Venus' Landscape

Venus' Landscape

If there are swamps, why not cyacads and dragonflies and perhaps even dinosaurs on Venus? Observation: There was absolutely nothing to see on Venus. Conclusion: It must be covered with life. The featureless clouds of Venus reflected our own predispositions. We are alive, and we resonate with the idea of life elsewhere. But only careful accumulation and assessment of the evidence can tell us whether a given world in inhabited. Venus turns out not to oblige our predispositions.

The first real clue to the nature of Venus came from work with a prism made of glass or a flat surface, called a diffraction grating, covered with fine, regularly spaced, ruled lines. When an intense beam of ordinary white lines passes through a narrow slit and then through a prism of grating, it is spread into a rainbow of colors called a spectrum.

Photo of Venus by NASA. With an insufficient data is easy to go wrong. Image: © Megan Jorgensen (Elena)

If Venus were soaking wet, it should be easy to see the water vapor lines in its spectrum. But the first spectroscopic searches, attempted at Mount Wilson Observatory around 1920, found not a hint, not a trace, of water vapor above the clouds of Venus, suggesting an arid, desert-like surface, surmounted by clouds of fine drifting silicate dust. Further studies revealed enormous quantities of carbon dioxide in the atmosphere, implying to some scientists that all the water on the planet had combined with hydrocarbons to form carbon dioxide, and that therefore the surface of Venus was a global oil field, a planet wide-sea of petroleum. Others concluded that there was no water vapor above the clouds because the clouds were very cold, that all the water had condensed out into water droplets, which do not have the same pattern of spectral lines as water vapor. They suggested that the planet was totally covered with water – except perhaps for an occasional limestone-incrusted island, like the cliffs of Dover. But because of the vast quantities of carbon dioxide in the atmosphere, the sea could not be ordinary water; physical chemistry required carbonated water. Venus, they proposed, had a vast ocean of seltzer.

The first hint of the true situation came not from spectroscopic studies in the visible or near-infrared parts of the spectrum, but rather from the radio region. A radio-telescope works more like a light meter than a camera. You point it toward some fairly broad region of the sky, and it records how much energy, in a particular radio frequency, is coming down to Earth. We are used to radio signals transmitted by some varieties of intelligent life – namely those, who run radio and television stations. But there are many other reasons for natural objects to give off radio waves. One is that they are hot.

And when, in 1956, an early radio telescope was turn toward Venus, it was discovered to be emitting radio waves as if it were at an extremely high temperature. But the real demonstration that the surface of Venus is astonishingly hot came when from the Soviet spacecraft of Venera series first penetrated the obscuring clouds and landed on the mysterious and inaccessible surface of the nearest planet. Venus, is turns out, is broiling hot. There are no swamps, no oil fields, no seltzer oceans.

Craters on the Moon

Craters on the Moon

As we move out past Mars we enter a very different regime – the realm of Jupiter and the other giant or jovian planets. These are great worlds, composed largely of hydrogen and helium, ammonia and water. We do not see solid surfaces here, only the atmosphere and the multicolored clouds. These are serious planets, not fragmentary worldlets like the Earth. A thousand Earths could fit inside Jupiter. If a comet or an asteroid dropped into the atmosphere of Jupiter, we would not expect a visible crater, only a momentary break in the clouds. Nevertheless, we know there has been a many-billion-year history of collisions in the outer solar system as well –because Jupiter has a great system of more than a dozen moons, five of which were examined close up by the Voyager spacecraft. Here again we find evidence of past catastrophes. When the solar system is all explored, we will probably have evidence for impact catastrophism on all nine worlds, from Mercury to Pluto, and on all the smaller moons, comets and asteroids.

There are about 10,000 craters on the near side of the Moon, visible to telescopes on Earth. Most of them are in the ancient lunar highlands and date from the time of the final accretion of the Moon from interplanetary debris. There are about a thousand craters larger than a kilometer across in the maria (Latin for “seas”), the lowland regions that were flooded, perhaps by lava, shortly after the formation of the Moon, covering over the pre-existing craters. Thus, very roughly, craters on the Moon should be formed today at the rate of about 10(0) years/10(4) craters, = 10(5) years/crater, a hundred thousand years between cratering events. Since there may have been more interplanetary debris a few billion years ago than there is today, we might have to wait even longer than a hundred thousand years to see a creater form on the Moon. Because the Earth has a larger area than the Moon, we might have to wait something like ten thousand years between collisions that would make craters as big as a kilometer across on our planet. And since Meteor Crater, Arizona, an impact crater about a kilometer across, has been found to be twenty or thirty thousand years old, the observations on the Earth are in agreement with such crude calculations.

