Lesson 9b extra-planets

Origin of the Solar SystemAnd extra-solar planets

• In the inner solar system it was cool enough for iron and silicate compounds to form and make rocky material. But not cool enough for ice to accumulate.

• The inner planets were devoid of these volatile compounds.

• Today it is thought that virtually all the water on Earth came from collisions with icy bodies.

• Many of these bodies probably came to Earth from the migration of Neptune and Uranus caused by the 1:2 resonance of Jupiter and Saturn.

• Even more interesting, comets have been found to contain amino acids. The building blocks of proteins and DNA.

• Comets might have seeded the Earth with the compounds of life.

Importance of comets

• Life needs water. Comet collisions provide this.

• Comets have amino acids, life needs this.

• It seems to be the case that without the giant planets in the solar system, we (humans) would not be here today. The planets shot almost all of the small icy bodies out into the Oort cloud.

Orion Nebula

Proto-stars with tails and disks

• http://www.youtube.com/watch?v=YbdwTwB8jtc

• http://www.youtube.com/watch?v=jhYEQgLW5NM

Formation of the Solar System

• Gas and dust in a nebula collapse under the force of gravity

• This cloud of gas and dust fragments into smaller clumps anywhere that the density is a little higher.

• The smaller clumps form stars with dust and gas still orbiting around the newly formed star.

Proto-stars with tails and disks

• Although the new proto-Sun is not yet a star, it emits enough radiation, from gravitational potential energy as it shrinks, to make the inner solar system hot.

• There is a frost line out to the asteroid belt, where no ice can form. It must be a gas.

• Planets inside the frost line are built up, first by weak electrical forces between molecules, rich in silicates and iron. These become meteroids and small asteroids.

• The largest of these have the strongest gravity, though very weak.

• At first the gravity just helps smaller objects to latch on to the little asteroid.

• As the object grows in mass, the gravity is stronger and soon these collisions are impacts.

• Outside the frost-line, a similar thing is occurring, only here ice (which is more abundant) helps in the growth of mass for a planet.

• After a while the outer planets have enough mass to start pulling hydrogen and helium right out of the disk of material.

• They then grow to enormous size compared to the inner planets.

• Finally, after about 500 million years, the Sun becomes a STAR!

Star formation

• A proto-star is hot and emits light from this heat before it actually becomes a star.

• It is considered a star the internal temperature is high enough to fuse hydrogen into helium.

Nuclear Fusion via the proton-proton chain

• The new star gives off enough radiation and charged particles to drive the entire disk out of the solar system. (Remember the comet tail)

• The only thing that remains around the Sun at this point, are object that can’t be pushed away by the solar wind. (small meteoroids, asteroids, moons, and planets)

• The planets continue to grow, at this point only from collisions.

• Although the gas is now gone, there are billions upon billions of small objects that remain in orbit around the Sun.

• These continue to impact the planets and moons. This is the Early Heavy Bombardment. (Remember the Highlands on the Moon?)

• Collisions between planets and smaller objects is aided by migration of the planets. As planets migrate, the smaller objects end up on elliptical orbits.

• Why do elliptical orbits help cause impact?

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50%50%1. Objects on elliptical orbits break apart easily and make more objects increasing the chances of impacts.

2. Objects on elliptical orbits cross the orbits of planets which are circular.

• One very great event like this occurred when Jupiter and Saturn hit a 1:2 resonance and moved Neptune and Uranus out into the Kuiper Belt. This was the Late Heavy Bombardment. (Remember the Maria on the Moon?)

• As time went by the Solar System was cleared of debris and the number of impacts dropped. (Remember the Moon crater analysis)

• The planets were still very hot inside and geologic activity continued to resurface parts of the surface.

• The smaller planets cooled the fastest and eventually geologic activity stopped. From then on, virtually all impacts were preserved.

• Planets, like Mars, that were a little bigger continued geologic activity for longer than the smaller objects, but also eventually stopped. (Remember crater density to determine surface age?)

• Atmospheres arose from volcanic activity but only planets with enough mass and/or low enough temperature could hold on to it.

Result

• Rocky smaller planets in the inner Solar System. (Mercury, Venus, Earth, Mars).

• Gas giants beyond the asteroid belt (Jupiter, Saturn, Uranus, Mars.

• Outer moons, planetoids and comets have lots of ice. (H2O, CO2)

• The asteroid belt are rocky pieces left over.

