Unit 2
Chapter 8
The Planet Mercury
Elongation of Mercury
The eccentricity of Mercury’s orbit allows to see it father from the sun sometimes.
Mercury as Seen from Earth
 Synchronous rotation 1:1
Our moon
All the large moons
 Mercury’s rotation 3:2
3 rotations to 2 revolutions
Comparison of Earth’s interior to that of Mercury
Mercury’s Magnetosphere
Mariner 10 Trajectory
Composite of the Mariner views of Mercury
Craters and Planes (?)
Scarp (Cliff)
Edge of Caloris Basin
The spacecraft MESSENGER in orbit around Mercury. Notice the shade designed to protect the
MESSENGER from the brilliant sunshine.
From its polar orbit MESSENGER is able to see the entire surface
Messenger may have found extinct volcanos
Some unusual features to be studied
Some features become more evident at different lighting
Some very strange terrain
Mercury & Dr. Einstein
 Curvature of light around a large mass
 Orbital Precession
Chapter 9
Beautiful Venus
Atmosphere on Venus and on Earth
Gasses from a Volcano on Earth
Evidence of Eruption on Venus
Greenhouse Effect
Greenhouse Effect on Venus
Venera Mission
Venera Lander
Visible images from Venus by Venera
Magellan Spacecrafrt
 Map of Venus by Magellan spacecraft
 More of Venus’s Sphere by Magellan
 Computer reconstruction
o One Face of Venus
o A volcanic crater
o Craters and lava flow
o A large volcano
o A lava field and an impact crater
o These are unusual ‘pancake’ lava flows
o Lava fields around several craters
o Lava field
Chapter 10
The Planet Mars
Early observers did not have photography and had to draw what they saw.
In the years from about 1890 to about 1910 Percival Lowell became enamored with the observations of
Schiapereli. Canali for him were canals. He believed in canals and the intelligent life forms needed to dig
them. He spent many years talking and writing about them.
Mars’ Properties
Dist from Sun=1.5+ or app. 1.6 AU (T-B)
Year = 1.88 Earth years
Sol (Mars day) = 24h 37 m
Axis inclination = 25+ deg
Dia = .533 Earth dia
Surface gravity = .38 Earth
Surface Temp = -140 deg C to 20 deg C
Comparison of the Atmospheres
of the Terrestrial Planets
Earth
Venus
N2
0.79
2
O2
0.20
< 0.001
Ar
0.01
0.005
CO2
0.0003
64
H2O
~ 0.02
~ 0.01
Total 1.00
90
Mars
3 x 10-4
0-7
2 x 10-4
0.009
~10-6
0.01
The interior of Mars has not been studied by seismic waves. Surface clues indicate that the interior as
shown is likely correct. Over time the interior has cooled and vulcanism has ceased.
The surface of Mars has been imaged and mapped at least as thoroughly as the Earth.
 No liquid water has been found although there is much evidence that there has been standing
and flowing water in the past.
 The Southern Hemisphere is somewhat higher in elevation and covered with craters appearing
much like The Moon.
 The lower Northern Hemisphere is much more earthlike. It has giant volcanoes and canyons.
 A topographical map of the Tharsis Rise shows giant volcanoes, a giant canyon, apparent dry
river beds and a dry ocean
 If Mount Olympus a giant volcano, were on Earth is would stand three times higher than Mount
Everest and would completely cover the State of Utah
 An image of a dry watershed
 An image of a dry river bed
 A topographic map of the mouth of a dry river entering a dry ocean
 A canyon land region called South Candor
 A panoramic view of a rocky rolling valley
The North Polar Cap seems to have water ice with much dry ice covering it. There is much information
in the apparent layers that have accumulated over eons.
Today
 Cold
 Dry
Anciently
 Warm
 Wet
Robots to Mars
 From the Mariner Probes in the early ‘60s to the extremely successful Curiosity Lander this year,
mankind has sent a variety of robot orbiters and landers to prepare the way for a future manned
mission to the exotic Red Planet.
 Viking Program
o Two Identical Systems
o Orbiter
o Lander
o Mid 70’s
o Search for Living Life
o Chemical not biological results
o Red color is iron oxide
o A view from the Viking 2 Lander in summer and winter. The occasional frost layer only
lasts until Sun up.
