Featured Research

from universities, journals, and other organizations

Meteorites From Inner Solar System Match Up To Earth's Platinum Standard

Date:
October 4, 2008
Source:
Europlanet
Summary:
Some of the world's rarest and most precious metals, including platinum and iridium, could owe their presence in the Earth's crust to iron and stony-iron meteorites, fragments of a large number of asteroids that underwent significant geological processing in the early Solar System.

Artist's impression of asteroid impact with early Earth that led to lunar formation.
Credit: ESA

Some of the world’s rarest and most precious metals, including platinum and iridium, could owe their presence in the Earth’s crust to iron and stony-iron meteorites, fragments of a large number of asteroids that underwent significant geological processing in the early Solar System.

Dr Gerhard Schmidt from the University of Mainz, Germany, has calculated that about 160 metallic asteroids of about 20 kilometres in diameter would be sufficient to provide the concentrations of these metals, known as Highly Siderophile Elements (HSE), found in the Earth’s crust. Dr Schmidt will be presenting his findings at the European Planetary Science Congress in Mόnster on Monday 22nd September.

Dr Schmidt said, “A key issue for understanding the origin of planets is the knowledge of the abundances of HSE in the crust and mantle of the Earth, Mars and the Moon. We have found remarkably uniform abundance distributions of HSE in our samples of the Earth’s upper crust. A comparison of these HSE values with meteorites strongly suggests that they have a cosmochemical source.”

During a 12-year study, Dr Schmidt and colleagues have analysed the concentrations of HSE at meteorite impact sites around the world, as well as in the samples from the Earth’s mantle and crust. In addition, he has compared the data from the Earth with data from impact breccias from the Moon brought by the Apollo missions and Martian meteorites, believed to be samples from the mantle and crust on Mars.

Although HSE were present in the nebula from which the Earth formed, as the young planet evolved and heated up they were stripped, along with other heavy elements, from the silicate mantle into the iron and nickel-rich metallic core. The presence of HSE in the mantle is still a matter of debate. However, a widely accepted theory is that HSE were added by meteorite impacts as a veneer of material over the Earth’s surface after the core had formed, about 20-30 million years after the planet’s accretion. This could have been by the collision with a Mars-sized impactor that led to the formation of the Moon.

Different classes of meteorites have characteristic elemental ratios of HSE that give indications where in the Solar System they formed. However, the characteristic ratios of HSEs in the Earth’s upper mantle (for example the ruthenium/iridium element ratio of about 2) match up with theoretical predictions for asteroids formed in the Mercury-Venus region.

The Earth is a differentiated body, with a iron-nickel core, a silicate mantle, and evolved silicate crust. Dr Schmidt’s study shows that the abundance ratios of HSE in the Earth’s crust are much higher than those found in stony meteorites, known as chondrites, which represent the pristine material from the early Solar System. The ratios of HSE found in the crust bear a much closer resemblance to iron or stony-iron meteorites. These are fragments of larger asteroids that have had enough internal heat in the past to form a molten metal core. The HSE concentrate preferentially in the liquid core and at the boundary with the solid, rocky envelope. However, the exact ratios of the different metals depend on the physical conditions under which they were formed.

The ratios of HSE found in the Earth’s upper mantle do not exactly match any specimens of meteorites found in collections around the world. Close to the mantle highly siderophile element ratios are data from the iron meteorite Charlotte.

To date, about 20 iron meteorites and about 20 stony meteorites, called chondrites, have been identified as projectiles of the 175 known impact craters on Earth. The projectiles for the other 135 impact craters on Earth are still unknown. No meteorites have been identified as being formed in the region between Mercury and Venus.

Intriguingly, some of the Martian meteorites which are probably most representative of

the Martian crust also have HSE values that resemble groups of iron meteorites and stony irons, suggesting that a similar process took place on Mars.

Dr Schmidt said “The first meteorite to be found on Mars was an iron meteorite, discovered by the Opportunity rover in January 2005. Analysis of the Nahkla, Shergotty and Zagami Martian meteorites strongly supports a genetic link with certain iron meteorites and pallasites.”

Notes: Siderophile (iron-loving) elements are a group of high-density transition metals that tend to bond with metallic iron in the solid or molten state. The HSE group includes rhenium (Re), osmium Os), iridium (Ir), ruthenium (Ru), rhodium (Rh), platinum (Pt), palladium (Pd) and gold (Au).


Story Source:

The above story is based on materials provided by Europlanet. Note: Materials may be edited for content and length.


Cite This Page:

Europlanet. "Meteorites From Inner Solar System Match Up To Earth's Platinum Standard." ScienceDaily. ScienceDaily, 4 October 2008. <www.sciencedaily.com/releases/2008/09/080922100455.htm>.
Europlanet. (2008, October 4). Meteorites From Inner Solar System Match Up To Earth's Platinum Standard. ScienceDaily. Retrieved September 22, 2014 from www.sciencedaily.com/releases/2008/09/080922100455.htm
Europlanet. "Meteorites From Inner Solar System Match Up To Earth's Platinum Standard." ScienceDaily. www.sciencedaily.com/releases/2008/09/080922100455.htm (accessed September 22, 2014).

Share This



More Space & Time News

Monday, September 22, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

NASA's MAVEN Spacecraft Has Finally Reached Mars

NASA's MAVEN Spacecraft Has Finally Reached Mars

Newsy (Sep. 22, 2014) — After a 10-month voyage through space, NASA's MAVEN spacecraft is now orbiting the Red Planet. Video provided by Newsy
Powered by NewsLook.com
Raw: SpaceX Rocket Carries 3-D Printer to Space

Raw: SpaceX Rocket Carries 3-D Printer to Space

AP (Sep. 22, 2014) — A SpaceX Rocket launched from Cape Canaveral, carrying a custom-built 3-D printer into space. NASA envisions astronauts one day using the printer to make their own spare parts. (Sept. 22) Video provided by AP
Powered by NewsLook.com
SpaceX Cargo Ship Blasts Off Toward Space Station

SpaceX Cargo Ship Blasts Off Toward Space Station

AFP (Sep. 21, 2014) — SpaceX's unmanned Dragon cargo ship blasts off toward the International Space Station, carrying a load of supplies and science experiments for the astronauts living there. Duration: 00:35 Video provided by AFP
Powered by NewsLook.com
NASA's MAVEN To Study Martian Atmosphere

NASA's MAVEN To Study Martian Atmosphere

Newsy (Sep. 21, 2014) — NASA's Maven will soon give information that could explain what happened to Mars' atmosphere. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins