I give talks about asteroid impacts quite often, and sometimes people ask me why we should worry about them. I reply, "Go outside and look at the Moon. Then tell me we don’t need to worry about asteroid impacts!" The Moon is covered in craters, and it really brings home — literally — the fact that we need to understand impacts better.
I’m not being facetious, either. Looking at the Moon is a great way to learn about craters. By measuring their size, position, and shape, we can find out a lot about the history of impacts in the Earth-Moon system. The problem is there are so many craters — billions, if you look at high enough resolution. How on Earth — haha — can any scientist or team of scientists possibly look at them all?
Well, it depends on how big the team is. Enter citizen science: non-professional-science people who nevertheless love science. If you’re reading my blog — and you are — then that means you! CosmoQuest.org is a group of astronomers, run by my friend Dr. Pamela Gay, who have created a series of projects where people like you can perform needed tasks that are real science… in this case, measuring craters on the Moon! Using MoonMappers, you can identify and measure craters using images from the Lunar Reconnaissance Orbiter, a spacecraft currently circling our Moon and taking thousands of high-resolution pictures.
I signed up and started right in, and find it somewhat addicting. You’ll need to register first through the CosmoQuest forum, which takes one minute and is free. Once you’ve done that, just go back to Moonmappers and dive in. I was able to identify dozens of craters in just a few minutes. Here’s a typical scene:
The blue circles are craters found using automated software. The green ones mark craters I found. The task is really simple: you can mark craters with your mouse, dragging the circle to match its size. If you miss a bit, you can easily adjust the circle’s position to re-center it. You only need to find craters bigger than 18 pixels in size, so it’s not an impossible chore! You can also flag odd features like linear cliffs, boulders, and so on, if you happen to see any. Several of the images I went through had them. One had lovely striations in an old lava flow, so you never know what you’ll see.
Sound like fun? It is! But hurry: right now, CosmoQuest has issued a Million Crater Challenge, to get 1,000,000 craters identified by full Moon, which is on May 5, just days away. As I write this they’re still a long way from their goal. How many can you find?
And remember: this isn’t just fooling around, this is real science. How are craters made? Why are they different shapes? How many are 10 meters across versus 20 versus 30 versus 100? All these questions are important in understanding impacts… especially that last one. Getting the scales of impacts, and how the numbers of them increase as the size gets smaller, is critical in being able to predict how often they happen. At some point, we’ll see a small asteroid headed toward Earth, and we’ll have to decide if it’s big enough to worry about and spend hundreds of millions of dollars deflecting it. The work you do here, quite seriously, can help inform that decision.
The Lunar Reconnaissance Orbiter is a NASA space probe that’s been orbiting the Moon since June 23, 2009. On March 19 it will mark its 1000th day in orbit! To celebrate, NASA released this cool animation showing the history of the Moon:
According to current thinking, the Moon itself formed after a planet roughly the size of Mars slammed into the Earth at a glancing blow. This colossal impact threw billions of gigatons of debris into space. Some of that fell back onto Earth, and some formed a huge disk around the (now once again liquefied) planet. This material eventually coalesced to form the Moon.
But the story wasn’t done: with impact after impact, wave after wave of bombarding material shaped and reshaped the Moon’s surface. The animation above is a bit fanciful – it has sound, of course, and it shows time as a variable that flows at different rates – but gives a lovely overview of the violent past of our satellite. I like how I could see various features forming, knowing eventually they would be the familiar sites (and sights) I see through my telescope eyepiece. It’s a good reminder that the way we see things now is not the way they’ve always been, and that sometimes the forces that shape our current circumstances are not necessarily gentle or subtle.
[My congrats to everyone on the LRO team for 1000 days of amazing science! If you want to see more about LRO, I've written about it dozens of times, and you can also check the Related Posts below.]