Astronomy Chapter 13 Review

· What is so unusual about Uranus's moons Miranda?

is the most unusual moon of Uranus; origin of the cracks and grooves is unknown. ridges, valleys, large oval faults, cliffs on a small moon

· When was the planet Neptune discovered?

1846, after analysis of Uranus's orbit indicated its presence. Half a Details of Neptune cannot be made out from Earth either

" Which planet had the Great Dark Spot in 1989, but had lost it by 1995"

Neptune

· Why are Neptune's atmospheric features more visible than that of Uranus?

The combination of extra heat and less haze may be responsible for the greater visibility of Neptune's atmospheric features, as its cloud layers lie at higher levels in the atmosphere than do those of Uranus.

Stellar Occultation

The dimming of starlight produced when a solar system object such as a planet, moon, or ring passes, directly in front of a star.

Radiation Darkening-

The effect of chemical reactions that result when high-energy particles strike the icy surfaces of objects in the outer solar system. The reactions lead to a build up of a dark layer of materiel.

· What is the total number of Moons of Neptune at last count?

has 13 moons, but only two can be seen from Earth: Triton and Nereid · Name the two moons of Neptune that are visible through earth-based telescopes.

What is erupting out of the geysers on Triton?

liquid nitrogen with carbon grit

· How were the rings of Uranus discovered?

were discovered in 1977 by three astronomers via stellar occultation. More than 200 years ago, William Herschel also reported observing rings, but modern astronomers are skeptical that he could have actually seen them, as they are very dark and faint.

Which statement about the magnetic fields of Uranus and Neptune is FALSE?

"Both pass directly through the cores of their planets, like all other fields."

Neptune and Uranus have a bluish tint because:

"their atmospheres contain methane, which absorbs red light."

How much energy does Neptune reflect back?

Although Neptune lies at a greater distance from the sun, the planet's upper atmosphere is actually slightly warmer that that of Uranus. Like Jupiter and Saturn, but unlike Uranus, Neptune has an internal energy heat source- in fact, Neptune radiates 2.7 times more heat that it receives from the sun.

· What are the names given to the rings of Uranus?

Apha, Beta, Eta, Gamma, Delta, Epsilon, 4,5,6

Moving outward from the Sun, explain how is the amount of ammonia and methane varies among the Jovian planets?

As we move outwards from the Sun in Jovian planets: amounts of ammonia decreases and methane increases. The reason for this variation is temperature. Ammonia gas freezes into ammonia ice crystals at about 70K. This temp is cooler than the cloud-top temps of Jupiter and Saturn but warmer than those of Uranus(58K) and Neptune (59K). Thus, the outermost Jovian planets have little or no gaseous ammonia in their atmospheres, so there spectra (which record atmospheric gases only) show only traces of ammonia.

Describe the discovery of Neptune. Or

Astronomers discovered a small discrepancy between the planet's predicted position and where they actually observed it. They could not find an elliptically orbit that fit the planet's trajectory to within the accuracy of their measurements. Half a century later the discrepancy had grown to a quarter of an arc minute, far too big to be explained away as observational error.

· What is odd about the magnetic fields of Uranus and Neptune?

Astronomers theorize that deep below the cloud layers, Uranus and Neptune may have high-density, slushy interiors containing thick layers of water clouds. It is also possible that much of the planets ammonia is dissolved in the hypothetical water, accounting for the absence of ammonia at higher levels. Such an ammonia solution would provide a thick, electrically conducting ionic layer that could conceivably explain the planets' misaligned magnetic fields if the circulating electrical current that generate the fields occur mainly in the regions far from the planets' centers and rotation axis.

· Based on Uranus's axial tilt, explain why does Uranus have extreme seasons?

Axis of rotation (98° tilt) lies almost in the plane of its orbit.

· Why is Uranus's rotation classified as retrograde?

Because the north pole lies below the ecliptic plane, the rotation of Uranus, like that of Venus is classified as retrograde

· What was the name of the feature on Neptune, which was similar to the Great Red Spot on Jupiter?

Great Dark Spot.

· What are the dominant gases in the atmospheres of both planets?

Hydrogen ~ 84 %, Helium ~ 14 %

how is Neptune unique among the Jovian planets?

Its atmosphere rotates more slowly than it's interior.

· Total how many rings have been discovered around Neptune to date?

