Chapter 18- Astronomy

In the early Universe there was....

mostly hydrogen and helium

Why did the Jovian planets form faster than the terrestrial planets?

must have accumulated most of their mass from gas in the surrounding solar nebula. That gas formed individual spinning disks (from which many satellites formed), and most likely it carried a lot of angular momentum as it fell onto the outer planets' cores, causing them to spin faster and faster as they coalesced.

Would you classify this planet as terrestrial or Jovian? Planet W, has 37 moons and rings

Jovian

Would you classify this planet as terrestrial or Jovian? Planet Y, located 25 AU away from it's star

Jovian

How does the solar nebula theory explain the formation of an asteroid belt between Mars and Jupiter rather than a planet at this location?

Jupiter formed early and its gravitational influence altered the orbits of nearby accreting planetesimals such that their collisions became destructive rather than constructive.

How did the solar nebula cleared up?

Once nuclear burning began in the Sun, it became a luminous object and cleared nebula as pressure from its light and solar wind pushed material out of Solar System

If the solar nebula theory is correct, then which of the following should be true?

Planets should be very common

True or False: Inside the frost line only rock and metal can condense, while outside the frost line only ices can condense.

True

True or False: Most of the carbon in your body was formed soon after the Big Bang.

True, the carbon in our bodies is billions of years old

What is the Jovian problem?

Two problems for the theory of planet formation: 1) Observations of extrasolar planets indicate that Jovian planets are common. 2) Protoplanetary disks tend to be evaporated quickly (typically within ~ 100,000 years) by the radiation of nearby massive stars. Too short for Jovian planets to grow!

Comets

a celestial object consisting of a nucleus of ice and dust and, when near the sun, a "tail" of gas and dust particles pointing away from the sun.

Uranus rotates on its side

possible collision (catastrophic)

Formation of Planetesimals: 3. Gravitational collapse

protoplanet is large enough to rapidly accumulate gas

microlensing

brightening of a background star due to focusing of its light by the gravity of a foreground extrasolar planet, allowing the planet to be detected and some of its characteristics measured

proto planets

massive object resulting from the coalescence of planetesimals in the solar nebula and destined to become a planet

outgassing

the release of gases from a planet's interior

Explain the concept of differentiation.

the separation of different constituents of planetary materials resulting in the formation of distinct compositional layers. Denser material tends to sink into the center and less dense material rises toward the surface.

differentiation

the separation of planetary material according to density

condensation sequence

the sequence in which different materials condense from the solar nebula at increasing distances from the sun

Terrestrial Planets

the small, dense, rocky planets of the inner solar system

Briefly explain the solar nebula hypothesis. Is it evolutionary or catastrophic?

the solar nebula (gaseous cloud), the sun and planets formed by condensation; the planets formed from the nebular crust that surrounded the Sun and broke apart. it is evolutionary

gravitational collapse

the stage in the formation of a massive planet when it grows massive enough to begin capturing gas directly from the nebula around it

accretion

the sticking together of solid particles to produce a larger particle

Half-life

the time required for half of the atoms in a radioactive sample to decay

What is the relationship between meteoroids, meteors and meteorites?

they all are rocks in space, the difference between them is how they interact with Earth and other planets

How was the angular momentum problem solved? Why was this problem important?

this was important because until it was solved, astronomers could not accept the nebular hypothesis.

True or False: If a star has a planet orbiting it, it can be detected using the transit method as long as your instruments are precise enough.

true, many planets can be missed through if the instruments are not precise.

In which ways can protoplanets heat up?

radioactive decay and heat formation

Asteroids

small, rocky world; most asteroids lie between Mars and Jupiter in the asteroid belt

Hot Neptunes and Hot Earths

smaller than Hot Jupiters

Heavier atoms are formed inside of.....

stars or in supernova explosions

The Kepler Planet

surveyed 150,000 stars 2500 plus exoplanets detected -planets have to pass in front of the star from our point of view, many planets are missed

Condensation sequence

terrestrial/ jovian division

Solar nebula collapsed into a disk

the orbits of the planets lie in the same plane

heavy bombardment

the period of intense meteorite impacts early in the formation of the planets, when the solar system was filled with debris

Which of the following is not evidence supporting the solar nebula theory?

the presence of hydrogen in the sun

What is accretion? What is its role in the formation of planetesimals?

the process in which solids agglomerate to form larger and larger objects and eventually planets are produced the role: solid particles sticking together, collected into the plane of the solar nebula which created planetesimals

Jovian Problem

the puzzle that protoplanetary disks around young stars don't seem to survive long enough to form Jovian planets by condensation, accretion, and gravitational collapse, yet Jovian-mass extrasolar planets are common

Could the very first generation of stars have Earth-like planets around them? (Hint: think of where the elements in rocks/ metal come from)

Yes, they could have. elements in rocks and metal were present which is how planets were formed.

