Transcript TEK 5D and F

5) Earth in space and time. The student
understands the solar nebular accretionary
disk model. The student is expected to:
(d) explore the historical and current hypotheses for
the origin of the Moon, including the collision of Earth
with a Mars-sized planetesimal;
• Thea planetesimal collision creates Earth’s Moon
(f) compare extra-solar planets with planets in our solar
system and describe how such planets are detected.
• Observation with telescopes of other star systems
based on the stars radial velocity caused by the
gravitational force between the planets and the star
(Wiggle Effect)
• Transit Method: Photometric method
There have been many
explanations as to the
origin of Earth’s one
natural satellite, the Moon.
The Sister Theory
This theory states that the Moon
formed in orbit around the Earth.
Theories state that physical
structures and compositions of the
planets depend on their distance from
the Sun.
• Mercury, which is closer to the
Sun than we are, is considerably
richer in dense materials
• Mars, which is further from the
Sun, is considerably richer in less
dense materials.
We discount the sister theory now, because the Moon has a density like that of
Mars, and considerably lower than that of the Earth. It would be much easier to
understand this low density if the Moon were formed near the orbit of Mars.
The Capture Theory
This theory states that the Moon was
captured from somewhere else.
When an object comes by a planet, it
can either run into it, or pass by it,
and if close enough, get captured by
it.
We discount the
capture theory today,
because while the moon
is less dense than the
Earth, it would be made
of materials that are
MUCH different than
Earth if it had formed
elsewhere, and it is not.
Four of Jupiter’s largest
naturaltheory
satellites
were
The capture
states
thought
have been
that Earth
wasto
sufficiently
“captured”,
as they are
large enough
to “capture”
the
largemoon
enough
to be
migrating
in its
considered
gravitational
field.dwarf
planets, were it not for
the fact that they orbit
Jupiter.
Remember, fission is what
occurs when objects “split”.
The fission theory states that
Earth's Moon probably formed
out of material splashed into
orbit by the impact of a large
body into the early Earth.
There is a problem with
the fission theory,
however. If the moon
was a piece of the
Earth it should be the
same in make-up, with
equal portions of iron,
nickel, and silicates.
.
The Moon's density is
substantially less than that of
Earth, due to its lack of a
large iron core.
What could be the answer to
this dilemma?
We now embrace a Big Crunch, or Big Collision theory in which an object about
the size of Mars runs into the Earth, knocking off a part of its mantle. This
incorporates a part of the “fission theory”. The pieces blasted out into space
orbit the Earth, and form into the Moon.
This theory is attractive
because it solves all the
problems of previous theories.
• The low density of the
Moon is explained by its
being made up mostly of
Earth mantle material.
•The similarity with Earth
rocks is explained by the
Moon having been part of
the Earth.
Differentiation on Earth had probably already separated many lighter materials
toward the surface, so that the impact removed a disproportionate amount of
silicate material from Earth, (lighter) and left the majority of the dense metal
behind.
1. Describe the “Sister Theory” as to the origin of the
Moon.
2. What’s wrong with the “Sister Theory”?
3. Describe the “Capture Theory” as to the origin of the
Moon.
4. What’s wrong with the “Capture Theory”?
5. Describe the “Fission Theory” as to the origin of the
Moon.
6. Why do scientists like the new “Big Crunch” fission
theory?
Any planet is an extremely
faint light source
compared to its parent
star.
In addition to the
incredible difficulty of
detecting such a faint
light source, the light
from the parent star
causes a glare that washes
it out. For those reasons,
Instead,
astronomers
have generally had to resort to
only
a very
few extrasolar
indirect
methods
planets have
been to detect extrasolar planets. At the
present
several different indirect methods have
observedtime,
directly.
yielded success.
A star with a planet will move in its own small orbit in response to the planet's
gravity. This leads to variations in the speed with which the star moves toward
or away from Earth. I.e. the variations are in the radial velocity of the star
with respect to Earth
This has been by far the most productive
technique used by planet hunters. It is
also known as Doppler spectroscopy. It is
generally only used for relatively nearby
stars out to about 160 light-years from
Earth.
