Transcript Linking Asteroids and Meteorites through Reflectance

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.
Exam #3
• The average was 77.3 and the grades ranged from
97.5s to a 35.
HW #16
• Due by April 20th at 1 pm
• I will take the top 20 HWs out of 24
• As of today, HW averages range from 99.3s to a 11.3
(without dropping any scores)
• If you want to make up a missing HW, you can write
a 10 page paper on a planetary science subject
Types of Planetary Missions
• Fly By
• Orbiter
• Lander
– Atmospheric Probe
– Rover
– Manned
• Sample Return
Mercury/Venus
• Mercury is the closest planet to the Sun
• Venus is next closest
• Both planets will be visible to the naked eye for
the next two weeks as bright, starlike objects that
will dominate the low western sky shortly after
sunset.
http://news.nationalgeographic.com/news/2010/04/100401-mercury-venus-planets-conjunction-april/
• http://www.skyandtelescope.com/observing/home
/89279827.html
Mercury
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orbit: 0.38 AU from Sun
diameter: 4,880 km (38.3% of Earth)
mass: 3.30 x 1023 kg (5.5% of Earth)
temperature:
90 K (minimum)
440 K (average)
700 K (maximum)
• Satellites: Zero
Difficult to study Mercury
• Because of Mercury's proximity to the Sun
– makes reaching it with spacecraft technically
challenging
– Earth-based observations difficult.
Mercury
• Videos
• http://www.gecdsb.on.ca/d&g/astro/html/Mercury
.html
Mariner 10
• The first spacecraft to approach Mercury was
NASA's Mariner 10 (1974-1975).
Caloris Basin
Caloris Basin
(Some of the hill are 1,800 meters tall)
Messenger data
Mariner 10 data
Caloris Basin
• A basin was defined by Hartmann and Kuiper (1962) as a
"large circular depression with distinctive concentric
rings and radial lineaments."
• Others consider any crater larger than 200 kilometers a
basin.
• The Caloris basin is 1,550 kilometers in diameter, and
was probably caused by a projectile larger than 100
kilometers in size.
• The impact produced concentric mountain rings three
kilometers high and sent ejecta 600 to 800 kilometers
across the planet.
Weird Terrain
The weird terrain is almost opposite
Caloris Basin. It consists of hills,
ridges and grooves that cut across craters.
The weird terrain my have been formed by
shock waves that raced through the center
of the planet and outward early in
Mercury's history.
Mercury has high density
• Its density is 5.44 g/cm3 which is comparable to
Earth's 5.52g/cm3 density.
• In an uncompressed state, Mercury's density is 5.5
g/cm3 where Earth's is only 4.0 g/cm3.
http://www.psrd.hawaii.edu/WebImg/MercuryCore.gif
Magnetic Field
• Despite its small size and slow 59-day-long
rotation, Mercury has a significant, and
apparently global, magnetic field.
• It is about 1.1% as strong as the Earth’s.
• Particularly strong tidal effects caused by the
planet's high orbital eccentricity would serve to
keep the core in the liquid state so it could have a
dynamo
Messenger
• Mission to Mercury
• Launched August 3, 2004
• Flew by Mercury in 2008
and 2009
• Will orbit Mercury in
2011
Messenger video
• A set of five 11-band images was captured by MESSENGER
just after the spacecraft crossed the night/day line (the
“terminator”), which are the highest-resolution color images
ever obtained of Mercury’s surface.
• At the beginning of this movie, it is dawn in that region of
Mercury, and the Sun is just off the horizon. The long
shadows that are cast by crater walls exaggerate the
ruggedness of the terrain and highlight variations in
topography.