Why is the existence of "hot Jupiters" puzzling?

"Hot Jupiters" are found near stars in very hot places where they should not have formed and show evidence of boiling away.

Jovian Planet Qualities

- Jupiter, Saturn, Uranus and Neptune - large, low density -thick, turbulent atmospheres -liquid-ice interiors -systems of satellites and rings

Lower opacity than predicted

- faster gravitational collapse

Age of the Solar System

4.6 billion years

Chemical Composition of the Solar Nebula

- mostly hydrogen -some helium -little metal

passing star hypothesis- about

- star collisions are very infrequent -the gas pulled would have been too hot -planets would not have stable orbits

How is the solar nebula theory supported by the motion of solar system bodies?

-All of the planets orbit the Sun near the Sun's equatorial plane. -All of the planets orbit in the same direction that the Sun rotates. -Six out of seven planets rotate in the same direction as the Sun. -Most moons orbit their planets in the same direction that the Sun rotates.

Name some pieces of evidence that support the solar nebula theory.

-Comets, asteroids, and meteorites recovered on Earth -astronomers have observed protoplanetary disk around distant newborn stars -saw that planets have the right characteristics to form a disk composed mainly of hydrogen around the Sun

From available samples

-Earth is at least 4.4 billion years old -The Moon is at least 4.5 billion years old -Mars is at least 4.5 billion years old -some meteorites are 4.56 billion years old

Why are Earth-like planets hard to detect? Give two reasons.

-If its orbit doesn't take it into a location that would block the path of light between its star and our telescopes -it could successfully block starlight, but the event could be lost amid natural variation in the brightness of the star as we perceive it on Earth

Massive planets can hold onto orbiting particles

-Jovian planets have systems of satellites -captured -formed in orbit around them -Jovian planets have ring systems

Terrestial Planet Qualities

-Mercury, Venus, Earth and Mars -small, dense, rocky -little or no atmosphere -cratered

Based on what you know about theories of Earth's origin, select all of the correct statements from the following list.

-Our solar system is believed to have formed from a disk of gas and dust. -An early theory of solar system origin was evolutionary. -An early theory of solar system origin was catastrophic. -The Sun and the solar system must have formed from the remains of earlier generations of stars.

Based on what you know about the solar system, select all of the correct statements from the following list.

-Planets like Earth have few or no moons and no rings. -Most of the objects in the solar system fit into a giant disk. -Meteoroids are objects that fall to planets.

Why are astronomers confident that planets often form in disks around protostars?

-They have found evidence of planets forming in protostellar disks. -They can detect disks of gas and dust orbiting protostars. -They have found lots of planets orbiting other stars.

Doppler Shifts

-a star and its planet will orbit their center of mass the stars will move slightly -astronomers can detect shifts in the stars spectrum as it moves

Direct collapse: about

-alternative to condensation and accretion -much faster formation

Heating sources

-decay of radioactive elements -heat of formation

Jovian problem

-disks around stars do not last long -massive planets take time to form

Outgassing

-gases from a planet's interior accumulate to create an atmosphere -Earth's atmosphere (water may have come from other planetesimals)

Microlensing

-gravitational lensing -exoplanet passed in front of a star, as seen from Earth

Solar wind

-helped radiation pressure remove dust and gas

Differentiation

-metals settle to the core -lighter materials float to the surface

Uranus and Neptune

-not enough material to form big planets so far away from the Sun -possibility: formed closer to the Sun, then migrated

Radiation pressure

-small particles of dust -individual atoms and molecules

The Kepler Planet Challenges

-small planet -long time intervals between transits

Formation of Planetesimals: 2. Accretion

-solid particles sticking together -collected into the plane of the solar nebula -planetesimals

Nebular Hypothesis-about

-spinning cloud -disk of material -planets orbiting a central star -angular momentum problem, eventually solved -solar nebular theory

Planets

-swept up space debris -heavy bombardment

Transits

-the brightness of a star decreases when a planet crosses in front of it -Jovian planets

Explain the transit method of detecting exoplanets.

