– First Map of Mars Electric Currents
MAVEN is a
spacecraft that’s orbiting Mars, it’s been there since 2014. MAVEN in this case
is an acronym, it stands for Mars Atmosphere and Volatile Evolution, and this
gives a clue as to what MAVEN’s real goal is. It’s to study the top of the
atmosphere and how the gases in the top of the atmosphere might escape from
Mars away to space.
atmosphere of Mars must have been a lot thicker about four billion years ago,
and today it’s very cold and dry. And MAVEN is meant to understand the
atmosphere as it is today and how it has evolved into this current cold dry
One of the
things that we’re trying to understand with MAVEN is whether a magnetic field
for a planet is important for regulating the climate, or allowing the planet to
keep an atmosphere. Earth has a global dynamo magnetic field, Mars does not, but
Mars has an induced magnetosphere, it has an induced magnetic field.
atmosphere of Mars is being ionized by solar radiation, and so the electrons are
being stripped from the atoms in the atmosphere. When that happens it turns
into what we call a state of plasma. This plasma in the upper atmosphere is
very conductive, it leads electric currents to flow through it.
currents, they shape the magnetic fields that are around them, and that’s
actually how we see them with MAVEN. We take magnetic field data and we map it
around the planet, and from that the currents emerge.
We’ve known how
the currents flow in the Earth’s magnetosphere for decades, but we don’t know
how that works around Mars. We don’t know how it influences the interaction
with the solar wind, because it determines how energy is flowing into the
atmosphere, how it’s transferred from the solar wind into the system, and
that’s what we’re trying to do with MAVEN.
When you just
look at the data as it comes down, you’re just seeing a little squiggly line,
essentially, you’re seeing the magnetic field’s strength and its direction vary
as the spacecraft is flying through different regions. And so what you have to
do is, you have to actually map it to the planet, and to its interaction with
the solar wind.
And then it
starts to emerge that you have a drape situation, where the magnetic field of
the solar wind encounters the planet and it starts to wrap around it. And the
reason it wraps around the planet is those electric currents that we were
field in the solar wind is straight lines, you can think of straight spaghetti
noodles, and it’s flowing towards the planet and those spaghetti noodles wrap
around this basketball-shaped planet. And that’s indeed what we saw in the data
– the magnetic field lines draping around Mars as a planet.
One thing that
wasn’t so expected was the specific configuration of the electric currents that
we derived from the magnetic field data. If Mars is a ball here, it’s sort of
this cup shape on the dayside that loops back on itself, maybe something that
looks like this (makes shape with hands).
What wasn’t so
intuitive to me was the directions of those currents, and the fact that it
wraps continuously around to the nightside, and it makes this marvelously
complex current system on the nightside as well.
This is the
first time that we’ve been able to actually map out the currents, so we can see
where the energy’s being transferred, we can see what actually forms the
underlying mechanisms creating these induced magnetospheres that are not just
common here in the solar system, they’re fifty percent of the planets that have
them – of the terrestrial planets.
And if you want
to understand how the atmospheres of Mars and Venus, why they’re so different
from the Earth, and why they’re so different from each other despite both being
non-magnetized, we need to understand their induced magnetospheres first.
So, knowing how
these global current systems are configured teaches us about how charged
particles near the planet are going to move – both charged particles in the
solar wind, and charged particles from the atmosphere itself that are in the
process of escaping to space.
So now we can
understand better where those particles came from, how they move near Mars, and
where they’re going to go next. That in turn teaches about atmospheric escape
from the planet, and the history of the atmosphere over time, how thick has it
been, how much has been removed.