Elena's Legacy. Texts written by Elena, excerpts from texts she liked, her artworks.

Friday, December 15, 2017

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.

The Stars and the Sky

Space has fascinated human kind for millenniums. The Ancient Babylonians, Sumerians, Mayas, Egyptians and other civilizations all mentioned celestial bodies in one way or another. While the Ancient Greeks and Roman believes the gods of the Pantheon resided on top of the Mount Olympus, they still had stories explaining stellar movement. For example, it was believed that Apollo, brother of Artemis, made the Sun get up each and every day in the East and rising in his immense carriage through the sky settle in the West each night.

Astrophysicists and astrobiologists study the stars and life on them, respectively, while astrologists try to predict people’s destinies according to stellar positions (an art, not a science, a pseudoscience at best – i.e. horoscopes, believed at one’s own risk). On the scientific side, complex calculations abound and impressive observatories (such as the one in Chile) allow gazing at spectacular views. Likewise, stargazing has been around for a very long time.

Sky at night in a non-starry location (LoL). Obviously, theoretically it is virtually impossible to look upwards on any part of the planet Earth, and not have a star, however distant above. Nonethelss, these can only be seen under certain circumstances and given appropriate conditions (light pollution, technology, distance, locations, clouds and other atmospheric interference, and so on). Image: Copyright © Megan Jorgensen (Elena)

Depending on one’s opinion, black holes may be the most interesting elements in the Cosmos. The mystery continues to fail to be completely understood, despite significant progress with telescopes such as Hubble, Voyager and theoretical advances in knowledge.

An artist’s rendition of a planet similar to Jupiter with one of its 64 moons (drawing not to scale). Jupiter is a gaseous giant and the proportion is closer to the that of planet Earth compared to Jupiter. Image: Copyright © Megan Jorgensen (Elena)

The Flame of Power

Stars Are Campfires

After we found the flame, I was sitting near the campfire wondering about the stars. Slowly, a thought came : The stars are flame, I thought. Then I had another thought: The stars are campfires that other hunterfolk light at night. The stars give a smaller light than campfires. So the stars must be campfires very far away. “But”, they ask me, “how can there be campfires in the sky? Why do the campfires and the hunter people around those flames not fall doww at our feet? Why don’t strange tribes drop from the sky?”

Those are good questions. They trouble me. Sometimes I think the sky is half of a big eggshell or a big nutshell. I think the people around those faraway campfires look down at us – except for them it seems up –and say that we are in their sky, and wonder why we do not fall up to them, if you see what I mean. But hunterfolk say, “Down is down and up is up.” That is a good answer, too.

Stars are campfires. I know another astonishing fact. The Earth, which includes Brooklyn, is a planet, and it goes around the Sun. (Quotations from Megan Jorgensen). © Megan Jorgensen (Elena)

What are the stars? What is different about our time is that at last we know some of the answers. Books and libraries provide a ready means for finding out what those answers are.

Imagine that you took the Sun and moved it so far away that it was just a tiny twinkling point of light. How far away would you have move it? I was innocent of the notion of angular size. I was ignorant of the inverse square law for light propagation. I had not a ghost of a chance of calculating the distance to the stars. But I could tell that if the stars were suns, they had to be very far away. But the Cosmos was much bigger than I had guessed.

There is a thought that one of us had. His thought is that night is a great black animal skin, thrown up over the sky. There are holes in the skin. We look through the holes. And we see flame. His thought is not that there is flame in a few places where we see stars. He thinks there is flame everywhere. He thinks flame covers the whole sky. But the skin hides the flame. Except where there are holes.

Some stars wander. Like the animals we hunt. Like us. If you watch with care over many months, you find they move. There are only five of them, like the fingers on a hand. They wander slowly among the stars. If the campfire thought is true, those stars must be tribes of wandering hunterfolk, carrying big fires. But I don’t see how wandering stars can be holes in a skin. When you make a hole, there it is. A hole is a hole. Holes do not wander. Also, I don’t want to be surrounded by a sky of flame.

A sky of flame would eat us all. Image: © Meg Jorgensen (Elena)

If the skin fell, the night sky would be bright – too bright – like seeing flame everywhere. I think a sky of flame would eat us all. Maybe there are two kinds of powerful beings in the sky. Bad ones, who wish the flame to eat us. And good ones who put up the skin to keep the flame away. We must find some way to thank the good ones.

