Heat Shield Rock
Encyclopedia
Heat Shield Rock is a basketball
Basketball
Basketball is a team sport in which two teams of five players try to score points by throwing or "shooting" a ball through the top of a basketball hoop while following a set of rules...

-sized iron-nickel meteorite found on Mars
Mars
Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...

 by the Mars rover Opportunity
Opportunity rover
Opportunity, MER-B , is a robotic rover on the planet Mars, active since 2004. It is the remaining rover in NASA's ongoing Mars Exploration Rover Mission...

 in January 2005. The meteorite was formally named Meridiani Planum meteorite by the Meteoritical Society
Meteoritical Society
The Meteoritical Society is a non-profit scholarly organization founded in 1933 to promote research and education in planetary science with emphasis on studies of meteorites and other extraterrestrial materials that further our understanding of the origin and history of the solar system.The...

 in October, 2005 (meteorites are always named after the place where they were found).

Discovery

Opportunity encountered the meteorite entirely by chance, in the vicinity of its own discarded heat shield
Heat shield
A heat shield is designed to shield a substance from absorbing excessive heat from an outside source by either dissipating, reflecting or simply absorbing the heat...

 (hence the name). Opportunity had been sent to examine the heat shield after exiting the crater Endurance
Endurance (crater)
Endurance is an impact crater on Mars that was visited by the Opportunity rover from May until December 2004. Mission scientists named the crater after the ship Endurance that sailed to the Antarctic in an exploration voyage organized by Ernest Shackleton.The rover entered the crater interior on...

. This was the first meteorite found on another planet and the third found on another Solar System body — two others, Bench Crater
Bench Crater meteorite
The Bench Crater meteorite is a meteorite discovered on the Moon in 1969. It was the first meteorite to be discovered on a solar system body other than the Earth. It is listed as a carbonaceous chondrite by the Meteoritical Society.-References:...

 and Hadley Rille
Hadley Rille meteorite
The Hadley Rille meteorite was a meteorite discovered on the Moon at coordinates 26° 26' 0" N, 3° 39' 20" E, during the Apollo 15 mission in 1971. It was the second meteorite to be discovered on a solar system body other than the Earth...

, were found on the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...

.

The rock was initially identified as unusual in that it showed, from the analysis with the Mini-TES
Mini-TES
]The Miniature Thermal Emission Spectrometer is an infrared spectrometer used for detecting the composition of a material from a distance...

 spectrometer, an infrared spectrum that appeared unusually similar to a reflection of the sky. In-situ measurements of its composition were then made using the APXS, showing the composition to be 93% Iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

, 7% Nickel
Nickel
Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...

, with trace amounts of Germanium
Germanium
Germanium is a chemical element with the symbol Ge and atomic number 32. It is a lustrous, hard, grayish-white metalloid in the carbon group, chemically similar to its group neighbors tin and silicon. The isolated element is a semiconductor, with an appearance most similar to elemental silicon....

 (~300 ppm) and Gallium
Gallium
Gallium is a chemical element that has the symbol Ga and atomic number 31. Elemental gallium does not occur in nature, but as the gallium salt in trace amounts in bauxite and zinc ores. A soft silvery metallic poor metal, elemental gallium is a brittle solid at low temperatures. As it liquefies...

 (<100 ppm). Mössbauer spectra show the iron to be primarily in metallic form, confirming its identity as an iron-nickel meteorite
Meteorite
A meteorite is a natural object originating in outer space that survives impact with the Earth's surface. Meteorites can be big or small. Most meteorites derive from small astronomical objects called meteoroids, but they are also sometimes produced by impacts of asteroids...

, composed of kamacite
Kamacite
Kamacite is a mineral. It is an alloy of iron and nickel, usually in the proportions of 90:10 to 95:5 although impurities such as cobalt or carbon may be present. On the surface of Earth, it occurs naturally only in meteorites. It has a metallic luster, is gray and has no clear cleavage although...

 with 5-7% nickel
Nickel
Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...

. This is essentially identical to the composition of a typical IAB iron meteorite found on Earth. The surface of the rock shows the regmaglypts, or pits formed by the ablation of a meteorite during passage through the atmosphere, characteristic of meteorites.

No attempt was made to drill into the meteorite using the Rock Abrasion Tool
Rock Abrasion Tool
The Rock Abrasion Tool is a grinding and brushing installation on NASA’s twin Mars Exploration Rovers, Spirit and Opportunity , which landed on Mars in January 2004...

 (RAT), because testing on iron meteorites on Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

 showed that the rover's drilling tools would be abraded and damaged. The RAT was designed to drill into ordinary rock, not into iron-nickel alloy. Meridiani Planum
Meridiani Planum
Meridiani Planum is a plain located 2 degrees south of Mars' equator , in the westernmost portion of Terra Meridiani. It hosts a rare occurrence of gray crystalline hematite...

, the part of Mars where this meteorite was found, is suspected to have once been covered by a layer of material with a thickness of as much as 1 km which has been subsequently eroded. This means that on impact this meteorite might have created a crater, but evidence of that crater may have been subsequently erased by millions, or even billions, of years of erosion. In any case, the meteorite does not show much sign of rust
Rust
Rust is a general term for a series of iron oxides. In colloquial usage, the term is applied to red oxides, formed by the reaction of iron and oxygen in the presence of water or air moisture...

. In the absence of detailed knowledge of the Mars environment, it is difficult to conclude whether it fell recently or was buried until recently. It also shows little sign of weathering.

Following the identification of Heat Shield rock as a meteorite, five similar iron meteorites were discovered by Opportunity (informally named "Block Island", "Shelter Island", "Mackinac
Island", "Oileán Ruaidh", and "Ireland"). Two nickel-iron meteorites were identified by the Spirit rover (informally named "Allan Hills" and "Zhong Shan"). Several candidate stony meteorites have also been identified on Mars.

Note that the term "Martian meteorite" usually refers to something entirely different: meteorites on Earth which are believed to have originated from Mars, a famous example being ALH84001
ALH84001
Allan Hills 84001 is a meteorite that was found in Allan Hills, Antarctica on December 27, 1984 by a team of U.S. meteorite hunters from the ANSMET project. Like other members of the group of SNCs , ALH 84001 is thought to be from Mars. However, it does not fit into any of the previously...

.

See also

  • List of rocks on Mars
  • Bounce Rock
    Bounce Rock
    Bounce Rock is a football-sized primarily pyroxene rock found on Mars by the Mars Exploration Rover Opportunity in April 2004. The rock was named for the fact that it was struck by Opportunity as the craft bounced to a stop during its landing stage....

  • Atmospheric reentry
    Atmospheric reentry
    Atmospheric entry is the movement of human-made or natural objects as they enter the atmosphere of a celestial body from outer space—in the case of Earth from an altitude above the Kármán Line,...


External links

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