Planetology and Astrogeology

Summary

Planetology and astrogeology are separate branches of science that examine the physical and chemical characteristics of the planets and minor bodies in the solar system. The principal difference between these two scientific disciplines is that planetology includes all planetary bodies, while astrogeology concentrates on worlds similar to Earth. Scientists in the field of planetology can study various topics including planetary atmospheres, interiors, orbital characteristics, the potential for life, and all aspects of planet formation and evolution. In comparison, astrogeology essentially concentrates on Earth’s various surface features and geological processes as seen in other worlds.

Definition and Basic Principles

The terms planetology and astrogeology describe the scientific disciplines that study the planets in the solar system and those objects, believed to be planets, that orbit other distant stars. Planetology is a more general term that includes the study of all planets in every respect.

Astrogeology is somewhat of a misnomer. During the space program in the 1960s, the term was used to describe geological situations on other planets. If taken in a literal sense, astrogeology refers to the geology of the stars, which is not the case. Geology is the science that deals with the history of Earth and life as recorded in rocks. The prefix astro indicates a place of origin beyond Earth and is used in conjunction with many other sciences such as astrobiology, astrophysics, and astronautics.

The uncrewed spacecraft missions of the 1960s to Mercury, Venus, the Moon, and Mars created the field of astrogeology. Traditional geologists could compare their understanding of Earth's processes to observations on these other planets. Geologists wondered how the craters had formed on the moon, but during the 1960s, it could not be determined with any certainty. The scientific community was equally divided between whether the craters resulted from impacts or volcanic activity. A definitive answer had to wait for the astronauts of the Apollo program, who brought back rock samples. For the first time, scientists had a verifiable piece of the moon to compare with Earth's rocks. Since the Apollo program, spacecraft have landed on Venus, Mars, Phobos (one of Mars's moons), Titan (Saturn's largest moon), and asteroids and comets. Spacecraft have also made intentional impacts into the atmosphere of Jupiter, but these missions did not make a landing, per se.

Background and History

The planets in the solar system have attracted the attention of humans since before recorded history. One of the first observations was the recognition that stars remain in fixed positions while planets move in the sky. With the development of writing and numbers, early astronomers accurately calculated and predicted planetary motion. This was the limit of planetary science until the invention of the telescope in 1607.

The telescope transformed the planets from bright little points of light into actual worlds with definable surface features and cloud formations. In 1610, Galileo's telescopic observations of Jupiter revealed a “miniature solar system” of revolving moons, and his discovery of the phases of Venus helped support the heliocentric model of the solar system (the plants revolving around the sun). Subsequent improvements in telescope design and quality led to the discovery of Saturn's rings and numerous moons, as well as the planets Uranus and Neptune. Further discoveries were limited only by technology.

The next breakthrough came in the 1950s with rocket technology and spacecraft design. For the first time, scientists could extend their observations beyond Earth's atmosphere and send instruments to the moon and various planets. By 1989, all the gas giant planets had been visited by spacecraft, leaving only Pluto as an unexplored world until 2015, when the New Horizons probe completed a flyby of the dwarf planet. In addition to gathering an enormous amount of data on each of these planets, the spacecraft also examined their major moons. Many of these moons turned out to be as interesting as their planets.

How It Works

The scientific disciplines of planetology and astrogeology attempt to answer fundamental questions concerning the origin and evolution of the planets in the solar system. To observe the planets from Earth requires the cooperation of several different sciences and technologies. Modern planetology includes such disciplines as astronomy, astrobiology, astrogeology, astrophysics, and cosmochemistry, coupled with various technologies such as computer science, electronic engineering, and mechanical engineering. Their approach to problem-solving involves a combination of direct observation and data collection with various laboratory experiments and computer simulation models.

Remote Sensing. Before the electronic age, planetary studies were limited by the vision of astronomers and the optics of their telescopes. In virtually all aspects of astronomy-related science, researchers must depend on indirect observations through various electronic instruments used for remote sensing, particularly if they are studying distant stars and galaxies. Astronomers must understand how the basic principles of light and other forms of electromagnetic energy affect what they see. Planetary scientists can see events happening on these planets in real time by employing a combination of Earth-based telescopic images and direct spacecraft observations.