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The Mars Global Surveyor took images in visible and infrared of the entire planet every day for
one full Mars year. Among its discoveries was this of recent gullies
One of the trickiest parts of the Mars Exploration is actually getting the rovers to Mars in
working condition.Imagine trying to drop a sophisticated robot about 11-12 stories without
breaking it (or even dropping an ordinary DVD player)
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When the Pathfinder lander and the Sojourner rover arrived in 1997 they began the era of
faster, cheaper spacecraft. Sojourner can be seen examining the rock “Yogi”
The next generation Rovers were two, called the Spirit and Opportunity.
o Spirit’s landing place was similar to the Vikings’; this is a 360° panoramic view
o Spirit View west from the Columbia Hills
o This is a view from Opportunity down into Victoria Crater. It spent nearly a full Earth
year finding the best way down into the crater and this is it.
o Opportunity has now left Victoria Crater in search of another crater to explore.
Here we see the robotic arm at work. It cleans the rock, examines it then analyses it for
elements.
o This is the Instrument complex with the RAT, imager and spectrograph
Discoveries
– Layering as if by water deposit
– Spherical pebbles such as in a stream
– Rust (color) same as the red iron oxide as in Southern Utah
Adventures
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– Stuck in sand dune
– Covered by dust in a storm
– Uncovered by a whirl wind
– Lived through a long Mars winter
Are still going strong (four times as long as expected
The Pheonix scooped up icy dirt that gave off liquid water when warmed.
Each Rover has become more become bigger and more complex as we have learned how to build them
and use them
Mars Pathfinder (Success)
Mars Global Surveyor (Success)
Actively taking pictures and gathering data
Mars Polar Lander (Failed)
Mars Atmosphere Observer (Failed)
2001 Mars Odyssey
-arrived Oct 24. 2001
-gathering data today
Landers (Future)
-biology and geology Laboratory
-to gather rocks and return them to Earth
Moons of Mars
Phobos (Fear) is the larger of the two.
They are both tiny and badly scarred by impacts but Phobos looks like it was nearly shattered.
The Chinese are planning to send a robot to pick up dirt and rock samples from Diemos (Terror)
to return them to Earth
JUPITER – Lord of the Planets
To discuss the Jovian Planets we must first talk about The Voyager program. The mission of Voyager 1 &
2 is to visit the Outer Solar System and beyond.
This is the Voyager 2 velocity profile showing the velocity flips at each planet. Our booster was barely
able to reach Jupiter without gravity assist. With gravity assist we have left the Solar System
Jupiter can be imaged well from Earth, even with a small telescope
Here: Jupiter with its Galilean moons
Properties
• Mass: More than twice as much as all other planets put together.
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Radius: 11.2 times Earth’s radius
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Density: Only 1.3 x the density of water – cannot be rocky or metallic as terrestrial planets are
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Rotation Rate: problematic, as Jupiter has no solid surface; different parts of atmosphere rotate
at different rates. The solution came from magnetic field, whose rotation period is 9 hr, 55 min
Early images of Jupiter showed the Great Red Spot and Stripes. As our instruments improved many
more details emerged. The spot became a giant storm and stripes became bands of rising and falling
gases.
Great Red Spot
 has existed for at least 300 years, possibly much longer.
 It seems to be and inverted storm dipping to the planet rather that rising above it.
 The colors have changed over the years from brick red to light brown.
 The size has changed from 3x the size of the Earth to just over 2x.
The Stripes
 Zones are rising warmer gasses from the interior, and are higher than belts.
 The Belts are cooler falling gases returning to be re-warmed.
 The many storms seen in the belts are due to turbulence caused by differential rotation in the
atmosphere
 No solid surface
 The lowest level of the atmosphere is the stripes.
 Telescopes can not see through it.
 Measurements by Galileo probe show high wind speeds even at great depth – probably due to
heating from inside the planet, not from Sun
 Lightning-like flashes have been seen; also
 longer-lived rotating storms One example: Brown Oval, really a large gap in clouds
Jupiter’s Interior
No direct information is available about Jupiter’s interior, but its main components, hydrogen and
helium, are quite well understood. The central portion is a rocky core.