-transit method is a photometric method that aims to indirectly detect the presence of one or more exoplanets in orbit around a star -the transit happen when a planet passes in front of its star. On the other hand, when the planet passes behind the star, it is called an eclipse

Direct Imaging

-visible light (Hubble) IR (Spitzer Space Telescope)

What are the three main steps in the formation of planetesimals?

1. Condensation 2.Accretion 3.Gravitational collapse

debris disks

A disk of dust found by infrared observations around some stars. The dust is debris from collisions among asteroids, comets, and Kuiper belt objects.

Hot Jupiters

A massive and presumably Jovian planet that orbits close to its star and consequently has a high temperature.

Meteorite

A meteor that has hit earth's surface.

Kuiper Belt Objects

An object in the Kuiper belt, a region beyond Neptune's orbit containing planetesimals remaining from the formation of the solar system. Pluto is one of the largest Kuiper belt objects.

How did Earth's atmosphere form?

As Earth cooled, an atmosphere formed mainly from gases spewed from volcanoes. It included hydrogen sulfide, methane, and ten to 200 times as much carbon dioxide as today's atmosphere. After about half a billion years, Earth's surface cooled and solidified enough for water to collect on it.

Is the passing star hypothesis evolutionary or catastrophic? Why was it discarded?

Catastrophic; it was discarded because it suggested that tidal forces determined the age of planets which is not correct.

How can astronomers know that disks of gas are common around young stars?

Disks of gas can be seen from telescopes like the Hubble Telescope. They are seen around younger stars which is how astronomers know this.

The Kepler Planet Goal

Earth-like planets

What is the role of catastrophic events in the solar nebula theory?

Event: uranus rotates on its side caused: possible collision event: venus rotates backwards caused: tidal collision

Evolutionary hypothesis

Explanation for natural events that involves gradual changes as opposed to sudden catastrophic changes-- for example, the formation of the planets in the gas cloud around the forming sun.

Catastrophic hypothesis

Explanation for natural processes that depends on dramatic and unlikely events, such as the collision of two stars to produce our solar system

True or False: As a material decays, the amount of parent atoms increases while the amount of daughter atoms decreases.

False, the amount of daughter atoms will increase and the amount of parent atoms will decrease

True or False: In the solar nebula there was plenty of material to form planets beyond the orbits of Saturn.

False, there was not enough material

Which of the following accurately describes the differentiation process?

High-density materials sink toward the center and low-density materials rise toward the surface of a molten body.

Easiest planets to detect

Hot Jupiters -massive -short orbital periods

Where do you expect to find dense planets, inside or outside the frost line? Why?

Inside the frost line because it is difficult for ice to form rapidly. This is why these planets stay dense

Explain one similarity and one difference between asteroids and comets.

Similarity: both celestial objects that orbit the Sun Difference: Asteroids are made of rocky material and metal and comets are made of ice, dusty and rocky materials

Would you classify this planet as terrestrial or Jovian? Planet X, with a mass half of Earth's

Terrestrial

Would you classify this planet as terrestrial or Jovian? Planet Z, with a density similar to water

Terrestrial

Direct collapse

The hypothetical process by which a Jovian planet might skip the accretion of a solid core, instead forming quickly and directly from the gases of the solar nebula.

transit

The passage of an extrasolar planet across the disk of its parent star as observed from Earth, partially blocking the light from the star and allowing detection and study of the planet

Passing star hypothesis

The proposal that our solar system formed when two stars passed near each other and material was pulled out of one to form the planets

solar nebula theory

The proposal that the planets formed from the same cloud of gas and dust that formed the sun.

nebular hypothesis

The proposal that the solar system formed from a rotating cloud of gas

What is the current hypothesis for how they formed?

These planets migrated recently from farther out to their current close distance.

Why are the Jovian planets rich in hydrogen?

They grew massive by accretion of large amounts of ices.

Why can't we find 4.6 billion year old rocks on Earth?

