nats 1311 - from the cosmos to earth primary characteristics of the solar system 1. patterns of...
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NATS 1311 - From the Cosmos to Earth
Primary Characteristics of the Solar System
1. Patterns of motion
• All planetary orbits are nearly circular and lie nearly in the same plane
• All planets orbit the Sun in the same direction - counterclockwise view from above the Earth’s north pole
• Most planets orbit in same direction they rotate - including Sun
• Most moons exhibit similar characteristics - orbit in planet’s equatorial plane in the same direction as planetary rotation
NATS 1311 - From the Cosmos to Earth
Solar System
Side view of the solar system - arrows indicate the orientation of the rotation axes of the planets and their orbital motion. Seen from above, all orbits except those of Mercury and Pluto are nearly circular. Most moons orbit in the same direction as the planets orbit and rotate--counterclockwise when seen from above Earth's North Pole.
NATS 1311 - From the Cosmos to Earth
Accurate Model of the Solar System Animation
NATS 1311 - From the Cosmos to Earth
NATS 1311 - From the Cosmos to Earth
NATS 1311 - From the Cosmos to Earth
2. Planets fall into two main categories• Terrestrial (i.e. Earth-like) - Mercury, Venus, Earth, Mars• Jovian (i.e. Jupiter-like or gaseous) - Jupiter, Saturn, Uranus,
Neptune• What is Pluto - icy moon? No longer classified as a planet.
Characteristics of the Solar System
NATS 1311 - From the Cosmos to Earth
Mars Neptune
Terrestrial Jovian
NATS 1311 - From the Cosmos to Earth
NATS 1311 - From the Cosmos to Earth
A Few Exceptions to the Rules…
• Uranus tilted on its side.
• Venus rotates “backwards” (i.e. clockwise).
• Triton orbits Neptune “backwards.”
• Earth is the only terrestrial planet with a relatively large moon.
NATS 1311 - From the Cosmos to Earth
3. Swarms of small objects - asteroids and comets - populate the Solar System
• Asteroids
– small rocky bodies that orbit the Sun much like planets - much smaller
– largest is Ceres - about 1000 km in diameter
• Comets
– icy leftover planetesimals orbiting the Sun - dirty snowballs
Characteristics of the Solar System
NATS 1311 - From the Cosmos to Earth
Asteroids
Calculated positions of 152,942 asteroids for midnight, 1 January 2004.
•Asteroids found mostly in Asteroid belt - between Jupiter and Mars
•Trojan asteroids are group of asteroids that share Jupiter’s orbit - clumped about 60º in front of and behind Jupiter
•Some asteroids pass through the inner solar system - including near-Earth asteroids that threaten the Earth
NATS 1311 - From the Cosmos to Earth
2 km
Near Earth Asteroids
Gaspra
Eros
NATS 1311 - From the Cosmos to Earth
Arizona Meteor Crater
Near-Earth asteroids are known to impact Earth. This crater was created by an asteroid about 50 m across about 50,000
years ago. It is more than a kilometer across and 200 m deep.
NATS 1311 - From the Cosmos to Earth
•Kuiper belt - extends from about Neptune’s orbit to about three times as far as Neptune (about 30 to 100 AU) - orbit Sun in same direction and nearly same plane as planets
•Oort cloud - may extent 1/4 of the way to nearest star - roughly spherical - orbits at all inclinations and planes - so vast that a trillion comets would still be separated by over a billion miles each
Comets come from two distinct regions of space:
NATS 1311 - From the Cosmos to Earth
Hale-Bopp Halley
West
Comets
Q4
“Dirty snowballs” heated up as they near the sun in their highly elliptical orbits. Two tails - dust tail of small particles and plasma tail of ionized gas. Tails always point away from Sun - carried away by solar wind.
NATS 1311 - From the Cosmos to Earth
Asteroids Kuiper Belt Comets Oort Cloud Comets
Made mostly of rock Made mostly of ice Made mostly of ice
Orbit in the inner solar system (most in asteroid belt)
Orbit between Neptune and about 100 AU from Sun
Orbit at great distance, as far away as one-fourth of the way to nearest star
Orbit in the same direction and nearly same plane as planets
Orbit in the same direction and nearly same plane as planets
Orbits inclined at every possible angle and going in all possible directions
NATS 1311 - From the Cosmos to Earth The Sun
•Huge ball of hot gas (about 6000º C)
•333,000 times mass of Earth
•Contains about 99.85% of mass in solar system (Jupiter has about 0.1% - rest of planets about 0.05%)
–Its gravity regulates the orbits of the planets.–Its heat is the primary factor which determines the temperature of the
planets.–It provides practically all of the visible light in the Solar System.–High-energy particles streaming out from the Sun influence planetary
atmospheres and magnetic fields.
