Celestial Tour: Impact Craters—Footprints in Time

Produced by the Space Telescope Science Institute's Office of Public Outreach in collaboration with NASA’s Universe of Learning partners: Caltech/IPAC, Center for Astrophysics | Harvard & Smithsonian, NASA Jet Propulsion Laboratory, and Sonoma State University

All images courtesy of NASA except:

(SPEECH) 

 [NO SPEECH] 

[MUSIC - COR BOLTEN AND PAUL PACK, "FLOATING AROUND"] 

(DESCRIPTION) 
 Title text, Impact Craters: Footprints of Time. 

Bright Moon against starry black sky. 

Text, When you gaze at the Moon, where does your mind wander? 

Do you have thoughts of beauty, romance, and wonder? Or of violence and destruction? 

Closer view of Moon covered with crater holes of various sizes. 

The Moon may seem beautiful and peaceful, but it bears the scars of the solar system's rowdy history. 

Its surface is covered with impact craters, excavated by objects slamming into the Moon at reckless speeds. 

But the Moon isn't the only one that's been beaten up. 

Moon with an orange glow, small deep craters. 

Evidence of this cosmic carnage disfigures nearly every solid surface in the solar system. 

Four views of Moon which show various craters, small and large, some deep and craggy, and some smoothed over. 

In fact, impact craters are the solar system's most common geologic feature. 

Blue Earth from Moon's grey surface. 

Text, Earth is the Moon's celestial neighbor. 

Why has it been spared the mutilation of impact craters? 

Earth against black background, atmosphere over continents. 

Actually, Earth has not escaped the assault of impacts. 

It just hides its scars well. 

A low plains area flooded with muddy water, a stretch of street broken off. 

Erosion, volcanism, tectonic activity, and other forces conspire to wipe away craters. 

Bright red lava cover rocks near a shoreline, a straight large crack in the ground, an area on a hill where land has sunk in. 

Earth's atmosphere also acts as a protective blanket, shielding us from some impacts. 

Small would-be impactors burn up as they pass through Earth's atmosphere. 

Text, Animation of a meteor burning up in atmosphere. 

Animation shows glowing ball shoot across blue sky followed by fiery tail, ball and tail then wither away. 

Small streak of light flies by among bright stars. 

The smallest debris produce meteors, or quote end quote shooting stars, that delight skywatchers. 

Three shots of shooting stars, bright streaks in night sky. 

The atmosphere also slows down many larger objects, moderating their destructiveness. 

The Moon's grey surface with crater impact holes. 

Text, The Moon has no such defense. 

Every piece of space debris it encounters leaves a mark on the lunar surface. 

And these craters do not go away easily. 

The only force that erases craters on the Moon are impacts, which make new craters. 

Text, What if Earth had kept its craters as our Moon has? 

What would our planet look like? 

We have an idea... 

Continent of Africa on Earth with several small and large round impact craters. 

South America with crater holes. 

Text, Because Earth resides in the same solar neighborhood as the Moon, it must have experienced the same history of bombardment. 

But Earth is bigger than the Moon and has more gravity to pull things in, so more asteroids and comets would have hit our planet. 

Map shows all continents. 

Not all impact craters have disappeared from Earth's surface though. 

Scientists have identified more than 150 impact craters on Earth. 

Orange dots appear on map, spread out across all continents. 

Text, Many are hidden, disguised, or grown over. 

Map highlights orange dot in Central Asia, Kara Kul. 

Orange dot in Northern Africa, Kebira 

In Brazil, Serra da Cangalha 

In North-Central Africa, Aorounga 

Text, But there are a few well-preserved young craters that stick out like sore thumbs. 

Map highlights orange dot in Australia, Wolfe Creek. 

In Western United States, Barringer. 

In East Africa, Tenoumer. 

Large crater hole surrounded by desert land. Text, Barringer Crater, Arizona. This crater in northern Arizona formed 50,000 years ago when a 150-foot-wide asteroid of iron and nickel slammed into the desert floor at 40,000 miles per hour. 

