Explanation: It is a hurricane twice the size of the Earth. It has been raging at least as long as telescopes could see it, and shows no signs of slowing. It is Jupiter's Great Red Spot, the largest swirling storm system in the Solar System. A better understanding  of the weather on Jupiter may help contribute to the better understanding of weather here on Earth. In the pictures on the left, the Hubble Space Telescope has captured Jupiter's Great Red Spot in various  states over the past  several years.

Using the PRS before and after class ...

Question 1: The hottest planet in the Solar System is:

1. Mercury
2. Venus
3. Earth
4. Pluto (Ooops, I forgot: Pluto is no longer a planet!)

Question 2: Approximately how long will Neil Armstrong's  footprint last on the Moon

1. One day
2. One month
3. One year
4. Forever

Question 3: Of all the "Terrestrial Planets" - Mercury, Venus, Earth, and Mars - which has (have) no atmosphere:

1. Mercury and Venus
2. Mercury and Mars
3. Venus and Earth
4. Mercury

Question 4: As comets approach the Sun their tails will point:

1. Towards the Sun
2. Away from the Sun
3. In random directions
4. Towards Polaris

My Very Educated Mother Just Served Us Nine Pickles

The Universe is believed to have been created - give or take a few billion years - 15 billion years ago in a colossal explosion that we now refer to as the Big Bang. About one billion years after the Big Bang, the first stars and galaxies were formed from primordial H and He. In some of the most massive stars heavier elements - such as C, N, and O, so important for life as we know it - were "cooked" inside these gigantic nuclear furnaces. Shortly after their creation (within a few million years) these massive stars died in violent Supernovae explosions, scattering the heavy elements into space. About 3 billion years after the Big Bang, a spiral galaxy started to form from these elements in a part of the Universe just like any other. This galaxy - the Milky Way - is our home. The Milky Way has a diameter of about 100,000 ly and contains over 100 billion stars. In one of its spiral arms, the so-called "Orion-Cygnus" arm, lives an inconspicuous G2 V star: Our Sun.

The Sun - our lone star - just as any other star, was formed when gravity pulled together a cloud of interstellar gas. The rotating ball collapsed into a thin disk about 4.5 billion and years ago, with the Protosun (cloud of gas that will develop into the Sun) located at the center. In the disk, solid material accumulates into larger and larger particles. These particles, clustered into clumps of up to a few kilometer across, are known as planetesimals. Protoplanets then form slowly by the accretion of planetesimals of similar composition. After the protoplanet has formed, the accumulation of heat from the radioactive decay of short-lived elements eventually melted the planet and allowed it to differentiate, namely, to separate materials according to their density. Thus, heavy metals, such as iron and nickel, settled in the core, while the lightest silicates "floated" to the surface.

An important clue to the origin and formation of the solar system is the clear division of the planets into two categories: Terrestrial, such as the Earth, and Jovian, such as Jupiter. The terrestrial planets are: Mercury, Venus, Earth, and Mars. They lie in the inner solar system and are small, dense, rocky worlds with less atmospheres than the Jovian planets: Jupiter, Saturn, Uranus, and Neptune. The Jovian planets lie in the outer solar system - beyond the asteroid belt - are large, gaseous, low-density worlds. Of course, poor Pluto does not fit either category very well: it is small, like the terrestrial planets, but lies far away from the Sun and has a low density just like the Jovian planets. This picture gives a sense of the relative size of the planets compared with the solar disk.
 
 

Orbital and Intrinsic Properties of Planets

Planet	Distance to the Sun (AU)	Period of the Orbit (years)	Diameter (km)	Mass/Mass(Earth)	Density (g/cm3)
Mercury	0.3871	0.24084	4,878	0.055	5.4
Venus	0.7233	0.61515	12,104	0.82	5.3
Earth	1.0000	1.00000	12,756	1.00	5.5
Mars	1.5237	1.88080	6,794	0.107	3.9
Jupiter	5.2028	11.8670	142,800	317.8	1.3
Saturn	9.5388	29.4610	120,540	94.3	0.7
Uranus	19.180	84.0130	51,200	14.6	1.2
Neptune	30.061	164.793	49,500	17.2	1.6
Pluto	39.440	247.700	2,200	0.0025	2.1

