Transcript 87 Sr

Astronomy 101
The Solar System
Tuesday, Thursday
Tom Burbine
[email protected]
Course
• Course Website:
– http://blogs.umass.edu/astron101-tburbine/
• Textbook:
– Pathways to Astronomy (2nd Edition) by Stephen Schneider
and Thomas Arny.
• You also will need a calculator.
• There is an Astronomy Help Desk that is open
Monday-Thursday evenings from 7-9 pm in Hasbrouck
205.
• There is an open house at the Observatory every
Thursday when it’s clear. Students should check the
observatory website before going since the times may
change as the semester progresses and the telescope
may be down for repairs at times. The website is
http://www.astro.umass.edu/~orchardhill/index.html.
HW #10, #11, #12, and #13
• Due March 30th at 1 pm
What are the assumptions to get an age?
What are the assumptions?
• No loss of parent atoms
– Loss will increase the apparent age of the sample.
• No loss of daughter atoms
– Loss will decrease the apparent age of the sample.
• No addition of daughter atoms or if daughter
atoms was present when the sample formed
– If there was, the age of the sample will be inflated
• These can possibly be all corrected for
Radioactive
Parent (P)
40K
87Rb
147Sm
232Th
235U
238U
Radiogenic
Daughter
(D)
Commonly Used Long-Lived Isotopes in Geochronology
40Ar
87Sr
143Nd
208Pb
207Pb
206Pb
Stable
Reference
(S)
36Ar
86Sr
144Nd
204Pb
204Pb
204Pb
Half-life,
t½
(109 y)
1.25
48.8
106
14.01
0.704
4.468
Decay
constant, l
(y-1)
0.58x10-10
1.42x10-11
6.54x10-12
4.95x10-11
9.85x10-10
1.55x10-10
How do you determine isotopic values?
How do you determine isotopic values?
• Mass Spectrometer
It is easier
• To determine ratios of isotopic values than actual
abundances
Example
• 87Rb  87Sr + electron + antineutrino + energy
• Half-life is 48.8 billion years
• 87Sr = 87Srinitial + 87Rb (eλt – 1)
• Divide by stable isotope
•
= 87Srinitial + 87Rb (eλt – 1)
86Sr
86Sr
86Sr
87Sr
Example
• Formula for line
• 87Sr = 87Srinitial + (eλt – 1) 87Rb
86Sr
86Sr
86Sr
y
= b
+mx
http://www.asa3.org/aSA/resources/wiens2002_images/wiensFig4.gif
= (eλt – 1)
Carbon-14
•
•
•
•
•
99% of the carbon is Carbon-12
1% is Carbon-13
0.0000000001% is Carbon-14
The half-life of carbon-14 is 5730±40 years.
It decays into nitrogen-14 through beta-decay
(electron and an anti-neutrino are emitted).
• Due to Carbon-14’s short half-life, can only date
objects up to 60,000 years old
• Plants take up atmospheric carbon through
photosynthesis
http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/cardat.html
• When something dies, it stops being equilibrium
with the atmosphere
http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/cardat.html
Why is Carbon-14 still present if it has
such a short half-life?
Why is Carbon-14 still present if it has
such a short half-life?
• Cosmic rays impact Nitrogen-14 and create Carbon-14
• Cosmic rays are energetic particles (90% are protons)
originating from space. From the Sun (solar cosmic
rays) or outside the solar system (galactic cosmic rays)
• n + 14N → 14C + p
• http://en.wikipedia.org/wiki/Image:Radiocarbon_
bomb_spike.svg
Composition of the Planets
Different bodies have different densities
• Density = Mass/Volume
• M = 42d3/GP2
V =4/3R3
Life of a Star
• A star-forming cloud is called a molecular cloud
because low temperatures allow Hydrogen to
form Hydrogen molecules (H2)
• Temperatures like 10-50 K
Region is approximately 50 light years across
Condensing
• Interstellar clouds tends to be lumpy
• These lumps tend to condense into stars
• That is why stars tend to be found in clusters
Protostar
• The dense cloud fragment gets hotter as it
contracts
• The cloud becomes denser and radiation cannot
escape
• The thermal pressure and gas temperature start to
rise and rise
• The dense cloud fragment becomes a protostar
When does a protostar become a star
• When the core temperatures reaches 10 million K,
hydrogen fusion can start occurring
Formation of Solar System
• Solar Nebula Theory (18th century) – Solar System
originated from a rotating, disk-shaped cloud of gas
and dust
• Modern theory is that the Solar System was born from
an interstellar cloud (an enormous rotating cloud of gas
and dust)
Composition
• ~71% is Hydrogen
• ~27% is Helium
• ~2% are other elements (Fe, Si, O) in the form of
interstellar grains
• Show animation
• Dust grains collide and stick to form larger and
larger bodies.
• When the bodies reach sizes of approximately one
kilometer, then they can attract each other directly
through their mutual gravity, becoming
protoplanets
• Protoplanets collide to form planets
– Asteroids such as Ceres and Pallas are thought to be
leftover protoplanets
• Condensation – conversion of free gas atoms or
molecules into a liquid or solid
• Volatile – Elements or compounds that vaporize
at low temperatures
Form atmosphere and oceans
If you want to find life
outside our solar system
• You need to find planets
Extrasolar Planets
• Today, there are over 400 known extrasolar
planets
• ~430 extrasolar planets known as of today
Star Names
• A few hundred have names from ancient times
• Betelgeuse, Algol, etc.
