An asteroid could easily wipe out all humanity, luckily NASA monitors them.
The Risk of Near Earth Objects
Near Earth objects continually put the planet at risk. There are a massive amount of them in space, over 15,000 being discovered so far. That means it’s only a matter of time until one heads in our direction. We must be ready or face the consequences. [1]
Although, the consequences are based on the size of the asteroid. Anything smaller than about 25 meters can be completely ignored, it will just burn up in our atmosphere. As an asteroid gets larger, about 150 meters, it hits the ground with more energy than the largest atomic bomb in history. Once it hits 300 meters an asteroid can impact the ground with an energy over 20 times that of the largest nuclear weapon. Once it gets a kilometer wide it could impact with almost 1000 times that same weapon, which is enough to eradicate an entire (smaller) country or cause a tsunami 32 meters high from as far away as 300 kilometers. An impact with an asteroid 10 kilometers wide would be he enough to cause 100 meter high tsunamis as far as 10,000 kilometers away. You can image what would happen to that continent.[2] [3]
Luckily events like this do not happen very often. On average a 150 meter asteroid strikes Earth every 16 thousand years. Or 300 meter asteroids it happens every 72 thousand years. Asteroids the size of one kilometer happen only once every 440 thousand years on average. [2]
You may think this gives us some breathing room, but not really. The real problem here is that we don’t actually know where all the Near Earth Objects are.
How The Sentry Pages Work
The sentry pages are split up into two main pages, the impact risk page and the main sentry page.
This page tracks the impact risk of NEOs. As new asteroids are discovered some will be put onto this page, because we don’t know where they will end up. After more observations and calculations are made asteroids are often taken off of this list. This category also does host a few “permanent resident” that have a very low but still non-zero chance of impact in the future.
This is often used as a reference source for scientists or the media. The calculations are complex and long, meaning there is large opportunity for error. This gives them a way to cross-check their work.
You can find the page here
The main sentry page is a collection of all objects that ever made it onto the impact risk page. All of the objects on this page pose basically zero risk and it is only used as a reference source.
Both of these pages use two different scales to measure the risk posed. One is the Torino Scale and the other is the Palermo Scale.
This scale is used mostly for communicating with the public. It takes into account how likely an impact is and how large the effect will be, but not the time until impact.
The scale ranges from 0-10. Most NEO are placed at zero, meaning that they either have a near zero chance of impacting Earth or will burn up in the atmosphere with no effect. Three is a close encounter with an object warranting an extra look by astronomers, this is usually reassessed back to zero. At six the NEO poses a major global threat, but it is still unknown if it will hit Earth and more assessment is needed. You can guess what ten means, a certain global catastrophe. Luckily this only happens once every 100,000 years.
You can see the scale here
The Palermo scale is more important to scientists. It compares the chance of impact with the chance of a random impact of the same size range. This is called relative risk. This scale is log base 10. Zero is equal to the average chance of the event occurring, a one on the scale means it is ten times more likely, a two means it is one hundred times more likely, and a negative one means that asteroid has 10% the chance of impacting as a random event in the same time period. [4]
This information is important to know, in the off chance that there is an emergency. Countries already have major problems working together, what do you think would happen if you added mass panic and a misunderstanding of the danger onto that.