Top Extraterrestrials and What Science Has Learned About Them

Roswell, Nevada is known for the mystery of a purported US Military "hush up" of a UFO with aliens aboard that crash landed in the nearby area. While Roswell aliens are in question, most of the extraterrestrials that visit the Earth are visible in museums around the world in the form of rocky materials. Analysis of the chemical properties of these ET's tells much about the origins of planets and life in the universe.

Signs that a rock is extraterrestrial in origin include:

- A fusion crust which is a glassy outer coating made up of the melting of minerals formed along the meteorite as it passes through Earth's atmosphere and then cools.

- They often contain chondrules-small crystallized iron and magnesium bearing silicate materials of early 4.4 billion years old dusty solar system materials heated to a liquid then smashed together into larger bodies over time.

- Elementary composition lacking in hydrogen and helium, but matching the solar system's original nebula

- And can contain different amino acids, up to 230 types were found including some found on earth and others that were not.

The main form of differentiation comes from the type of minerals found in the meteorite. The important thing to know is that by testing for the types of minerals, scientists can find their age, thus dating the solar system.

Stony Carbonaceous Chondrites

These meteorites contain water or minerals altered in the presence of water and many which were never heated above 50C. An example of a stony carbonaceous chondrite is the Barwell Meteorite that was purchased by the British Museum. A second was found in Murchison, Australia and contained many amino acids.

Stony Enstatite Chondrites

These meteorites often contain a large number of sulfides, metallic iron, are of igneous origin. These are believed to have come from parent bodies inside the orbits of Venus and maybe Mercury or from the asteroid Psyche.

Ordinary Chondrites

Ordinary Chondrites are stony meteorites that a recent study used near-earth orbit ion flux weathering to show a likely source of higher olivine content L-class meteorites to be a parent body from the inner edge of the main asteroid belt. The H-class with more pyroxene mineral content to have a parent body withing the middle belt to 2.96 AU[2]. A well known ordinary chondrite is the Inisfree Meteorite that fell in Inisfree, Canada.

Achondrites

Achondrites are an evolved type of meteorite. Shortly after they were formed, they were heated from inside and melted, probably by a collision with another body. They include the meteorites listed below as Mars meteorites and Moon Meteorites.

Iron Meteorites

These meteorites are known from the forms of the crystallization inside them. Hexahedrite have a cubic crystallization cleavage. The best example of an ataxite chondrite is the 55,000 kg Hoba Meteorite that is found on a farm in Grootfontein Namibia and is known because it is primarily made up of taenite. The best example of an octahedrite meteorite is found at American Museum of Natural History in New York after it was purchased by Robert Peary from the Inuit. Octahedrite is known by the Widmanstatten pattern that is seen when it is sliced and etched with weak acid and polished, the pattern formed by the eight-sided crystals of kamacite crystals with a filling of fine grained materials.

Stony Iron Meteorites

Stony Iron meteorites come in a number of classes, including mesosiderite that appears to be formed by a parent body with a still liquid center and a parent body with a solidified crust. They contain about half and half of silicates and iron nickel. A second class called Pallasite have peridots within a iron-nickel material.

Micrometeorites

Micrometeorites are usually smaller than 50 mm in size and some are found in the stratosphere as small as 50 micrometers. A study in Sweden found micrometeorites fossils in a layer of rock from the Ordovician era with ages from about 463 million years ago[3].

Mars Meteorites

Mars Meteorites are a subclass of achondrite meteorites with a mineral makeup that includes trapped gases that data from the Viking Lander missions showed matched that of Mars atmosphere and most are newer i.e. with materials from from 1.35 to 0.15 billion years ago.

Moon Meteorites

Moon meteorites are also a subset of achondrite meteorites and are chunks of moon rock that have been found on Earth as opposed to collected on the moon. Two significant finds provide data , one that with differences from the Apollo Missions and another that shows recent volcanism on the moon, from about 2.8 billion years ago.

Moon Rock

These are about 382 kilograms of rocks brought back from the Apollo missions and about 300 grams from remote Russian missions collected on the moon and brought back to earth and most are stored in the lunar sample building at Johnson Space Center, Houston [4].

Although these extraterrestrials aren't green or have antennae, yet, meteors, the visible path of a meteorite on the way to Earth and the meteorites themselves, do provide a wealth of information about the creation of the solar sytem, beautiful displays when Earth crosses the dusty orbit left by a comet, and sometimes holes in our roofs.

[1] David Darling, Universal Book of Astronomy From the Andromeda Galaxy to the Zone of Avoidance, 2004, John Wiley

[2] Cristina A. Thomas, Richard P. Binzel, Identifying Meteorite Source Regions through Near-Earth Object Spectroscopy, Icarus, August, 2009

[3] Per Thorslund & Frans E. Wickman, Middle Ordovician Chondrite in Fossiliferous Limestone from Brunflo, Central Sweden, Nature, January, 1981

[4] http://www-curator.jsc.nasa.gov/lunar/