Issue 45: Impact Craters
September 29, 2022
We celebrate NASA DART’s successful mission with some scars of Earth’s past; concentric circles emerge in a Japanese forest; and an old salt lake transforms through the seasons in India.
This is an archived issue. Sign up here to receive the Planet Snapshots newsletter every Thursday morning.
Feature Story: Impact Craters
Earth has finally struck back after eons of rolling with the extraterrestrial punches. This Monday, NASA’s DART spacecraft collided with an asteroid named Dimorphos at 14,000 mph (22,500 kmh). The planetary defense mission was testing the feasibility of redirecting an asteroid by kinetic impact. While data on its altered trajectory won’t be available for a few weeks at least, the mission was by all accounts a success. Meaning we can tentatively cross off one existential threat from the growing list.
It can be easy to forget we’re moving through a locust-swarm of swirling asteroids at all times. Even though extraterrestrial debris showers our planet everyday, most are small and burn up in the atmosphere. The extinction-sized ones — like the infamous dinosaur-ender — occur only once every 100 to 200 million years. But the Earth is old and has the scars to prove it. So this week we wanted to take a look at some of the planet’s greatest hits and the impact craters they left behind.
Meteor impacts are, as you may have guessed, a big deal. These collisions are so great that their shock waves fracture and melt rock and eject enormous amounts of material outwards, resulting in the large cavities seen in these images. Large impacts can heat Earth’s surface temperature, cause tsunamis and earthquakes, and disrupt photosynthesis by blocking sunlight. Plus they can alter entire ecosystems, as happened 66 million years ago when 75% of animal species died after the 10 km (6 mi)-wide Chicxulub impactor hit Earth.
Craters are a common landform for planets in the solar system. The moon itself has over 100,000 visible crater impacts, which give it its characteristic pock-marked look. You’d think the Earth, which is roughly four times larger in width than the moon, would have more than that. Yet its count is only in the hundreds. This is because, unlike the other planets, erosion, plate tectonics, and volcanism over time erase the ones that penetrate the atmosphere.
Australia’s Yarrabubba meteor crater is the oldest known impact crater at over 2.2 billion years. A lot of craters are actually found in Australia since it’s the oldest crust on Earth and its dry climate helps prevent major weathering. So it’s a good place to spot and study historical craters, like the 142-million-year-old Gosses Bluff.
Earth’s meteoric scars remind us of our humbling and precarious position within the cosmos. NASA DART’s success is a historic step for our space-based capabilities. And while it’s still a far cry from preventing a full-scale extinction-level impact, we’re glad we’ve got folks keeping watch among the distant stars and throwing long-distance-bullseyes at potential threats.
Bonus: Not all impact craters have an immediately recognizable circular shape. Some are, well, more interesting. Ephemeral salt lakes overlap with the Shoemaker Crater in Western Australia to create this wild, complicated, but beautiful scene.
Experimental Forestry
Forests have an intrinsically wonderful order to them, yet their arrangement may look random to us. But sometimes we plant them in circles in the name of science and it creates a whole new kind of spectacle. Fifty years ago, Japanese researchers planted cedar trees in concentric circles to study the effects of forest growth and spacing. They found that the trees on the outer rings grew taller than the ones towards the center. We’re not entirely sure what the results from this experiment mean, but hey, it looks great, so we’re all for it.
Change of the Week: Sambhar Salt Lake
If you like traveling to see flamingos, and your partner is salty because you travel too much to see flamingos, then boy do we have the perfect vacation spot for the both of you. The salt evaporation ponds at Sambhar Salt Lake have been farmed for a millennium and are a haven for multiple flamingo species. Take a look as the landscape moves from vibrant green to a dramatic red throughout the year.
Weekly Revisit
Last week we took a reprieve from the environmental doom and gloom parade and celebrated some climate wins. So check it out in case you want to feel motivated about the incredible work folks are doing across the world. And take a look at the whole archive if you’re extra curious.