• Another system:
• A star gets name depending on what constellation
it is in
• With a Greek letter at the beginning
– Alpha Andromeda, Beta Andromeda, etc.
• Only works for 24 brightest star
Star Names now
• Stars are usually named after the catalog they were
first listed in
• HD209458 is listed in the Henry Draper (HD) Catalog
and is number 209458
• HD209458a is the star
• HD209458b is the first objects discovered orbiting the
star
Our Solar System has basically two types
of planets
• Small terrestrial planets – Made of Oxygen, Silicon, etc.
• Large gaseous giants – Made primarily of hydrogen and a
little helium
–
–
–
–
Jupiter - 90% Hydrogen, 10% Helium
Saturn – 96% Hydrogen, 3% Helium
Uranus – 83% Hydrogen, 15% Helium
Neptune – 80% Hydrogen, 20% Helium
Things to Remember
• The Milky Way has at least 200 billion other
stars and maybe as many as 400 billion stars
• Jupiter’s mass is 318 times than the mass of the
Earth
Question:
• How many of these stars have planets?
What is the problem when
looking for planets?
What is the problem when
looking for planets?
• The stars they orbit are much, much brighter than
the planets
• Infrared image of the star GQ Lupi (A) orbited by a
planet (b) at a distance of approximately 20 times the
distance between Jupiter and our Sun.
• GQ Lupi is 400 light years from our Solar System and
the star itself has approximately 70% of our Sun's mass.
• Planet is estimated to be between 1 and 42 times the mass
of Jupiter.
•
http://en.wikipedia.org/wiki/Image:GQ_Lupi.jpg
So what characteristics of the planets may
allow you to “see” the planet
So what characteristics of the planets may
allow you to “see” the planet
• Planets have mass
• Planets have a diameter
• Planets orbit the star
http://upload.wikimedia.org/wikipedia/commons/d/de/Extrasolar_Planets_2004-08-31.png
• Jupiter
–
–
–
–
H, He
5.2 AU from Sun
Cloud top temperatures of ~130 K
Density of 1.33 g/cm3
• Hot Jupiters
–
–
–
–
–
–
H, He
As close as 0.03 AU to a star
Cloud top temperatures of ~1,300 K
Radius up to 1.3 Jupiter radii
Mass from 0.2 to 2 Jupiter masses
Average density as low as 0.3 g/cm3
10
100
1,000
(lightyears)
Some Possible Ways to detect Planets
• Radial Velocity (Doppler Method)
• Transit Method
• Direct Observation
Center of Mass
• Distance from center of first body = distance between the bodies*[m2/(m1+m2)]
• http://en.wikipedia.org/wiki/Doppler_spectroscopy
Radial Velocity (Doppler Method)
http://www.psi.edu/~esquerdo/asp/shifts.jpg
• http://astronautica.com/detect.htm
Wavelength
http://www.psi.edu/~esquerdo/asp/method.html
www.physics.brandeis.edu/powerpoint/Charbonneau.ppt
Bias
• Why will the Doppler method will preferentially
discover large planets close to the Star?
Bias
• Why will the Doppler method will preferentially
discover large planets close to the Star?
• The gravitational force will be higher
• Larger Doppler Shift
Transit Method
• When one celestial body appears to move across
the face of another celestial body
• When the planet crosses the star's disk, the visual
brightness of the star drops a small amount
• The amount the star dims depends on its size and
the size of the planet.
• For example, in the case of HD 209458, the star
dims 1.7%.
•
http://en.wikipedia.org/wiki/Extrasolar_planets#Transit_method
One major problem
• Orbit has to be edge on
Direct Observation
• Infrared Image
Visible
•
•
Infrared
http://www.news.cornell.edu/stories/March05/extrasolar.ws.html
http://nai.nasa.gov/library/images/news_articles/319_1.jpg
http://en.wikipedia.org/wiki/Image:Extrasolar_planet_NASA2.jpg
How did these Hot Jupiters get orbits so
close to their stars?
How did these Hot Jupiters get orbits so
close to their stars?
• Formed there – but most scientists feel that Jovian
planets formed far from farther out
• Migrated there - planet interacts with a disk of
gas or planetesimals, gravitational forces cause
the planet to spiral inward
• Flung there – gravitational interactions between
large planets
Kepler Mission
• Kepler Mission is a NASA space telescope
designed to discover Earth-like planets orbiting
other stars.
• Using a space photometer, it will observe the
brightness of over 100,000 stars over 3.5 years to
detect periodic transits of a star by its planets (the
transit method of detecting planets) as it orbits our
Sun.
• Launched March 6, 2009
Kepler Mission
http://en.wikipedia.org/wiki/File:Keplerpacecraft.019e.jpg
Kepler Mission
• The Kepler Mission has a much higher probability
of detecting Earth-like planets than the Hubble
Space Telescope, since it has a much larger field
of view (approximately 10 degrees square), and
will be dedicated for detecting planetary transits.
• There will a slight reduction in the star's apparent
magnitude, on the order of 0.01% for an Earthsized planet.
www.physics.brandeis.edu/powerpoint/Charbonneau.ppt
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Any Questions?