Sir Isaac Newtons laws of planetary motion and

Sir Isaac Newton’s laws of planetary motion and his Universal Law of Gravity allow astronomers to calculate the position of celestial objects (and spacecraft and satellites!) at any time in space. This is referred to as Newtonian Celestial Mechanics. F = G x m 1 x m 2 r 2 (Universal Law of Gravity), where F = gravitational force; G = universal constant of gravitation; m 1 and m 2 = the masses of two bodies; and r = the distance between them. “Two bodies attract each other with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them”.

U. J. J. Leverrier Neptune was discovered by pencil and paper!!! 1790: Delambre’s calculations of orbits of Uranus based on Newtonian Celestial Mechanics are up to 2 minutes of arc off from observation. Was Newton wrong? ? ? 1841: Graduate student J. C. Adams noted that in the first quarter of the 19 th century, Uranus seemed to be accelerating slightly, in the second quarter slowing down; could be explained by gravitational perturbations from 8 th, previously unknown planet beyond the orbit of Uranus. Adams predicted its position in the sky, but Royal Astronomer Sir Airy ignored Adams. 1846: Leverrier suggested that an 8 th planet deflected Uranus from its orbit. Predicted its position in sky and wrote to astronomer J. J. Galle. September 23, 1846: J. J. Galle received the letter from Leverrier and found Neptune the same night!!!

Lick Observatory image of Neptune and two of its moons

January 23, 1989, images of Neptune, 2 hours apart, taken by the approaching Viking spacecraft. Moving across the planet at ~30° S latitude is a bright cloud feature.

High-altitude cirrus-like clouds in Neptune’s atmosphere 50 – 150 km wide and maybe 50 km above main clouds

Hubble and Keck views of Neptune, showing storms with Equatorial winds of 1, 400 km/hour

Neptune’s Great Dark Spot (“Scooter”) moving east around planet, driven by strong, 700 miles/hour west winds

Relative cloud motion in Neptune’s atmosphere

Neptune’s Dark Spot (“Scooter”) and smaller Dark Spot 2 moving eastward around the planet at different speeds

Neptune’s Great Dark Spot (“Scooter”) and white cirrus-like clouds

Magnetic field of Neptune. For comparison, the magnetic field of earth is ~ 0. 35 Gauss

The 2 most prominent, clumpy rings of Neptune (clumping of material) discovered by Voyager. Neptune is overexposed to show rings.

New moon of Neptune, 1989 N 1, discovered by Voyager. The large crater is 400 km in diameter.

Crescent of Neptune with its moon Triton in the background

Neptune’s moon Triton is 2, 705 km in diameter. Bright ice cap in southern hemisphere (top) (notice black streaks), and dark terrain with “highways” below.

Dark, active nitrogen geysers on Triton; constant direction of streaks hints at a very thin atmosphere

“Cantelope terrain” on Triton hints at tectonic processes

Possible frozen lakes (of water, ammonia and salts? ) on Triton

Neptune’s moon Triton Imaged by Voyager 2 in 1989 Triton moves around Neptune opposite to the planet’s rotation and movement around the Sun, but synchronous, i. e. , the same side of Triton always faces Neptune The diameter of Triton is 2, 705 km, 3/4 the size of our Moon It was probably captured, just like Pluto Its surface is made of solid methane (CH 4) and N 2, with T = - 400° F Its pinkish color is due to organic compounds that formed from CH 4 and N 2 There are no large impact craters; hence, the surface is young (constantly being resurfaced) The albedo is very high, 0. 80 and, hence, the moon is bright (presence of ices) S pole region has N 2 fumaroles; ejecta are wind-blown, thus, there is a tenuous atmosphere The density = 2. 1 g/cm 2, hence, there must be ices present

Neptune’s moon Nereid is 340 km in diameter. It has the most eccentric orbit of any moon in the Solar System. Separation from Neptune varies from 1. 4 to 9. 6 million km

Neptune’s moon Nereid Discovered in 1949 Not well imaged by Voyager 2, but the spacecraft discovered 6 smaller moons Most eccentric orbit of any moon in the Solar System, hence, it was probably also captured like Triton and Pluto Nereid is 340 km in diameter Its albedo is low, 0. 15, so Nereid is dark like our Moon