Astronomy Picture of the Day

Question

Which of the following provides the most useful

information about the Earth's interior?

A) drilling

B) laser-ranging

C) x-rays

D) seismic waves (S- & P- waves)

Question

The _____ theory of lunar formation best accounts for the observed similarities and differences between the Earth and the Moon.

A) fission

B) coformation

C) capture

D) impact

Question

Which planet has a surface similar to Earth's Moon

and has no appreciable atmosphere?

A) Mercury

B) Venus

C) Mars

D) Jupiter

The Jovian Planets

Jupiter Saturn

Uranus Neptune

(roughly to scale)

Earth

General Characteristics of Jovian Planets:

Made up mostly of Hydrogen & HeliumLarge massesLarge Radii

Low average densities (Saturn would float!)Strong gravitational fields

No solid surface of any kindShort rotation periods

Three of Four have significant internal heating

How do we get information about these distant giants? Space probes, for example Galileo (video clip)

Jupiter and Saturn were known to the ancient astronomers. Uranus, barely visible to the naked eye, was discovered in 1781.

Neptune is not visible to the naked eye. How was it discovered?

Discovery of Neptune

Neptune predicted to exist because of irregularities in Uranus' orbit.

Discovered in 1845 by Johann Galle.

Kepler’s and Newton’s laws in action!

Nice example of how the scientific method works.

Gravitational “Slingshots”

Voyager 2 passed by ALL of the Jovian planets during its flight. To do so, it made use of “gravity assists”.

How can a satellite “borrow” energy from a planet that is orbiting the Sun?

Gravity Assists

Satellite “borrows” energy from orbiting planet

Conservation of energy and Newton’s third law

(Demo)

Gravity Assists (cont.)Precalculated before satellite is launchedAlso shows how gravity can eject “Planetesimals” from early solar system

Jupiter's Bands

Lighter-colored "zones" and darker-colored "belts".

Shadow of a moonGreat Red Spot

Belt

Zone

QuestionZones and belts are, respectively, high and low

pressure systems on Jupiter.

What process would you expect to be taking place

between such regions?

Why do the zones and belts stretch all the way

around Jupiter?

- Convection occurs between zones and belts

- Jupiter's rapid rotation stretches bands around the entire planet.

- Temperature difference between zones and belts => different chemistry =>

different coloration.

Banded structure on other Jovian planets is present, but not as distinct due to more uniform cloud coverage.

Neptune

Saturn

Uranus: bands obscured by haze in stratosphere

Storms on Jovian Planets

Jupiter's Great Red Spot: A hurricane twice the size of Earth. Has persisted for at least 300 years.

Neptune's Great Dark Spot: Discovered by Voyager 2 in 1989. About the size of the Earth.

Why do storms on Jovian planets last so long?

Other Rotational Effects

Is the rotational bulge of the Jovian planets more or less pronounced than that of the terrestrials?

A) More

B) Less

Rapid rotation causes Jupiter and Saturn to bulge:

Gravity

without rotation with rotation

Gravity

Jupiter and Saturn rotate once every ~10 hours. Radius at equator several % larger due to gaseous-liquid composition of the Jovians.

The Jovians are not solid bodies. What other effect does this have on their rotations?

Differential Rotation

Jupiter

Saturn

Uranus

Neptune

Near poles versus At equator

A bit slower (6 min)

Slower (by 26 min)

Faster (by about 2 hours)

Faster

Reflects large-scale wind flows in the planets atmosphere.

How do we know? Tracking storms at various latitudes, or using Spectroscopy and Doppler shift.

Question

Uranus' axis of rotation lies almost in the plane of its orbit! What effect does this have on the Uranian seasons?

Uranus' rotation axis is tilted by 98o

Why? Unknown. Perhaps an early, grazing collision with another large body. Most extreme seasons of any planet! Polar regions - alternately light and dark for 42 years