Lunar Science: Light Amid the Heat

Lunar Science: Light Amid the Heat

Before man’s first Lunar landing, most scientists thought of the Moon as a Rosetta stone: an untouched repository of precious clues that would help reveal its origin and history, to say nothing of providing new insights about the evolution of the Earth and other planets. After first successful landings, most of these fondest hopes have been realized. The Apollo missions brought back 594 lbs or lunar rocks and soil, thousands of photographs and a flood of data that have changed some of man’s basic concepts about the Moon. But many of the mysteries remain. Indeed, the very act of exploration has created new lunar puzzles. “The Moon”, said once Geophysicist Gerald Wasserburg, whose laboratory at Caltech dated many of the lunar rocks, “is giving us answers that we don’t even questions for”.

Apollo samples showed, for example, that the Moon and Earth have significantly different chemical compositions. That finding challenged the old idea that the Moon was ripped from the Earth. Yet scientists are still at a loss to explain how – or when – it was formed. Paleomagnetic studies of lunar rock indicate that the Moon once had an unexpectedly strong magnetic field – and thus a large molten iron core. Yet equally valid data suggest that a core of significant size could not have existed. Even the ages of the rock present new problems.  The oldest specimens show that the Moon’s surface underwent a violent event about 3, 9 billion years ago that remelted them, but scientists are still debating what might have caused that cataclysm.

For all the heat, Apollo’s missions shed considerable light on the Moon. It revealed that the Moon – and presumably the Earth – was under incredibly intense bombardment by great chunks of space debris in the first 600 million to 800 million years after its formation 4, 6 billion years ago. But 3, 1 billion years ago this bombardment stopped. The evidence returned by Apollo shows that the Moon’s surface has remained virtually unchanged through those eons of time. Perhaps most important of all, exploration of the Moon has shown that it is not a simple, uncomplicated sphere but a true planetary body with a complex history and evolution of its own. Like the Earth, the Moon was once at least partially molten, and thus became differentiated (many heavier elements sank toward its center, while lighter elements floated to the surface to form a crust). In the words of Apollo’s chief scientist in the 1970s, Noel Hinners “It is a piece of the solar pot from which all the inner planets are made. We had no idea of that before we went there.” Indeed, it is the rich load of Moon data already brought back by Apollo that makes the premature conclusion of the program such a bitter disappointment to many lunar scientists.

Nonetheless, all the missions were scientifically very productive and scientist-astronaut Harrison Schmitt was the first professional geologist on the Moon. The Taurus-Littrow landing site contained what may be small volcanically created cinder cones; they seem to be miniature versions of earthly features like Honolulu’s Diamond Head. The cones may well be remnants of what NASA Geochemist Robin Brett called “some of the last belches of lunar activity before the Moon turned off”. Apollo 17 planners scheduled a program of experiments and observation far more sophisticated than any of the earlier scientific efforts on the Moon. For Apollo 17 four wholly new instruments were included in the ALSEP package: a mass spectrometer to measure the Moon’s tenuous atmosphere; a detector that let earthbound scientists monitor the bombardment of cosmic dust particles and micrometeorites on the Moon’s surface; an array of four listening devices – geophones – that can pick up shock waves from explosive charges that were detonated after the astronauts had left and told much about the substructure of the landing site; an extremely sensitive gravimeter that was designed to pick up minuscule variations in lunar surface gravity.

The Moon

Gravity Waves

Recording those tiny variations on the Moon went a long way toward settling an argument raging among physicists. In the 1960s, University of Maryland Physicist Joseph Weber astonished his colleagues with the announcement that he had detected gravity waves. Predicted by Einstein’s 1916 general theory of relativity, such waves are the vehicles presumed to transmit gravitational energy across space. Critics contended that Weber’s detectors probably sensed some of the Earth’s own rumblings. But if sudden variations in gravity are simultaneously picked up by a detector on the Moon and a comparable device on Earth, the sceptics may well be silenced.

During their travels across Taurus-Littrow, astronauts Cernan and Schmitt also performed several new “traverse” experiments. They took on the spot measurements to determine local fluctuations in the Moon’s gravitational field in hope of learning something about the density and structure of the material under the site. With data from a device called a “neutron probe”, scientists were able to calculate how long a particular sample has been lying on or near the lunar surface. The astronauts also sent penetrating microwaves into the lunar surface with a radio transmitting-receiving system. The pattern of the reflected signals could indicate, among other things, whether water is present up to a mile under the surface.