I don’t know if the stars are campfires in the sky. Or holes in a skin through which the flame of power looks down on us. Sometimes I think one way. Sometimes I Think a different way. Once I thought there are no campfires and no holes but something else, too hard for me to understand.

Rest your neck on a log. Your head goes back. Then you can see only the sky. No hills, no trees, no hunterfolk, no campfire. Just sky. Sometimes I feel I may fall up into the sky. If the stars are campfires, I would like to visit those other hunterfolk – the ones who wander. Then I feel good about falling up. But if the stars are holes in a skin, I become afraid. I don’t want to fall up through a hole and into the flame of power. I wish I knew which was true. I don’t like not knowing.

I do not imagine that many members of a hunter/gatherer group had thoughts like these about the stars. Perhaps, over the ages, a few did, but never all these thoughts in the same person. Yet, sophisticated ideas are common in such communities. For example, the !Kung Bushmen of the Kalahari Desert in Botswana have an explanation for the Milky Way, which at their latitude is often overhead. The call it “the backbone of night”, as if the sky were some great beast inside which we live. The explanation makes the Milky Way useful as well as understandable. The !Kung believe the Milky Way holds up the night; that if it were not for the Milky Way, fragments of darkness would come crashing down at our feet. It is an elegant idea. (! The exclamation point is a click, made by touching the tongue against the inside of the incisors, and simultaneously pronouncing the K).

About Venus

Venus has almost the same mass, size and density as the Earth (it is incidentally, some 30 million times more massive than the most massive comet known). As the nearest planet, it has for centuries been thought of as the Earth’s sister. What is our sister planet really like? Might it be a balmy, summer planet, a little warmer than the Earth because it is a little closer to the Sun? Does it have impact craters, or have they all eroded away? Are there volcanoes or mountains? Oceans? Life?

The first person to look at Venus through the telescope was Galileo in 1609. He saw an absolutely featureless disc. Galileo noted that it went through phases, like the Moon, from a thin crescent to a full disc, and for the same reason: we are sometimes looking mostly at the night side of Venus and sometime mostly at the day side, a finding that incidentally reinforced the view that the Earth went around the Sun and not vice versa.

Venus. Most people go about their daily lives as if nothing is happening. Unthinking, uncaring… (quotations from Megan Jorgensen). Image: Schaller

As optical telescopes became larger and their resolution (or ability to discriminate fine detail) improved, they were systematically turned toward Venus. But they did no better than Galileo’s. Venus was evidently covered by a dense layer of obscuring cloud. When we look at the planet in the morning or evening skies, we are seeing sunlight reflected off the clouds of Venus. But for centuries after their discovery, the composition of those clouds remained entirely unknown.

The absence of anything to see on Venus led some scientists to the curious conclusion that the surface was a swamp, like the Earth in the Carboniferous Period. The argument – if we can dignify it by such a word – went something like this :

– I can’t see a thing on Venus.

– Why not?

– Because it’s totally covered with clouds!

– What are clouds made of?

– Water, of course.

– Then why are the clouds of Venus thicker than the clouds on Earth?

– Because there’s more water there.

– But if there is more water in the clouds, there must be more water on the surface. What kind of surfaces are very wet?

– Swamps.

And if there are swamps, why not cyacads and dragonflies and perhaps even dinosaurs ou 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 everywhere. 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.

Note: The Adda cylinder seal, dating from the middle of the third millennium B.C., prominently displays Inanna, the goddess of Venus, the morning star, and precursors of the Babylonian Ishtar.

Venus is Old

When I greet a friend, I am seeing her in reflected visible light, generated by the Sun, say, or by an incandescent lamp. The rays bounce off my friend and into my eyes. But the ancients, including no less a figure than Euclid, believed that we see by virtue of rays somehow emitted by the eye and tangibly, actively contacting the object observed.

This is a natural notion and can still be encountered, although it does not account for the invisibility of objects in a darkened room. Today we combine a laser and a photocell, or a radar transmitter and a radio telescope, and in this way make active contact by light with distant objects. In radar astronomy, radio waves are transmitted by a telescope on Earth, strike, say, that hemisphere of Venus that happens to be facing the Earth, and bounce back. At many wavelength the clouds and atmosphere of Venus are entirely transparent to radio waves. Some places on the surface will absorb them or, if they are very rough, will scatter them sideways and so will appear dark to radio waves.

