Présentation podcast dnl terminale "origines de l'eau sur Terre"

« My document is a podcast from the Npr which is entitled Comets, asteroids, and planets: The likely origins of Earth’s water.

It was published on January 5, 2026 and in this podcast, the one who’s interviewed is Michael Wong, an astrobiologist and planetary scientist at Carnegie Science in Washington, DC.

It deals with the 2 most likely origins of Earth’s water. To begin with, Wong explains that we know that planets form in what's called a protoplanetary disk, And there's this point where the temperature can condense H2O.

Water can form ice. And we call that the snow line.

Interior to the snow line, scientits think that material would have been pretty bone dry.

And Earth, is interior to where this primordial snow line was. So it was thought that Earth formed dry and then had to have its water delivered from outside the snow line into Earth.

And there was a big debate over, OK, so was it comets which are these big, dirty snowballs in space that delivered the water or was it asteroids which are rockier, but do still have ice, so water ? And the biggest clue comes in what's called the deuterium-to-hydrogen ratio of the water.

So, as we now water is made of two hydrogen atoms and an oxygen atom.

And you can substitute every once in a while a deuterium for the hydrogen.

It's a heavy form of hydrogen.

So it's got a proton and a neutron.

And so instead of H2O, you get HDO.

And the amount of HDO that you have in water is a clue to where it came from.

So scientists got a rough estimate for, like, what the D-to-H ratio was for the Earth and then they compared that to specific kinds of asteroids called carbonaceous chondrites, which.... »