Presentation on theme: "Neptune. Discovery John Couch Adams, Cambridge mathematician, predicted the existence of an unseen planet. Uranus was being pulled slightly out of position."— Presentation transcript:
Discovery John Couch Adams, Cambridge mathematician, predicted the existence of an unseen planet. Uranus was being pulled slightly out of position in its orbit (1845). His work was ignored by the Royal observatory Greenwich Until a French mathematician, Urbain Leverrier, published a similar prediction. Search started in July 1846 lead by Prof. Challis at Cambridge university Leverrier with the help of Johann Galle at Berlin Observatory found the planet on the 23rd September 1846 Leverrier and Adams are now jointly credited with their “discovery”
Neptune Discovered in 1846 at position predicted from gravitational disturbances on Uranus’ orbit. Blue-green color from methane in the atmosphere 4 times Earth’s diameter; 4 % smaller than Uranus
Neptune is a cold, bluish world with Jupiterlike atmospheric features No white ammonia clouds are seen on Neptune Presumably the low temperatures have caused almost all the ammonia to precipitate into the interiors of the planets All of these planets’ clouds are composed of methane Much more cloud activity is seen on Neptune than on Uranus.
Appearance Neptune shows color variation in bands Also, As season progresses, southern bands brighten (near IR)
The Atmosphere of Neptune Cloud-belt structure with high-velocity winds; origin not well understood. Darker cyclonic disturbances, similar to Great Red Spot on Jupiter, but not long-lived. The “Great Dark Spot” White cloud features of methane ice crystals
Composition 79% H 2 18% He 3% CH 4 Traces of N 2, HCN, H 2 S, NH 3, CO
Neptune’s Banded Structure
Keck AO Infrared image No more Great Dark Spot Dynamic weather patterns Wind speed up to 1500 km/h (half the speed of sound)
Zonal Winds Far fewer bands than on Jupiter and Saturn Neptune -300m/s(0 o ), 0(±50 o ), 225(±75 o ) Less sunlight = less turbulence = flow less disturbed
Clouds methane ice (CH 4 )<1bar (limit of probing) Probably have: Methane droplets? hydrogen Sulfide (H 2 S)2-5bar more H 2 S, so no NH 3 clouds? NH 4 hydrosulfide (NH 4 SH)15-30bar water15-50bar
Neptune’s Clouds Much more cloud activity is seen on Neptune than on Uranus
High altitude clouds
Great Dark Spot Comparable in size to GRS Storm? (1200mph, counterclockwise rotation, anticyclone) Below the tropopause Moved towards equator, dissipated, new one formed in the northern hemisphere
Great Dark Spot Hole in the methane droplet cloud deck? Like the ozone hole over Antarctica?
The Dark Spot
Neptune contains a higher proportion of heavy elements than Jupiter and Saturn Neptune may have a rocky core surrounded by a mantle of water and ammonia Electric currents in the mantles may generate the magnetic fields of the planets Internal Structure of Neptune
Interior Structure Ice and rock in core (same size than Earth –Not enough pressure to force hydrogen into metallic hydrogen –Off-axis and offset magnetic field probably due to polarized water or ammonia dissolved in water in outer core
Neptune’s Structure Similar composition than Jupiter: 84% H and 14% He, CH 4 (3%) (blue color). No NH 3 since T condensation = 70 K and T outtermostplanets ~58 K Far more atmospheric activity than Uranus b/c of Interior heat (3 times more energy) + less haze –Modest axial tilt may allow for more atmospheric mixing –Storm activity seen and seems to change
The magnetic field of Neptune is oriented at an unusual angle The magnetic axis of Neptune is steeply inclined from its axis of rotation The magnetic and rotational axes of all the other planets are more nearly parallel The magnetic field of Neptune is also offset from the center of the planet The magnetic field of Neptune
The Rings of Neptune Made of dark material, visible in forward- scattered light. Interrupted between denser segments (arcs) Focused by small shepherd moons embedded in the ring structure. Ring material must be regularly re-supplied by dust from meteorite impacts on the moons.
Neptune has a system of thin, dark rings
The Moons of Neptune Two moons (Triton and Nereid) visible from Earth; 6 more discovered by Voyager 2 Unusual orbits: Triton: Only satellite in the solar system orbiting clockwise, i.e. “backward”. Nereid: Highly eccentric orbit; very long orbital period (359.4 d).
Neptune has 13 satellites, one of which (Triton) is comparable in size to our Moon or the Galilean satellites of Jupiter Triton has a young, icy surface indicative of tectonic activity The energy for this activity may have been provided by tidal heating that occurred when Triton was captured by Neptune’s gravity into a retrograde orbit Triton has a tenuous nitrogen atmosphere Triton is a frigid, icy world with a young surface and a tenuous atmosphere Neptune’s Satellites
Triton Probably a captured Kuiper belt object: orbiting Neptune opposite Neptune’s direction of rotation. Smaller than Earth’s Moon, yet has recent geological activity.
The Surface of Triton → Triton can hold a tenuous atmosphere of nitrogen and some methane; 10 5 times less dense than Earth’s atmosphere. Very low temperature (34.5 K) Surface composed of ices: nitrogen, methane, carbon monoxide, carbon dioxide. Possibly cyclic nitrogen ice deposition and re-vaporizing on Triton’s south pole, similar to CO 2 ice polar cap cycles on Mars.
The Surface of Triton Ongoing surface activity: Surface features probably not more than 100 million years old. Large basins might have been flooded multiple times by liquids from the interior.