Jupiter’s Magnetic Field
 Jupiter is surrounded by belts of charged particles, much like the Van Allen belts but vastly
larger Magnetosphere is 30 million km across
 Intrinsic field strength is 20,000 times that of Earth
 The tail of the magnetosphere can extend beyond the orbit of Saturn
Moons of Jupiter
 More than 60 moons have now been found orbiting Jupiter, but most are very small.
 The four largest are the Galilean moons, so called because they were first observed by Galileo:
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They were named for the mythical companions of the great God Jupiter; Io, Europa, Ganymede,
Callisto. Each is unique. Each is interesting.
Galilean moons have similarities to terrestrial planets; orbits have low eccentricity, largest is
somewhat larger than Mercury, and density decreases as distance from Jupiter increases
The Small moons move in mostly eccentric orbits far from Jupiter. Here, the orbits of the
Galilean moons can be seen in the center near the planet.
The Galileo Probe has given us a very good feel for their interiors
Io
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Io is the most dense of Jupiter’s moons, and the most geologically active object in the solar
system.
It has many active volcanoes, some quite large.
It can change surface features in a few weeks
There are no impact craters; they fill in too fast – Io has the youngest surface of any solar system
object.
The many colors come from sulfur at different temperatures
The vulcanism on Io is due to tidal forces. Io is very close to Jupiter in a rather eccentric orbit,
and also experiences gravitational forces from Europa and Ganymede. The tidal forces are huge
and provide the energy for the Volcanoes.
This image of Io is the discovery image for the volcanos
Volcanic eruptions also eject charged particles; these interact with Jupiter’s magnetosphere and
form a plasma torus
Europa
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The moon Europa has no impact craters,
The surface is water ice, likely with liquid water below
Tidal forces likely heat the interior enough to keep a layer of water liquid
Tidal forces stress and crack the ice allowing liquid water to flow out keeping surface glass
smooth
Ganymede and Calisto
 Ganymede is the largest moon in the solar system – larger than the planet Mercury
 Impact history similar to Earth’s Moon, but water ice and dirt instead of lunar rock
 Surface areas of Ganymede once thought to be cratered and flat turn out to have structures.
These may be due to a form of plate tectonics
 Calisto is similar to Ganymede except there is no evidence of plate activity.
Jupiter’s Ring
 One of the big surprises of the Voyager program was the discovery of a ring around Jupiter. This
is the discovery image.
 Four moonlets are associated with Jupiter’s ring. The two tiniest, Metis and Adastria are
embedded in the ring and seem to be shattering to feed the ring. The other two, Amalthea and
Thebe, are “Shepherd” moons.
 Images made by the Galileo spacecraft show more details.
 Especially evident are the sharp outer edge and the diffuse inner edge of the ring and the detail
within the rings are explained by the presence of the moonlets.
Chapter 12
Saturn
Properties
 Mass: 5.7 × 1026 kg
 Radius: 60,000 km
 Density: 700 kg/m3 – less than water!
 Rotation: rapid and differential, enough to flatten Saturn considerably
 Rings very prominent; wide but extremely thin
Atmosphere
 Saturn’s atmosphere is similar to Jupiter’s, except the pressure is lower
 Three cloud layers
 Cloud layers and the haze layer are deeper than Jupiter’s and more dense
 Like Jupiter Saturn has stripes and differential rotation. They are much more subdued and are
rarely seen through Saturn’s haze and cloud cover.
 Jupiter-style “spots” are rare on Saturn. They don’t form as often and quickly dissipate if they do
Saturn’s Interior
 Similar to J. but with a less thick layer of liquid metallic hydrogen.
 Saturn also has a strong magnetic field, but only about 5% as strong as Jupiter’s.
 It has Van Allen Belts where charged particles from the Solar Wind are trapped and they
produce aurorae.
Rings
 Historically , only one ring was seen. As our instruments got better we were able to distinguish
more detail.
 The rings are labeled by letter in the order of their discovery.
