Neptune
After the discovery of Uranus, it was noticed that its orbit was not as it should be in accordance with Newton’s laws. It was therefore predicted that another more distant planet must be perturbing Uranus’ orbit. Neptune was first observed by Galle and d’Arrest on 1846 Sept 23 very near to the locations independently predicted by Adams and Le Verrier from calculations based on the observed positions of Jupiter, Saturn and Uranus. An international dispute arose between the English and French (though not, apparently between Adams and Le Verrier personally) over priority and the right to name the new planet; they are now jointly credited with Neptune’s discovery. Subsequent observations have shown that the orbits calculated by Adams and Le Verrier diverge from Neptune’s actual orbit fairly quickly. Had the search for the planet taken place a few years earlier or later it would not have been found anywhere near the predicted location. More than two centuries earlier, in 1613, Galileo observed Neptune when it happened to be very near Jupiter, but he thought it was just a star. On two successive nights he actually noticed that it moved slightly with respect to another nearby star. But on the subsequent nights it was out of his field of view. Had he seen it on the previous few nights Neptune’s motion would have been obvious to him. But, alas, cloudy skies prevented obsevations on those few critical days. Neptune has been visited by only one spacecraft, Voyager 2 on Aug 25 1989. Much of we know about Neptune comes from this single encounter. But fortunately, recent ground-based and HST observations have added a great deal, too. Because Pluto’s orbit is so eccentric, it sometimes crosses the orbit of Neptune making Neptune the most distant planet from the Sun for a few years. Neptune’s composition is probably similar to Uranus’: various “ices” and rock with about 15% hydrogen and a little helium. Like Uranus, but unlike Jupiter and Saturn, it may not have a distinct internal layering but rather to be more or less uniform in composition. But there is most likely a small core (about the mass of the Earth) of rocky material. Its atmosphere is mostly hydrogen and helium with a small amount of methane. Neptune’s blue color is largely the result of absorption of red light by methane in the atmosphere but there is some additional as-yet-unidentified chromophore which gives the clouds their rich blue tint. Like a typical gas planet, Neptune has rapid winds confined to bands of latitude and large storms or vortices. Neptune’s winds are the fastest in the solar system, reaching 2000 km/hour. Like Jupiter and Saturn, Neptune has an internal heat source – it radiates more than twice as much energy as it receives from the Sun. At the time of the Voyager encounter, Neptune’s most prominent feature was the Great Dark Spot (left) in the southern hemisphere. It was about half the size as Jupiter’s Great Red Spot (about the same diameter as Earth). Neptune’s winds blew the Great Dark Spot westward at 300 meters/second (700 mph). Voyager 2 also saw a smaller dark spot in the southern hemisphere and a small irregular white cloud that zips around Neptune every 16 hours or so now known as “The Scooter” (right). It may be a plume rising from lower in the atmosphere but its true nature remains a mystery. However, HST observations of Neptune (left) in 1994 show that the Great Dark Spot has disappeared! It has either simply dissipated or is currently being masked by other aspects of the atmosphere. A few months later HST discovered a new dark spot in Neptune’s northern hemisphere. This indicates that Neptune's atmosphere changes rapidly, perhaps due to slight changes in the temperature differences between the tops and bottoms of the clouds. Neptune also has rings. Earth-based observations showed only faint arcs instead of complete rings, but Voyager 2’s images showed them to be complete rings with bright clumps. One of the rings appears to have a curious twisted structure (right). Like Uranus and Jupiter, Neptune’s rings are very dark but their composition is unknown. Neptune’s rings have been given names: the outermost is Adams (which contains three prominent arcs now named Liberty, Equality and Fraternity), next is an unnamed ring co-orbital with Galatea, then Leverrier (whose outer extensions are called Lassell and Arago), and finally the faint but broad Galle. Neptune’s magnetic field is, like Uranus’, oddly oriented and probably generated by motions of conductive material (probably water) in its middle layers. Neptune can be seen with binoculars (if you know exactly where to look) but a large telescope is needed to see anything other than a tiny disk.
Task 9. Read and translate the text about Pluto:
Pluto
Pluto orbits beyond the orbit of Neptune (usually). It is much smaller than any of the official planets and now classified as a “dwarf planet”. Pluto is smaller than seven of the solar system’s moons (the Moon, Io, Europa, Ganymede, Callisto, Titan and Triton). orbit: 5,913,520,000 km (39.5 AU) from the Sun (average)diameter: 2274 kmmass: 1.27e22 kgIn Roman mythology, Pluto (Greek: Hades) is the god of the underworld. The planet received this name (after many other suggestions) perhaps because it’s so far from the Sun that it is in perpetual darkness and perhaps because “PL” are the initials of Percival Lowell. Pluto was discovered in 1930 by a fortunate accident. Calculations which later turned out to be in error had predicted a planet beyond Neptune, based on the motions of Uranus and Neptune. Not knowing of the error, Clyde W. Tombaugh at Lowell Observatory in Arizona did a very careful sky survey which turned up Pluto anyway. After the discovery of Pluto, it was quickly determined that Pluto was too small to account for the discrepancies in the orbits of the other planets. The search for Planet X continued but nothing was found. Nor is it likely that it ever will be: the discrepancies vanish if the mass of Neptune determined from the Voyager 2 encounter with Neptune is used. There is no Planet X. But that doesn’t mean there aren’t other objects out there, only that there isn’t a relatively large and close one like Planet X was assumed to be. In fact, we now know that there are a very large number of small objects in the Kuiper Belt beyond the orbit of Neptune, some roughly the same size as Pluto. Pluto has not yet been visited by a spacecraft. Even the Hubble Space Telescope can resolve only the largest features on its surface (left and above). A spacecraft called New Horizons was launched in January 2006. If all goes well it should reach Pluto in 