The Earth Seen From the Moon. We should not expect the Moon struck by a meteorite in the near future (Image Grey and Purpler Pattern Painting © Megan Jorgensen)

The actual impact of a small comet or asteroid with the Moon might make a momentary explosion sufficiently bright to be visible from the Earth. We can imagine our ancestors gazing idly up on some night a hundred thousand years ago and noting a strange cloud arising from the unilluminated part of the Moon, suddenly struck by the Sun’s rays. But we would not expect such an event to have happened in historical times. The odds against it must be something like a hundred to one.

Asteroids

Asteroids

Between the orbits of Mars and Jupiter are countless asteroids, tiny terrestrial planets. The largest are a few hundred kilometers across. Many of them have oblong shapes and are tumbling throught space. In some cases there seem to be tow or more asteroids in tight mutual orbits. Collisions among the asteroids happen frequently, and occasionally a piece is chipped off and accidentally intercepts the Earth, falling to the ground as a meteorite. In the exhibits, on the shelves of our museums are the fragments of distant worlds.

The asteroid belt is a great grinding mill, producing smaller and smaller pieces down to motes of dust. The bigger asteroidal pieces, along with the comets, are mainly responsible for the recent craters on planetary surfaces. The asteroid belt may be a place where a planet was once prevented from forming because of the gravitational tides of the giant nearby planet Jupiter; or it may be the shattered remains of a planet that blew itself up. This seems improbable because no scientist on Earth knows how a planet might blow itself up, which is probably just as well.

As far as we know, the first essentially nonmystical attempt to explain a historical event by cometary intervention was Edmund Halley’s proposal that the Noachic flood was the casual Choc of a Comet. Image : Psychodelic Racing Track © Elena

The rings of Saturn bear some resemblance to the asteroid belt: trillions of tiny icy moonlets orbiting the planet. They may represent debris prevented by the gravity of Saturn from accreting into a nearby moon, or they may be the remains of a moon that wandered too close and was torn apart by the gravitational tides. Alternatively, they may be the steady state equilibrium between material ejected from a moon of Saturn, such as Titan, and material falling into the atmosphere of the planet.

Jupiter and Uranus also have ring systems, discovered only recently, and almost invisible from the Earth. Whether Neptune has a ring is a problem high on the agenda of planetary scientists. Rings may be a typical adornment of Jovian-type planets throughout the cosmos.

Major recent collisions from Saturn to Vegus were alleged in a popular book, Worlds in Collision, published in 1950 by a psychiatrist named Immanuel Velikovsky. He proposed that an object of planetary mass, which he called a comet, was somehow generated in the Jupiter system. Some 3,500 years ago, it careered in toward the inner solar system and made repeated encounters with the Earth and Mars, having as incidental consequences the parting of the Red Sea, allowing Moses and the Israleites to escape from Pharaoh, and the stopping of the Earth from Rotating on Joshua’s command. It also caused, he said, extensive vulcanism and floods. Velikovsky imagined the comet, after a complicated game of interplanetary billiards, to settle down into a stable, nearly circular orbit, becoming the planet Venus – which he claimed never existed before then.

A Jewel Box in the Sky

A Jewel Box in the Sky

There is something puzzling. Observations with a sensitive radio antenna carried near the top of the Earth’s atmosphere in a U-2 aircraft have shown that the background radiation is, to first approximation, just as intense in all directions – as if the fireball of the Bing Bang expanded quite uniformly, an origin of the universe with a very precise symmetry.

But the background radiation, when examined to finer precision, proves to be imperfectly symmetrical. There is a small systematic effect that could be understood if the entire Milky Way Galaxy (and presumably other members of the Local Group) were streaking toward the Virgo cluster of galaxies at more than a million miles an hour (600 kilometres per second). At such a rate, we will reach it in ten billion years, and extragalactic astronomy will then be a great deal easier.

Why should we be rushing toward the Virgo cluster? (Quotations from Megan Jorgensen, image: © Elena)

The Virgo cluster is already the richest collection of galaxies known replete with spirals and elliptical and irregulars, a jewel box in the sky.