 Ring particles range in size from fractions of a millimeter to tens of meters
 They are made of dust and rock covered with water ice
 Why rings? They are too close to planet for moon to form – tidal forces would tear it apart
 Closest distance that a moon could survive is called the Roche limit; planetary ring systems are
all inside this limit
 The Voyagers showed Saturn’s rings to be much more complex than originally thought
 The Cassini division turns out not to be completely empty. The gap seems to be caused by an
orbital resonance with other ring particles and Saturn’s innermost moon
 Voyager also found radial “spokes” that formed and then dissipated; this probably happens
frequently
 It was expected that sharp edges and divisions in the Rings would be caused by ‘Shepherd
Moons’. It was not so. The other edges and divisions in the rings now seem to be the result of
resonance.
 However, a “Shepherd” moon does define the outer edge of the [A] ring through gravitational
interactions.
 Strangest ring is the F ring . It appears to have braids and kinks. F ring’s oddities are probably
caused by’ two ‘Shepherd Moons’, one of which can be seen here.
 Details of ring formation are unknown. It is thought that rings are too active to have lasted since
the birth of the solar system Either they must be continually replenished, or they are the result
of a catastrophic events
 Saturn’s many moons appear to be made of water ice or carbon based rocks covered with ice
Saturn’s Moons
 Besides the small moons, Saturn has: Six medium-sized moons (Mimas, Enceladus, Tethys,
Dione, Rhea, and Iapetus)
 One large moon (Titan) which is almost as large as Ganymede
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Titan has an atmosphere thicker and denser than Earth’s.
It is made mostly of nitrogen and argon but it also has some very interesting chemistry
in its upper atmosphere.
o The surface can NOT be seen through the haze. This image was taken by Voyager I
from only 4000 km away
o After Voyager there was much desire to learn more about Titan and the Saturn system.
The Cassini Orbiter and the Huygens Probe were sent to make that Study.
o The Huygens Probe analyzed the atmosphere of Titan as it descended.
o Many trace chemicals mostly derived from methane make the atmosphere chemically
complex
o During its descent Huygens imaged the surface below. Here we see a shore line of a lake
and a watershed feature that looks like a river system.
o The liquid is not water but liquid methane. The light colored patches seem to be
methane frost or snow,
o On 9/16/05 Huygens landed on a slushy area dotted with boulders composed of water
ice, under orange clouds composed of complex hydrocarbons
Medium Size Moons
o Mimas, Enceladus, Tethys, Dione, and Rhea all orbit between 3 and 9 planetary radii
from Saturn, and
o all are tidally locked – this means they have “leading” and “trailing” surfaces.
o Rhea, the largest, has a highly reflective, heavily cratered surface. The wispy features
are on the trailing side but not the leading; their origin is not yet fully understood
o Dione and Tethys are similar, having icy, heavily cratered surfaces
o Mimas is the closest moon to Saturn, and has a crater covering one-third of its surface,
the result of an impact that must have almost destroyed the moon
o Iapetus orbits 59 radii away, and is also tidally locked. Iapetus is two-faced: its leading
side is very dark (reflects 3% of incoming light), while its trailing side is bright (reflects
50% of incoming light).
o Enceladus orbits close to Mimas, but is very shiny, indicating a surface covered with ice
crystals. This moon possesses a region of terrain near its south pole that is dramatically
devoid of impact sites. Scientists suspected it is geologically active. The discovery in
2009 of material jetting from the pole and creating a great plume of icy particles
confirmed these suspicions. The Cassini continues to study it because it seems to have
liquid water inside
o Hyperion, orbiting between Titan and Iapetus, is so affected by their gravitational fields
that its orbital speed and the orientation of its axis are constantly changing, in a neverrepeating pattern.
Chapter 12
Uranus and Neptune
Uranus
Uranus was discovered in 1781 by Herschel; first planet to be discovered in recorded history.
William Herschel
Born in Germany he anglicized his name when he came to England with the Hanover Kings. He was a
musician from a musical family.
As an amateur Astronomer he looked at the sky with telescopes he built himself. Among other things in
the sky he found what he thought was a comet. After further study he realized he had found a planet, the
first in recorded history. Because of the fame of that discovery he became the Court Astronomer to King
George III.
Orbit
Most of the planets have their axes slightly tipped with respect to the plane of their orbits. Uranus is
unusual in that it is tipped more than 90 degrees. As a result the rotation of the planet is retrograde.
