Week 7 Day 3 AnnouncementsGrades

• Participation scores will be up to date after Spring Break• Email Dr. Saul if there are discrepancies (include your iClicker number)

Homework:• Homework counts for 22% of your grade• NOT DOING HOMEWORK REDUCES YOUR CHANCES OF A

GOOD GRADE IN THIS CLASS

Extensions• Since Extensions remove late penalties, you can keep working on your

homework assignments while waiting for an extension to be granted

Email• Make sure you include ASTR 101 in email subject and your name at the

end of the message text.

The Solar System (Cont.)Chapter 4

Ingredients?

● The Sun● Planets● Moons and Rings● Comets ● Asteroids (size > 100 m) ● Meteoroids (size < 100 m)● Kuiper Belt● Oort cloud● Zodiacal dust● A lot of nearly empty space

Solar System Formation Video – Bring up Quicktime

Result from computer simulation of planet growth

Shows growth of terrestrial planets. If Jupiter's gravity not included, fifth terrestrial planet forms in Asteroid Belt. If Jupiter's gravity included, orbits of planetesimals there are disrupted. Almost all ejected from Solar System.

Simulations also suggest that a few Mars-size objects formed in Asteroid Belt. Their gravity modified orbits of other planetesimals, before they too were ejected by Jupiter's gravity.

Asteroid Ida

Clicker Question:

In the leading theory of solar system formation, the planets:

A: were ejected from the Sun following a close encounter with another star.

B: formed from the same flattened, swirling gas cloud that formed the sun.

C: were formed before the Sun.

D: were captured by the Sun as it traveled through the galaxy.

Clicker Question:

We can tell something of the composition of the planets by looking at their:

A: spectra

B: radius

C: mass

D: magnetic fields

Zodiacal Dust

What is it?

• Cosmic dust in the solar system between the planets• Thin pancake cloud of dust in the plane of the planets• Dust band is distributed evenly across the ecliptic

What causes it?

• Fragmentation of comets near Jupiter• Dust enters into elliptical orbits around the sun

• Appears as a triangular cloud best seen just after sunset (West - Spring) or before sunrise (East - Autumn)

Seen?

Zodiacal dust

Dust particles on the plane of the orbits of the planets. (size: 1 to 300 x 10-6 m)

What Killed the Dinosaurs?

The larger an impact is, the less often we expect it to occur.

The dinosaurs may have been killed by the impact of a large meteor or small asteroid.

Dinosaur Killer Impact 65 million years ago: an asteroidwith diameter roughly 10 km

High levels of iridium in RatonPass (I25)

The Fossil Record is Marked by Mass Extinction Events

Extinction Genus loss

End Ordovician 60%

End Devonian 57%

End Permian 82%

End Triassic 53%

End Cretaceous 47%

From Solé & Newman 2002

Interplanetary Matter: Earth Impacts

The impact of a large meteor can create a significant crater.

The Barringer meteor crater in Arizona

Interplanetary Matter: Earth Impacts

The Manicouagan reservoir in Quebec

Clicker Question:

An asteroid impact like the one that killed off the dinosaurs is expected once every:

A: year

B: hundred years

C: thousand years

D: hundred thousand years

E: hundred million years

The Structure of the Solar System

~ 45 AU~ 5 AU

L4

L5

L3

Lagrange Points

Interplanetary Matter: Asteroids

The inner solar system, showing the asteroid belt, Earth-crossing asteroids, and Trojan asteroids

Interplanetary Matter: Asteroids

Large picture: The path of Icarus, an Earth-crossing asteroid

Inset: Ceres, the largest asteroid

Asteroids and meteoroids have rocky composition; asteroids are bigger.

(above) Asteroid Ida with its moon, Dactyl

(below) Asteroid Gaspra

(above) Asteroid Mathilde

Interplanetary Matter: Asteroids

Interplanetary Matter: Asteroids

Asteroid Eros

Comets are icy, with some rocky parts.

The basic components of a comet

Interplanetary Matter: Comets

Interplanetary Matter: Comets

The solar wind means the ion tail always points away from the Sun.

The dust tail also tends to point away from the Sun, but the dust particles are more massive and lag somewhat, forming a curved tail.

Interplanetary Matter: Comets

The internal structure of the cometary nucleus

Oort Cloud

The size, shape, and orientation of cometary orbits depend on their location. Oort cloud comets rarely enter the inner solar system.

Meteor Showers

Meteor showers are associated with comets – they are the debris left over when a comet breaks up.

Meteor Showers

Stellar Spectra

Spectra of stars are different mainly due to temperature and composition differences.

Star

'Atmosphere', atoms and ions absorb specific

wavelengths of the black-body spectrum

Interior, hot and dense, fusion

generates radiation with black-body

spectrum

We've used spectra to find planets around other stars.

Star wobbling due to gravity of planet causes small Doppler shift of its absorption lines.

Amount of shift depends on velocity of wobble. Also know period of wobble. This is enough to constrain the mass and orbit of the planet.

As of today ~400 extrasolar planets known. Here are the first few discovered.

Molecules

Two or more atoms joined together.

They occur in atmospheres of cooler stars, cold clouds of gas, planets.

Examples

H2 = H + H

CO = C + OCO

2 = C + O + O

NH3 = N + H + H + H (ammonia)

CH4 = C + H + H + H + H (methane)

They have - electron energy levels (like atoms) - rotational energy levels - vibrational energy levels

Searching for Habitable planets around other stars

Molecule vibration and rotation