Geomorphology studies the features on planetary surfaces and reconstructs the history of their formation, inferring the physical processes that acted on the surface. Planetary geomorphology includes the study of several classes of surface features:. The history of a planetary surface can be deciphered by mapping features from top to bottom according to their deposition sequence , as first determined on terrestrial strata by Nicolas Steno.
For example, stratigraphic mapping prepared the Apollo astronauts for the field geology they would encounter on their lunar missions. Overlapping sequences were identified on images taken by the Lunar Orbiter program , and these were used to prepare a lunar stratigraphic column and geological map of the Moon.
One of the main problems when generating hypotheses on the formation and evolution of objects in the Solar System is the lack of samples that can be analysed in the laboratory, where a large suite of tools are available and the full body of knowledge derived from terrestrial geology can be brought to bear.
Off the radar
Direct samples from the Moon, asteroids and Mars are present on Earth, removed from their parent bodies and delivered as meteorites. Some of these have suffered contamination from the oxidising effect of Earth's atmosphere and the infiltration of the biosphere , but those meteorites collected in the last few decades from Antarctica are almost entirely pristine. The different types of meteorites that originate from the asteroid belt cover almost all parts of the structure of differentiated bodies: meteorites even exist that come from the core-mantle boundary pallasites.
The combination of geochemistry and observational astronomy has also made it possible to trace the HED meteorites back to a specific asteroid in the main belt, 4 Vesta. The comparatively few known Martian meteorites have provided insight into the geochemical composition of the Martian crust, although the unavoidable lack of information about their points of origin on the diverse Martian surface has meant that they do not provide more detailed constraints on theories of the evolution of the Martian lithosphere.
Many were found in either Antarctica or the Sahara Desert.
There’s a snowman in space
During the Apollo era, in the Apollo program , kilograms of lunar samples were collected and transported to the Earth, and 3 Soviet Luna robots also delivered regolith samples from the Moon. These samples provide the most comprehensive record of the composition of any Solar System body beside the Earth.
The numbers of lunar meteorites are growing quickly in the last few years —  as of April there are 54 meteorites that have been officially classified as lunar. Eleven of these are from the US Antarctic meteorite collection, 6 are from the Japanese Antarctic meteorite collection, and the other 37 are from hot desert localities in Africa, Australia, and the Middle East.
Space probes made it possible to collect data in not only the visible light region, but in other areas of the electromagnetic spectrum. The planets can be characterized by their force fields: gravity and their magnetic fields, which are studied through geophysics and space physics. Measuring the changes in acceleration experienced by spacecraft as they orbit has allowed fine details of the gravity fields of the planets to be mapped. For example, in the s, the gravity field disturbances above lunar maria were measured through lunar orbiters, which led to the discovery of concentrations of mass, mascons , beneath the Imbrium, Serenitatis, Crisium, Nectaris and Humorum basins.
If a planet's magnetic field is sufficiently strong, its interaction with the solar wind forms a magnetosphere around a planet.
- Geologic studies are a big part of upcoming space missions.
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Early space probes discovered the gross dimensions of the terrestrial magnetic field, which extends about 10 Earth radii towards the Sun. The solar wind , a stream of charged particles, streams out and around the terrestrial magnetic field, and continues behind the magnetic tail, hundreds of Earth radii downstream. Inside the magnetosphere, there are relatively dense regions of solar wind particles, the Van Allen radiation belts. Geophysics includes seismology and tectonophysics , geophysical fluid dynamics , mineral physics , geodynamics , mathematical geophysics , and geophysical surveying.
Planetary geodesy , also known as planetary geodetics deals with the measurement and representation of the planets of the Solar System, their gravitational fields and geodynamic phenomena polar motion in three-dimensional, time-varying space. The science of geodesy has elements of both astrophysics and planetary sciences. The shape of the Earth is to a large extent the result of its rotation, which causes its equatorial bulge, and the competition of geologic processes such as the collision of plates and of vulcanism , resisted by the Earth's gravity field.
Some or all of these geologic principles can be applied to other planets besides Earth. The Earth geoid is essentially the figure of the Earth abstracted from its topographic features. Therefore, the Mars geoid is essentially the figure of Mars abstracted from its topographic features. Surveying and mapping are two important fields of application of geodesy. The atmosphere is an important transitional zone between the solid planetary surface and the higher rarefied ionizing and radiation belts. Besides the four gas giant planets, almost all of the terrestrial planets Earth , Venus , and Mars have significant atmospheres.
Two moons have significant atmospheres: Saturn 's moon Titan and Neptune 's moon Triton. The four program elements of ESD design the science and technology, launch airborne and space missions, analyze the data and observations, and develop ways to put the information to use for societal benefit. ESD also sponsors research and extends science and technology education to learners of all ages, inspiring the next generation of explorers.
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Water and Energy Cycle. Olsen and Kent, however, used uranium-lead dating in a study last year and found the geological record in the Newark sequence is complete for the relevant timespan. Even with gaps in the rock record, some scientists think that Olsen is onto something.
Science in space
Hinnov says that the challenge now is to fill in the gap between about 50 and million years ago. Currently, the geological data and astronomical models have been matched for 0 to about 50 million years ago, as well as between about and million years ago. The Geological Orrery may be incomplete, and like computational models of planetary systems, it may only be accurate to a point. But among the marvels of the cosmos, we are starting to learn how the motions of celestial bodies, millions of miles away and millions of years ago, have shaped the very world we walk on.
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