Download Pluto

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.
Final
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May 7th
Friday
4 pm
Totman Gym
Cumulative
Review Session
– Hasbrouck 20, 6:15 pm, Wednesday (May 5th)
Formulas
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p2 = a3
F = GMm/r2
F = ma
T (K) = T (oC) + 273.15
c = f*
E = h*f
KE = 1/2mv2
E = mc2
Density = mass/volume
Volume = 4/3r3
HW
• Homeworks #21, #22, #23, and #24
Uranus
Uranus
• Discovered by William Herschel in 1781
• In 1977, the first nine rings of Uranus were
discovered
Atmosphere
• The atmosphere of Uranus is composed of 83%
hydrogen, 15% helium, 2% methane and small
amounts of acetylene and other hydrocarbons.
• Methane in the upper atmosphere absorbs red
light, giving Uranus its blue-green color.
Unusual
• Tipped on its side
• Why?
Probably
• Due to a collision
Uranus’ Satellites
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Cordelia
Ophelia
Bianca
Cressida
Desdemona
Juliet
Portia
Rosalind
2003U2
Belinda
1986U10
Puck
2003U1
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Miranda
Ariel
Umbriel
Titania
Oberon
2001U3
Caliban
Stephano
Trinculo
Sycorax
2003U3
Prospero
Setebos
2002U2
• Instead of being named after people from classical
mythology, Uranus' moons take their names from
the writings of William Shakespeare and
Alexander Pope.
Neptune
Neptune
• After the discovery of Uranus, it was noticed that its orbit
was not as it should be in accordance with Newton's
laws.
• It was therefore predicted that another more distant
planet must be perturbing Uranus' orbit.
• Neptune was first observed by Johan Galle and Heinrich
d'Arrest on 1846 Sept 23 very near to the locations
predicted from theoretical calculations based on the
observed positions of Jupiter, Saturn, and Uranus.
Galileo
• Galileo's astronomical drawings show that he had
first observed Neptune on December 27, 1612,
and again on January 27, 1613;
• On both occasions Galileo had mistaken Neptune
for a fixed star
• Neptune's blue color is largely the result of
absorption of red light by methane in the
atmosphere
Great Dark Spot
• Thought to be a hole
Scooter
Small dark spot
Great Dark Spot has disappeared
Neptune’s Rings
Triton
• Largest moon of Neptune
• Has retrograde orbit
(orbits the planet in the opposite
direction as the planet is rotating)
• May be captured Kuiper Belt Object
Pluto
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Pluto is a Dwarf Planet
Smallest planet
Diameter = 2306 ± 20 km (18% of Earth)
Mass = (1.305±0.007)×1022 kg (0.0021 Earths)
• In the late 19th century, astronomers started
speculating that Neptune's orbit was being
disturbed by another planet.
• Pluto was discovered after
an extensive search by
Clyde Tombaugh at the
Lowell Observatory in
Arizona in 1930
Pluto
• Venetia Burney (born 1919) was the first person
to suggest the name Pluto for the 9th planet
However
• Pluto is far too small to have the effect on
Neptune's orbit that initiated the search.
• The discrepancies in Neptune's orbit observed by
19th century astronomers were due instead to an
inaccurate estimate of Neptune's mass.
• Pluto’s orbit is exceptional among the planets
– high inclination (>17 °) and eccentricity (~0.25).
– Only Mercury's orbit shows a significant inclination
(~7°) and eccentricity (~0.2)
• Other planets follow quasi-circular, near–ecliptic
orbits
Density
• 2.03 g/cm3
• What does this mean?
Satellites
• Charon
– discovered in 1978 by astronomer James Christy
• Two smaller, provisionally designated ones
– Nix
– Hydra
• Barycenter (center of mass) lies above the planet's
surface.
• Charon is large relative to Pluto
– Diameter is half of Pluto
• Some astronomers label it a double planet system
• Pluto's icy surface is 98% nitrogen (N2).
• Methane (CH4) and traces of carbon monoxide
(CO) are also present.
• The solid methane indicates that Pluto is colder
than 70 Kelvin.
Pluto
Pluto
Kuiper Belt
• Pluto is thought to be one
of the largest Kuiper Belt
Objects (KBOs)
• Kuiper Belt is a region of the Solar System
beyond the planets extending from the orbit of
Neptune (at 30 AU) to approximately 55 AU
from the Sun
• Over 1,000 Kuiper Belt Objects (1,130) are
known
Eris
• It has a moon - Dysnomia
• Larger than Pluto
Eris
New Horizons
Mission
• Will characterize the global geology and
morphology of Pluto and its moon Charon
• Map their surface composition and characterize
Pluto's neutral atmosphere and its escape rate
• Will also photograph the surfaces of Pluto and
Charon.