Text, Animation of impact. 

Animation shows black rock as it flies through space toward Earth. Once it enters Earth's atmosphere, it glows bright yellow and slams into desert ground, creating large yellow ball of fire. 

Text, When it hit, most of the space rock instantly melted or vaporized, along with some of the Earth rock. 

Rock and debris were blasted into the air and rained down around the crater, with some chunks landing miles away. 

Impact simulation using projectile fired into sand. 

Simulation shows object dropped onto red sand, sand flies up and out in a cone shape. 

Another simulation shows object which plunges into Earth's layers, The deeper the object goes the wider debris flies. 

Text, At the impact site, a shock wave squeezed the rock and pushed it aside, carving a hole three-quarters of a mile wide and 700 feet deep. 

Rock around the edge of the crater was pushed upward, forming a rim that today rises 100 to 200 feet above the surrounding terrain. 

Crater impact hole in middle of reddish-brown desert land, A shadow is partially cast onto walls of impact hole. 

Text, Small impact craters like Arizona's Barringer crater, also known as Meteor Crater, form with a simple bowl shape. Thousands of years of weather have deformed the Arizona crater. 

But unaltered quote end quote simple craters abound on other worlds. 

Moltke Crater, Moon. Side by side views of Barringer and Moltke, Moltke with a smoother edge. 

Daedalus Crater, Moon. One large rough impact surrounded by several smaller impacts. Text, Larger craters, excavated by larger impactors, are more complex. The sides of a big crater slump inward, often forming an uneven edge and terraces along the crater wall. 

Rock that was pushed outward during the impact can rebound and converge at the bottom of the crater to form a central peak, plateau, or ring. 

A bumpy area of rocks at bottom of crater is highlighted. 

Text, Gosses Bluff, Australia. These features, along with clues in the rocks, help us identify hidden or eroded impact craters on Earth and distinguish them from volcanic craters. 

Australia's Gosses Bluff impact crater stands out thanks to its central peak, which today takes the shape of a 3-mile-wide ring of hills. 

View of Gosses Bluff from above, Outline of impact crater is highlighted with ring shape. 

Text, Hints of the eroded outer rim appear in images from space as a larger circular feature. 

Circular shape which surrounds small ring of rocky crater impact is highlighted. 

Water in a ring shape. 

Text, Manicouagan Crater, Canada. A distinctive watery ring traces the shape of Canada's Manicouagan impact crater. 

Soft sediments that had slumped inward from the crater's rim were later carved out by a glacier, forming the ring-shaped valley. 

A central uplift forms a circular island in the center of the reservoir. 

Colorized elevation map highlights purple oval shape in center of lake. 

Text, The island's Mount Babel is the crater's central peak. 

Burnt orange land with impact marks in a spiral shape. 

Text, Aorounga Crater, Chad. A crater's size and shape can also tell us about the object that made the crater. 

Low-speed impacts, like throwing a rock into mud or sand, produce depressions that are only slightly bigger than the impactor. 

Crater formed by a rock thrown into sand. Small white rock in middle of hole in sand. 

But most meteor impacts are high-speed events, producing craters on Earth that are roughly 10 to 20 times bigger than the impactor. 

The comet or asteroid that created the 10.5-mile-wide Aorounga crater was probably less than a mile wide. 

Two lakes beside each other, one smaller and one larger, the larger with a ring of elevation in middle. 

Text, Clearwater Lakes, Canada. The Clearwater Lakes in Canada occupy a pair of craters carved simultaneously by a pair of asteroids of different sizes. 

In this case, the bigger partner created the larger crater, which has a central uplift that sticks out of the water as a ring of islands. 

Two crater impressions side by side in a figure eight shape. 

Text, Double craters, like this pair on Mars, are common on other worlds. 

In black and white, a straight line of crater impressions. 

Davy Crater Chain, Moon. 

Outline of each crater impression is highlighted. Text, Crater chains tell tales of tortured space rocks torn into many pieces. 

Several crater chains are punched into the frozen surfaces of Jupiter's moons, Calisto and Ganymede. 

Close-up of Ganymede. Straight line of depressions in surface. 

This evidence suggests that Jupiter has a habit of breaking comets apart with its enormous gravity. 

In fact, astronomers discovered one such cometary victim in 1993. 

Comet Shoemaker-Levy 9 had broken into at least 21 pieces after passing too close to Jupiter the previous year. 

In pitch dark, a line of several holes lights up. 

Text, Instead of slamming into one of Jupiter's moons though, this broken-up comet targeted Jupiter. 

Planet Jupiter with stripes of yellow brown and white against the blackness of space. 

In July 1994, the fragments of Comet Shoemaker-Levy 9 hit Jupiter one by one. 

With no solid surface to slam into, the comet fragments couldn't make craters. 

Instead, they generated gigantic fireballs and left a series of Earth-sized black marks in Jupiter's atmosphere that endured for months. 

Five dark marks which form a streak are highlighted. 

Planet shines bright, small rocks along a ring. 

Jupiter's gravitational influence on comets and asteroids might have helped protect Earth throughout history. 

Without Jupiter's ability to pull these celestial vagabonds away from our planet, Earth might have more impact craters than it does. 

Jupiter with a large red spot on surface. 

Text, However, Jupiter's moons have not been afforded the same protection. 

Two spherical bodies, one with a purple tint and the other dark with glowing spots. 

An intense history of bombardment is written on the surfaces of Calisto and Ganymede. 

Many craters pockmark their surfaces. Close-up of Ganymede, Close-up of Calisto. 

Black and white image of Ganymede shows a long streak on its surface, Image of Callisto has crater depressions of various sizes. 

Two large moons. Text, Europa, I.o. -- Curiously, Jupiter's two other large moons have considerably few craters. 

On volcanic I.o., lava and other deposits obliterate impact craters almost as soon as they form. This active resurfacing makes I.o.'s surface extremely quote end quote young. 

The fracturing and movement of ice on Europa modify its surface, but not as quickly as volcanism does on I.o. 

Europa. Blue planetary body covered with brown spots and lines. 

Text, Craters can still be found on Europa's relatively young surface. 

Pwyll Crater. One bright area on Europa with small dark spot in center. 

Text, Older surfaces have more craters because they've had more time to collect them. 

From the numerous craters on Mercury, we know its surface is ancient. 

Silver surface of Mercury with several areas of impact. 

Venus has far fewer craters than Mercury does. 

Its thick atmosphere is partially responsible because many impactors burn up in the atmosphere before they reach the surface. 

But the thousand or so craters on Venus identified by radar explorations are all young, with well-defined features that show little erosion. 

Text, Impact craters on Venus. Black and white image shows three round depressions alongside scratch-like marks. 

The scarcity of craters and the youthfulness of those that do exist suggest that the Venusian surface is not very old. 

The planet was probably resurfaced by its many volcanoes relatively recently in its history. 

Text on image, Computer-generated image of a Venusian volcano. Image shows rocky volcano in orange and yellow tint. 

Round blue Earth with patches of land. 

Text, Earth's surface is even younger than that of Venus. 

Among Earth's continents though, Australia's surface is relatively old. 

It has preserved more impact craters than most other places on our planet. 

Images of various Australian crater impacts appear. Wolfe Creek Crater, Shoemaker Crater, Acraman Crater, Spider Crater, Gosses Bluff Crater, Goat Paddock Crater. 

Glowing orange planetary body against blackness of space. 

Text, Mars has a split personality, seeming almost to be two planets in one. 

Craters blanket the highlands that dominate the Martian southern hemisphere, while the northern lowlands have relatively few craters. 

Image shows brownish-red close-up view of Mar's surface. 