Voyager Visit
During the Voyager encounter in l985 we only saw a featureless face as the Sun shone on the pole of the
planet. Several years later When the HST looked at it we could see stripes and storms.
As the Uranus axis of rotation lies almost in the plane of its orbit , the seasonal variations are extreme.
Rings
Rings around Uranus were discovered from Earth and we saw 3 narrow rings and 2 broad rings. The
Voyager saw a system of hundreds of ringlets.
Moons
The moon Miranda has large chunks of rock and large fields of ice. It looks like it has been shattered in the
near past and is now pulling itself back together. All of the parts have not yet found their final places.
Neptune
Neptune was discovered in 1846, after analysis of Uranus’s orbit indicated its presence. Any new planet
could not fit the Titus Bode Rule, hence the English and French Astronomical Societies ruled out another
Planet. However, an Englishman, Adams , and a Frenchman, Le Verrier , gave their calculations to a
German, John Gottfried, who found Neptune immediately
Voyager found a Great Dark Spot. It was determined to be a large storm. There were other smaller
storms. Of special interest were the fast moving white clouds, demonstrating that the winds were the
fastest in the Solar System.
Rings
The rings of Neptune were discovered from the Earth but they looked like arcs. Voyager found complete
rings but some of them were ’lumpy’. Neptune has five rings, three narrow and two broad. Our ring
theories have been badly stretched by these rings. They do NOT seem to obey any preconceived rules.
Moons
Two moons, Triton and Nerid, were discovered from the Earth. Eleven more were found by Voyager.
The moon of most interest is Triton. Triton is unique in many ways. It’s temperature is the lowest of any
body in the Solar System that we have visited, 32 deg. K. It has an atmosphere, high winds, active geysers
and evidence of plate tectonics, frozen lakes and water volcanoes. Nitrogen geysers have been observed
on Triton, contributing to the surface features
Uranus and Neptune
Properties:
Uranus
Mass 14.5 × E
Radius 4.0 × E
Neptune
17.1 × E
3.9 × E
Density 1.3 x H2O 1.6 x H2O
Magnetic fields
Uranus and Neptune both have substantial magnetic fields, but at a large angle to their rotation axes.
The rectangle within each planet shows a bar magnet that would produce a similar field. Note that both
Uranus’s and Neptune’s are significantly off center.
Chapter 14
Debris in the Solar System
Rocks are Asteroids. Dirty Snowballs are Comet Nuclei
Asteroids
Asteroids are quite small, and most have eccentric orbits in the asteroid belt between
Mars and Jupiter.
Two other families are Apollo Asteroids and Trojan Asteroids
The Titus-Bode Rule predicted that there was a Planet at 2.8 AU from the Sun. It was tentatively named Aster.
When the field of rocks instead of a Planet was discovered at that distance the tiny objects were called Asteroids.
Now all rocks in space are called Asteroids.
Motions of Asteroids
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There are several motions of the Asteroids in the Solar System that have been identified:
 Each in own elliptical orbit
 Crossing orbits
 Dissipation of Belt
 Captures by Jupiter
 Captures by Mars
 Captures by Earth
 Most finally fall into the Sun
Belt Asteroids
Belt Asteroids are classified in types:
C-type: carbonaceous
S-type: silicate
M-type: metallic; iron and nickel
The three largest Belt Asteroids are
Ceres (940 km), now a Dwarf Planet
Pallas (580 km)
and Vesta (540 km)
Shown is the Asteroid Vesta, 3rd largest asteroid but 1st stop of the mission of the Spacecraft
Dawn. In order to obtain this image of Vesta against the background stars and still show its true
size , they over exposed one frame to show the sky which is way over exposed Vesta. Then they
imaged just Vesta and superimpose it. The result is the tiny white dot in the middle of the black
dot.
Belt Asteroids are rocky; about 200,000 have been identified so far.
Two small S-type asteroids, Gaspra and Ida, were visited by the Galileo probe. Gaspra (left) is in false
color; it is really gray. Note that Ida (right) has a small moon, Dactyl.
Near Earth Asteroids
A 2nd family of asteroids have orbits so eccentric that they cross Earth’s orbital plane. They are called
Apollo Asteroids, or Near Earth Asteroids, and raise the concern of a possible collision. These are survivors
left over from creation and were not picked up during the Early Intense Bombardment.
