By Brendt C. Hyde, ROM Mineralogy Technician
Meteorites can come from a variety of locations. Most often we think of them as pieces of rock ejected off of asteroids during big collisions in space. However, these collisions also happen on the planets and moons in our solar system. The Earth has luckily been able to collect a number of meteorites from our moon and from the planet Mars. This month we take a look at a rock from Mars.
A number of the meteorites you will see in the “meteorite of the month” blog will have names starting with “NWA”. This is probably a good time to teach everyone what these letters represent. Meteorites are named for where they are found on Earth and in this case (and in many others) our meteorite was found in Northwest Africa. Most meteorites are found in hot and cold deserts. This is not because meteorites hit these areas more often, it just happens to be easier to spot a dark rock from space sitting in the middle of a barren desert.
Rocks from Mars are broken down into three categories: shergottites, nakhlites and chassignites. This is why you may hear martian meteorites referred to as SNC meteorites. This month we are looking at a shergottite. NWA 5298 is similar to rocks on Earth that form from volcanic activity, in fact, it is thought to have formed in a thick lava flow. You are probably now thinking – well if these types of rocks can form on Earth, how do we know they are from Mars? Good question. Martian meteorites were first shown to originate from Mars by examining gases trapped in the meteorites. The elements in these trapped gases matched those found in the martian atmosphere. Since this discovery, a number of other lines of evidence have been found to link all of the martian meteorites. Most rely on elemental and isotopic compositions that I will not go into here.
The ROM holds 425 g of NWA 5298 including the main mass which measures 8.5 x 7.5 x 3.5 cm. It was found in March of 2008 and has a distinctive brown exterior caused by weathering (rusting) from sitting on the Earth’s surface. The interior is much fresher and contains a mixture of minerals, such as pyroxene and plagioclase, and glass. This glass was likely formed during the high pressure impact event that sent the rock hurtling towards the Earth. This meteorite is currently on loan from Dr. David Gregory awaiting future donation and can be seen in the Teck Suite of Galleries: Earth’s Treasures.
The shergottite meteorites are very intriguing scientifically. There has been a long debate about the actual age of these rocks. Some believe they formed as part of the ancient martian crust near the beginning of the solar system, while others believe they are much younger. The actual age of meteorites from Mars is important for a number of reasons. The ages help scientists determine how long Mars was volcanically (or otherwise) active. This has implications for studying how planets evolve over time. It could also help scientists determine if heat from the martian interior or from large impacts was sufficient to help support life. The ROM’s outstanding collection of martian main masses gives ROM scientists a wide variety of rocks for study and there are several research projects currently underway. ROM scientists hope to help settle the age debate and are devoting a lot of study to the martian meteorite collection.