NATS 1311 - From the Cosmos to Earth
11-Year Solar Cycle
NATS 1311 - From the Cosmos to Earth
Fig. 8-13, p. 157
11-Year Solar Cycle
NATS 1311 - From the Cosmos to Earth
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NATS 1311 - From the Cosmos to Earth
Photospheric Features
Granulation: the tops of convection cells seen “bubbling” on the Solar surface
Sunspots: dark spots on the surface where the temperature is cooler.
Regions of strong magnetic fields - suppress convection from below
Sunspots occur in pairs - magnetic fields loop from one sunspot to a neighboring sunspot
NATS 1311 - From the Cosmos to Earth
Close up of a sunspot
A sunspot is cooler than the rest of the Sun’s surface and looks darker. They last anywhere from hours to months.
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NATS 1311 - From the Cosmos to Earth
So the Sun’s surface looks like boiling oatmeal or soup
NATS 1311 - From the Cosmos to Earth
Sunspots and the Sun’s surface can change very quickly - this movie covers half an hour.
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NATS 1311 - From the Cosmos to Earth
NATS 1311 - From the Cosmos to Earth
Sunspot-Associated Solar Events
Solar Flare - when a magnetic loop breaks, it releases matter and energy into space
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NATS 1311 - From the Cosmos to Earth
NATS 1311 - From the Cosmos to Earth
Coronal rain as cooled material falls back to the surface
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NATS 1311 - From the Cosmos to Earth
Various configuration of an inferior planet are defined as shown here. Any planet whose orbit is smaller than Earth’s orbit is called a “inferior” planet. Mercury and Venus are the only inferior planets.
Aspects of an Inferior Planet.
NATS 1311 - From the Cosmos to Earth Mercury
No
data
Desolate, cratered, essentially no atmosphere - temperature 800ºF to -240ºF Least studied of all the terrestrial worlds - difficult with telescopes because of proximity to Sun - only been visited by one spacecraft with three flybys by Mariner 10 in 1974 - 1975.
NATS 1311 - From the Cosmos to Earth
Mercury, Mariner 10 photo.
Large valley at bottom is 4
miles wide and 60 miles
long.
It leads into crater 50 miles
in diameter.
NATS 1311 - From the Cosmos to Earth
Crater at lower left
is 40 miles in
diameter.
Shows flow front
extending across
crater floor.
NATS 1311 - From the Cosmos to EarthMessenger’s Journey to Mercury
Gravity assist maneuver usually used to speed up a spacecraft. But it can be used to slow down a spacecraft.
NATS 1311 - From the Cosmos to Earth
The Mystery of Mercury’s Orbit
Mercury’s (and Uranus’) orbit inconsistent with Newton’s Law of Universal Gravitation
French astronomer Urbain Leverrier had accurately predicted presence of a planet outside Uranus - Neptune - to explain Uranus’s orbit
Suggested the presence of a planet called Vulcan inside Mercury’s orbit - doesn’t exist
Required Einstein general theory of relativity 40 years later
Deals with gravitational effect on space - warping Accurately predicted Mercury’s orbit
NATS 1311 - From the Cosmos to Earth Mercury
Property Earth Mercury
Equatorial Diameter 1 0.4
Density (gm/cm3) 5.5 5.4
Avg. Distance from Sun (AU) 1 0.4
Orbital Period (days) 365 88
Sidereal Rotation Period (days) 1 59
Inclination of axis to orbital plane 23.5° 7°
Inclination of orbit to ecliptic plane 0° 7°
Maximum angle from sun ~ 28°
Surface temperature ~ Day: 800°F
~ Night: -280°F
Atmosphere - pressure 1 atmosphere 10-15 atmosphere
Atmosphere - composition N2, O2 Helium, sodium, potassium, oxygen
NATS 1311 - From the Cosmos to Earth
As viewed from Earth, Mercury can be seen only near times of greatest eastern or western elongation.
• At greatest western elongation (when the planet is farthest west of the sun in the sky), Mercury rises about 1 1/2 hours before sunrise.