Over 2600 such asteroids have been discovered so far, of which about 600 have been designated as
potentially hazardous, due to their size, over one mile.
The NEAR –Shoemaker spacecraft visited the C-type asteroid Mathilde, on its way to its main target, Eros.
Mathilde, like many other asteroids, has a very low density, and is probably not solid, but rather like a
compact gravel pile.
Eros does seem to be solid. It is covered with craters, as expected, but it also has free rocks sitting on it,
not expected
The NEAR program presented an interesting challenge. Not only did we need to go to a new orbit but we
had to go to a new orbital plane. The maneuver was successful and we also landed on the Asteroid
Trojan Asteroids
The Trojan Asteroid Family is located at the LaGrangian points for Jupiter at L4 and L5
Comets
Comet Nuclei are described as “Dirty Snowballs”. They reside in the Oort Cloud which is a spherical cloud
surrounding the Sun. It came from the Tsunami caused when the Sun went nuclear. The nuclei are
Irregular shaped objects of ices laced with dust and rock
The spherical Oort Cloud of Comet Nuclei is very large but not densely populated. The trajectories go in
every direction.
The Kuiper Belt Objects are more in the plane of the planets and are closer to the orbit of Neptune. They
are roughly the same composition as the Comet Nuclei but many are much larger
The Kuiper Belt begins around 40 AU from the Sun but continues out until it finally blends in with the Oort
Cloud. The KBO orbits are irregular but move roughly in the prograde direction.
Some of these Objects are quite large, larger even than Pluto.
Comets have a very small Nucleus, a Coma of gas and dust that is the most visible part that can be very
large, a Hydrogen Envelope, a Dust Tail, and an Ion Tail. The Nucleus and the Hydrogen Envelope are not
normally seen.
Comets have very eccentric orbits. The comet’s tail always points away from the sun, due to the sunshine
and the solar wind. The ion tail is straighter than the dust tail.
Long-period comets; over 2000 years
Short-period comets; less common, and have periods of less than 200 years.
The theory of Jupiter adjusting the orbit of an incoming comet would be much less viable if we had not
seen Jupiter capture an incoming comet.
Halley’s comet is one of the most famous short period comets; it has a period of 76 years and has been
observed since antiquity. Its most recent visit, in 1986, was not spectacular. Halley’s comet has a short
period, just 76 years. Its orbit is not in the plane of the solar system so as it revolves around the Sun it
passes through the plane of the Earth’s orbit at a spot closer to the Sun than the Earth. Some passes it is
closer to the Earth than on other passes. This close up image was made by a Japanese spacecraft in 1986.
It shows how the gas Coma is developed from the Sun side of the Nucleus as it rotates on its axis.
Meteor showers
Occasionally the Earth passes through a debris cloud left behind in the path of Comets. The interaction of
the Atmosphere with these tiny particles looks like a Shower of Meteors. Meteor Showers repeat every
year as the Earth passes through that part of the sky.
Meteorites
Meteorites are defined as any particle from space that survives to reach the surface. Most matter from
space falls in slowly and does not make a crater. These come mostly from the asteroid belt.
Meteorites are mostly very old – 4.4 to 4.6 billion years – and carry valuable information about the early
stages of the solar system.
Most meteorites are rocky and often have a polished look from passing through the atmosphere They are
distinguishable from Earth rock by their internal structure.
A few are made of iron and can be identified by their grain structure, Iron like this can not be duplicated
on Earth
Some large objects impact the earth when their orbits intersect the Earth’s orbit. These are often larger
from the Apollo (Near Earth) asteroids and their impact velocity can be very large and their impact craters
also large.
Some large objects impact the earth when their orbits intersect the Earth’s orbit. These are often larger
from the Apollo (Near Earth) asteroids and their impact velocity can be very large and their impact craters
also large.
The event called Cretaceous-Tertiary Extinction likely resulted from a giant meteorite impact near Mexico
65 million years ago. It caused a 10 year long “Nuclear Winter” that probably killed the dinosaurs along
with 90% of the living things on Earth and from which only 25% of the species recovered. The event was
likely due to an impact of a Near Earth Asteroid