George Smoot and his colleagues, who made these high-altitude observations, suggest that the Milky Way is being gravitationally dragged toward the center of Virgo cluster; that the cluster has many more galaxies than have been detected heretofore; and, most startling, that the cluster is of immense proportions, stretching across one or two billion light-years of space.

Some myth from the Pacific Basin and other lands. These myths are tributes to human audacity. The chief difference between then and our modern scientific myth of the Big Bang is that science is self-questioning, and that we can perform experiments and observation to test our ideas. But those other creation stories are worthy of our deep respect:

“First there was the great cosmic egg. Inside the egg was chaos, and floating in chaos was P’an Ku, the Undeveloped, the divine Embryo. And P’an Ku burst out of the egg, four times larger than any man today, with a hammer and chisel in his hand with which he fashioned the world” (The P’an Ku myths, China, around third century).

No Arean sat alone in space as a cloud that floats in nothingness. He slept not, for there was no sleep; he hungered not, for as yet there was no hunger. Se he remained for a great while, until a thought came to his mind. He said to himself, “I will make a thing” (a myth form Maiana. Gilbert Islands.

Before heaven and earth had taken form all was vague and amorphous… That which was clear and light drifted up to become heaven, while that which was heavy and turbide solidified to become earth. It was very easy for the pure, fine material to come together, but extremely difficult for the heavy, turbid material to solidify. Therefore heaven was completed first and earth assumed shape after. When heaven and earth were joined in emptiness and all was unwrought simplicity, then without having been created things came into being. This was the Great Oneness. All things issued from this Oneness but all became different (Huai-nan tzu, China, around first century B.C.).

A Jewel box in the Sky. Illustration by Elena.

A Typical Comet

A Typical Comet

A fairly typical comet would look like a giant tumbling snowball about 1 kilometer across. Most never penetrate the border marked by the orbit of Pluto. But occasionally a passing star makes a gravitational flurry and commotion in the cometary cloud, and a group of comets finds itself in highly elliptical orbits, plunging toward the Sun. After its path is further changed by gravitational encounters with Jupiter or Saturn, it tends to find itself, once every century or so, careering toward the inner solar system. Somewhere between the orbits of Jupiter and Mars it would begin heating and evaporating. Matter blown outwards from the Sun atmosphere, the solar wind, carries fragments of dust and ice back behind the comet, making an incipient tail. If Jupiter were a meter across, our comet would be smaller than a speech of dust, but when fully developed, its tail would be as great as the distances between the world.

When within sight of the Earth on each of its orbits, it would stimulate outpourings of superstitious fervor among the Earthlings. But eventually they would understand that it lived not in their atmosphere, but out among the planets. They would calculate its orbit. And perhaps one day soon they would launch a small vehicle devoted to exploring this visitor from the realm of the stars.

The Solar Wind determines the fate of a Comet. What about our fate? (Quotations from Megan Jorgensen, image : Elena)

Sooner or later comets will collide with planets. The Earth and its companion the Moon must be bombarded by the comets and small asteroids, debris left over from the formation of the solar system. Since there are more small objects than large ones, there should be more impacts by small objects than by large ones. An impact of a small cometary fragment with the Earth, as at Tunguska, should occur about once every thousand years. But an impact with a large comet, such as Halley’s Comet, whose nucleus is perhaps twenty kilometers across, should occur only about once every billion years.

When a small, icy object collides with a planet or a moon, it may not produce a very major scar. But if the impacting object is larger or made primarily of rock, there is an explosion on impact that carves out a hemispherical bowl called an impact crater. And if no process rubs out or fills in the crater, it may last for billions of years. Almost no erosion occurs on the Moon and when we examine its surface, we find it covered with impact craters, many more than can be accounted for by the rather sparse population of cometary and asteroidal debris that now fills the inner solar system. The lunar surface offers eloquent testimony of a previous age of the destruction of worlds, now billions of years gone.

Impact craters are not restricted to the Moon. We find them throughout the inner solar system – from Mercury, closest to the Sun, to cloud-covered Venus to Mars and its tiny moons, Phobos and Deimos. There are the terrestrial planets, our family of worlds, the planets more or less like the Earth. The have solid surfaces, interiors made of rock and iron, and atmospheres ranging from near-vacuum to pressures ninety times higher than the Earth’s. They huddle around the Sun, the source of light and heat, like campers around a fire. The planets are all about 4,6 billion years old. Like the Moon, they all bear witness to an age of impact catastrophism in the early history of the solar system.