• Though Mercury’s true colors are subtle, the 11 color bands
of MDIS were combined in a statistical method used to
highlight differences in color units. Older, low-reflectance,
and relatively blue material is encroached by younger,
relatively red smooth plains. Several lobate scarps or cliffs
are observed, which are places where compressional stresses
caused Mercury’s crust to fracture and shorten.
http://messenger.jhuapl.edu/news_room/presscon5_images/Robinson%20Image%205.7.mov
Mercury
Much of the image to the right of the Kuiper crater (in the centre here)
had never been imaged by a spacecraft before. Researchers were
surprised to see long crater rays that extend thousands of kilometers from
a crater at the planet's north pole
http://space.newscientist.com/data/images/ns/cms/dn14893/dn14893-1_450.jpg
Mercury
Dark material, shown in deep blue in the enhanced colour image at
right (a composite of visible and near-infrared images), was kicked up
by impacts. The material seems to be widespread but patchy,
suggesting the planet's interior is not homogenous.
http://space.newscientist.com/data/images/ns/cms/dn15077/dn15077-1_600.jpg
Mercury
• Double ringed basin
• 290 km in diameter
• Appears young (few
craters on it)
• ~ 1 billion years old
• Lava may have
covered up the central
part of the basin
http://messenger.jhuapl.edu/gallery/sciencePhotos/pics/presscon6_img4_5_lg.jpg
• 160 km in diameter
http://en.wikipedia.org/wiki/File:Mercury_Double-Ring_Impact_Basin.png
Spectra of Mercury
Weak to absent absorption features – no iron in the silicates
Mercury’s Surface
• Possibly made of Enstatite (MgSiO3) – Mg-rich
pyroxene
• Possibly made of material like the Lunar
Highlands
– Plagioclase feldspar - CaAl2Si2O8
Questions:
• Why does Mercury have such a large iron core?
One possibility
• Mercury may have been struck by a planetesimal
of approximately 1/6 its mass and several hundred
kilometers across.
• The impact would have stripped away much of
the original crust and mantle, leaving the core
behind as a relatively major component.
Venus
• orbit: 0.72 AU from Sun
• diameter: 12,103.6 km (94.9% of Earth)
(called Earth‘s twin)
• mass: 4.869 x 1024 kg (81.5% of Earth)
• Temperature on surface:
726 K(average)
• Satellites: Zero
Venus’ atmosphere
• Atmospheric pressure at surface is 92 times the
pressure on the Earth’s surface
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•
•
•
Atmospheric content:
Carbon dioxide
96.5 %
Nitrogen
3.5 %
Sulfur dioxide
150 ppm
Argon
70 ppm
Water vapor
20 ppm
Venus’ clouds
• Venusian clouds are thick and are composed of
sulfur dioxide and droplets of sulfuric acid.
• These clouds reflect about 75% of the sunlight
that falls on them,
Greenhouse Effect
• The greenhouse effect is the rise in temperature
that a planet experiences because certain gases in
the atmosphere (H2O, CO2, CH4) trap energy
emitted from the surface.
• Visble light hits the surface
• Surface warms and emits infrared radiation
• Atmospheric gases absorb some of the infrared
light
• Surface and Atmosphere heat up
Stefan-Boltzman Law
Emitted power (per square meter of surface) = σT4
λ·Tmax = 2,900,00 nm
Runaway Greenhouse Effect
• Runaway greenhouse effect to describe the effect
as it occurs on Venus
• Venus is sufficiently strongly heated by the Sun
that water is vaporized and so carbon dioxide is
not reabsorbed by the planetary crust
Why does Venus has such
a thick atmosphere?
• The luminosity of the Sun has increased by 25%
from 3.8 billion years ago
• The atmosphere of Venus up to around 4 billion
years ago maybe was more like that of Earth with
liquid water on the surface.
• The runaway greenhouse effect may have been
caused by the evaporation of the surface water
and the rise of the levels of greenhouse gases that
followed.
Surface
• Mapped by Magellan
spacecraft (1990-1994)
• How was it mapped if it
has a dense atmosphere?
How did it do it?
• Used Radar (radio waves)
• Most of Venus' surface consists of gently rolling
plains with little relief.
• Data from Magellan's imaging radar shows that
much of the surface of Venus is covered by lava
flows.
