My name is Kelly Fast and I work with NASA's Planetary Defense Coordination
Office and with teams looking for asteroids that could come close to Earth.
Now, what does it mean when you hear about an asteroid that's going to make a
close approach to Earth, and what are you supposed to think when you hear that an
asteroid is going to swing by Earth at ten times the distance from the Earth to
the Moon? Is that really close? Well, here's something that you can do at home
to find out. All you need to do this is a basketball or a similar sized ball to be
the Earth, a tennis ball or a similar sized ball to be the Moon, and finally a
grain of salt to be the asteroid, and even that is too large to represent the
asteroids that tend to approach Earth on a fairly regular basis. So, if the Earth
were the size of a basketball and the Moon were the size of a tennis ball,
you'd have to spread them out 25 feet to correspond to what they'd actually look
like in space and you could do that outside or in your house. I'm going to
try to do that in my house. Okay, so let's put our basketball, the Earth, in one end
of the house and let's walk it out. It's not quite a foot long but I don't have
to put them in to end entirely and so let's walk it out. 1, 2, 3, 4, 5, 6, 7, 8, 9, 10
11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25. And here is where our Moon goes. Okay, here's our Moon so where's our
Earth? Wow! So if the Earth were the size of a
basketball the Moon would be the size of a tennis ball and they'd be 25 feet
apart and so what does that mean for a close approach? If somebody says that a
close approach asteroid is going to come within 15 times the distance of the
Earth to the Moon, that's 15 times this distance here. That would be a couple of
blocks away. Okay, let's leave our Earth, the basketball, here and let's
walk down and get that asteroid. So, going back to my table let's see when I get
that little grain of salt. Ah. Okay, let's see what happens here if it approaches the
Moon. Hmm, look at that. Look how far away the Earth is from here this grain of
salt asteroid might be large compared to the asteroids we're talking about that
regularly approached Earth but it's about the right size to represent the
asteroid responsible for the demise of the dinosaurs. Now, let's say that this
grain of salt asteroid that's too big passes between the distance of the Earth
to the Moon, so what happens there? Okay, here we go.
There it goes. Oh, and look, there's the Earth and there's the Moon. Space is pretty big.
A close approach asteroid is really starting to get close maybe when it gets
within like the distance of the weather satellites. And so to demonstrate that,
I'm going to use Snuggles. Okay so here's our Earth here. And I'm going to put Snuggles here. So orbit the Earth Snuggles.
So if the Earth were the size of a basketball, and the Moon then would be the size of a tennis ball,
it would be very far away, 25 feet away, like over my shoulder and so an asteroid
would have to approach a lot closer than that to be of concern, and we do want to
know where asteroids are because we do want to know if they're going to
approach really close. But if you hear about a close approach that's going to
be many lunar distances away, that was still pretty far away because even our
Moon is pretty far away. If you have a question about close approach asteroids
or planetary defense leave a comment or use hashtag #askNASA.