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♪♪♪

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[David Brain]
MAVEN is a spacecraft that’s orbiting Mars,

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it’s been there since 2014.

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MAVEN in this case is an acronym, it stands for

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Mars Atmosphere and Volatile Evolution,

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and this gives a clue as to what MAVEN’s real goal is.

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It’s to study the top of the atmosphere and
how the gases in the top

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of the atmosphere might escape from Mars away to space.

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[Robin Ramstad]
So, the atmosphere of Mars must have been a lot thicker

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about four billion years ago, and today it’s very cold and dry.

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And MAVEN is meant to understand the atmosphere
as it is today

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and how it has evolved into this current cold dry state.

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[David Brain]
One of the things that we’re trying to understand with MAVEN

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is whether a magnetic field for a planet is important
for regulating the climate,

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or allowing the planet to keep an atmosphere.

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Earth has a global dynamo magnetic field,
Mars does not,

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but Mars has an induced magnetosphere,
it has an induced magnetic field.

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[Robin Ramstad]
The upper atmosphere of Mars is being ionized by solar radiation,

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and so the electrons are being stripped from
the atoms in the atmosphere.

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When that happens it turns into what we call a state of plasma.

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This plasma in the upper atmosphere is very conductive,
it leads electric currents to flow through it.

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Electric currents, they shape the magnetic fields
that are around them,

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and that’s actually how we see them with MAVEN.

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We take magnetic field data and we map it
around the planet,

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and from that the currents emerge.

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We’ve known how the currents flow in the Earth’s
magnetosphere for decades,

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but we don’t know how that works around Mars.

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We don’t know how it influences the interaction
with the solar wind,

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because it determines how energy is flowing into
the atmosphere,

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how it’s transferred from the solar wind into the system,

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and that’s what we’re trying to do with MAVEN.

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When you just look at the data as it comes down,
you’re just seeing a little squiggly line,

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essentially, you’re seeing the magnetic field’s
strength and its direction

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vary as the spacecraft is flying through different regions.

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And so what you have to do is, you have to actually
map it to the planet, 

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and to its interaction with the solar wind.

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And then it starts to emerge that you have a drape situation,

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where the magnetic field of the solar wind encounters the planet
and it starts to wrap around it.

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And the reason it wraps around the planet is those electric
currents that we were seeing.

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[David Brain]
The magnetic field in the solar wind is straight lines,

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you can think of straight spaghetti noodles,

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and it’s flowing towards the planet and those spaghetti noodles

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wrap around this basketball-shaped planet.

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And that’s indeed what we saw in the data – 

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the magnetic field lines draping around Mars as a planet.

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One thing that wasn’t so expected was the
specific configuration

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of the electric currents that we derived from
the magnetic field data.

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If Mars is a ball here, it’s sort of this cup shape
on the dayside

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that loops back on itself, maybe something
that looks like this.

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What wasn’t so intuitive to me was the directions
of those currents,

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and the fact that it wraps continuously around
to the nightside,

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and it makes this marvelously complex current system
on the nightside as well.

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[Robin Ramstad]
This is the first time that we’ve been able to actually

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map out the currents,

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so we can see where the energy’s being transferred,

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we can see what actually forms the underlying mechanisms

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creating these induced magnetospheres that are

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not just common here in the solar system, they’re
fifty percent of the planets that have them –

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of the terrestrial planets.

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And if you want to understand how the atmospheres
of Mars and Venus, 

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why they’re so different from the Earth,
and why they’re so different from each other 

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despite both being non-magnetized, 

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we need to understand their induced
magnetospheres first.

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[David Brain]
So, knowing how these global current systems are configured 

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teaches us about how charged particles near the
planet are going to move –

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both charged particles in the solar wind,
and charged particles from the atmosphere itself

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that are in the process of escaping to space.

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So now we can understand better where those
particles came from,

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how they move near Mars, and where they’re
going to go next.

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That in turn teaches about atmospheric escape
from the planet,

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and the history of the atmosphere over time,

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how thick has it been, how much has been removed.

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♪♪♪