Episode 168 // NEOs — Near Earth Objects
What is a NEO?
Near Earth Objects are really just that. These are celestial objects that come near to the Earth
and there are broadly two classes: Near Earth Asteroids and Comets.
Where do these objects come from?
The Near Earth Asteroids, they mostly come from the asteroid main belt
which is between Mars and Jupiter and it can happen that because of a collision
or because of an interaction with one of the planets, one of them falls down from its orbit in the main belt
to an orbit that brings it closer to the Sun and therefore closer to the Earth.
How many NEOs are there?
The Near Earth Objects, there are a few big ones, there are many more small ones
and there are many many more very small ones.
We know most of the big ones, big is one kilometre or more. For those that are 100 metres we know about 10 percent.
For those that are 10 metres we know less than one percent of them. So that’s annoying, because an object that is 10 metres in diameter
on impact with the Earth, would release about the same energy as a Hiroshima bomb.
We are trying to characterise everything that is bigger than 20 or 50 or 100 metres
where we are at 10 percent now, so we still need to find 90 percent.
In terms of numbers, we know 10, 20 thousand of them and we are still missing 90 percent
so there is a lot of work to find them and to track them.
How can we search for them?
To discover Near Earth Objects, you need a super wide-angle telescope
and then you just scan the whole sky night after night in order to see everything that is moving.
The asteroids are moving, and so we have computer programmes that will find them
measure their position and from this position we can extrapolate the orbit and we refine the orbit
until we have an orbit that is good enough that we will not lose the asteroid again.
How often do impacts on Earth occur?
We know from history, and also looking at the Moon that there are many impacts.
On average a small one, which is like a few tens of metres, that happens every few years.
Bigger ones are fortunately less frequent because there are fewer of these objects.
Very big ones are even less frequent because there are very very few of them.
So if you take a very big one, a 15 or 20 kilometre asteroid, hitting the Earth, last one was 65 million years ago.
That was bad for the dinosaurs, and historically we see this kind of giant impact every 50 million years or so.
What we can do to predict impacts and what role does ESO’s Very Large Telescope play?
To predict an impact with a Near Earth Asteroid, a Near Earth Object, you need to know its orbit very precisely.
And so to do that you need to measure the position of the object on the sky over and over and over.
It’s difficult because many of these objects are small and they are not always near the Earth.
They can be on the other side of the Solar System.
The combination of their size and their distance makes them extremely faint
which means that most of the time the telescope that discovered them, which is a 2-metre class telescope
can observe them only for a few days and then they cannot see them anymore because they become too faint.
That’s where the VLT, the 8-metre, big telescope, comes into play
because with the collecting power of the huge mirror we can see much fainter asteroids.
What is the VLT in particular used for?
Using the VLT, we refine the orbit of the Near Earth Object
the threatening ones that could have a collision, in order to make sure that the orbit is known
well enough either to rule out a collision, that’s ideal, or to characterise a collision.
Is there anything we can do to prevent NEO impacts?
To protect ourselves from a Near Earth Object
we must know them, and prepare in advance before a collision.
So if we have enough time, 20 years or so, we can send a rocket and do something to the asteroid.
That can be nuke it; you know — atomic bomb — either to try to destroy it or to push it.
There are some more gentle ways. A cute way to do it is to spray paint the asteroid with bright white paint
because that will change the way it reflects the sunlight and that can be sufficient to push it away from its orbit.
Or you could also land a small rocket on the asteroid and let this small rocket push it.
Or if it’s a very small asteroid you can go cast a net and grab it and pull it away.
Transcribed by ESO; Translated by —