14 billion years ago: start of the known universe… …but a rapid expansion of material known as the “Big Bang” Not really an “explosion”… The element ‘Hydrogen’ soon dominates…

Galaxies and early stars formed from the initial hydrogen… “Normal” stars produce some elements as fusion occurs (like Helium)… Many LARGE stars formed! …and Supernova form heavier elements like lead and uranium! Large stars are unstable, and destroy themselves as Supernova…

But where did our planet Earth (and the Solar System it’s in) come from? Here’s a brief description of how…

Vast clouds of dust and gas “drift” through the galaxies…some of it “debris” from supernova explosions! These Nebula are “Star Factories”!

The clouds are disturbed… by gravitational forces due to galactic collision, or perhaps by shockwaves from stellar explosions (supernova)… …causing star formation

…and this exposes the stars within. As parts of a nebula condense, stars form. Dust and gases are “blown away”…

Galaxies fill the Universe!

Unlike stars, Galaxies are large compared to the space between them!

They interact! Their gravitational pull reaches out to their neighbors…

This CAN tear them apart, or completely rearrange their structure…

This can cause clouds of dust and gas to condense into star systems…

New stars formed in disturbed galaxy…

Large clouds of gas and dust act as “star factories”…

New star systems?

Stars and planets may be forming here…

And the stars shine through! As nebula clouds condense, the light of new stars drives off dust…

New stars forming!

New Stars!

Eventually, the new stars drive off the gas, leaving a star cluster. Each star may have a planetary system…

Earth! Feeling SMALL yet?

A VAST difference in star size exists! Our Sun!

So what happens as these dust clouds contract, and stars form? Our Solar System formed from a rotating cloud of DUST and GAS… …due to internal collisions, and external gravitational disturbances. The Nebular Hypothesis (now known as the Solar Nebular Model, but originally proposed by Immanuel Kant in 1755!):

The cloud was composed of Hydrogen, Helium, plus substantial amounts of other elements formed by supernova. Approximately 5 billion years ago, the nebula had contracted to a point where… …the rotation of the nebula had formed a flat disc.

…and the sun formed at the center where most of the mass was concentrated. Cold, outer areas retained large amounts of icy material (comet material).

…Planets formed closer to the Sun.

Protoplanets formed by accretion, eventually forming planets. Outer planets retained much of their original gases. Inner planets lost most of the light gases and are mostly rock

This left the Solar System with 4 small rocky or stoney planets near the Sun... …and 4 giant planets, with ice-covered cores, and dense atmospheres located farther away!

But does this happen to most stars? Do such “protoplanetary discs” routinely produce planets? They should! …if we’re right about the way star systems form! But if they DO… we should find other planets! And we have!

Old hypotheses about planet formation invoked unusual events… …such as a collision or near-miss between 2 stars. If this were true planets would be RARE!

But…! Almost 2,000 Extra Solar planets have been found in recent years. Current thinking means that planets SHOULD be fairly common! But HOW do we FIND Extra Solar planets??? They are too faint to see… (so far!) (and about 800 just in 2014!)

Planets can be detected when they pass in front of their stars; the passage of the planet reduces (by a TINY amount) the light we see from that star. Light Intensity Time

The KEPLER Space Telescope has found 100’s of Exoplanets in this way!

In addition, new stars are surrounded by extensive discs of dust. The formation of planets “clears out” the area of the planets’ orbits… …AND… the dust clouds emit INFRARED light!

The Spitzer Infrared Telescope has detected such rings of dust around young stars. Areas between the rings are cleared out, showing where planets have formed.

These recent discoveries indicate that planets are COMMON… Until recently, only large planets had been discovered…due to limitations of our present telescopes. Kepler is now finding Earth-size planets. Within a few years, scientists hope to be able to actually image these planets!

Now we know that the sky is full of such planets! Earth! Until recently, we knew of only 2 planets that might harbor life! Mars!

And recently, The VERY LARGE TELESCOPE has actually photographed a planet orbiting another star! (We apparently have run out of good names for telescopes!) The next few years may reveal amazing new discoveries! Star (masked) Planet