Interference from Earth's atmosphere has always been a problem for optical astronomers, especially when attempting to view surface details on terrestrial planets such as Mercury or Mars. Planets with dense atmospheres such as Venus also present a problem for astronomers because their thick cloud layers prevent direct surface observations. To overcome this difficulty, in the 1950s astronomers developed a technique using radar imaging to reveal surface features. Radar signals can easily penetrate clouds and are reflected by the items they hit. By timing the rate of return for these signals, astronomers assembled computer-generated maps indicating the high and low elevations. Although the quality of these early surface radar images was quite poor, they gave astronomers an idea of the nature of the geology of Venus. Later, orbiting spacecraft provided much higher quality images, which were used to construct a complete geological surface map of Venus. A similar technique employing laser technology has been used to map the elevations of geological features on Mars with pinpoint accuracy.

Direct Observation. The geologist primarily depends on fieldwork to construct geological maps and determine the location of mineral resources. All twelve Apollo astronauts who went to the moon were trained in geology, but only one, Harrison Schmitt, was a professional geologist. Supplied with detailed lunar maps and reports of surface materials, the Apollo astronauts were able to successfully land at six locations and collect more than 400 kilograms of rock. Scientists continue to examine these materials and make exciting discoveries with technologies that did not exist at the time of the moon landing. Extraterrestrial fieldwork has been limited to the moon. In 2020, the OSIRIS-REx space probe touched down on an asteroid named Bennu. The probe collected samples of rock and dust and blasted off from Bennu in 2021 returning to Earth's orbit in September 2023 to drop its collected samples into the Utah desert. Instead of landing, the spacecraft began a new mission, OSIRIS-APEX, to collect samples from the asteroid Apophis.

Before the Apollo moon landings, geologists had the opportunity to study extraterrestrial materials in the form of meteorites. By studying the chemical and mineralogical composition of meteorites and comparing them with Earth rocks, scientists were able to confirm their extraterrestrial origin. Meteorites proved to be older than Earth and are believed to have originated in the asteroid belt between Mars and Jupiter. They represent some of the oldest solid materials in the solar system and are the building blocks of the terrestrial planets.

Applications and Products

Global Resource Management. One of the major benefits derived from the study of the other planets in the solar system is the ability to turn that technology around and study Earth. Observing Earth from space allows scientists to view Earth as a single entity rather than a collection of apparently unrelated components. The technique of multispectral imaging has been used to map the mineral composition of the moon's surface and search for evidence of water. Similar technology has also been employed in mineral exploration on Earth. Vast regions of Earth's surface, including parts of Siberia and central Australia, remain virtually unexplored and are believed to contain great mineral wealth. Using remote-sensing satellites allows geologists to assess a site's potential without setting foot on the ground. Although determining a site's true value still requires fieldwork, remote-sensing data obtained from space certainly makes the work more efficient and reduces expenses.

Food production management is another area that can directly benefit from planetary monitoring technology. Space-age technology, by providing information about global conditions, can help farmers increase food production capabilities and manage resources to meet these demands. People in the fishing industry can employ satellite data to help track schools of fish to increase the efficiency and productivity of their efforts. They can also use this information to monitor their fishing grounds and preserve them.

Planetary monitoring can help address another concern, the availability of an abundant supply of drinkable water, by keeping track of global water resources. The problem of maintaining an adequate supply of water affects the world's population in that water is also used for many other purposes, including irrigating crops.

Meteorology. Meteorologists use part of the data planetologists derived from their studies of planets with dense atmospheres. Satellite technology originally designed to study the atmosphere of another planet has been adapted to monitor Earth's dynamic weather. Studying Venus, with its extremely dense atmosphere and its runaway greenhouse effect, provides Earth scientists with working models to use when trying to understand the effects of greenhouse gases in Earth's atmosphere. Observing the various weather systems in the atmospheres of the Jovian planets also helps meteorologists understand wind and weather patterns on Earth. Jupiter's Great Red Spot is essentially a 350-year-old hurricane, and Neptune exhibits the highest velocity winds of any planet in the solar system. Meteorologists have benefited from studying the dust devils seen blowing across the surface of Mars. These small dust storms closely resemble tornadoes on Earth. Periodically, Mars also experiences global dust storms that lift huge quantities of dust high into the atmosphere and block out most of its surface features for months on end.

Climate Change. The effects of climate change—the shrinking polar ice caps and the expansion of the deserts—can be seen clearly from space. The deforestation of the Brazilian rainforest and the amount of sediment that a river carries into the ocean each year can be precisely measured from satellite observations. Oceanographers can use the data from satellite observations in their studies of ocean currents and the effects of pollution on surface water and coastlines. City planners can use satellite technology to monitor urban sprawl and help develop better methods of waste management and disposal. Climatologists can study the localized weather patterns that develop over major cities and how they affect the smaller communities downwind. In the United States, these localized weather patterns are most apparent in the Great Lakes region and on the eastern seaboard. Similarly, the inadequacy of environmental controls in industrial countries such as India and China is apparent from space. The pollution generated affects populations in India, China, and neighboring areas.

