Mars is littered with craters.
Although Mars has an atmosphere, this atmosphere is very thin, meaning even small meteors manage
to impact the surface before they burn up.
The HiRISE camera onboard NASA’s Mars Reconnaissance Orbiter has been able to image a lot of these
craters in exquisite detail, meaning we can examine craters on another planet like never
before.
I’m Alex McColgan, and you’re watching Astrum, and together we will look at some
of Mars’ most interesting craters, and I’ll explain what it is you are looking at.
We will start small.
Here is a very small and very fresh crater that likely formed sometime between 2006 and
2008.
New craters have some very distinct characteristics, specifically defined craters walls, and evidence
of fresh ejecta.
Although this crater is just a few meters across, you can see the ejecta spread out
over hundreds of meters.
But this is over a flat surface.
What if a meteor hits a slope?
Well that’s exactly what happened here.
The dust on Mars is extremely fine, meaning it can move quite easily.
You can see the recent impact crater on this slope here, which caused an avalanche of dust
down the slope.
The area around the avalanche looks fuzzy because ejecta also spread out around the
impact site.
The dust is clearly precariously balanced as there have even been smaller avalanches
seen a little bit higher up.
So, if an impact caused this avalanche, what caused it in these larger craters?
What you are looking at here is slope streak formation, one of the few active geological
processes on Mars that we know of.
We don’t exactly know why these streaks are formed, but the leading theory is that
due to the tiny size of Mars’ dust particles, the smallest trigger like a gust of wind can
make the dust tumble and act like a fluid, like in a snow avalanche of Earth.
The darkest streaks are the youngest, the whiter streaks are older, the brightening
caused by dust settling on them over time.
It is quite the beautiful sight!
Let’s move on to a particularly flat area of Mars.
This area is quite boring and featureless.
But zooming out a bit we come across this big kilometre wide crater which seems to have
a scar on one of its walls.
This is actually caused by lava flowing down from the lowest point in the crater wall,
the lava coming from a nearby volcano that has repeatedly covered this area in lava from
its eruptions.
That’s why the surrounding area is quite featureless, this used to be a large lava
plain back when Mars was more geologically active.
That makes the surrounding area here the youngest surface on Mars.
I can only imagine what this area once looked like!
The game “the floor is lava” would be quite apt!
Let’s have a look at another crater heavily influenced by lava.
This is near Elysium Planitia, the second largest lava plain on Mars.
This 3D view, acquired from a stereo pair of images shows the basin of this crater is
very flat, this is again due to lava flowing and filling the area from this vent found
in the centre of the crater.
This is an old, inactive vent now, meaning the surface hasn’t been renewed for some
time, evidenced by the many craters dotted around the basin floor.
There’s another, really curious crater I want to have a closer look at.
This bizarre crater is found within the big Schiaparelli crater, and it kind of looks
like a giant bullseye.
We don’t really know why it’s formed like this, although it could be due to there being
sedimentary layers in the bedrock that have been eroded smooth, or it could be that this
is actually a flat surface which just appears concave because the crater has been filled
up by sedimentary deposits over time, meaning the innermost layer would also be the youngest.
We don’t have a stereo view of this crater, so we can’t quite tell either way right
now.
What about craters that haven’t been filled up by one thing or another?
This is Palikir crater, a several kilometre-wide crater that has also had the 3D treatment.
This crater is pretty deep, stretching several hundred meters down from the rim, and along
the crater wall you will notice what looks to be old water channels flowing down the
bank.
While liquid water can’t exist on the surface of Mars, it is theorised that water could
still flow under Mars’ surface.
Salty water that flows out of the ground could make its way down a steep slope like this
for a little while before it evaporates.
On a different crater, this flowing has been observed, notice the differences over the
years.
Although, we haven’t confirmed this process is due to water yet, even if it is the leading
theory, it could still be just fine dust that flows down the slope.
Let’s have a look now at a very old and deep crater.
At first glance, you can see inflow channels going into the crater, and that is was once
even deeper than this, but it has since been filled somewhat by sand dunes.
Zooming in, we can see the sedimentary layers near the crater walls.
Had this crater not been filled in by sand, perhaps it would resemble the previous crater
we looked at in Schiaparelli.
Somehow this crater’s age just makes it look even more impressive!
For the last crater we’ll look at today, we’ll have a look at another 3D view.
This unnamed, 15km wide crater is found in the Domoni region, and seeing it from this
angle is quite the sight to behold.
Going over the crater walls, you’ll notice this crater has two tiers of walls, and some
peaks in the centre.
This is due to the size of the crater.
Smaller, simple craters tend to have smooth walls all the way down to the basin, larger
ones have tiered walls with uplift at the centre.
They are known as complex craters.
Usually complex crater would be too big to fit in a HiRISE image, but this is a combination
of several images which gives us an unprecedented view of a such a large Martian crater.
Coming closer to the crater walls, you’ll again notice these water channels coming down
the side.
You’ll also notice the smooth appearance of the terrain, which implies dust has had
a lot of time to settle here.
So, there you have it, some of the most interesting craters on Mars.
There are a lot more that I could have talked about, but sadly they will have to wait for
another time.
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Want more of Mars?
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And see you next time.