The Origin of Our Solar System Part 1

Survey of the solar system

Testing the Solar Nebula Theory

• Astronomers search the present solar system for evidence of the past.

• We are going to compile a list of our solar system’s most significant characteristics that are potential clues on how it formed.

• For the Solar Nebula Theory (SNT) to be successful, it must explain all of the phenomena we encounter.

Planets Revolve Around the Sun

• Planets revolve around the sun in orbits that lie close to a common plane. – Except for Mercury which is inclined 7% to Earth’s

orbit, all of the other planets are inclined no more than 3.4%.

– As you can see, the solar system is flat and disk shaped (next slide).

Artists Rendition of the Disk

Rotation and Revolution of Planets

• Rotation of the sun and planets on their axes also seems related to the rotation of the disk. – There is a preferred rotational direction –

counterclockwise (with the exceptions of Uranus and Venus).

• All planets revolve counterclockwise around the sun. – Almost all of the solar system’s moons also revolve

counterclockwise around their planets.

The two kinds of planets

• “Most striking clue” to the origin of the solar system comes from the division of the planets into two groups: terrestrial and Jovian planets.

• The 2 kinds of planets are distinguished by location.– Four inner terrestrial planets are very different

from the 4 outer Jovian planets.

The two kinds of planets

Frost line is 150 degrees Kelvin or negative 190 degrees Fahrenheit.

The two kinds of planets

• Craters are common on almost every solid surface in solar system (SS).

• The 2 groups are also distinguished by properties such as presence or absence of rings and numbers of moons.

• The planets have evolved since their formation, so other evidence is necessary. – Clues can be found in the smaller objects in solar

system.

Distinctions

• The differences between Jovian and terrestrial planets is “dramatic.”

• The inner four planets are rocky, small, and dense worlds with little or no atmosphere.

• Jovian planets, outer planets, are low-density with thick atmospheres and liquid or ice interiors.

Distinctions

• Orbits– Terrestrial planets lie quite close to sun.– Jovian planets are spread far from the sun.

Orbits to

scale

Distinctions

• Earth is the most massive of the terrestrial planets but is much less massive compared to the Jovian planets.

Planets and sun to scale. Jupiter

is over 300 “Earth masses” and

Saturn over 100 Earth masses.

Distinctions

• Terrestrial planets have rock and metal-like densities.

• Jovian planets have low densities and “Saturn’s density is only 70% that of water and would float in a big enough bathtub.”

• The Jovian planets’ atmospheres are turbulent and often marked by great storms, like Jupiter’s Great Red Spot.

Distinctions

• All four Jovian Planets have ring systems.– Jupiter, Uranus, and Neptune’s rings are from dark

rocky particles.– Saturn’s rings are made of ice particles.

Distinctions

• Jovian interiors contain small cores of heavy metals such as metals, surrounded by liquid. – Jupiter and Saturn contain hydrogen in a liquid

state due to high pressure.– Uranus and Neptune contain heavy-element cores

surrounded by partially solid water mixed with rocks and minerals.

• Jovian planets have extensive moon systems.

“Space Debris”• Space debris is also a product of the solar

nebula. • Three types of debris:

1. Asteroids2. Comets3. Meteroids

• They represent a small fraction of SS’s mass but are important sources of information about the planets.

Asteroids

• Small rocky worlds – most orbit sun in a best between Mars and Jupiter.

• >100,000 asteroids have charted orbits.– About 2,000 have paths that bring them into the

inner solar system (creating collision possibilities).• Asteroids are not planets that have broken

apart (like was once hypothesized) but are debris left over from the failure of a planet to form at 3 AU (90,000,000 miles) from the sun.

Asteroids

Asteroids

• 200 asteroids are >60 miles in diameter.• 10s of 1000s are >6 miles in diameter.• >1,000,000 that are >0.6 miles in diameter.• Asteroid surfaces are rocky and metallic.– Photographs from a robotic spacecraft show

asteroids as irregularly shaped and covered with craters.

• Rocks, metals, and collisions played a major role in the SS’s formation.

Craters

• As already stated, craters are common on all surfaces in the solar system strong enough to retain them (i.e. on terrestrial planets).

• Earth has about 150 impact craters, though many have been erased by erosion (we are finding new ones).

• When astronomers see a rocky or icy surface with few craters, know the surface is young.

Impact Crater in Arizona

Size and Ages of Some Craters• Vredefort , Free State, South Africa, 300km diameter, 2023

millions of years old• Sudbury Ontario, Canada, 250 km diameter, 1849 million

years old• Chicxulub, Yucatán, Mexico, 180 km diameter, 65 million

years old• Kara, Nenetsia, Russia 120 km, 70.3 million years old.• Manicouagan, Quebec, Canada, 100 km diameter 215 million

years old.• Popigai, Siberia, Russia 100 km diameter, 35.7 million

years old.

Kuiper Belt• In 1992 >1,000 small, dark, icy bodies orbiting

the outer fringes of the solar system, beyond Neptune, were discovered (named after Gerard Kuiper who predicted their existence in the 1950s).

• There are probably >100,000,000 bodies larger than 1 km (0.6 miles) in the Kuiper Belt (KB).

• For the Solar Nebula Theory, or any theory to be successful, it must explain how the KB came to be.

Kuiper Belt

Comets

• Comets can occasionally be visible to the naked eye as they fly through the inner solar system.

• They appear as glowing balls with an extended tail of gas and dust.

• Comet nuclei are ice-rich bodies – a few kms to 10s of kms in diameter. – They are left overs from the origin of the planets

(called “dirty snowballs” or “icy mudballs).

Comets

• From comets, can conclude the solar nebula had abundant icy materials.

• Comets appear as they do because as they fly toward the sun, the sun’s heat vaporizes the ice, releasing gas and dust (creating the tail).

• A comets tail can be longer than an AU.

Comets

Meteors (shooting stars)

• Flash across the sky in momentary streaks of light.

• They are small bits of rock and metal colliding with Earth’s atmosphere and bursting into incandescent vapor because of friction with the air about 50 miles above the Earth (just inside of the space Earth boundary).

Meteors

• In space, before arriving to our atmosphere, they are called meteoroid.

• Any part that makes it to Earth’s surface is known as a meteorite.

• Most meteoroids are dust, grains of sand, or pebbles. – Most meteors we see are from meteoroids that

weigh less than 1 gram.

Meteors

• Few meteoroids are massive enough to survive the plunge to Earth’s surface (though it does happen and sometimes with spectacular effects).

• Video from Russian meteorite: https://www.youtube.com/watch?v=W4N_FpEcxk4

• Meteorites are effective in aging the SS.

Meteorites

Perseid Meteor Shower time lapse