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Caitlin: If there’s anything we’ve learned from more than 50 years of space travel, it’s that space can be dangerous. Which is why we have robots to help us deal with some of those dangers. Last week, NASA invited teams to sign up for a competition to build some of the most advanced space robots yet. It’s called the Space Robotics Challenge, and the prizes add up to a million dollars.

NASA’s already built a humanoid robot, called Robonaut 5, or Valkyrie. For the challenge, teams will program a virtual version of Valkyrie. First, there’s a qualifying round, where a simulation of Valkyrie has to complete basic tasks like identifying a pattern of colored lights or walking through a doorway. Which sounds easy, but it is not!

The teams that pass that round will advance to the official competition, which involves performing three tasks after a computer-simulated dust storm on Mars. Large dust storms happen several times a year on Mars, so a future space robot would probably have to make these kinds of repairs all the time. First, the robot will have to grab the handles on a communications dish and adjust it to within five degrees of the target.

Next, it’ll walk to a rover, collect a solar panel, and install it into an existing array. Finally, Valkyrie will walk to a habitat, climb the stairs to get inside, and use a leak detector tool to find an air leak. Then it’ll press a button on the virtual repair tool to stop the leak.

Once all that’s done, the simulated robot will head over to the finish line. Each team’s simulation will need to complete five rounds of the tasks, with the positions of the objects changing every time. And there’s a time limit, too: depending on the task, Valkyrie will have between 30 minutes and 2 hours to finish.

The top four teams of the virtual challenge will be awarded time with a real Valkyrie for at least two weeks, where they can put their code to the test and prepare for a real-life, physical version of the challenge in late 2017. Eventually, NASA hopes humanoid robots like Valkyrie will assist human crews traveling to Mars with basic tasks and repairs. These robots will also be useful here on Earth, for things like disaster relief and industrial plant maintenance. If you’re interested in competing, there’s a link to the competition website in the description. Good luck!

Meanwhile, astronomers are discovering new things much farther from home. In a study published this week in the journal Nature, researchers announced that they’ve discovered the first direct evidence for hibernating novas. Novas are different from supernovas, those beautiful, powerful explosions that happen when a star is dying. Novas are much smaller explosions, and the star usually doesn’t die in the process. Regular novas happen only in binary star systems, where a white dwarf and another small star orbit their center of mass.

The white dwarf pulls hydrogen away from its partner star, and eventually, the gas builds up and causes a runaway fusion reaction in the white dwarf. In this reaction, tons of hydrogen is fused into heavier elements, which makes the star erupt with a huge amount of heat and light. Boom – a nova!

Novas are the most common explosions in the galaxy, and they’re usually visible to the naked eye, so we’ve known about them for a while. But we’re only now finding the first direct evidence of nova systems going through cycles and exploding multiple times. In 2003, a team of astronomers from the University of Warsaw in Poland began monitoring a nova over 20,000 light years from Earth that we now call Nova Centauri 2009.

As its name suggests, the nova erupted in 2009, but because the team had been monitoring it for six years before the explosion, they were able to study exactly how the system evolved. They found the mass-transfer rate of the system — that is, the rate the white dwarf takes hydrogen from its partner — isn’t constant. When the astronomers began monitoring the system, it had a relatively low mass-transfer rate, meaning that not a lot of hydrogen was moving to the white dwarf. But it was enough to cause an explosion.

Right after the eruption, though, the mass-transfer rate went way up. In 2011, it was 800 times higher than before the explosion! This kind of behavior almost exactly matches what’s known as the nova hibernation hypothesis, and it’s the first direct evidence we have to support it.

The idea is that novas go through a kind of life cycle, exploding, staying active for a while, then hibernating before they wake up and explode again. If the hypothesis is correct, then the mass-transfer rate of a nova system should increase dramatically right after an explosion and stay high for hundreds of years. Then the rate should decrease for thousands or millions of years.

The system enters hibernation, where the mass-transfer rate is low. Eventually, the nova should start collecting hydrogen more rapidly, leading to another explosion, and starting the process all over again. With Nova Centauri 2009, we’ve now seen a few of these steps.

The only difference between this system and what the hypothesis predicts is that Nova Centauri 2009 may have never entered total hibernation. This system is probably too small to go into complete hibernation — instead, the mass-transfer rate just decreases between explosions. Larger novas would go into hibernation and then wake up before exploding. We don’t yet know why novas to wake up. But we do know that their nap-times have very dramatic endings.

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