Neptune is surrounded by five dark rings. Galle, Leverrier, Lassell, Arago, and Adams. Three are quite narrow, like the rings of Uranus; the other two are broad and diffuse. All the rings lie within Neptune's Roche limit. Adams is noticeably clumped in places. From earth, we see not a complete ring, but only partial arcs- the unseen part of the ring are simply too thing (unclumped) to be detected. One of the two fainter rings lie between the inner bright ring Leverrier and the planet. The other lie between the leverrier ring and the outer bright (Adams) ring.

· What are the average rotation speeds of Neptune's atmosphere and its interior?

Neptune's clouds show more variety and contrast than do those of Uranus. The average rotation period of Neptune's atmosphere is 17.3 hours. Measurements of Neptune's radio emissions showed that the magnetic field of the planet, and presumably also its interior, rotates once every 16.1 hours.

· How much the axis of Neptune tilted?

Neptune's' axis of rotation is inclined 29.6 degrees to a line perpendicular to the planet's orbital plane, quite similar to the 27-degree tilt of Saturn.

Roche Limit-

Often called the tidal stability limit, the Roche limit gives the distance from a planet at which the tidal force (due to the planet) between adjacent objects exceeds their mutual attraction. Objects within this limit are unlikely to accumulate into larger objects. The rings of Saturn occupy the region within Saturn's Roche limit.

Great Dark Spot

Prominent storm system in the atmosphere of Neptune observed by voyager 2, near the equator of the planet. The system was comparable to the size of earth!

· What are the similarities between the rings of Uranus and Neptune?

Ring systems are relatively short lived, their formation must be a fairly common event. Otherwise, we would not expect to find rings around all four Jovian planets at once.

· What is the possible source of Neptune's excess energy?

Some scientist have suggested that Neptune's excess methane has helped insulate the planet, tending to maintain its initially high internal temperatures. If so, then the sour of Neptune's internal heat is that same as Jupiter's: Energy leftover from the planet's formation.

· How are the rings of Uranus different from Saturn's?

The rings are dark, narrow, and widely spaced. With the exception of the epsilon ring and the diffuse innermost ring, the rings are all less than about 10 km wide and the spacing between them ranges from a few hundred to about a thousand km Radius from the planet's center: 44,000 to 51,000 km. All lie within the Roche limit of Uranus (62,000 km). Dark, narrow, and widely spaced. Width < 10 km, thickness < few tens of meters (except Epsilon) The spacing between them ranges from a few hundred to about a thousand kilometers. Ring particles - less reflective Epsilon Ring- Slightly eccentric (0.008) Circumference: 300,000 km Width: 30 km Depth: ~30 meters!

· Total how many rings have been discovered around Uranus to date?

Total of nine thin rings.

· What properties make Neptune's moon Triton special?

Triton is one of the six larger moons of outer planets. Triton is one of the six large moons in the outer solar system. Triton has retrograde orbit around Neptune. Triton is doomed to be torn apart by Neptune's tidal gravitational field, probably in no more than 100 million years, and change into rings. Triton: A fractured and cratered world of ice. Triton has a very thin atmosphere of nitrogen Nitrogen geysers with carbon grit have been observed on Triton, contributing to the surface features. Also, there appear to be ice volcanoes on Triton.

"As with Saturn's F ring, shepherd moons play a major role in the structure of the thin narrow rings around Uranus."

True

"Uranus was discovered by accident, and mistaken for a comet at first"

True

. John Adams reached the solution in September 1845 and in June the following year, Urbain Leverrier came up with essentially the same answer. Adam found nothing during the summer of 1846

True

Atmospheric clouds and flow patterns move with wind speeds ranging from 200 to 500 km/h in east-west direction.

True

Earth based observations of the Doppler shifts in spectral lines first indicated that Uranus's day was between 10 and 20 hours long.

True

Neptune is the windiest planet in the Solar System. The planet's weather can change in as little as a few rotation period, and winds blow at speeds in excess of 1500km/h- almost half the speed of sound in Neptune's upper atmosphere. With storms the size of earth more the rule than the exception.

True

Neptune was the first planet discovered through mathematical calculations.)

True

Their densities imply that large rocky cores constitute a greater fraction of the planet's masses than to the core of either Jupiter or Saturn. The cores are probably comparable in size, mass, and composition to those of the two larger planets.

True

Their orbits lie just inside the Kuiper belt, for which Uranus and Neptune are largely responsible.

