not fully understood (but involving Sulphur compounds). Different colours implies we are viewing different depths in atmosphere. Clouds in 3 main layers.

13 Layered Atmosphere Top of Troposphere is 0 km, as no solid surface. Ammonia ice: K (~ -140C) Ammonia + H 2 S ~200K (~ - 73C) Water ice/vapour

14 Galileo: Atmospheric Probe, 1995 Survived ~1hr before crushed at 150km! High Winds very deep in atmosphere Heated from surface? - rather than sunlight No pre-biotic compounds found! Galileo s entry point

15 Weather Systems: Jupiter s Great Red Spot White oval is ~ size of Earth and seen since Eye of a Hurricane Persistence due to no solid surface like Hurricanes

16 Red Spot s Stability Red Spot s size varies: in 1979 ~20,000km x 10,000km In 1976/7 ~40,000km x 14,000km

17 Smaller storms quite common. White Ovals Brown Oval hole in upper cloud layer. Only appear >20 N Last ~1-10 years Reasons for different colours not known. Jovial Storms

18 Shoemaker- Levy 9 comet July 1994 Jupiter s tidal forces broke up passing comet into 23 pieces. Hit on far side Biggest hit 600Megatons same as all Earth s Nuclear Weapons. Spectral analysis of explosions is hard

19 Views of Shoemaker-Levy 9 remnants from Hubble Over a period of weeks the high winds gradually erased the impact scars.

20 Jupiter s Emits Heat Based on distance from the Sun, expected cloud top temperature was 105K (-168C) Actually 125K (-148C) Small difference but it implies Jupiter emits 2x what it receives! Not due to radioactivity or fusion. Gravitational Energy converted to Heat

21 Jupiter s Internal Structure Mainly from theoretical modelling not direct evidence. No real surface Just gets denser, gradually becomes liquid. Super high densities and temperature. Interior has hydrogen in liquid metallic state Center is small rocky core Chemically like rocks not physically

22 Jupiter s Internal Structure II

23 Jupiter s Magnetic Field Very powerful magnetic Field due to rapid rotation of metallic hydrogen interior. Intrinsic strength ~ 20,000x Earth s Magnetosphere larger that the Sun s size and ~1million x bigger that that of Earth. Tail extends beyond Saturn s orbit. Magnetic Axis is offset by ~10 and poles are opposite to that of Earth. High-speed ions hostile to passing spacecraft!

24 Jupiter s Magnetosphere Inner region has a flat current sheet, charged particles forced into equatorial plane by rapid rotation. Plasma Torus due to Moon: Io (Discussed later)

25 Aurora on Jupiter! Inserts are UV photos of ions colliding with atmospheric gases!