• Lava flows stopped ~300-500 million years ago
• Very few craters
• Most volcanoes on Venus are shield volcanoes
• Low viscosity lava
Maat Mons
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Highest volcano on Venus
8 km high
Shield Volcano
Could be active
Volcanoes
• ~170 giant volcanoes over 100 km across
• On Earth, only the Big Island of Hawaii is this
large
• This is due to Venus’ crust being older
• Earth’s crust is continually being recycled by
subduction
Craters
• Venusian craters range from 3 km to 280 km in
diameter.
• There are no craters smaller than 3 km because
the dense atmosphere stops small incoming
objects.
• 200 km long channel
• 2 km wide
http://hyperphysics.phy-astr.gsu.edu/hbase/Solar/venusurf.html
Pancakes Domes
• Flattened lava domes are attributed to upwellings
of molten rock which then subsided.
• The solid crust left behind
then flattened and cracked.
Coronae
• Corona is an oval-shaped feature.
• hot rising bodies of magma reach the crust and
cause it to partially melt and collapse
• Generates volcanic flows and fault
patterns that radiate from the
central structure.
100 km in diameter
http://pds.jpl.nasa.gov/planets/captions/venus/vencor.htm
Arachnoids
• concentric ovals surrounded by a complex network of
fractures, and can span 200 kilometers
• Almost all Venusian surface features are named
after historical and mythological women.
• The only exceptions are Maxwell Montes, named
after James Clerk Maxwell, and two highland
regions, Alpha Regio and Beta Regio
Venera
• Venera probes were launched by the Soviet Union
and enter Venus’ atmosphere
• 1961-1984
• Venera 3-16
• 10 probes landed on surface
Venera 9
Venera 9 and 10 pictures
Venera 13
Venera 13
Venera 13
Pioneer
• Pioneer Venus 1 or Pioneer Venus Orbiter was
launched in 1978 and studied the planet for more
than a decade after orbital insertion in 1978.
• Pioneer Venus 2 or Pioneer Venus Multiprobe
sent four small probes into the Venusian
atmosphere.
Pioneer 2
Pioneer 2 bus
• The Pioneer Venus bus portion of the spacecraft was targeted
to enter the Venusian atmosphere at a shallow entry angle and
transmit data until destruction by the heat of atmospheric
friction.
• The objective was to study the structure and composition of the
atmosphere down to the surface, the nature and composition of
the clouds, etc.
• With no heat shield or parachute, the bus made upper
atmospheric measurements down to an altitude of about 165 km
before disintegrating on December 9, 1978.
Pioneer 2 Large Probe that entered
the atmosphere
• Had parachute
• a neutral mass spectrometer to measure the atmospheric
composition
• a gas chromatograph to measure the atmospheric composition
• a solar flux radiometer to measure solar flux penetration in the
atmosphere
• an infrared radiometer to measure distribution of infrared radiation
• a cloud particle size spectrometer to measure particle size and shape
• a nephelometer to search for cloud particles
• temperature, pressure, and acceleration sensors
3 small probes
• No parachute
Venus Express
• Launched November 9, 2005 (Soyuz-Fregat from
Baikonur, Kazakhstan)
• First global monitoring of composition of lower
atmosphere in near-infrared transparency ‘windows’
• First coherent study of atmospheric temperature and
dynamics at different levels of atmosphere, from surface
up to ~200 km
• First measurements from orbit of global surface
temperature distribution
Mostly spare parts from
Mars Express or Rosetta
• ASPERA-4 - Neutral and ionised plasma analysis - Mars
Express
• MAG - Magnetic field measurements - Rosetta Lander
• PFS - Atmospheric vertical sounding by infrared Fourier
spectroscopy - Mars Express
• SPICAV - Atmospheric spectrometry by star or Sun
occultation - Mars Express
• VeRa - Radio sounding of atmosphereFrance)VeRaRadio
sounding of atmosphere - Rosetta
• VIRTIS - Spectrographic mapping of atmosphere and surface
- Rosetta
• VMC - Ultraviolet and visible imaging Mars Express and
Rosetta
• http://www.hulu.com/watch/94012/the-universemercury-and-venus---the-inner-planets
Any Questions?