• At greatest eastern elongation (when the planet is farthest east of the sun in the sky), Mercury sets about 1 1/2 hours after sunset.
The Orbit of Mercury
At an average distance of only 58 million kilometers (36 million miles) from the sun, Mercury takes a mere 88 days to go around its orbit.
NATS 1311 - From the Cosmos to Earth
Mercury Transit of the Sun Movie
NATS 1311 - From the Cosmos to Earth
Comparison of Venus and Earth
Parameter Venus Earth
• Distance from Sun (AU) .72 1.00 (million KM) 108 150
• Sidereal Period (year) (earth days) 225 365
• Rotation Period (day) (earth days) 243 1.00
• Direction of rotation Retrograde Direct
• Equatorial Diameter 0.96 1.00
• Escape velocity (km/Sec.) 10.3 11.2
• Inclination of axis 3 23.5• Seasons No Yes
VENUS
NATS 1311 - From the Cosmos to Earth
Comparison of Venus and Earth• Parameter Venus Earth
• Surface Temperature 480C (900F) 15C (60F)
• Surface atmospheric pressure 90 1
(atmospheres)
• Atmospheric gases CO2 N2, O2
• Cloud cover Total Partial
• Surface Solid 3/4 water
• Number of satellites 0 1
VENUS
NATS 1311 - From the Cosmos to Earth
Differences Between Venus and Earth
1. Venus rotation rate is very slow and in retrograde direction.
2. Venus surface consists of 1 plate; earth has 9 plates.
3. Venus has little or no magnetic field.
4. Venus' atmosphere pressure is 90 times that of earth.
5. Dominant gas in the Venus atmosphere is carbon dioxide.
6. Venus' surface temperature is 900° F.
7. Venus has very little water vapor in its atmosphere.
8 Venus has a very strong greenhouse effect.
9. There is no water on Venus' surface.
10. Venus has a very dense cloud cover.
NATS 1311 - From the Cosmos to Earth
Venus
Cloud covered, thick atmosphere - carbon dioxide - greenhouse affect - surface temperature near 900ºF - rains sulfuric acid
NATS 1311 - From the Cosmos to Earth
Surface features unknown because of heavy cloud cover until the Magellan spacecraft mapped surface with radar. The surface of Venus is covered with abundant lava flows and tectonic features, along with a few large impact craters. In the following images dark and light areas correspond to how well radio waves are reflected, not visible light. Nonetheless, geological features stand out well.
Images of Venus’ SurfaceRussians probes actually landed on Venus four times in the 70’s - probes lasted up to two hours before failure. NASA’s Pioneer Venus sent probe into atmosphere - had on-board instrument (mass spectrometer) built at UTD.
Venera 13
NATS 1311 - From the Cosmos to Earth
Two of Venus' relatively rare impact craters
Shield volcanoes like this one are common on Venus.
Radar Images of Venus’ Surface
Tectonic forces have fractured and
twisted the crust in this region.
Circular cracks and volcanic bumps make up a corona, probably caused by pressure of a mantle plume below.
NATS 1311 - From the Cosmos to Earth
Venus orbit tilted 3.4º to the ecliptic
Transits of Venus only occur in pairs about 8 years apart every ~120 years.
Transit occurred in 2004 - next in 2012
Edmund Halley one of few to observe first transit in 1677 after invention of telescope - called upon future astronomers to observe subsequent transits.
Captain Cook traveled to Tahiti to observe transit of 1769 in an attempt to estimate the distance from the Earth to the Sun using triangulation and the parallax effect - discovered Hawaii on the way.
Measurements not very accurate: - intense sunlight filtering through Venus' atmosphere fuzzed the edge of the disk and decreased the precision with which Cook could time the transit- his measurements disagreed with those of ship's astronomer Charles Green, who observed the transit beside Cook, by as much as 42 seconds.
Venus Transits
NATS 1311 - From the Cosmos to Earth
- Cook and Green also observed the "black drop effect." When Venus is near the limb of the sun - the critical moment for transit timing - the black of space beyond the Sun's limb seems to reach in and touch the planet - made it hard to say just when the transit began or ended.
- a problem for observers elsewhere - observations of Venus' 1769 transit from 76 points around the globe not precise enough to set the scale of the solar system. Astronomers didn't manage that until the 19th century when they used photography to record the next pair of transits.
NATS 1311 - From the Cosmos to Earth
Venus Transit of the Sun