Jovian Wrapup – Uranus and Neptune

1. Jovian Wrapup – Uranus and Neptune • Uranus was discovered by accident • Neptune was found via predictions from gravitational physics. Uranus Neptune

2. William Herschel's Discovery of Uranus • In 1781 William Herschel noticed a moving object (moving night-to-night) that he supposed was a comet. • He reported the “comet” and people around the world began to observe it. • They soon realized that the object was in a circular orbit around the Sun beyond Saturn – a new planet!

3. Neptune's Discovery • By the mid-1800's Uranus had completed an orbit around the Sun since its discovery. • Astronomers noted that it was not quite following the path predicted by Newton's physics and gravitation • It was likely that a massive unknown planet beyond Uranus was tugging Uranus off of its expected path. • Working backwards English mathematician Adams and French mathematician LeVerrier independently calculated the location of the unknown planet. • LeVerrier contacted astronomers in Berlin who found Neptune within an hour of the start of the search (only a finger's width away from the predicted position). Adams LeVerrier

4. Uranus and Neptune • Uranus and Neptune are Jovian worlds dominated by Hydrogen/Helium mantles.

5. Uranus and Neptune • Jupiter and Saturn have “solar” composition. • Uranus and Neptune are more dominated by ice (and rock).

6. Uranus and Neptune • Jupiter and Saturn have “solar” composition. • Uranus and Neptune are more dominated by ice (and rock).

7. Uranus and Neptune • Methane gas absorbs red light but lets blue light pass into the atmosphere, off the particulates, and back to us giving them their blue-green color. • Since they are colder than Jupiter and Saturn the high white clouds are made of methane ice crystals.

8. Uranus and Neptune

9. Uranus and Neptune • Uranus and Neptune both have systems of thin rings Infrared views reveal/exaggerate the Uranian rings since the planet is quite dark at these wavelengths. Visible light views hardly show them at all.

10. Uranus and Neptune • Uranus and Neptune both have systems of thin rings

11. Uranus and Neptune • Uranus and Neptune both have systems of thin rings Neptune's Rings

12. Uranus/Neptune Wrapup • Uranus and Neptune both have systems of icy moons

13. Uranus/Neptune Wrapup • Uranus and Neptune both have systems of icy moons

14. Triton • Triton is a Pluto-sized world with a “youthful” icy surface. • It holds on to a thin nitrogen atmosphere. • It orbits Neptune “backwards” and is likely a captured cousin of Pluto

15. Triton • Like Enceladus and the Uranian satellites, Triton is dominated by water/ice and is rich in volatiles like ammonia, nitrogen and methane. This mix enables geological activity at the frigid temperatures of the outer Solar System with only modest interior warmth. • Triton is likely to be representative to what we will find when we arrive at Pluto in 2015. Frozen lakes on Triton?

16. Triton's Atmosphere, Ice Caps and Geysers • Triton's south pole is just coming out of a decades-long winter where it is so cold the thin nitrogen atmosphere has frozen solid on the surface. • The dark streaks arise from nitrogen/ice geysers that shoot material into the atmosphere. • The nitrogen atmosphere freezes out at the poles in winter. Warmed in the summer, the gas bursts out from below the frozen surface layers.

17. The dark streaks arise from nitrogen/water/ice geysers that shoot material into the atmosphere.

18. Pluto: Major Planet or Minor Nuisance? • Pluto/Charon is a double world at the outskirts of the Jovian Planet region of the Solar System

19. Pluto: Major Planet or Minor Nuisance? • Smaller than the Earth's Moon, it's status as a “major” planet, secure for 70 years, was recently lost.

20. Pluto: Major Planet or Minor Nuisance? • From its discovery in 1930 until its demotion in 2006 Pluto was regarded as one of nine major planets in the Solar System. Pluto and its satellite Charon

21. Pluto: Major Planet or Minor Nuisance? • The formal definition of Pluto as a “dwarf planet” by the International Astronomical Union in 2006 brought strong reaction from both astronomers and non-scientists.

22. Pluto: Major Planet or Minor Nuisance? • The formal definition of Pluto as a “dwarf planet” by the International Astronomical Union in 2006 brought strong reaction from both astronomers and non-scientists.

23. Solar System Debris:Comets and Asteroids If you want to understand the issues surrounding Pluto's planetary status, then you first must understand... • Primarily found in two zones in the solar system. The Asteroid Belt (rocky, between Jupiter and Mars) The Edgeworth/Kuiper Belt (beyond Neptune) and Oort Cloud (way out there) – sources of comets (icy)

24. Solar System Debris • Why do comets and asteroids exist?.... Solar system formation is a messy process.

25. Solar System Debris • During the accretion of the planets, the planets sweep up and fling out most of the debris but stable/protected zones remain.

