By Jonny Lupsha, Wondrium Staff Writer
NASA’s plan to bring Martian rocks to Earth may have some tiny stowaways. Despite what our favorite science fiction tells us, if there are any Martians, they’re probably still viruses or bacteria. Microbes still count as aliens, right?
In H. G. Wells’ novel The War of the Worlds, seemingly invincible aliens launch ships from Mars and attack humanity, only to run afoul of our diseases. At NASA, scientists are considering an inversion of this famous story: What if a mission that brought soil and rocks from Mars back to Earth for examination contained microorganisms like viruses or bacteria?
Farfetched as it may sound, it’s still a possibility—an unlikely one, but a possibility nonetheless. Despite the wilder conspiracy theories about life on other planets, there is much legitimate scientific study of the idea. In his video series Understanding the Misconceptions of Science, Dr. Don Lincoln, Senior Scientist at Fermi National Accelerator Laboratory, explains the science of aliens—and why they’re probably not silicon-based.
Better Living through Chemistry
All life on Earth is carbon-based, and carbon is the fourth most abundant element in the known universe. So why is life carbon-based? A look at its column in the periodic table provides a hint.
“When we get to the column containing carbon, silicon, germanium, and tin, we have elements that can make four atomic bonds,” Dr. Lincoln said. “Carbon is an amazing and versatile element. It’s because of its ability to make four atomic bonds with other elements that is why life is based on it. Just look at organic molecules compared to inorganic ones.”
Inorganic molecules include ammonia, or NH3; and water, or H2O. These elements tend to include just a few atoms connected by a couple bonds. Organic molecules, on the other hand, are exceedingly complex. Even the most basic, like caffeine, has the formula C8H10N4O2. Our DNA is a molecule as well, despite its complexity.
“In order to make such complex structures, it’s crucial that molecules are involved that can make lots and lots of bonds, and carbon is your guy,” Dr. Lincoln said. “Bottom line, carbon makes life possible.”
Is Silicon-Based Life Possible?
On the periodic table, silicon is below carbon, meaning it can also make four atomic bonds with other elements. This has led many to speculate that, since silicon has the potential for such complex molecular structures, just like carbon, silicon-based life could exist in other star systems. However, Dr. Lincoln suggested otherwise.
“When carbon makes four atomic bonds with all of its neighbors, the bonds tend to be the same strength,” he said. “In silicon, the first bond is much stronger than the others, which means the first bond is far more stable than the others. It’s because the first bond is formed when the electrons from each atom reach directly to the other atom in a metaphorical handshake.
“The other bonds are formed from electrons that are further away and they effectively don’t get as good a grip.”
Furthermore, when we breathe, we inhale oxygen and exhale CO2, or carbon dioxide. If a silicon-based lifeform used oxygen for its energy cycle, it would exhale SiO2, or silicon dioxide. The common name for silicon dioxide is rock. Therefore, any silicon-based lifeform that uses oxygen would exhale sand.
In the unlikely event that any simple life forms exist on Mars and are brought back with study samples, it’s even less likely that they would be silicon-based lifeforms.