NATS 1311 - From the Cosmos to Earth Primary Characteristics of the Solar System 1. Patterns of...

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


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.


Accurate Model of the Solar System Animation


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


Mars Neptune

Terrestrial Jovian


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.


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


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


2 km

Near Earth Asteroids

Gaspra

Eros


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.


•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:


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.


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.


11-Year Solar Cycle


Fig. 8-13, p. 157

11-Year Solar Cycle


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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


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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So the Sun’s surface looks like boiling oatmeal or soup


Sunspots and the Sun’s surface can change very quickly - this movie covers half an hour.

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Sunspot-Associated Solar Events

Solar Flare - when a magnetic loop breaks, it releases matter and energy into space

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Coronal rain as cooled material falls back to the surface

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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.


Mercury, Mariner 10 photo.

Large valley at bottom is 4

miles wide and 60 miles

long.

It leads into crater 50 miles

in diameter.


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.


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


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.


Mercury Transit of the Sun Movie


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


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


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.


Venus

Cloud covered, thick atmosphere - carbon dioxide - greenhouse affect - surface temperature near 900ºF - rains sulfuric acid


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


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.


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


- 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.


Venus Transit of the Sun

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