Lynn Carter

these layers show up because every time the radar hits something that has different properties so a different density a different composition you get an echo off of that too so as the radar wave goes down it bounces off of all these little layers and pieces of it come back and sure doesn't see quite to the base of the polar cap everywhere but it does like in this example it will see to the base

So that's sort of how the radar works.

And as it goes over the surface, it collects all of these pictures of what the subsurface stratigraphy looks like.

And so that's what we try and use to understand the geology of Mars and how that works with climate.

So Mars climate is really more variable than the Earth's.

So there's more dramatic seasons and that's mostly because the tilt of its axis can change a lot over time.

So the Earth's axis is 23 and a half degrees.

But Mars, right now, it's at about 25 degrees.

But it can actually vary a whole lot.

So obliquity is the tilt here.

So Mars goes through periods of time where the axis is nearly straight up and down.

But then it also goes through periods where it's tipped over by 40 degrees.

And you can see here, it actually gets up to like 40, 45 degrees.

And it can even go higher.

And you can look at how fast this happens.

And this is millions of years.

down here so I mean this is like the tilt is swinging back and forth pretty dramatically over pretty short time scales so this means that Mars has some crazy seasons going on so we would expect to see that in the rock record and so this is one of the things that we'll look for and also one of the things that could have caused Mars to be habitable sometimes and not habitable other times is this swinging around of the tilt of the orbit really changes the seasons on Mars a lot and it makes some places

more habitable or a better climate to have life than at other times it's just colder.

Okay, so one of the first things we did with Sharad was look at the polar caps.

One of the advantages of ice to the radar is that it's really transparent.