While his buddies worked on the Moon, Ron Evens marked his scientific contributions from high above in America. Besides intensive picture taking with both hands-held and automatic cameras, he examined the moon with a battery of experiments, including an ultraviolet spectrometer that made measurements of the thin lunar atmosphere that was used for comparison with those from the ground-based ASLEP spectrometer, and an infra-red scanner that took continuous temperature readings of the moon’s surface (its margin of accuracy within 2 degrees F). Evans did also his own detailed description of what he saw below him. Besides, it was just such “eyeball” observations by Apollo 15’s Al Worden that discovered the tantalizing cinder-cone-like features in the Taurus-Littrow region and played a key role in its selection as the landing site for the final lunar mission in the XXth century.

Cosmic Rays and Genetic Code

Cosmic Rays and Genetic Code

Some key steps in the development of our genetic code, or the Cambrian explosion, or bipedal stature among our ancestors were initiated by cosmic rays.

Indeed, Cosmic rays, mainly electrons and protons, have bombarded the Earth for the entire history of life on the planet, and we are listening to cosmic rays today, produced in another age in the depths of space.

Every star destroys itself gradually and produces cosmic rays that spiral through the Milky Way Galaxy for thousands or millions of years until, quite by accident, some of them strike the Earth, and our hereditary material. Can we see or sense these rays? The answer is “yes”.

On July 4, in the year 1054, Chinese astronomers recorded what they called a “guest star” in the constellation of Taurus (the Bull). A star never before seen became brighter than any star in the sky. Halfway around the world, in the American Southwest, there was then a high culture, rich in astronomical tradition, that also witnessed this brilliant new star (Moslem astronomers noted it as well. But there is not a word about it in all the chronicles of Europe).

Bright Star. Supernovae are routinely observed in other galaxies. Image: © Elena

The explosion was seen on China with the naked eye for three months. Easily visibly in broad daylight, the Chinese could read by it at night. The remarkable star, 5,000 light-years distant, is now called the Crab Supernova and the Crab Nebula is the remains of a massive star that blew itself upon the Milky Way, after the event of 1054.

There also was a supernova observed in 1572, and described by Tycho Brahe, and another, just after, in 1604, described by Johannes Kepler.

On the average, a supernova occurs in a typical galaxy about once every century. During the lifetime of a given galaxy, about ten billion years, a hundred million stars will have exploded – a great many, but still only about one star in a thousand.

Supernovae can be observed in the deep night. Illustration by Elena.

How High Up is Outside the Atmosphere?

How High Up is Outside the Atmosphere?

The answer is the air just keeps getting thinner and thinner as you go up, and we are not exactly sure where it completely stops. Satellites that are orbiting about 100 miles up are outside nearly all the atmosphere, but there are still a few air molecules even at that altitude, and when the satellite bumps into them it is slowed down a little bit. And when it is slowed – even a very small amount – it drops to a slightly lower orbit, where there are still more molecules of air to bump into and where the pull of gravity is more powerful. And so it goes until it is slowed down so much that the pull of gravity wins the tug-of-war, and the satellite plunges down through the air, usually burning up on the way because its high velocity creates such intense heat from friction with Earth’s atmosphere. Even at extremely high altitudes – say, 2000 miles or more where there are no air molecules – there are other things to bump into. For example, there is cosmic dust (debris ejected from comets), as well as solar wind (electrified particles of gas which stream outward from the Sun), and even radiation pressure from the rays of the Sun. The effects of these things are very small, of course, but over long periods of time they will generally cause any orbit to decay.

The result of this is that satellites at low altitudes, say about 100 miles, stay up for only a few weeks. Those that are as high as 1000 miles can stay up for many years, and as we know the moon has been up there for millions of years.

Old Tree. “Without atmosphere a painting is nothing.” (Rembrandt). Illustration: Elena

Satellite orbits come in different sizes and shapes, depending on what people want to use the satellite for. If you just launch a satellite into orbit to see if you can do it (that was the main idea with the first few satellites launched), it will go into an elliptical orbit. The point in that ellipse where the satellite comes closest to the Earth is called the perigee, and the point where it is farthest away is called the apogee.

Sometimes people want a satellite to be in an elliptical orbit. One of the first little Environmental Research Satellites (ERS) vehicles was sent up to measure particles in the Van Allen radiation belt, and for this purpose the TRW wanted it to pass through many different layers at different distances from the Earth. So they put it in a highly elliptical orbit, with a perigee of 5357 miles and an apogee of 69,316 miles, or about 13 times as far from the Earth as the perigee.