True

Triton is in a retrograde orbit; Nereid's orbit is highly eccentric. Triton's surface has few craters, indicating an active surface.

True

Uranus and Neptune are very similar in size and mass.

True

Uranus is mostly featureless, except a few ice crystal clouds at low-lying warmer levels in the atmosphere. Uranus is blandest of all Jovian planets. Neptune has more activity than Uranus.

True

Uranus was the first planet discovered telescopically

True

Around which ring of Uranus do the shepherd satellites exist?

Two shepherd moons (Ophelia and Cordelia) keep the epsilon ring from diffusing. The theory of shepherd satellite was first worked out to explain the rings of Uranus which had been detected by stellar occultation even before voyager 2's encounter with Saturn.

· What is the name of the darkest moon of Uranus?

Umbriel: One of the darkest bodies in the solar system, although it has a bright white spot on its sunward side.

Which planet has 27 moons?

Uranus

· Rotation of the Planets:

Uranus Rotation: 17 Hours in RETROGRADE. Neptune's Rotation: 16 hours.

· Why are Uranus bluish-green and Neptune blue in color? Or how the amount variation of ammonia and methane give both of these planets their characteristic colors?

Uranus and Neptune are cold enough that ammonia freezes; methane dominates and gives the characteristic blue color. Methane absorbs long wavelength red light quite efficiently, so sunlight reflected from the planet's atmospheres is deficient in red and yellow photons and appears bluish-green or blue. As the concentration of methane increases, the reflected light should appear bluer- just the trend that is observed: Uranus with less methane, looks bluish green, whereas Neptune with more, looks distinctly blue

Compare the properties of Uranus's and Neptune's magnetic fields with that of and with that of the Earth.

Uranus and Neptune both have substantial magnetic fields —about 100 times stronger than Earth's field, but spread out over far larger volumes. Their magnetic axis are inclined at large angles to their rotation axes. The rectangle within each planet shows a bar magnet that would produce a similar field. Note that both Uranus's and Neptune's magnetic fields are significantly off centered. Magnetic fields of Uranus and Neptune must not be produced by dynamos, as the other planets' fields are. Uranus and Neptune are not massive enough to have metallic hydrogen in their interiors, so hydrogen stays in its molecular form all the way in to the planets' cores.

· What is the total number of Moons of Uranus at last count?

Uranus has 27 moons, five of which are major: Miranda, Ariel, Umbriel, Titania, and Oberon

· When and who discovered the planet Uranus?

Uranus was discovered in 1781 by Herschel; first planet to be discovered in more than 2000 years.

· Density of the planets:

Uranus- 1300kg/m^3 Neptune- 1600kg/m^3

Their masses

Uranus- 14.5 Neptune- 17.1

· How far (in AU) are Uranus and Neptune from the Sun?

Uranus- 19.2 Neptune- 30.1

· How big are Uranus and Neptune in radius as compared to that of the Earth?

Uranus- 4.0 Neptune- 3.9

· What is Uranus and Neptune composed of?

Uranus: Hydrogen ~ 84% Helium ~ 14 % Methane ~2 % Ammonia : just a little trace Neptune: Hydrogen ~ 84 % Helium ~ 14 % Methane ~3 % Ammonia : just a little trace

· What is occultation?

When a planet's orbit sometimes places it between a star and the Earth. During an occultation of a star by Uranus, the starlight intensity was noticed to decrease both before and after the planet's disk crossed. This was due to the rings surrounding the planet.

· Do all the jovian planets have rings?

Yes

· How much the axis of Uranus tilted?

axis of rotation lies almost within that plane-98 degrees from the perpendicular to be precise.

"Unlike the other jovian planets, Uranus"

has no internal energy source.

ÿ Small deviations in a planet's orbital motion

imply the nearby presence of a massive body.

· Why on Uranus during the spring and autumn equinox the day and night are each 8.5 hours long; and during the summer and winter the day and night are each about 20 years long?

the planet experiences the most extreme seasons known in the solar system. The equatorial regions have two "summers" (warm seasons, around the times of the two equinoxes) and two "winters" (cool seasons, at the solstices) each year, and the poles are alternately plunged into darkness for 42 Earth years at a time.

· What is the rotation speed of different parts of Uranus? Which part of Uranus rotates faster?

y rotates FASTER at the poles (Where the period is 14.2 hours) Than near the equator (Where the period is 16.5 hours.)