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Envisioning the end of the world.

CHESLEY BONESTELL (1888-1986) is considered by many as the father of the American astronomical painting and the greatest space artist of all time. Trained as an architectural draftsman, he went on to become a highly paid Hollywood special-effects artist, creating matte paintings for such films as Citizen Kane and The Hunchback of Notre Dame.

But he didn't really find his forte until the mid-1940s, when he combined his art with a lifelong fascination with astronomy. Bonestell's fantastical, other worldly landscapes were based on the latest scientific theories. His views of Saturn and Jupiter as seen from their satellites graced the pages of Life magazine, while his landscapes of the Moon and Mars were used in films such as The War of the Worlds. The famed astronomy popularizer Carl Sagan said of his works, "I didn't know what other worlds looked like until I saw Bonestell's paintings of the solar system."

Bonestell was prolific, producing thousands of drawings and paintings while illustrating, authoring, or coauthoring several books during his lifetime. When he was just getting his "space legs" in the late 1940s, he frequently developed illustrations for magazines like Life and Scientific American. One such commission came from Coronet magazine for its July 1947 issue. Founded in 1936, Coronet was a Reader's Digest-size monthly that was variously characterized as a family, women's, or general-interest magazine. Bonestell's article, titled "The End of the World," depicts several astronomical catastrophes that could conceivably befall Earth. And each is made more horrific by their familiar settings: places such as New York, Paris, and Chicago.

Keep in mind that Bonestell was portraying planetscapes at a time when no spacecraft had yet launched, let alone landed on the Moon, Venus, or Mars. His paintings reflect the relatively primitive state of astronomical knowledge at the time. I recommend that any reader suspend his or her disbelief long enough to be a little bit frightened by Bonestell's apocalyptic visions.

Target: Earth

Above [1], a "small" comet has just plowed into our planet, apparently somewhere around the Mediterranean Sea. Bonestell assumed a 10,000-mile (16,000-kilometer) diameter for the coma, the foggy envelope surrounding the much smaller nucleus. In a collision with Earth, the ice-and-rock nucleus, not the vacuous gas-and-dust coma, would inflict the real damage. Many astronomers in the 1940s thought that a typical cometary nucleus could be several hundred kilometers across, but today we know that the largest nuclei are no more than 50 km in diameter. So Bonestell's collision would not really be the end of the world, right?

Maybe not, but it would have devastating and long-lasting global consequences. The object that blasted a 180-km-wide crater in Mexico's Yucatan Peninsula 65 million years ago was probably only about 10 km across. Even so, it likely caused tsunamis, forest fires, and a dust veil around our planet that helped to wipe out more than half the world's animal species (including the dinosaurs).

How long will it be until another cosmic impact occurs of similar magnitude? According to interpretations of marine-fossil evidence, mass extinctions occur roughly every 60 million years, going back to more than 500 million years ago. A favorite explanation for this cycle is that the Sun passes through a massive spiral arm in the plane of our Milky Way Galaxy every 62 million years, with the extra gravity disturbing the Oort Cloud of comets surrounding the solar system. This interaction sends some of the icy bodies inward to wreak havoc. Such claims remain highly controversial, but the fact that the most recent mass extinction occurred 65 million years ago might cause the faint-hearted some unease.

Impacts and Airbursts

Below [2] is a much more limited impact event: a "meteor" has struck lower Manhattan. We are viewing the scene after the impact's initial fireball--many kilometers across--has dissipated. Now only lingering fires blaze on the periphery. The impactor would have produced an explosion that dwarfed the atomic bomb dropped on Hiroshima. Such a direct hit on one of the world's largest cities would be extremely unlikely. For one thing, Earth's surface is 71% water, making a wet landing much more probable; for another, dense population centers like Manhattan comprise only a small fraction of the land area.

But an asteroid doesn't have to hit the ground for its effects to be devastating. At bottom right [3] Paris gets flattened by the shock wave created in the atmosphere by an exploding asteroid. In the foreground the spire of Notre Dame topples while the stately apartments lining the Seine collapse like houses of cards.

Such an airburst has occurred in modern times. On June 30, 1908, an object disintegrated about 8 km above an unpopulated area near the Tunguska River in Siberia. Witnesses 150 km away reported seeing a brilliant fireball in the daytime sky and hearing a thunderous roar. The closest humans, reindeer herders 30 km from "ground zero," were blown from their tents (one of them eventually died of his injuries). More than 1,400 square km of forest were leveled by the blast (S&T: December 1998, page 68).

Researchers found no impact crater or meteorite fragments in the area despite many expeditions to the swampy, mosquito-infested taiga to look for them. Experts suggest that the object was a stony asteroid roughly 60 meters in diameter. Some astronomers predict that there is about a 30% chance of a Tunguska-size airburst occurring somewhere on Earth during the 21st century.

Rogue Dwarfs

Above [4] Earth has been kidnapped from the Sun by a passing "dark star." We are looking down upon Rio de Janeiro, over the shoulders of the Cristo Redentor statue, at a world shrouded in ice and snow. The feeble light of our new "Sun" provides little warmth, and all life on Earth is presumed to have perished.

