The long journey of the Tagish Lake meteorite

The Tagish Lake meteorite contains abundances of carbonaceous material. Photo: Michael Holly, Creative Services, University of Alberta
The Tagish Lake meteorite contains abundances of carbonaceous material. Photo: Michael Holly, Creative Services, University of Alberta

Mainz, July 2nd, 2019

An international research team has found that the Tagish Lake meteorite, which hit Canada 19 years ago, contains abundances of carbonaceous material formed in the outer reaches of the solar system. The discovery sheds new light on the celestial body’s origin.

It was just before nine o'clock on a cold January morning in 2000, when a fireball lit up the sky over the Canadian province of British Columbia. Shortly after, a 200-ton meteorite crashed on the frozen surface of Tagish Lake. The loud explosion caused earth tremors over a wide area.

The Tagish Lake meteorite shattered into hundreds of small pieces. Since then, scientists from all over the world have been examining these black fragments. An international team including Peter Hoppe, Research Group Leader at the Max Planck Institute for Chemistry in Mainz, have now discovered more about the origins of the meteorite.

Having analyzed the carbon isotopes in the rock fragment, the scientists infer that the parent body of the Tagish Lake meteorite originated in the cold outer areas of our solar system where Uranus and Neptune formed, or even further from the sun in the Kuiper belt. The Kuiper belt comprises a multitude of smaller objects. Many comets originate from this area of the solar system.

The Tagish Lake meteorite is classified as a carbonaceous chondrite and is a fragment of a D-type asteroid. Asteroids are small celestial bodies found mainly in an area between the orbits of Mars and Jupiter known as the asteroid belt. D-type asteroids have a surface which is mostly composed of silicates with carbon contents. They have a very low albedo, meaning that they only reflect a small amount of incoming radiation. D-type asteroids are comparatively rare and are located in the outer regions of the asteroid belt or in orbits similar to that of Jupiter.

“The ambient temperature under which an asteroid formed is critical to pinpointing its original position and is determined by the abundance of volatiles the asteroid contains,” explains Hoppe. The researchers measured the abundance of carbonates and the ratio between the carbon isotopes 13C and 12C in the Tagish Lake meteorite and found a high amount of 13C. This amount is higher than in other meteorites, but similar to that of CO2 in comet 67P/Churyumov-Gerasimenko, as recently measured by the Rosetta spacecraft. “Carbonates are produced by aqueous reactions of CO2 with calcium or another element. This discovery suggests that there was once a large amount of 13C-rich CO2 ice in the parent asteroid,” explains Hoppe.

From this, the scientists conclude that the parent body of the found meteorite must have originated in the outer area of the solar system, where the temperatures are low enough for CO2 to freeze. The scientists discovered a further important indication in the CO2/H2O ratio. The measured ratio in the Tagish Lake meteorite is significantly greater than that in other carbonaceous chondrites. These results are however similar to the ratio found in comets. From this, the team has concluded that some D-type asteroids formed in the cold outer solar system and were subsequently transported into the inner solar system due to gravitational interactions with the giant planets Jupiter, Saturn, Uranus and Neptune.