Text on image, Mercator projection of Martian surface. Why the northern plains of Mars are younger than the southern highlands is a mystery. 

Some speculate that a vast ocean once covered the northern plains. Text on image, Elevation map of Mars, blue is low elevation. Computer-generated image shows expanse of blue at the top of Mars. 

Like the heavily cratered highlands of Mars and Mercury, the Moon's battered highlands preserve billions of years of impact history. 

In contrast, the dark plains, or quote end quote Maria, are younger regions where volcanic flows wiped away craters that came before. 

Person in white space suit with NASA emblem on arm, Four rock-like masses. Text, Lunar samples returned by the Apollo astronauts, and meteorites blasted from other parts of the Moon reveal something interesting. 

Nearly all of the Moon's giant impact craters, and most of the smaller ones, are about 3.9 billion years old. 

Most of the Moon's craters must have formed during a swarm of impacts 3.9 billion years ago. 

Earth must have been under attack at the same time. 

But the scars have long since faded away. 

However, this cataclysmic event might explain why we can't find evidence of life on Earth more than 3.85 billion years old. 

Mexico peninsula from space. 

Text, Some craters on Earth provide other clues about the evolution of life on our planet. 

A large crater straddling the tip of Mexico's Yucatan Peninsula suggests an impact doomed the dinosaurs. 

Drawing, dinosaur birds fly through air as a large ball streaks from the sky and creates an upward wave. 

The crater formed 65 million years ago, the same time that the dinosaurs and most other creatures and plants living on Earth at the time were exterminated. 

Mexico peninsula shaded green, with darker green around edges, Text on image, Yucatan relief map. 

Submerged under water and buried under land, the 110-mile-wide Chicxulub crater reveals itself in gravitational studies and in a ring of troughs and groundwater springs. 

Ring-shaped area of peninsula is highlighted. 

Image shows large mass slam into Earth, creating a wave that shoots upward and ripples that roll out. 

Text, Could a future impact similarly end humankind's reign on Earth? 

Comet Shoemaker-Levy 9's collision with Jupiter proved that catastrophic impacts still happen. 

Dome-shaped building with a roof that slides left and right, Text above door, Samuel Oschin Telescope. 

Astronomers are on the lookout for large objects that could meander a little too close for comfort. 

But it's hard to find everything, especially smaller threats. 

A depression in the earth filled with muddy water and surrounded by caution tape. 

In September 2007, Peruvian villagers saw a fireball race across the afternoon sky before hearing a loud bang and feeling tremors. 

They soon discovered a crater about 40 feet wide partially filled with subsurface water. 

Group of people stand near the depression's edge, one holds a camera up. 

Photo shows five grey rocks on blue mat. Text, When fragments of the rocky impactor were found, tests proved that it was extraterrestrial. 

Earth's newest impact crater was made by a rather small space rock. 

Large crater impression in desert land. 

Text, When will the next big one hit? 

We don't know. 

But the solar system's countless craters prove that impacts come with the territory. 

It's just a matter of time until Earth is hit again. 

Credits. Special thanks to Dan Durda and Clark Chapman, Southwest Research Institute. Produced by the Space Telescope Science Institute, Office of Public Outreach. 

All images courtesy of NASA except Full Moon image, Bill Arnett, Gibbous Moon image, NASA slash J.P.L., Mars mosaic featuring Schiaparelli crater, NASA slash J.P.L, U.S.G.S., image processing by Jody Swann, Tammy Becker, Alfred McEwen. 

Music courtesy of Associated Production Music. Written by Vanessa Thomas. Designed by Krista Wildt and John Godfrey. 

To view more pictures of impact craters on Earth and throughout the solar system, visit visible Earth dot NASA dot gov, Photo Journal dot j.p.l. dot NASA dot gov slash index dot html. 

The Space Telescope Science Institute is operated by the Association of Universities for Research in Astronomy, Inc for NASA, under contract with NASA's Goddard Space Flight Center, Greenbelt Maryland.