26. Solar System Debris: Asteroids • Jupiter interfered with the formation of a planet between Mars and Jupiter. Some fraction of the debris remains today as the asteroid belt. • Jupiter stirred up the planetesimals so that collisions were violent rather than gentle.

27. Asteroids • Asteroids are small, rocky, cratered and irregularly shaped. • They are the collisionally modified remains of leftover planetesimals between the orbits of Mars and Jupiter.

28. Asteroids • Asteroids are small, rocky, cratered and irregularly shaped. • They are the collisionally modified remains of leftover planetesimals between the orbits of Mars and Jupiter.

30. Asteroids • Asteroids are small, rocky, cratered and irregularly shaped. • They are the collisionally modified remains of leftover planetesimals between the orbits of Mars and Jupiter.

31. Asteroids • Millions of these objects orbit in the Asteroid belt – staying between Mars and Jupiter. • Some have orbits that cross the inner planets.

32. Asteroids • Millions of these objects orbit in the Asteroid belt – staying between Mars and Jupiter. • Some have orbits that cross the inner planets.

33. Asteroids • Some asteroids are “binary” objects.

34. Asteroids • The original “parent bodies” that were the predecessors of the asteroids were large enough to differentiate. • some asteroids are metallic, consisting of the core fragments of a large parent body. • the largest asteroids may be intact parent bodies. The DAWN mission, now in orbit around Ceres targets two of the largest – Ceres and Vesta.

35. The Dawn Mission • The Dawn spacecraft, launched in 2007, arrived at Ceres (2011) and will travel on to Vesta (arriving in 2015).

36. The Dawn Mission • Ceres and Vesta are thought to represent substantially intact planetesimals from the early Solar System.

37. Vesta from Dawn Click on the image for a movie of Vesta's rotation

38. Vesta from Dawn

39. Asteroids and Meteorites • Meteorites that fall to Earth are just small asteroids. They tell the story of the differentiation and fragmentation of the asteroids. • Some are entirely metallic, some are stony, some appear to come from unmodified undifferentiated objects.

40. Asteroids and Meteorites • Meteorites that fall to Earth are just small asteroids. They tell the story of the differentiation and fragmentation of the asteroids. • Some are entirely metallic, some are stony, some appear to come from unmodified undifferentiated objects.

41. Meteorites • If you want to find a meteorite, go to a place on Earth where Earth-rocks are rare. • Antartica and the Sahara Desert are good choices.

42. Asteroids and Meteorites • Meteorites that fall to Earth are just small asteroids. They tell the story of the differentiation and fragmentation of the asteroids. • Meteorites are often spectral fingerprint matches to distant asteroids. You can hold a piece of Vesta in your hand with certainty.

43. Meteorites • There are four major classes of meteorites • Stones: rocky meteorites with iron flecks. • Stones represent the majority of “falls” but are found in equal numbers with “iron” meteorites.

44. Meteorites • There are four major classes of meteorites • Stones tend to be composed of chondrules – glassy beads making up most of the mass of the rock. • Astronomers still argue about the origin of chondrules – how did these glassy beads form during the formation of the Solar System?

45. Meteorites • There are four major classes of meteorites • Irons represent the other significant type of meteorite. • Only about 6% of “falls” are irons, but they represent the majority of “finds” because they are so recognizable as something completely odd.

46. Meteorites • There are four major classes of meteorites • Irons represent the other significant type of meteorite. • When etched with nitric acid a crystalline patter appears in cross sections of iron meteorites. • This pattern can only arise from the slow cooling of molten iron (one degree every million years) consistent with formation in the center of a huge differentiated asteroid!

47. Meteorites • There are four major classes of meteorites • “Stony-iron” meteorites (a.k.a. Pallasites) appear to have come from the core-mantle boundary in a differentiated asteroid. They are quite rare.

48. Meteorites • There are four major classes of meteorites • “Carbonaceous chondrites are possibly the most interesting of meteorites of all. They represent about 1% of falls. • Carbonaceous chondrites are undifferentiated and largely unprocessed. They must come from small parent objects too small to become hot and melt and differentiate. • Some carbonaceous chondrites contain amino acids formed in the Solar Nebula – the building blocks of protiens.

49. Meteorites • Meteorites are important astronomically because they represent material preserved from the time of the origin of the Solar System. • Recall that radioactive dating uniformly finds an age of 4.56 billion years for all of these objects.

50. Pluto: Major Planet or Minor Nuisance? • The formal definition of Pluto as a “dwarf planet” by the International Astronomical Union in 2006 brought strong reaction from both astronomers and non-scientists.