Heaven and Hell

Heaven and Hell

Venus, our neighboring world turns out to be a dismally unpleasant place. But we will go back to Venus. It is fascinating in its own right. Many mythic heroes in Greek and Norse mythology, after, all, made celebrated efforts to visit Hell. There is also much to be learned about our planet, a comparative Heaven, by comparing it with Hell.

The Sphinx, half human, half lion, was constructed more than 5,500 years ago. Its face was once crisp and cleanly rendered. It is now softened and blurred by thousands of years of Egyptian desert sandblasting and by occasional rains. In New York City there is an obelisk called Cleopatra’s Needle, which came from Egypt. In only about a hundred years in the city’s Central Park, its inscriptions have been almost totally obliterated, because of smog and industrial pollution – chemical erosion like that in the atmosphere of Venus. 

Arbre solitaire. There are mighty weather systems on the Earth – and in the high atmosphere of Venus and on Jupiter. Image: Trees by © Elena

Erosion on Earth slowly wipes out information, but because they are gradual – the patter of a raindrop, the sting of a sand grain – those processes can be missed. Big structures, such as mountain ranges, survive tens of millions of years; smaller impact craters, perhaps a hundred thousand; and large-scale human artifacts only some thousands. In addition to such slow and uniform erosion, destruction also occurs through catastrophes large and small. The Sphinx is missing a nose. Someone shot it off in a moment of idle desecration – some say it was Mameluke Turks, others, Napoleonic soldiers. (More precisely, an impact crater 10 kilometers in diameter is produced on the Earth about once every 500,000 years; it would survive erosion for about 300 million years in areas that are geologically stable, such as Europe and North America. Smaller craters are produced more frequently and destroyed more rapidly, especially in geologically active regions.

On Venus, on Earth and elsewhere in the solar system, there is evidence for catastrophic destruction, tempered or overwhelmed by slower, more uniform processes: on the Earth, for example, rainfall, coursing into rivulets, streams and rivers of running water, creating huge alluvial basins; on Mars, the remnants of ancient rivers, perhaps arising from beneath the ground; on Io, a moon of Jupiter, what seem to be broad channels made by flowing liquid sulfur.

Traveling to Mars

Traveling to Mars

The first expedition to Mars did not wish to land in too rough a place. The spacecraft might have tipped over and crashed, or at the least its mechanical arm, intended to acquire Martian soil samples, might have become wedged or been left waving helplessly a meter too high above the surface. Likewise, we did not want to land in places that were too soft. If the spacecraft’s three landing pods had sunk deeply into a loosely packed soil, various undesirable consequences would have followed, including immobilization of the sample arm. But the humans did not want to land in a place that was too hard either – had they landed in a vitreous lave field, for example, with no powdery surface material, the mechanical arm would have been unable to acquire the samples vital to the projected chemistry and biology experiments.

The best photographs then available of Mars – from the Mariner 9 orbiter – showed features no smaller than 90 meters (100 yards) across. The Viking orbiter pictures improved this figure only slightly. Boulders one meter (three feet) in size were entirely invisible in such photographs, and could have had disastrous consequences for the Viking lander. Likewise, a deep, soft powder might have been undetectable photographically. Fortunately, there was a technique that enabled the scientists to determine the roughness or softness of a candidate landing site: radar. A very rough place would scatter radar from Earth off to the sides of the beam and therefore appear poorly reflective because of the many interstices between individual sand grains.

Safe harbors are, by any large, dull. Image : Brown Mosaic by Elena

While the scientists were unable to distinguish between rough places and soft places, they did not need to make such distinctions for landing site selection. Both, they knew, were dangerous. Preliminary radar surveys suggested that as much as a quarter to a third of the surface area of Mars might be radar-dark, and therefore dangerous for Viking. But not all of Mars can be viewed by Earth-based radar, only a swath between 25 degrees North and about 25 degrees South. The Viking orbiter carried no radar system of its own to map the surface.

There were many constraints – perhaps, the scientists feared, too many. The landing sites had to be not too high, too windy, too hard, too soft, too rough or too close to the pole. It was remarkable that there were any places at all on Mars that simultaneously satisfied all safety criteria. But it was also clear that the search for safe harbors had led the scientists to landing sites that were, by any large, dull.

Spiral Pattern

Spiral Pattern

Light Is Also Wave

The speed of any given star around the center of the Galaxy in generally not the same as that of the spiral pattern.

The Sun has been in and out of spiral arms often in the twenty times it has gone around the Milky Was at 200 kilometres per second (roughly half a million miles per hour). On the average, the Sun and the planets spend forty million years in a spiral arm, eighty million outside, another forty million in, and so on. Spiral arms outline the region where the latest crop of newly hatched stars in being formed, but not necessarily where such middle-aged stars as the Sun happen to be. In this epoch, we live between spiral arms.

The periodic passage of the solar system through spiral arms may conceivably have had important consequences for us. About ten millions years ago, the Sun emerged from the Gould Belt complex of the Orion Spiral Arm, which is now a little less than a thousand light-years away (interior to the Orion arm is the Sagittarius arm; beyond the Orion arm is the Perseus arm).

