#### Investigating Meteor-Impact Theory

For the Creation of Volcanoes on Mars

*by Rania Kashi*

One of the theories put forward by Joe Kolecki to explain the formation
of volcanoes on Mars was that of the meteor impact theory. It goes
something like this: some of the volcanoes on Mars can be explained
if we consider that a meteor had crashed into the planet at some point.
The force of such an impact would reverberate through the planet and
force volcanoes to 'bulge' out on the other side.

This sounded like a pretty straightforward explanation for the formation
of some of the features evident on Mars, such as the Helles crater
and the Tharsis bulge. On investigating Helles and Tharsis further
we found that Tharsis was not actually on the point 180° from
Helles as one would have expected if assuming meteor theory was correct.
We questioned as to why this was not the case and figured that if
Mars had a molten core, like the Earth's, then the energy waves that
would have been given out by the impact would pass through this core
and be refracted, thus changing the angle at which they would leave
the core. This would result in the energy waves surfacing at a point
not 180° away from the point of impact (see Fig. 1). This line
of reasoning would then explain as to why Helles and Tharsis are where
they are on Mars.

[Click here to see the animated
version of this graphic on our site]

Figure 1: Sketch of meteor crash into Mars and the propagation of
energy through the planet.

Once we had explained one apparent anomaly, we went on to try to
provide further proof of whether or not the meteor theory could explain
volcanic formation on Mars.

If indeed a meteor had crashed into Mars to provide us with the Helles
crater and the Tharsis bulge, we reasoned that such a meteor would
most likely come from the asteroid belt. We could calculate the energy
that would have been necessary on impact to create a crater the size
of Helles, the energy gained by the meteor due to gravitational acceleration
by the sun and the mass of Tharsis. These calculations would enable
us to see whether or not the impact that could have created Helles
had enough energy to go on and produce a bulge the size of Tharsis.

First we calculated the energy that would have been produced by an
impact creating a crater the size of Helles:

Then we calculated the energy the meteor would have gained due to
the gravitational acceleration by the Sun:

Now, taking into account the mass of 10^16 kg, the energy results
an ~10^30J.

Next we calculated the energy to melt such a mass by considering
the latent heat of fusion, or the enthalpy of melting, for basalt.

These values that we calculated showed that the energy required to
melt a mass the size of Tharsis would be produced by a meteor impact
of the size of the diameter of the Helles.

We also considered the situation where the Tharsis bulge was only
one third of the total mass, like icebergs on Earth where only one
third of the ice mass is showing above the water. Even with 3 times
the energy required to melt this mass it was still within the energy
boundary that was calculated to have been produced on impact.

We decided to further investigate the meteor relationship by calculating
the impact energy and mass of Argyre and Elysium as for Helles and
Tharsis. Again we found that the impact energy in this case was sufficient
to produce the bulge mass. Therefore, if the meteor theory is correct
for Helles-Tharsis then it is correct for Argyre-Elysium. If this
is so, then crystal thickness of the area can be calculated.

We assumed a direct relationship between the diameter of a crater
on Earth and the crustal thickness, using Vredefort in SA as our example.

Then we imposed this ratio on the crater diameter size on Mars to
calculate the crustal thickness.

We calculated that for Argyre and Elysium the crustal thickness was
about 60 km. For Helles and Tharsis it was 200 km. This further provided
us with proof that the meteor theory was correct because of the multi-ring
basin present for Argyre-Elysium, which was not present for Helles-Tharsis
due to the thicker crust in the latter case.

Following these investigations we were able to conclude that the
meteor theory for Mars could have a part to play in producing volcanoes
on Mars.