A group of notable meteorites comes to auction this season in Sotheby's Natural History sale – open for online bidding from the 23 November – 3 December.
F or the vast majority of us, the opportunity to explore outer space first-hand isn't just a moon shot – it's a pipe dream. Luckily, the next best thing is still spectacular: meteorites. Extraterrestrial rocks – from asteroids, the Moon and even Mars – offer scientists and amateur enthusiasts alike a chance to experience the vast universe beyond our own planet Earth.
Each meteorite is remarkably old (those originating from asteroids are about ~4.5 billion years old, those from the Moon range from 4.5 – 2.9 billion years old and Martian meteorites range from 200 million – 4.5 billion years old) and exceedingly rare. As the vast majority of meteorites (90-95%) do not survive the journey through the earth’s atmosphere, there are only about 60,000 or so documented specimens, of which only a few hundred originate from the Moon or Mars. But of the 60,000, just a third of meteorites are available on the public market – making meteorite collecting a quite competitive, and lucrative hobby.
But where to start? Here, we offer a guide to beginning your own meteorite collection (along with some exquisite examples on offer from our November auction, Natural History).
The Basics of Determining Meteorite Value
The commercial value of meteorites can range from a few thousand dollars to a few million, depending on a few important factors:
Fall vs. Find
A meteorite that can be traced to a documented "fall" – that is, someone witnessed the meteorite shoot through the sky and land on Earth – is more valuable than a "find" – one that is discovered, by chance, thanks to a keen eye. This metric is more important when considering the value of asteroidal meteorites than for Lunar or Martian meteorites, given the rarity of the latter two categories.
As with gemstones, the weight of meteorites correlates directly with value – larger meteorites are more expensive than smaller samples.
As with fine art, a good history (or a well-documented log of ownership) can increase a meteorite's value.
Rarity of Type
Three types of meteorites excel in value thanks to overall rarity: Lunar, Martian and pallasites.
The Three Types of (Asteroid) Meteorites
The vast majority (about 99.8%) of meteorites are known to have originated from asteroids. Of these, there are three main groups of meteorites: stony-iron, iron and stony.
Stony-iron meteorites are the rarest of the three types, comprising less than 1 percent of all known falls. Consisting of equal parts iron-nickel metal and silicate material (and sometimes including semi-precious or precious gemstones), these meteorites are also considered especially beautiful. Within the stony-iron meteorite group, there are two sub-groups: pallasites and mesosiderites.
- Pallasites contain magnesium-iron silicate called olivine – which appear as large, beautiful, crystals – suspended in nickel-iron material. The observed patterns of olivine in meteorites vary; sometimes the crystals are scattered throughout the pallasite or clustered together, and other times they run through the crystals as a vein. While olivine is naturally a green color, the color can vary as a result of terrestrial weathering – resulting in exquisite gold, yellow or brown tones.
- Mesosiderites contain roughly an equal amount of metallic iron-nickel and silicate. Many mesosiderites are breccias and appear as a collage of mineral fragments (consisting of igneous silicate and metal clasts) and other, finer materials. The fragmented appearance of these meteorites is thought to be a result of their bumpy origin: meteoriticists theorize that when two asteroids collide, debris from the collision creates mesosiderites.
Thought to originate from the core of asteroids, the iron group of meteorites consists mostly of iron-nickel metal, with traces of sulfide and carbide minerals. Identifying markers of iron meteorites high density and a strong magnetic attraction. Unusual for terrestrial materials, iron meteorites often contain a relatively high percentage of nickel. Iron meteorites comprise about 4 percent of all known falls.
Stony meteorites are the most common, comprising about 95 percent of all known falls. These meteorites consist of silicate materials, and the vast majority are thought to originate from the crust of asteroids. There are two sub-groups of stony meteorites: chondrites and achondrites.
- Formed over 4.5 billion years ago, chondrites are some of the oldest rocks in the solar system. Chondrules, or spheres of silicate minerals mixed with sulfides and iron-nickel metal, give these meteorites a distinctive, spotted design. Chondrite meteorites are the most common of all meteorites (though of course, ‘common’ is a relative term when it comes to meteorites).
- Achondrites are stony meteorites that do not contain chondrules; this subcategory includes meteorites from asteroids, the Moon and Mars. These meteorites contain very little iron if any. Achondrites are igneous, meaning at some point they melted into magma.
A lunar meteorite, or lunaite, is one that originates from the Moon. Lunar meteorites are extremely rare, comprising only about 0.1% of all known meteorites. All lunar meteorites form from impacts on the Moon, which create lunar craters; after leaving the Moon, the meteorites likely enter the Earth’s orbit, until eventually yielding to our planet’s gravitational pull.
It can be difficult to tell that a meteorite originates from the Moon just by looking at it, as lunar meteorites can closely resemble terrestrial rocks in density and mineral composition. Lunar meteorites are often breccias composed of the dark grey basalt that comprise the mare, or lowlands of the Moon, along with the light-colored, calcium-aluminum silicate that comprises the terra, or highlands.
The first documented discovery of a Lunar meteorite occurred in 1982; that year, explorer John Schutt happened upon a usual meteorite while on exhibition in Antarctica. Schutt sent the meteorite to Washington, D.C., where a geologist at the Smithsonian Museum noticed similarities between the specimen and Moonrock samples collected by the Apollo program. Further analysis of mineralogy, chemical composition and isotopic composition corroborated the hunch. A few years later, Japanese scientists used the findings to retroactively classify a meteorite discovered in Antarctica by their scientists in 1979 as a Lunar meteorite, as well.
As with lunar meteorites, only about 0.1% of all known meteorites are confirmed to have come from Mars. These meteorites formed on the Red Planet and made their way to Earth following a long journey (likely lasting millions of years) through interplanetary space. The majority of Martian meteorites can be divided into three sub-grouping based on their composition (though all are considered stony meteorites): shergottites, nakhlites and chassignites. Dubbed the SNC group, the first Martian meteorites were ‘discovered’ quite recently; in 1983, scientists were able to prove, based on the composition of various gases trapped in the rock, that a basaltic meteorite found in Antarctica originated from Mars.
As both Lunar and Martian meteorites are few and far between, their commercial and scientific value is exponential.