Analytical Instrumentation. Before the Apollo moon landings, meteorites were the only extraterrestrial materials available for astrogeologists to study. Usually, the classification of a meteorite requires a certain amount of destructive analysis. In many cases, the most interesting and rare meteorites are available only in very small quantities, thereby limiting the amount of material available for analysis. Similarly, only small amounts of the rocks recovered from the moon were available for analysis. The National Aeronautics and Space Administration (NASA) deliberately preserved a large quantity of lunar material for future scientists to study with instruments not yet invented. They realized that another trip to the moon might not occur for many years.

To cope with the limited availability, astrogeologists developed techniques to gain the maximum amount of data from the least amount of material. They needed the help of technicians to invent the electronic equipment and to develop the procedures needed to analyze the material. Radiation has become an important component of modern analytical technology. Geologists often employ X-ray diffraction and X-ray fluorescence to identify the minerals in a rock. By using a mass spectrometer, the half-life decay rates of certain radioactive isotopes can be measured to obtain the age of moon rocks or to determine the cosmic-ray exposure age of meteorites. Other instruments such as the electron microprobe, an instrument that can analyze particles as small as a few microns in size, are the primary tools of the scientists who study extraterrestrial materials.

The scanning electron microscope is another valuable tool that allows scientists to magnify the object they are studying to an incredibly high power. This instrumentation is especially useful to astrobiologists attempting to prove that fossils of microbial life forms are present in certain meteorites. If their theory is correct, then these extremophile life forms could have originated elsewhere in the solar system and have been brought to Earth by either comets or meteorites very early in Earth's history.

Careers and Course Work

Students interested in making either planetology or astrogeology their career must first complete an undergraduate degree program in one of the fundamental sciences, which include biology, chemistry, geology, or physics. Adding computer science, mathematics, or electrical or mechanical engineering as a double major would increase job prospects. Most students pursue graduate work in a specialty. A master's degree is usually the minimum requirement for most technicians, while a doctorate is more appropriate for a senior scientist position. There are many ways to become employed in space science research, and students should possess various technical skills to complement their academic training. The industrial job market for highly skilled scientists and technicians in space science is quite unpredictable, but positions are likely to be available for the best applicants.

University teaching positions present an opportunity for scientists with doctorates to find employment while pursuing their research interests. Major universities expect their professors to conduct independent research and encourage collaborative efforts with government agencies or major museums. Postdoctorate positions are usually available to recent graduates so that they can work with and learn from senior scientists in their field. Federal grants are available to scientists to support their research, although such grants can be difficult to obtain. Governmental agencies such as NASA, the National Oceanographic and Atmospheric Administration (NOAA), the National Science Foundation (NSF), and the US Geological Survey (USGS) all employ earth scientists and geologists in various positions. The USGS has an astrogeology branch in Flagstaff, Arizona, where maps are created from data returned from many of the planetary missions.

Social Context and Future Prospects

Historians have often stated that the twentieth century will likely be remembered for its two world wars and the realization of space travel. The wars and the weapons race are in a way responsible for humankind's venturing into space. However, in addition to powerful rockets and brave astronauts, sending people into space required major advancements in technology to create the necessary hardware. Technology originally developed in connection with the space program can be found in most modern technological necessities, such as cell phones, personal computers, and medical diagnostic instrumentation.

Although the primary motivation for sending a human to the moon was political, it momentarily opened the eyes of the world to something greater than nationalism. The images of Neil Armstrong and Buzz Aldrin on the moon on July 21, 1969, show what humankind can achieve. The subsequent lunar landings drew less public interest, however, and grand plans of human exploration of the solar system were largely put on hold. Still, many more robotic missions have been carried out or planned, with planetary probes providing unimaginable visions of worlds. Improved technology has also led to major leaps in the detection and scientific understanding of exoplanets, or planets outside our solar system, providing whole new areas of research within planetology and astrogeology. Astronomers have discovered more than 5,000 exoplanets and were considering more than 9,000 potential candidates for future discovery. The rise of commercial space ventures in the early twenty-first century also pointed to future opportunities for exploration and discovery.

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