IN 2005, one day before the comet Tempel 1 made its closest approach to the Sun, NASA scientists got a chance to embrace their inner Hulks. Like rambunctious schoolchildren giddy to cause a little mayhem, they smashed an 820-pound impactor into the comet at tremendous speed, and then -- undoubtedly with large grins plastered upon their faces -- watched what happened.

Almost instantly, a massive cloud of dust began spewing from the 72-trillion-kilogram comet. Subsequent analysis from the nearby Deep Impact probe revealed the presence of silicates, carbonates, metal sulfides, amorphous carbon, and hydrocarbons, as well as water ice, within the plume -- in short, the stuff that life is made of. When the enriched dust cloud dissipated, scientists were able to view their handiwork: a crater 328 feet wide and 98 feet deep.

In the wake of NASA's Deep Impact mission, interest in comets grew by orders of magnitude. Scientists had their first concrete evidence that the frozen hunks of water, rock, and various gases contained the building blocks of life. No longer mere objects to be charted by astronomers and ogled by sky watchers, comets now demanded an existential reverence.

TRAVEL BACK 4 billion years and you might find yourself in the middle of a storm of cataclysmic proportions. At this time, when the planets of the young Solar System weren't neatly synced into their elliptical orbits, it has been theorized that Uranus and Neptune rammed into a reservoir of icy comets, sending asteroidal and cometary debris raining down on the inner planets. During the Late Heavy Bombardment, as the event is called, the Earth was getting slammed, so much, in fact, that if life existed, the surface may have been sterilized. As many as 22,000 objects rocked our home over a period of 300 million years. However, in subsurface cracks created by the pummeling, life could have been boosted, or even seeded. Recent research suggests that impacts of comets containing organic compounds could generate peptides, the building blocks of proteins. The Solar System's most cataclysmic storm could very well have been a drizzle of life.

EVEN MORE ASTOUNDING, some of the comets that struck Earth could have already contained life. The chances are remote, but it is possible. According to recent research published to the journal Astrobiology, large comets with a radius of over 10 kilometers could contain liquid water at their cores. The decay of radioactive isotopes of aluminum or iron could supply the heat necessary to melt the inner ice. Katharina Bosiek, along with her colleagues Michael Hausmann and Georg Hildenbrand, suggest that a thick layer of dust could protect the core's liquid environment from solar radiation, echoing learned speculations found in prior research. Their findings make the hopeful words of Nalin Chandra Wickramasinghe, the Cardiff University astrobiologist who was one of the earliest proponents of panspermia, believable.

"Supposing comets were seeded with microbes at the time of their formation from pre-solar material, there would be plenty of time for exponential amplification and evolution within the liquid interior," he wrote in 2009.

In this view, large comets could be seen as enchanting snow globes just waiting to be smashed upon fertile ground, thus releasing the microbial life contained inside. It's not inconceivable. Some of Earth's extremophiles display surprising resilience to the inhospitable conditions of space, and they didn't even evolve there.

Skepticism is called for, however. Given the sometimes transient nature of comets and the harsh conditions of space, it's hard to imagine that life, if it ever existed inside them, could still exist today. Still, the tantalizing notion makes a mission to the Solar System's Kuiper Belt or Oort Cloud, where as many as 100,000 comets reside, that much more tempting.

Reference: Bosiek Katharina, Hausmann Michael, and Hildenbrand Georg. "Perspectives on Comets, Comet-like Asteroids, and Their Predisposition to Provide an Environment That Is Friendly to Life." Astrobiology. March 2016, ahead of print. doi:10.1089/ast.2015.1354.

(Image: NASA)