Light is also a wave. A Heart Planet by © Elena

When the Sun passes through a spiral arm it is more likely than it is at present to enter into gaseous nebulae and interstellar dust clouds and to encounter objects of substellar mass. It has been suggested that the major ice ages on our planet, which recur every hundred million years or so, may be due to the interposition of interstellar matter between the Sun and the Earth.

W. Napier and S. Clube have proposed that a number of the moons, asteroids, comets and circumplanetary rings in the solar system once freely wandered in interstellar space until they were captured as the Sun plunged through the Orion spiral arm. This is an intriguing idée, although perhaps not very likely. But it is testable. All we need do is procure a sample of, say Phobos or a comet and examine its magnesium isotopes.

The relative abundance of magnesium isotopes (all sharing the same number of protons, but having differing numbers of neutrons) depends of the precise sequence of stellar nucleo-synthetic events, including the timing of nearby supernova explosions, that produced any particular sample of magnesium. In a different corner of the Galaxy, a different sequence of events should have occurred and a different ration of magnesium isotopes should prevail.

Doppler Effect

The Doppler Effect

The discovery of the Big Bang and the recession of the galaxies came from a commonplace of nature called the Doppler effect. We are used to it in the physics of sound. An automobile driver speeding by us blows his horn. Inside the car, the driver hears a steady blare at a fixed pitch. To us, the sound of the horn elides from high frequencies to low. A racing car traveling at 200 kilometers per hour (120 miles) per hour) is going almost one-fifth the speed of sound. Sound is a succession of waves in air, a crest and a trough, a crest and a trough.

The Dopler effect: a stationary source of sound or light emits a set of spherical waves. If the source is the motion from right to left, it emits spherical waves progressively. The Dopler effect is the key to cosmology.

The object itself might be any color, even blue. Image © Elena

Unlike sound, light travels perfectly well through a vacuum. The Doppler effect works here as well. If instead of sound the automobile were for some reason emitting, front and back, a beam of pure yellow light, the frequency of the light would increase slightly as the car approached and decrease slightly as the car receded. At ordinary speeds the effect would be imperceptible. If, however, the car were somehow traveling at a good fraction of the speed of light, we would be able to observe the color of the light changing toward higher frequency, that is, toward blue, as the car approached us; and toward lower frequencies, that is, toward red, as the car recede from us. An object approaching us at very high velocities is perceived to have the color of its spectral lines blue-shifted. This red shift, observed in the spectral lines of distant galaxies and interpreted as a Doppler effect, is the key to cosmology.

The object itself might be any color, even blue. The red shift means only that each spectral line appears at longer wavelengths than when the object is at rest; the amount of the red shift is proportional both to the velocity and to the wavelength of the spectral line when the object is at rest.

Milton Humason

Milton Humason

During the early years of the 20th century, the world’s largest telescope, destined to discover the red shift of remote galaxies, was being built on Mount Wilson, overlooking what were then the clear skies of Los Angeles. Large pieces of the telescope had to be hauled to the top of the mountain, a job for mule teams. A young mule skinner named Milton Humason helped to transport mechanical and optical equipment, scientists, engineers and dignitaries up the mountain. Humason would lead the column of mules of mules on horseback, his white terrier standing just behind the saddle, in front paws on Humason’s shoulders.

The young man was a tobaccochewing roustabout, a superb gambler and pool player and what was later called a ladies’ man. In his formal education, Humason had never gone beyond the eighth grade. But he was bright and curious, and naturally inquisitive about the equipment he had laboriously carted to the heights. He was keeping company with the daughter of one of the observatory engineers, a man who harboured reservations about his daughter seeing a young man who had no higher ambition than to be a mule skinner.

Edwin Hubble provided the final demonstration that the spiral nebulae were in fact “island universes”. Image : Spiral © Elena

So Humason took odd jobs at the observatory – electrician’s assistant, janitor, swabbing the floors of the telescope he had helped to build. One evening, so the story goes, the night telescope assistant fell ill and Humason was asked if he might fill in. He displayed such skill and care with the instruments that he soon became a permanent telescope operator and observing aide.

After World War I, there came to Mount Wilson the soon-to-be famous Edwin Hubble – brilliant, polished, gregarious outside the astronomical community, with an English accent acquired during a single year as Rhodes scholar at Oxford. It was Hubble who provided the final demonstration that the spiral nebulae were in fact “island universes”, distant aggregations of enormous numbers of star, like our own Milky Way Galaxy. Hubble had figured out the stellar standard candle required to measure the distances to the galaxies.

Hubble and Humason hit it off splendidly, a perhaps unlikely pair who worked together at the telescope harmoniously. Following a lead by the astronomer V. M. Slipher at Lowell Observatory, they began measuring the spectra of distant galaxies. It soon became clear that Humason was better able to obtain high-quality spectra of distant galaxies than any professional astronomer in the world. He became a full staff member of the Mount Wilson Observatory, learned many of the scientific underpinnings of his work and died rich in the respect of the astronomical community.

(By Carl Sagan)