Earth
• Is the only planet known to have life
SETI
• Search for Extra-Terrestrial Intelligence
• SETI programs tend to survey the sky to detect
the existence of transmissions from a civilization
on a faraway planet
Intelligent Life
• You have to be able to build a radio telescope
• Of electromagnetic radiation, only radio and
gamma can cross the Milky Way Galaxy
• It takes far less energy to produce radio waves
than gamma rays
Europa
• Moon of Jupiter
• Has an outer layer of ice
http://en.wikipedia.org/wiki/Image:Europa-moon.jpg
Europa
• Is thought to have a liquid ocean beneath an icy
surface
• Energy source provided by tidal heating (keeps
ocean from freezing)
• Proposed as possibly as possibly having
extraterrestrial life
www.physics.brandeis.edu/powerpoint/Charbonneau.ppt
The only star we know that has
Earth-Like Planets is the Sun
• Sun is sometimes called Sol
Galactic Habitable Zone
• It is the area in the galaxy whose boundaries are
set by its calm and safe environment, and access
to the chemical materials necessary for building
terrestrial planets similar to the Earth.
http://astronomy.swin.edu.au/GHZ/
green is habitable zone
Habitable Zones
• http://en.wikipedia.org/wiki/Image:Habzonethinkquest.gif
HabCat
• Catalog of Nearby Habitable Systems made by
Jill Tarter and Margaret Turnbull
• These Sun-like, habitable stars have just the right
distance, constancy, and temperature to qualify in
a forthcoming enlarged radio search.
What do else do you need?
• You need “metals” to make planets
–Metals are elements heavier in mass
than helium
For simple life
• You need a planet with an atmosphere and some
water
• Stars must remain nearly constant in
brightness over billions of years for complex
life to have time to develop.
– On Earth, single cells may have developed
after only 800 million years or so, but the
fossil record indicates that it took another
3 to 4 billion years before multi-cellular
life flourished.
• The number of HabCat stars,
as a function of distance
• M-type stars (solid red
histogram)
• K stars (dark-hatched green
histogram)
• G stars (light-hatched violet
histogram)
• F stars (horizontal-lined yellow
histogram)
• all stars (open blue histogram).
http://www.astrobio.net/news/article436.html
Drake Equation
• The Drake Equation is an attempt to estimate the
number of extraterrestrial civilizations in our
galaxy with which we might come in contact.
• http://www.activemind.com/Mysterious/Topics/SETI/drake_equation.html
Number of habitable planets
• 100 billion?
Fraction of Planets that have life in the Galaxy
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Fraction of the Life-Bearing Planets in the
Galaxy upon which a Civilization capable of
interstellar communication
has at some time arisen
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Intelligent Life
• Intelligent life that we can detect is usually
defined as life that can build a radio telescope
Radio
• Transmitting information over radio waves is very
cheap
• uses equipment that is easy to build
• has the information-carrying capacity necessary
for the task
• The information also travels at the speed of light.
Fraction of all civilizations that have existed
in the galaxy that exist now
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Fermi’s Paradox
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Where are they?
Fermi’s Paradox
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Why have we not observed alien civilizations
even though simple arguments would suggest
that some of these civilizations ought to have
spread throughout the galaxy by now?
Reason for question
• Straightforward calculations show that a
technological race capable of interstellar travel at
(a modest) one tenth the speed of light ought to be
able to colonize the entire Galaxy within a period
of one to 10 million years.
Explanation
• Interested in us but do not want us (yet) to be
aware of their presence (sentinel hypothesis or
zoo hypothesis)
Explanation
• Not interested in us because they are by nature
xenophobic or not curious
Explanation
• Not interested in us because they are so much
further ahead of us
Explanation
• Prone to annihilation before they achieve a significant
level of interstellar colonization, because:
(a) they self-destruct
(b) are destroyed by external effects, such as:
(i) the collision of an asteroid or comet with their
home world
(ii) a galaxy-wide sterilization phenomenon (e.g. a
gamma-ray burster
(iii) cultural or technological stagnation
Explanation
• Capable of only interplanetary or limited
interstellar travel because of fundamental
physical, biological, or economic restraints
Fermi’s paradox
• The Fermi paradox is the apparent contradiction
between high estimates of the probability of the
existence of extraterrestrial civilizations and the
lack of evidence for, or contact with, such
civilizations.
• http://en.wikipedia.org/wiki/Fermi_paradox
Any Questions?
Any Questions?