If you should want to put your satellite into a circular orbit, the easiest way to do it is first to put it into an elliptical orbit with the apogee at the same altitude you want for your circular orbit. Then when the satellite arrives at apogee, you point it along that circular path and fire a small rocket engine, often called an apogee motor. That adds enough speed so that the satellite will now stay in the circular orbit instead of falling back down to its old perigee as it goes around the Earth. Very often, the apogee motor is carried in the satellite itself and is not a part of the launch vehicle.

For satellites that are “looking” at the Earth with cameras or radio beacons – such as weather or communication satellites – we prefer circular orbits, so that they will stay at the same altitude all the time.

Chryse Site Looks Rough

Chryse Site Looks Rough

By William K. Hartmann

Instead of the featureless, smooth, dusty plain that had been hoped for, the Viking orbiting pictures of Chryse revealed myriad different geologic structures. Although large impact craters were lacking in the area, clusters of small, 100-yards pits were common in some localities. These were apparently formed by ejects blasted out of some large craters. Other high rimmed craters and conical hills may have been volcanic in origin. Large streamlined hills, 20 to 30 miles long, were probably formed by water flow or etched by windblown dust: they showed cliffs indicating erosion. Nearby, some regions showed incredibly intricate complexes of gullies about 100 yards across: landing in such an area might be fatal to Viking. Another landform, possibly related, was a light-floored complex of shallow channels several miles wide and bounded by bluffs, suggesting dangerous slopes. Floors of such channels might be smoother, perhaps covered by light dust.

One problem is site selection was that the Viking lander could be targeted with 99 percent certainty only in an elliptical area about 31 miles by 75 miles. It is difficult to find such a large area in Chryse totally devoid of ominous topography.

Chryse Planitia. Photo: NASA

From June 22 through 26, photos were received showing still more details in the Chryse site. It became clear that many kinds of geologic processing had occurred in the area since the channels deposited their sediments. Geologists could recognize some stratigraphic units of known source, such as crater ejecta, and other units of unknown origin. At a meeting of June 25, all available information was considered by mission planners, who faced the decision of whether to target for the July 4 landing in Chryse. The consensus was that no one could predict whether 20 degrees slops and 10 inch boulders might exist in the region, since no one was sure of the geologic processes that had formed meter scale relief in the region.

The decision was announced on June 27 to delay the landing. The purpose was to allow more time to study the geology of other possible sites, such as the backup site at Tritonis Lacus, in a relatively “featureless” area east of Syrtis Major. Would small scale, secondary craters, gullies and bluffs dominate the small scale geography in all parts of Mars? Or can some smooth area perhaps formed by deposition of sediments, be found? Late June and early July will be spent trying to answer these questions.

(Astronomy, August 1976, vol. 4, #8).

Striking Appearance for Venus

A Striking Appearance for Venus

Venus, the planet named for the Greek goddess of love and beauty, lives up to its name in every June with a series of beautiful apparitions in the evening sky. Venus reaches its greatest elongation – its greatest separation from the Sun as viewed from Earth – on June 13. On that evening, the planet appears at its highest in the sky and remains visible in the west in the Northern hemisphere several hours after sunset.

But even more spectacularly, Venus appears very near two other bright planets, Mars and Jupiter, in June. Early on the evening of June 17, as seen from the Western Hemisphere, Venus passes 1.2 north of Jupiter. Six days later Venus appears just 0.3 from the Red Planet Mars. You can follow the celestial meandering of the three planets throughout the month by observing them every clear night.

Venus is by far the brightest of the three planets, with Jupiter next and Mars last. Aside from the Moon, Venus is the brightest object in our night sky.

Venus Magellan View. A false-colour image of Venus. Photo: Magellan Imaging

The planet Venus is bright for two reasons. First, it is very near Earth (at least in astronomical terms), whisking to within 26 million miles of our planet at its nearest point. Second, Venus is shrouded by by a veil of bright clouds that reflects nearly two-thirds of the sunlight reaching the planet.

For centuries, the clouds kept astronomers from peering at Venusian surface and helped foster the planet`s image as Earth’s heavenly twin. But American and Soviet Venusian space probes have given us a picture not of paradise but of hell: a surface awash in dusky reddish-orange light, an atmospheric pressure more than ninety times as great as Earth’s, as a surface temperature of 900 Fahrenheit. The highly reflective clouds are composed of sulfuric acid droplets.