Anaximander of Miletus argued that we are so helpless at birth that, if the first human infants had been put into the world of their own, they would immediately have died. Image: Gorgeous Anime Girl with Fuschia Hair by © Meg Jorgensen (Elena)

By following the surface features moving with Venus as it rotates, it was possible for the first time to determine reliably the length of its day – how long it takes Venus to spin once on its axis. It turns out that, with respect to the stars, Venus turns out every 243 Earth days, but backwards, in the opposite direction from all other planets in the inner solar system. As a result, the Sun rises in the west and sets in the east, taking 118 Earth days from sunrise to sunrise. What is more, it presents almost exactly the same face to the Earth each time it is closest to our planet. However, the Earth’s gravity has managed to nudge Venus into the Earth-locked rotation rate, it cannot have happened rapidly. Venus could not be a mere few thousand years old, but rather must be as old as all the other objects in the inner solar system.

Radar pictures of Venus have been obtained, some from ground-based radar telescopes, some from the Pioneer Venus vehicle in orbit around the planet. They show provocative evidence of impact craters. There are just as many craters that are not too big or to small on Venus as there are in the lunar highlands, so many that Venus is again telling us that it is very old. But the craters of Venus are remarkably shallow, almost as if the high surface temperatures have produced a kind of rock that flows over long periods of time, like taffy or putty, gradually softening the relief.

There are great mesas here, twice as high as the Tibetan plateau, an immense refit valley, possibly giant volcanoes and a mountain as high as Everest. We now see before us a world previously hidden entirely by clouds – its features first explored by radar and by space vehicles.

If you see a schematic diagram of the electromagnetic spectrum, you’ll see that the wavelength of light is measured in Angstroms, micrometers, centimeters and meters.

Arecibo Observatory

The largest semi-steerable radio-radar observatory on the planet Earth is the Arecibo facility, which Cornell University operates for the Us National Science Foundation. In the remote hinterland of the island of Puerto-Rico, it is 305 meters (a thousand feet) across, its reflecting surface a section of a sphere laid down in a pre-existing bowl-shaped valley. It receives radio waves from the depths of space, focusing them onto the feed arm antenna high above the dish, which is in turn electronically connected to the control room, where the signal is analyzed.

Alternatively, when the telescope is used as a radar transmitter, the feed arm can broadcast a signal into the dish, which reflects it into space. The Arecibo Observatory has been used both to search for intelligent signals from civilizations in space and, just once, to broadcast a message – to M13, a distant globular cluster of stars, so that our technical capability to engage in both sides of an interstellar dialogue would be clear, at least to us.

Advanced civilizations may have graduated far beyond radio for the own communication. Image : Superexteraterrestrial Sorceress on Rive Shore – Fantasy Art © Megan Jorgensen

In a period of a few weeks, the Arecibo Observatory could transmit to a comparable observatory on a planet of a nearby star all of the Encyclopaedia Britannica. Radio waves travel at the speed of light, 10,000 times faster than a message attached to our fastest interstellar spaceship. Radio telescopes generate, in narrow frequency rages, signals so intense they can be detected over immense interstellar distances. The Arecibo Observatory could communicate with an identical radio telescope on a planet 15,000 light-years away, halfway to the center of the Milky Way Galaxy, if we knew precisely where to point it.

And radio astronomy is a natural technology. Virtually any planetary atmosphere, no matter what its composition, should be partially transparent to radio waves.

Radio messages are not much absorbed or scattered by the gas between the stars, just as a San Francisco radio station can be heard easily in Los Angeles even when smog there has reduced the visibility at optical wavelengths to a few kilometres. There are many natural cosmic radio sources having nothing to do with intelligent life – pulsars and quasars, the radiation belts of planets and the outer atmospheres of stars; from almost any planet there are bright radio sources to discover early in the local development of radio astronomy. Moreover, radio represents a large fraction of the electromagnetic spectrum. Any technology able to detect radiation of any wavelength would fairly soon stumble on the radio part of the spectrum.