Extra-solar Planets.• Today, we know of over 2000 planets orbiting

other stars.• Detecting these planets are very difficult

because they are small compared to the stars they are orbiting.

• Directly imaging them is virtually impossible today because they only reflect the brilliant star’s light. It will be possible when the James Webb Telescope is launched in the next 5 years.

NOT DRAWN TO SCALE!!!!

Where are we in the Milky Way?

The Fifth-Thirds Bank Building is 410 feet tall.

So try to picture this..

• The solar system is the width of a hair.• The Milky Way is about 3 times the size of New Circle

Drive.• It has a thickness almost 2 times the height of the

largest building in Lexington.• And the distance from us to the next closest star is

about 1 meter.• Our current planetary search extends to about 75

meters on this scale.

How do we find planets?

• One way is by searching for planets that eclipse their stars.

How do we find planets?

• One way is by searching for planets that eclipse their stars.

• For this technique to work, what must be true?

How do we find planets?

• One way is by searching for planets that eclipse their stars.

• Another way is to measure the wobble of the star as the planet orbits. (Remember Newton’s Third Law)

• This is done by measuring slight changes in the velocity of the star, as it wobbles.

Velocity changes in a star

Real data

• This is done by measuring slight changes in the velocity of the star, as it wobbles.

• It has only been in the past 15 years that our technology has advanced to the point that we can make this measurement.

• What exoplanets are going to be the easiest to discover?

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20% 20% 20%20%20%

1. Large planets near the star.2. Large planets far from the star.3. Small planets near the star.4. Small planets far from the star.5. Small planets because there are

more of them.

Jupiter Mass

Earth Mass

Earth Orbital Distance

• It is easiest to detect large mass planets that are close to their stars. The high mass gives a bigger wobble to the star, and the closer distance also makes gravity stronger, causing a larger wobble.

• The vast majority of these planets are gas giants (like Jupiter) and less than 1 A.U. from their star. Some are even 100 times closer than the Earth’s distance to the Sun.

• It is easiest to detect large mass planets that are close to their stars. The high mass gives a bigger wobble to the star, and the closer distance also makes gravity stronger, causing a larger wobble.

• The vast majority of these planets are gas giants (like Jupiter) and less than 1 A.U. from their star. Some are even 100 times closer than the Earth’s distance to the Sun.

• How can a gas giant planet be that close to its star?

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33% 33%33%

1. The frost line must have been closer to the star than it was for the Sun.

2. There must have been enough silicates and iron to grow a planet large enough to capture the gas from the disk.

3. They must have formed farther out and migrated to their current orbit.

• There is no known way for gas giants to form close to a star.

• They likely migrated there through interactions between either planets or other stars.

Super-Earths

• There have, in the past few years, been discoveries of a few planets that have been called super-Earths. They are have masses that are 5 – 10 times the Earth’s mass.

• These some of these planets are likely a transition between a gas planet like Neptune and a terrestrial world like Earth.

• Density estimates show several are lower density than Earth and scientists suspect…

.. They are ocean worlds

Super-Earth size

Gliese 581 C

• Given the number of super-Earths found so far, and the expectation that there should be more smaller planets than big planets, it is possible to at least estimate the number of Earth-like planets, orbiting Sun-like stars in the Milky Way Galaxy.

• Sun-like stars represent 7.6% of the stars in the Galaxy.

• There are 400 billion stars in the Milky Way.• That means there are 30 billion Sun-like stars.• Current exoplanet research only concentrates

on Sun-like stars.• So if 15% have Earth-like planets, then there

are about 4.5 billion Earth-like planets in the Galaxy.

• There are 400 billion stars in the Milky Way.• That means there are 30 billion Sun-like stars.• Current exoplanet research only concentrates

on Sun-like stars.• So it 15% have Earth-like planets, then there

are about 4.5 billion Earth-like planets in the Galaxy.

• One caveat: For life to exist, like on the Earth, these planets need to be at the correct distance, where water can exist as a liquid.

• Continuing this on, there are 100 billion known galaxies in the observable universe.

• That would mean 450

• Continuing this on, there are 100 billion known in the observable universe.

• That would mean 450 million

• Continuing this on, there are 100 billion known in the observable universe.

• That would mean 450 million, trillion Earths in the Universe. (4.5 x 1020)

• Do you think it is probable that there is life somewhere else in the Universe?

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50%50%1. Yes2. No

• Do you think it is probable that they are visiting us in UFOs?

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50%50%1. Yes2. No