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What Exactly Is Astrovirology?

Could Europa harbor life…or viruses? (Image: an artist’s rendition of Europa, NASA / JPL-Caltech)

It’s the prefixes, really. The inner geek in all of us is irrationally impressed by longer titles of scientific fields, whose extra syllables connote don’t-worry-about-it, you-wouldn’t-understand importance.

This, ultimately, was the argument a friend of mine once made when explaining his choice to study astrophysics rather than regular old vanilla physics in college. Sure, there was something about the subject matter in there too, but it was mostly about the cool factor, amplified by that prefix.

Which is all to say that Dale Warren Griffin, a scientist at the U.S. Geological Survey in St. Petersburg, Florida, may have just created the coolest scientific field ever: astrovirology.


In a recent paper published in the journal Astrobiology, Griffin makes the case for viruses as an important target for future life-detection missions beyond Earth. After all, “viruses are the most numerous entities on Earth,” he writes, and while there is debate over whether they technically qualify as life, they are pervasively associated with biology. Each milliliter of seawater contains several million viruses, and an estimated 1031 inhabit the entire planet, wreaking biological havoc in hot springs, the deep ocean, and even inside glaciers. In a particularly irrelevant factoid, Griffin notes that, if stretched end-to-end, the Earth’s viruses would extend 10 million light years (~6×1019 miles) into space.

All told, viruses are the most abundant biologically associated entities we know of; indeed, the modern biological milieu is almost unimaginable without viruses, as they’ve shuttled genes between cells for billions of years, driving evolution in fundamental ways.

So what might extraterrestrial viruses look like? In the tradition of astrobiology, we probably need look no further than analog environments on Earth to find viruses capable of surviving on other planets. Griffin notes that viable viruses have been detected in Yellowstone and Italian acidic hot springs (93 C, pH 1.5), as well as sub-zero sea ice brine (-12 C). Viruses are also capable of surviving extended dry spells: Nearly 100 percent activity recovery was recorded after 40 years at -70 C, and almost a third of tested species remained viable after ten years at room temperature. With the ability to wait out lean times, viruses would be well suited to pounce on occasional biological blooms or hitchhike on a meteor’s interplanetary journey.

The prospect of viruses on other planets raises two noteworthy corollaries: 1) should be we looking for them as a tent pole of the astrobiological remit?, and 2) could they pose a real threat to life on Earth?

Viruses may well be more abundant than cells in an astrobiological context, but they almost certainly represent a small proportion of overall “biomass” / “biovolume”. A typical virus occupies about 1/1000 the volume of a small bacterial cell; as a matter of strategy, it’s probably smarter to develop detection tools for the haystack, not the needle. And since they require full-blown cells to survive, it’s difficult to imagine scenarios in which viruses would be the only sign of biological activity.

Griffin is relatively sanguine about the risks posed by extraterrestrial viruses brought back to Earth. On the one hand, viruses on this planet are known for their host specificity: In an energetically competitive world, a virus is well advised to focus on adaptations that will overcome specific host defenses and open up a promising niche. Earth life, which presumably will have evolved for billions of years independently of life elsewhere, would likely fall outside of the specificity range of the new viruses.

However, if we find newly evolved viruses, whose form is templated around clay minerals, things could get ugly. As Grffin writes, “it is possible that extraterrestrial viruses at an early evolutionary stage of cellular coevolution may not have yet acquired host specificity and, if encountered, are capable of infecting cellular life of Earth origin.”

There’s no need to stock up on canned goods and retreat to the bunkers just yet, but Griffin’s new field astutely extends an axiom of terrestrial life to the search for life beyond Earth: Where there’s life, there are viruses.