Asteroid carried unlikely cargo.
They also brought some mystery. Scientists have discovered some unexpected hitchhikers in the meteorites: amino acids. Here on Earth, we know about amino acids because they're an important part of proteins, and proteins are crucial to life. Every life form, including humans, uses proteins, which are made of strings of amino acids. For this reason, amino acids are often called the "building blocks" of proteins - and the building blocks of life.
Amino acids are also called organic compounds because they contain atoms of carbon, another basic ingredient for life. Amino acids are important to life - but they're not life itself. In other words, the meteorites did not ferry extraterrestrial life from outer space to Earth's surface. But finding amino acids that come from beyond the confines of our planet makes scientists more optimistic about finding life in outer space.
"Amino acids are forming in environments that we really didn't think were possible," Daniel Glavin told Science News. Glavin, a researcher at NASA's Goddard Space Flight Center in Greenbelt, Md., has been studying the asteroid's rocky remains.
Finding amino acids in the asteroid fragments was surprising for many reasons. These types of amino acids are either rare or nonexistent on Earth, so they're different from the kinds that make up life as we know it. That means the amino acids were most likely part of the rocks before those rocks fell to Earth.
The asteroid, called 2008 TC3, was probably a fragment of a planet that existed in the earliest days of the solar system. That planet would have formed when temperatures were high enough to melt iron - and way too high for amino acids to stay together. So it doesn't seem likely that the amino acids formed when the planet formed. They must have come later.
There's more to the mystery. On Earth, amino acids cannot form unless there's water around. But the meteorite where Glavin and his team found the amino acids is the kind that comes from asteroids that don't have water.
These puzzle pieces lead Glavin to wonder whether there are other ways to form amino acids - ways that don't require water. Ways scientists have not yet discovered. If there are, then maybe there are other recipes for life itself.
If there's another, yet unknown way to make amino acids, then it "increases the likelihood, in my opinion, of life existing elsewhere in the universe," Glavin told Science News.
The early days of the solar system were rough and violent, and that early planet probably flew through space, smashing into other giant rocks and breaking into pieces. Some pieces from those other rocks stuck to the asteroid - and as a result, the meteorites that fell in Africa in 2008 contained many types of rock. It's possible, but not likely, that the amino acids came from some of those other rocks.
Glavin, though, suspects the amino acids formed on the asteroid, but long after it had cooled down. They may have come about through a chemical process that involved gases such as carbon monoxide, hydrogen, ammonia and a metal such as iron or nickel.
This discovery is the kind that energizes scientists who are looking for life beyond Earth. Nature often exceeds our imaginations - and always merits more investigation.
meteorite A mass of rock or metal that has fallen to Earth's surface from outer space without burning up in Earth's atmosphere.
asteroid Any of numerous small celestial bodies that orbit the sun, chiefly between Mars and Jupiter. Most have diameters between a few and several hundred kilometers.
amino acids Organic compounds that link together to form proteins.
protein A complex organic molecule that contains carbon, hydrogen, oxygen, nitrogen and usually sulfur and is composed of chains of amino acids. Proteins are vital to life.
* Going Deeper:
Cowen, Ron. 2010. "Space Rock Surprise," Science News, Dec. 21. Available at http://www.sciencenews.org/view/generic/id/67932/title/Space_rock_surprise
Ornes, Stephen. 2009. "The Earth-bound asteroid scientists saw coming," Science News for Kids, Apr. 15. Available at http://www.sciencenewsforkids.org/articles/20090415/Note3.asp
Gaidos, Susan. 2008. "Meteorites may have sparked life on Earth," Science News for Kids, Dec. 17. Available at http://www.sciencenewsforkids.org/articles/20081217/Note2.asphttp://www.sciencenewsforkids.org/articles/20110112/Note1.asp From Science News for Kids January 12, 2011. Copyright (c) 2010 Science Service. All rights reserved.