This is because a planet has to be older than anything we can find on their surface.

Which of the following best describes the ice line?

Water vapor could freeze outside the ice line.

How do we know that extrasolar planets are orbiting other stars?

We see a star's light dim as a planet passes in front of the star and detect alternating Doppler shifts in the spectra of some stars.

Meteoroid

a meteor in space before it enters Earth's atmosphere

Meteors

a small body of matter from outer space that enters the earth's atmosphere, becoming incandescent as a result of friction and appearing as a streak of light.

Age of the Sun: 3.5-6.5 billion years

all solar system bodies formed together -helioseismological observations -mathematical models

Frost Line: Outer Solar System

also ices

SNT: The star would transfer...

angular momentum to the disk

Jupiter's gravitational field could disturb the motion of nearby planetesimals:

asteroid belt instead of another planet

How have astronomers estimated the age of the Solar System?

astronomers can look at the oldest stars or by measuring the rate of expansion of the Universe

Why do all planets orbit the Sun in the same direction?

because of the conservation of angular momentum and also flattens the cloud, which is the reason why the Solar System is near-planar. When the cloud finally collapses, it forms a star and shortly after planets.

Why are massive exoplanets easier to detect with the Doppler method?

because the parent star will wiggle more with a large planet nearby, thereby creating a larger and more easily detectable spectral shift.

Condensation of Solids: Uncompressed Density

closer to the Sun= higher uncompressed density

Icy planetesimals

comets and KBOs

What's the origin of the solar wind?

created by the outward expansion of plasma (a collection of charged particles) from the Sun's corona (outermost atmosphere). This plasma is continually heated to the point that the Sun's gravity can't hold it down. It then travels along the Sun's magnetic field lines that extend radially outward.

radioactive isotopes:

decay into other isotopes -parent/daughter atoms -half life

Age of a rock

determined by the last time it solidified -known percentages of elements when a rock solidifies

Solar nebula

evolutionary theory but catastrophic events are considered

Formation of Planetesimals: 1. Condensation

formation of dust grains

All protons, electrons and neutrons.....

formed a few minutes after the Big Bang

In our solar system, Jovian planets

formed far from the Sun and can migrate

Jovian planets....

formed faster

The sun and the planets....

formed from the solar nebula -same ages

SNT: Planets form in disks of what?

gas and dust around the young Sun

Why do astronomers think there is no planet between Mars and Jupiter?

gravitational perturbations from Jupiter imbued the protoplanets with too much orbital energy for them to accrete into a planet

Larger planetesimals...

grow faster

heat of formation

in planetology, the heat released by the infall of matter during the formation of a planetary body

frost line

in the solar nebula, the boundary beyond which water vapor and other compounds could form ice particles

Motion of the material in the solar nebula

objects mostly rotate and revolve in the same direction

planetesimals

one of the small bodies that formed from the solar nebula and eventually grew into protoplanets

Frost Line: Inner Solar System

only rock and metal can condense

Once an object in the solar nebula becomes massive enough to clear its lane, it is known as which of the following?

planet

Extrasolar planet/ exoplanet

planet orbiting another star

Circumstellar Disks: Debris disks

planet sized objects

Circumstellar Disks: Dense disks of gas and dust

planetesimals and protoplanets

Low-speed collisions

planetesimals can combine

Eccentric orbits and/ or large inclinations:

planets can interact with each other and change orbits

extrasolar planets

planets orbiting stars other than our Sun

What are exoplanets?

planets that orbit a star other than our sun

uncompressed densities

the densities the planets would have if their gravity did not compress them

condensation

the growth of a particle by addition of material from surrounding gas, one atom or molecule at a time

Jovian Planets

the large, outer planets made of gas - Jupiter, Saturn, Uranus, & Neptune

Venus rotates backwards

tidal effects from the Sun (evolutionary) or collision (catastrophic)

Which method(s) would you use to confirm the existence of an extrasolar planet?

transit method and radial velocity

What method of detecting exoplanets did the Kepler mission use?

used the transit method; an event in which a planet passes in front of a star as seen from Earth

Do we find any hot Jupiters in our own Solar System?

yes, there are about 400 planets that roughly fit the definition of a hot jupiter

SNT: Such disks are common around.....

young stars, planets should be common