Today "dark star" is an informal term that often refers to a black hole, but it sometimes signifies what is now known as a brown dwarf, a body that has condensed in a dusty star-forming region of a galaxy but lacks sufficient mass to sustain nuclear fusion.

We now know that Bonestell's "death by freezing" scenario doesn't require kidnapping at all. The close passage of any kind of star could exert gravitational tidal forces on the planets, throwing Earth into a larger or at least more eccentric orbit. If our planet wound up more distant from the Sun for even part of its orbital cycle, the steep drop in temperature would make conditions most uncomfortable for life.

But what if the encounter was closer, or something more massive wandered by? At upper right [5] is the painting from this series that made the greatest impression on me. People, cars, buses, and even ships are drawn inexorably upward by the gravitational field of a dense white dwarf that has strayed into the solar system. I had seen paintings of the second coming of Christ where both the deceased and living are ascending into the clouds to meet their maker--but they always do so in orderly fashion. This rising tide of humanity is chaos!

In order for humans to still be alive during their thrill ride upward--that is, not toasted beforehand--the rogue star would have to be coming in fast and among the coolest of white dwarfs (say, not much hotter than the Sun's surface). But even so, the ride would be short-lived. In his text Bonestell writes that it would take only a few minutes for Earth to disintegrate due to gravitational tidal forces.

The Inconstant Sun

In the text that accompanies the top image on the next page Bonestell writes, "According to astronomers, internal disturbances may suddenly cause the Sun to expand to as much as three times its normal size." He illustrates this [6] by showing a Chicago in which Lake Michigan and the Chicago River have boiled away due to the increased heat. It isn't clear what sort of solar process he was referring to, but it can't be something that has happened before because there's no evidence that Earth has ever lost and regained its water.

In the light of current theory we can retain this "baked world" not as a depiction of something that could occur suddenly, but as a snapshot of a stage of solar evolution about 2 billion years from now--assuming Chicago is still around! Since its formation, the Sun has been gradually brightening and warming as hydrogen is converted into helium in its core. The Sun is already about 30% more luminous than it was in its infancy. In another billion years it will be 10% brighter. Whatever is left of Earth's polar caps will melt, and the oceans will warm enough to drastically increase their evaporation rate. Scientists think the increased water vapor in the atmosphere will trap more solar heat, leading to a moist greenhouse effect, a runaway condition in which the increased warming leads to yet higher evaporation. Eventually sunlight will split upper atmospheric water molecules into oxygen and hydrogen. The lightweight, fast-moving hydrogen atoms will increasingly escape into space, making it impossible to replenish our planet's water supply. In this scenario most of the water could be gone before the surface reaches the boiling point.

Extra! Extra! Earth Melts!

Bonestell intended his final Coronet image [7] to depict Earth after the Sun has exploded as a nova, which he writes is something that involves "giving off [its] vast atmosphere of hot gas." But what Bonestell describes is actually a Type II supernova involving the collapse of a stellar core that can no longer sustain nuclear fusion. The resulting shock wave blows off the star's outer layers. Yet our Sun cannot produce a supernova because it isn't nearly massive enough.

But let's instead expropriate Bonestell's painting to represent Earth billion of years from now. In reality, the Sun will exhaust the supply of hydrogen in its core and begin burning hydrogen in a surrounding shell, accelerating its energy production and expanding its outer envelope. The Sun will eventually swell into a full-fledged red giant, attaining more than 2,000 times its present luminosity, with its bloated outermost portions extending to Earth's current orbit. As a result, Earth's crust will melt and its atmosphere will boil away. After a few hundred million years more, the Sun will have exhausted all of its usable nuclear fuel (including helium, which is burned during a few brief intervals); it will then shed its outer layers and its core will become a white dwarf.

We now recognize that most of Bonestell's 1947 paintings depicted limited or low-probability disasters. But, given that astronomers think that the foregoing description of the Sun's fate is accurate, it's hard to escape the conclusion that the loss of Earth's water supply would represent the end of life on the planet. Indeed, "trial by fire" instigated by a red-giant Sun, might truly be the end of the world.

For Further Reading

* The paintings in the July 1947 issue of Coronet were also used to illustrate the book The End of the World: A Scientific Inquiry by Kenneth Heuer (Rinehart & Co., 1953).

* For a description of the artistic career of Chesley Bonestell, see Ron Miller and Frederick C. Durant III's book The Art of Chesley Bonestell (Paper Tiger, 2001).

* The "End of the World" series is archived at www.bonestell.com/the_chesley_bonestell_archives032.htm.

Thomas J. Sherrill worked in orbital mechanics and mission planning for Lockheed Corporation (now Lockheed Martin) for 29 years, 18 of them on the Hubble Space Telescope. He continues to consult for Lockheed Martin, working on the Terrestrial Planet Finder and Constellation-X.
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Title Annotation:Chesley Bonestell
Author:Sherrill, Thomas J.
Publication:Sky & Telescope
Article Type:Biography
Geographic Code:1USA
Date:Jun 1, 2006
Words:1928
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