2015. Fortunately, Pluto has a satellite, Charon. By good fortune, Charon was discovered (in 1978) just before its orbital plane moved edge-on toward the inner solar system. It was therefore possible to observe many transits of Pluto over Charon and vice versa. By carefully calculating In late 2005, a team using the Hubble Space Telescope discovered two additional tiny moons orbiting Pluto. Provisionally designated S/2005 P1 and S/2005 P2, they are now known as Nix and Hydra. They are estimated to be between 60 and 200 kilometers in diameter. Pluto’s radius is not well known. JPL’s value of 1137 is given with an error of +/-8, almost one percent. Though the sum of the masses of Pluto and Charon is known pretty well (it can be determined from careful measurements of the period and radius of Charon’s orbit and basic physics) the individual masses of Pluto and Charon are difficult to determine because that requires determining their mutual motions around the center of mass of the system which requires much finer measurements – they’re so small and far away that even HST has difficulty. The ratio of their masses is probably somewhere between 0.084 and 0.157; more observations are underway but we won’t get really accurate data until a spacecraft is sent. Pluto is the second most contrasty body in the Solar System (after Iapetus). There has recently been considerable controversy about the classification of Pluto. It was classified as the ninth planet shortly after its discovery and remained so for 75 years. But on 2006 Aug 24 the IAU decided on a new definition of “planet” which does not include Pluto. Pluto is now classified as a “dwarf planet”, a class distinct from “planet”. While this may be controversial at first (and certainly causes confusion for the name of this website) it is my hope that this ends the essentially empty debate about Pluto’s status so that we can get on with the real science of figuring out its physical nature and history. Pluto has been assigned number 134340 in the minor planet catalog. Pluto’s orbit is highly eccentric. At times it is closer to the Sun than Neptune (as it was from January 1979 thru February 11 1999). Pluto rotates in the opposite direction from most of the other planets. Pluto is locked in a 3:2 resonance with Neptune; i.e. Pluto’s orbital period is exactly 1.5 times longer than Neptune’s. Its orbital inclination is also much higher than the other planets’. Thus though it appears that Pluto’s orbit crosses Neptune’s, it really doesn’t and they will never collide. (Here is a more detailed explanation.) Like Uranus, the plane of Pluto’s equator is at almost right angles to the plane of its orbit. The surface temperature on Pluto varies between about -235 and -210 C (38 to 63 K). The “warmer” regions roughly correspond to the regions that appear darker in optical wavelengths. Pluto’s composition is unknown, but its density (about 2 gm/cm3) indicates that it is probably a mixture of 70% rock and 30% water ice much like Triton. The bright areas of the surface seem to be covered with ices of nitrogen with smaller amounts of (solid) methane, ethane and carbon monoxide. The composition of the darker areas of Pluto’s surface is unknown but may be due to primordial organic material or photochemical reactions driven by cosmic rays. Little is known about Pluto’s atmosphere, but it probably consists primarily of nitrogen with some carbon monoxide and methane. It is extremely tenuous, the surface pressure being only a few microbars. Pluto’s atmosphere may exist as a gas only when Pluto is near its perihelion; for the majority of Pluto's long year, the atmospheric gases are frozen into ice. Near perihelion, it is likely that some of the atmosphere escapes to space perhaps even interacting with Charon. NASA mission planners want to arrive at Pluto while the atmosphere is still unfrozen. The unusual nature of the orbits of Pluto and of Triton and the similarity of bulk properties between Pluto and Triton suggest some historical connection between them. It was once thought that Pluto may have once been a satellite of Neptune’s, but this now seems unlikely. A more popular idea is that Triton, like Pluto, once moved in an independent orbit around the Sun and was later captured by Neptune. Perhaps Triton, Pluto and Charon are the only remaining members of a large class of similar objects the rest of which were ejected into the Oort cloud. Like the Earth’s Moon, Charon may be the result of a collision between Pluto and another body. Pluto can be seen with an amateur telescope but it is not easy.
Exercise 2. Using the information from your text above, the ideas of your own, the following table and questions given below make up a dialogue and present it to the group (underlined words may be substituted):
1. How is the planet called? – The planet is called … 2. Are there any signs of life on this planet? – There are no any signs of life on this planet./ There are no some signs of life on this planet. 3. How large is the Earth in the solar system? – The planet is the fifth largest in the solar system. 4. How far is this planet from the sun? – The distance from the sun is … 5. In what time does Mercury complete its orbit around the sun? – The planet completes its orbit around the sun in … earth’s days. 6. How long is the radius of Saturn? – The radius of the planet is … 7. How long is the diameter of Pluto? – The diameter of the planet is … 8. Is it a hot or a cold planet? – It is a hot/cold planet. 9. What is the temperature on the surface of Venus? – The temperature of the surface is … 10. How many satellites does Jupiter have? – The planet has … satellites. 11. What is the mass of Neptune? – The mass of the planet is …. 12. What is the chemical composition of Mars? – The chemical composition of the planet is … 13. Is it known when was the planet discovered and by whom? 14. What is the surface of Venus like? 15. Does Mercury have atmosphere? 16. Is Uranus easily visible to the unaided eye? 17. What is equatorial rotation velocity of Neptune? 18. What is the orbital period of Jupiter? 19. What is the average orbital speed of Pluto? 20. What is the mean density of Uranus?
|
Neptune is the eighth planet from the Sun and the fourth largest (by diameter). Neptune is smaller in diameter but larger in mass than Uranus.
A history of what we’ve learned about Pluto from ground by Dr. Alan Stern, principal investigator on the New Horizons mission to Pluto.
which portions of which body would be covered at what times, and watching brightness curves, astronomers were able to construct a rough map of light and dark areas on both bodies.