It easily finds massive planets that are
close to stars, but detection of those
orbiting at great distances requires many
years of observation.
One of the main disadvantages of the
radial-velocity method is that it can only
estimate a planet's minimum mass.
A pulsar is produced by a neutron star: the
small, ultra-dense remnant of a star that has
exploded as a supernova. Pulsars emit radio
waves extremely regularly as they rotate.
Because the rotation of a pulsar is so regular,
slight changes in the timing of its observed
radio pulses can be used to track the pulsar's
motion.
Like an ordinary star, a pulsar will move in its
own small orbit if it has a planet. Calculations
based on pulse-timing observations can then
reveal the size and shape of that orbit, and the
probable planet.
The main drawback of the pulsar-timing method
is that pulsars are relatively rare, so it is unlikely
that a large number of planets will be found
this way.
Also, and perhaps more importantly, life as we
know it could not survive on planets orbiting
pulsars since high-energy radiation there is
https://youtu.be/t2xTlv_I6ac
extremely intense.
When a planet crosses in front of a
star, then the star’s brightness dims
by a small amount.
This is the detection method used
by space telescopes that were
launched in the last decade.
One limitation of this method is
that it is only possible to detect
these crossings, also known as
transits, when the planet and the
star are perfectly aligned with the
line of sight of the detection
instrument.
This method, also called the
photometric method can determine
the radius of a planet.
The amount the star dims depends on
the relative sizes of the star and the
planet.
About 10% of planets with small orbits
have such alignment, and the fraction
decreases for planets with larger
orbits.
The transit method also
makes it possible to study
the atmosphere of the
transiting planet.
When the planet transits
the star, light from the star
passes through the upper
atmosphere of the planet.
By studying the stellar
spectrum carefully, as it
filters through that
planet’s atmosphere, one
can detect elements
present in that
atmosphere.
Missing frequencies through the spectroscope are clues, indicating elements or
compounds that absorb light at those frequencies are present in the
atmosphere.
For example, if the light frequencies corresponding to methane and carbon
monoxide are missing from an analysis of the starlight, the atmosphere contains
methane and carbon monoxide, which absorbed the missing light.
We use similar methods to determine atmospheric components around planets
in our own solar system.
Being able to identify the gases in an orbiting
planet’s atmosphere is most important to a branch
of science known as astrobiology.
These scientists are interested in finding Earth-like
planets, and in doing so, finding the signatures of
life.
What types
of elements
and
molecules
would you
Carl Sagan
expect
to
find in the
atmospheres
of these
planets?
Neil deGrasse Tyson
Oxygen?
Water Vapor?
Ozone?
Carbon Dioxide?
Nitrogen?
Michio Kaku
The extrasolar planets that
have been easiest to detect are
large, and in small, close orbits.
Many of these are gas giants
like the planet Jupiter but
orbiting as close to their sun as
planet Mercury.
This type of planet has been
called a “hot Jupiter”.
Why couldn’t planets like
hot Jupiters have formed
close to the sun in our
solar system?
At this stage, it appears to be fairly common for Sun-like stars to have
planets. Our current estimates are that it is possible as many as 40% of
Sun-like stars have some type of orbiting planet. This would mean there
is an enormous number of planets in our galaxy, given there are at least
200 billion stars.
7. Why must scientists resourt to “indirect methods” to detect
extrasolar planets?
8. What indirect methods do we use to detect extrasolar planets?
9. Why is it more difficult to detect planets farther away from the
star, than close-up?
10. What is the main problem with the Pulsar Timing method of
extrasolar planet detection?
11. What is the transit/photometric method of extrasolar planet
detection?
12. What characteristics about a planet can you determine using
the transit method?
13.
does the transit method pose?
14. What
What limitation
is a Hot Jupiter?