Scientists who want to study the effects of weightlessness have always had precious few options. There's the "vomit comet," NASA's Weightless Wonder plane that creates a few seconds of weightlessness during parabolic flights. Or they could convince the space agency to actually launch their experiments into the great beyond.
But there might be an easier and cheaper way: levitation.
, physicist Richard Hill and colleagues used superconductive magnets to levitate fruit flies for an extended period of time, allowing them to study the long-term effects of weightlessness on the insects' biology. A fruit fly is a far cry from a human, but studying insects in weightlessness here on Earth is much cheaper than doing so inside a satellite 220 miles away in space, and even fruit flies could tell scientists something about how humans and their DNA will react to long-duration spaceflight.
Hill and his team, working at the University of Nottingham in England, used a powerful superconducting magnet to produce a magnetic field of approximately 16 Tesla, nearly 350,000 times stronger than the strength of the Earth's field. Operating at ultralow temperatures, superconductors offer no electrical resistance and, key to this experiment, they expel magnetic fields, which means they repel magnets. This repulsion can be stronger than the force of gravity, which leads to levitation.
The magnet created what's known as a diamagnetic force, which can be large enough to balance the force of gravity, lifting the Drosophila melanogaster flies and suspending them midair. Diamagnetic materials, such as water, are pushed away by magnetic fields, so a powerful magnetic field can hold up small organisms like flies and frogs because they're mostly made up of water.
The Nottingham team studied fruit flies because previous research has shown that spaceflight does funny things to them. Weightless fruit flies move their legs and wings more quickly than flies under normal Earth gravity, Hill says. But it remained unclear if microgravity was behind this behavior, rather than other aspects of space travel, such as g-forces experienced during launch. His study reveals that zero gravity is, in fact, the reason the flies act so strangely.
"The flies in the levitation conditions behave in exactly the same way that they do on board the International Space Station," Hill says. "So what we found with this technique, is we can re-create effects and reproduce behavior that they're seeing in orbit, on the ground."
"The type of weightlessness provided by levitation is not nearly perfect as you'd get on a space station for example, but doing these experiments on the ground is tremendously cheaper and more convenient than it is in space," he says. "It's possible to investigate the likely effects of weightlessness on biological organisms before spending all that money launching them into orbit."
Why Study Fruit Flies?
Floating flies is just the first step. Hill says he now wants to pinpoint exactly which biological mechanism zero gravity affects to change the flies' behavior. "Once that is identified, then it may very well be that there could be some indications for human biology [in zero gravity]," he says.
Indeed, we have more in common with the common fruit fly than you might think. Approximately 75 percent of known human disease genes have a recognizable match in D. melanogaster's genome, which was sequenced in 2000. Fifty percent of fly protein sequences have mammalian homologs. Fruit flies were the first animals sent into space, traveling aboard a U.S.-launched rocket in 1947, and they're one of the most commonly studied creatures in science. That means researchers already have a deep well of knowledge about the fruit fly to help them understand what's happening to it in zero-g, and what that could mean for other organisms.
For now, superconducting magnets can levitate only small organisms, such as mice and frogs—the diamagnetic forces that supeconductors create aren't powerful enough to overcome gravity in the case of a person. But simulating zero gravity this way means experiments can be sustained longer and allow for more observation compared with other kinds of weightlessness tests, both on land and in space. That, Hill says, could help scientists to investigate some of the major challenges of sending humans into space for long durations.
"Astronauts' bones become weak and brittle after long periods in space, and these experiments may be something we could do with levitation," Hill says. "We can keep organisms levitating for days or weeks or even months at a time."
Plus, he says, if humans are serious about making lengthy space journeys in the future, then they'd probably want to take some animals along. So it's important to determine how space travel will affect all involved—not just people.
"In terms of human survival in that context, then it's very important to determine the effect of weightlessness on a whole range of biological organisms, and fruit flies are a very good model to start with," Hill says.