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How Deadly Would Extraterrestrial Bacteria Be to Humans?

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How deadly would a bacterium be to humans if it was brought from a completely different star system?

Drew Smith:

The chance that extraterrestrial bacteria would be deadly to humans is zero. Not just very, very small. Zero.

Pathogenesis requires intimacy. This intimacy is attained through millions of years of co-evolution. The need for intimacy is apparent when you look at how bacteria and viruses cause infections and disease.

Infection requires binding to a cell surface. Bacteria (and viruses) bind to human cells through proteins that recognize human proteins and carbohydrates. The structure of these human proteins and carbohydrates is, to a first approximation, arbitrary. There are an almost infinite number of permutations of them that could exist and work just fine. But only one does exist. The chance that an alien bacteria would have evolved to stick to that protein is infinitesimally small.

Even if this alien bacterium were able to stick to a cell surface, this alone would not establish an infection. Infecting bacteria secrete all kinds of toxins and virulence factors. These toxins and factors bind to specific human proteins. They block or modify their activity in ways that degrade cells and tissues, releasing nutrients that the bacteria can feed upon.

Again, the target proteins have fairly arbitrary structures. They are the result of billions of years of evolutionary history and their precise structure—and even their existence is not at all predictable. The chance that an alien bacterium would have evolved toxins that precisely target them is infinitesimally small.

Pathogenicity is extremely rare on Earth. There are millions, perhaps billions, of species of bacteria. The number of potential human pathogens among them is very small, no more than a couple hundred. And only a couple dozen are able to infect otherwise healthy humans. These are bacteria that have been with us for millions of years, evolving as we evolve, becoming intimately familiar with our proteins, our cells, our immune systems.

This knowledge is stamped into their genomes; it is a diary of their long association with us. It is not a book that could be written in an alien language. Alien bacteria are no more likely to be human pathogens than intelligent aliens are likely to speak Urdu as their native tongue. It just isn’t possible.

This post originally appeared on Quora. Click here to view.

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Space
The Fascinating Device Astronauts Use to Weigh Themselves in Space

Most every scale on Earth, from the kind bakers use to measure ingredients to those doctors use to weigh patients, depends on gravity to function. Weight, after all, is just the mass of an object times the acceleration of gravity that’s pushing it toward Earth. That means astronauts have to use unconventional tools when recording changes to their bodies in space, as SciShow explains in the video below.

While weight as we know it technically doesn’t exist in zero-gravity conditions, mass does. Living in space can have drastic effects on a person’s body, and measuring mass is one way to keep track of these changes.

In place of a scale, NASA astronauts use something called a Space Linear Acceleration Mass Measurement Device (SLAMMD) to “weigh” themselves. Once they mount the pogo stick-like contraption it moves them a meter using a built-in spring. Heavier passengers take longer to drag, while a SLAMMD with no passenger at all takes the least time to move. Using the amount of time it takes to cover a meter, the machine can calculate the mass of the person riding it.

Measuring weight isn’t the only everyday activity that’s complicated in space. Astronauts have been forced to develop clever ways to brush their teeth, clip their nails, and even sleep without gravity.

[h/t SciShow]

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Watch Astronauts Assemble Pizza in Space
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Most everyone enjoys a good pizza party: Even astronauts living aboard the International Space Station.

As this video from NASA shows, assembling pizza in zero gravity is not only possible, it also has delicious results. The inspiration for the pizza feast came from Paolo Nespoli, an Italian astronaut who was craving one of his home country’s national dishes while working on the ISS. NASA’s program manager for the space station, Kirk Shireman, sympathized with his colleague and ordered pizzas to be delivered to the station.

NASA took a little longer responding to the request than your typical corner pizzeria might. The pizzas were delivered via the Orbital ATK capsule, and once they arrived, the ingredients had to be assembled by hand. The components didn’t differ too much from regular pizzas on Earth: Flatbread, tomato sauce, and cheese served as the base, and pepperoni, pesto, olives, and anchovy paste made up the toppings. Before heating them up, the astronauts had some fun with their creations, twirling them around like "flying saucers of the edible kind,” according to astronaut Randy Bresnik.

In case the pizza party wasn’t already a success, it also coincided with movie night on the International Space Station.

[h/t KHQ Q6]

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