[♪ INTRO] Life in our universe can sometimes be precarious.

Animals are going extinct, huge asteroid collisions, runaway climate change… there’s a lot that can go wrong. Two stories that have been in the news over the past couple of weeks really drive that point home, starting with the asteroid that got a little too close for comfort.

If you didn’t hear about it, uh, neither did astronomers. Until a few days later when they noticed it zooming away from us. Around 3:30 in the morning Universal Time on July 21, asteroid 2017 OO1 passed within 125,000 kilometers of Earth, or less than a third the distance to the Moon.

And astronomers didn’t detect it until July 23. Not really how we wanna be doing things. It’s not exactly tiny, either.

The asteroid is somewhere between 35 and 75 meters wide, or around three times the size of a house, and was moving at more than 37,000 kilometers an hour. If it did hit Earth, the impact wouldn’t have been enough to wipe us out like the dinosaurs or anything, but it definitely would’ve created some fireworks. For comparison, the viral-video inspiring 2013 asteroid that entered Earth’s atmosphere near Chelyabinsk in Russia was just 20 meters across, and even that was pretty dramatic.

The Chelyabinsk asteroid was brighter than the Sun as it approached, could be seen 100 kilometers away, and damaged thousands of buildings. And that’s all despite the fact that it was still 29 kilometers above the ground when it exploded. An asteroid like 2017 OO1 hitting a city would be like a small nuclear bomb.

And we didn’t even notice it until after it passed by. That’s a little scary, I mean, most of Earth isn’t a city, but some of it is. Right now, we do a pretty good job keeping track of things bigger than a kilometer with orbits that take them close enough to Earth’s orbit to be dangerous.

We think we’ve found about 90% of them. But it’s really hard to spot a lot of the asteroids that are smaller than that. And OO1 was especially faint because it doesn’t reflect a lot of light.

The problem is, of course, asteroids smaller than a kilometer can still do plenty of damage. Which is why a lot of scientists think we need to be putting more resources into watching our backs. Of course, just finding dangerous asteroids isn’t enough, we have to be able to actually do something about it.

And that’s hard, because asteroids are big and they’re fast. It’s not easy to make them turn around and go somewhere else. But NASA and the ESA are actually working on a plan to do exactly that, starting with an attempt to redirect a small asteroid that is not a threat to us.

It’s called the Asteroid Impact and Deflection Assessment mission. It involves hitting the asteroid with a small spacecraft about the size of a fridge in 2022. The hope is that the impact will be enough to change the path of the asteroid, because even a tiny change in angle while an asteroid is far from Earth adds up by the time it gets here.

For a future asteroid that’s actually a threat, that might be enough to stop it from crashing into Earth. So here’s hoping it works. But it’s not just life on Earth that’s precarious.

As we learn more about other planets and moons, we’re narrowing down the best places in the universe to look for extraterrestrial life. In a study published this week in Nature Geoscience, researchers announced that there might be fewer life-friendly worlds than we thought. Using a new, more advanced way to model climates, the team found that lifeless, icy planets and moons might be doomed to stay that way for the long haul.

We’re pretty sure life needs liquid water to evolve and survive, so if an icy world is too cold for liquid water, that’s kind of a deal-breaker. But stars increase in brightness over the middle part of their life, and scientists have long thought that when this happens, it might be enough to melt the ice on distant worlds and make them habitable. In other words, it would shift the star’s “Goldilocks zone” where it’s not too hot for liquid water, not too cold for it either.

It’s just right. In our solar system, for example, icy moons like Europa and Enceladus could become a lot more life-friendly in a few billion years. And if this happens to icy worlds on a regular basis, it would mean that there are a lot of warmed-up places to look for life outside our solar system.

But the results of this new study suggest that instead of gradually warming up until they’re habitable, icy moons and planets might go straight from fully frozen to intensely hot, totally skipping those friendlier temperatures in between. The problem is that many of these icy worlds don’t have thick atmospheres like we have on Earth. On our planet, gases like carbon dioxide hold in a lot of the heat we get from the Sun, which helps keep the climate more stable.

Without that, a planet or moon relies completely on the energy it gets from the star at any given moment. And ice happens to be super reflective. Icy planets and moons reflect so much of their parent star’s energy that without gases to trap the heat, the star needs to get way hotter to melt the ice than it otherwise would.

Then, once all of that reflective white stuff is gone, suddenly the much darker water is absorbing a lot of light and heat. Worlds like these would get really hot, really fast, and the water would evaporate before it had the chance to support the kind of water-based life that we see on Earth. So it looks like “the Goldilocks zone” is an even better name than we thought.

Goldilocks will have to keep searching for “just right”, and so will we. Thanks for watching this episode of SciShow Space News. If you’re interested in learning more about some of the most devastating collisions Earth has experienced, you can check out our video on the 3 biggest space impacts ever. [♪ OUTRO]