Far from the burning Sun, in the coldest regions of space, icy planetesimal survived, while in the warmer regions near the Sun, these planetesimals are made of rock and metal; materials cooked billions of years ago in the core of massive stars. At first, these planetesimal were closely packed. Yet, over time some of them collided gently enough to coalesce into larger objects; others collided so fast that they were further broken up. In what is the outer solar system, four very large masses formed and became the four Jovian planets. All of these planets grew to have masses of at least 15 times the mass of the Earth. Once a planet has grown to such a large mass, it has a strong enough gravitational pull to begin capturing gas directly from the solar nebula, the material from which the Sun was formed: 74% Hydrogen, 24% Helium, and 2% of the heavier elements. Thus, the Jovian worlds are low-density worlds rich in hydrogen and helium. These large planets grew disks of their own, out of which moons condensed, leading to the formation of minute solar systems. Indeed, we know well over a dozen moons orbit the planet Jupiter. With about 10 times the mass of the Earth, the gravitational pull of each of these giants was large enough to attract and hold on to a thick atmosphere of gas from the solar nebula.

In the inner part of the solar system there were simply too many collisions for large planets to form; from the four terrestrial planets Earth is the most massive one - with only 1/320 times the mass of Jupiter - Venus (with 82% percent of the Earth's mass) is the next, and then Mars (10% of the Earth's mass) and Mercury (5% of the Earth's mass) are the lightest. Their surfaces were under constant bombardment which inhibit their growth. Thus, terrestrial planets are not large enough to exert a large pull on the solar nebula and are thus poor in hydrogen and helium. The terrestrial planets are dense worlds - with low hydrogen and helium content - because they are composed mostly from the 2% of the heavier elements contained in the solar nebula.

Once the Sun became a luminous object, it cleared the nebula as the pressure from its light and solar wind pushed the material out of the solar system. The planets helped by absorbing some planetesimals and ejecting others. Once the solar system was clear of debris, planet building ended. Yet, the solar system is filled with smaller bodies, such as satellites (moons), asteroids, and comets. Our own moon was probably created in a catastrophic collision between the Earth and a Mars-size planet. Eventually, most planetesimals got destroyed in collisions, and were ejected to the remote parts of the solar system. Some of these smaller bodies, however,  have settled in the asteroid belt between Mars and Jupiter, while a few were captured as the moons of planets. The asteroid Gaspra was photographed (October 1991) by the Galileo spacecraft on its mission to Jupiter. Comets develop from icy rocks once they reach the warm vicinity of the sun. Tails of comets point away from the surface of the Sun because of the pressure from the solar wind. The comet West which was in the sky during March 1976. Rings around the giant planets, such as the ones in Saturn:

are probably the result of stray planetesimals being torn apart by gravity when they ventured too close to the planet. Venus, Earth and Mars acquired their atmospheres at a later stage in the formation of the solar system. The most likely scenario is from outgassing, namely, from the gas blown out of volcanos. On Earth, the Oxygen, essential to animals, was produced by plants breaking down the carbon dioxide.

Today,  all solid surfaces are scarred by craters from impacts by meteorites. Our own Moon, as well as many other satellites and rocky planets were crated by heavy and steady bombardment for about one million years.

At 10:56 pm EDT on July 20, 1969, Neil Armstrong became the first human to set foot on the Moon. "That's one small step for man, one giant leap for mankind."

Large rocks crashing down from space are far less common than in the early solar system. Still, the probability of collision of two astronomical bodies in the  solar system is not zero. Indeed, only in July 1994, a large comet - Shoemaker-Levy - was torn apart by Jupiter's immense gravitational pull breaking it into various fragments; some of these collided with Jupiter and left visible scars. The picture show a Hubble Space Telescope Color Image of Fragment G. Impact. Click on the picture below to find more about the extraordinary event and the probability of such an event happening to us!

Remember, however, that only 65 million years ago a 10 mile object striking the Earth led instantly to the mass extinction of many species including the dinosaurs. So if it happened once ... it could happen again!