WEBVTT FILE

1
00:00:00.166 --> 00:00:01.101
♪♪♪

2
00:00:01.101 --> 00:00:03.570
[David Brain]
MAVEN is a spacecraft that’s orbiting Mars,

3
00:00:03.570 --> 00:00:05.839
it’s been there since 2014.

4
00:00:05.839 --> 00:00:08.608
MAVEN in this case is an acronym, it stands for

5
00:00:08.608 --> 00:00:11.811
Mars Atmosphere and Volatile Evolution,

6
00:00:11.811 --> 00:00:15.081
and this gives a clue as to what MAVEN’s real goal is.

7
00:00:15.081 --> 00:00:19.452
It’s to study the top of the atmosphere and
how the gases in the top

8
00:00:19.452 --> 00:00:23.356
of the atmosphere might escape from Mars away to space.

9
00:00:23.356 --> 00:00:26.159
[Robin Ramstad]
So, the atmosphere of Mars must have been a lot thicker

10
00:00:26.159 --> 00:00:29.062
about four billion years ago, and today it’s very cold and dry.

11
00:00:29.062 --> 00:00:32.365
And MAVEN is meant to understand the atmosphere
as it is today

12
00:00:32.365 --> 00:00:35.869
and how it has evolved into this current cold dry state.

13
00:00:35.869 --> 00:00:38.872
[David Brain]
One of the things that we’re trying to understand with MAVEN

14
00:00:38.872 --> 00:00:43.309
is whether a magnetic field for a planet is important
for regulating the climate,

15
00:00:43.309 --> 00:00:46.079
or allowing the planet to keep an atmosphere.

16
00:00:46.079 --> 00:00:50.483
Earth has a global dynamo magnetic field,
Mars does not,

17
00:00:50.483 --> 00:00:54.521
but Mars has an induced magnetosphere,
it has an induced magnetic field.

18
00:00:55.021 --> 00:00:58.591
[Robin Ramstad]
The upper atmosphere of Mars is being ionized by solar radiation,

19
00:00:58.591 --> 00:01:02.195
and so the electrons are being stripped from
the atoms in the atmosphere.

20
00:01:02.195 --> 00:01:04.864
When that happens it turns into what we call a state of plasma.

21
00:01:04.864 --> 00:01:09.502
This plasma in the upper atmosphere is very conductive,
it leads electric currents to flow through it.

22
00:01:09.502 --> 00:01:12.739
Electric currents, they shape the magnetic fields
that are around them,

23
00:01:12.739 --> 00:01:14.641
and that’s actually how we see them with MAVEN.

24
00:01:14.641 --> 00:01:17.243
We take magnetic field data and we map it
around the planet,

25
00:01:17.243 --> 00:01:19.079
and from that the currents emerge.

26
00:01:19.646 --> 00:01:23.216
We’ve known how the currents flow in the Earth’s
magnetosphere for decades,

27
00:01:23.216 --> 00:01:25.285
but we don’t know how that works around Mars.

28
00:01:25.285 --> 00:01:28.621
We don’t know how it influences the interaction
with the solar wind,

29
00:01:28.621 --> 00:01:31.691
because it determines how energy is flowing into
the atmosphere,

30
00:01:31.691 --> 00:01:34.527
how it’s transferred from the solar wind into the system,

31
00:01:34.527 --> 00:01:36.629
and that’s what we’re trying to do with MAVEN.

32
00:01:37.397 --> 00:01:41.835
When you just look at the data as it comes down,
you’re just seeing a little squiggly line,

33
00:01:41.835 --> 00:01:44.804
essentially, you’re seeing the magnetic field’s
strength and its direction

34
00:01:44.804 --> 00:01:47.574
vary as the spacecraft is flying through different regions.

35
00:01:47.574 --> 00:01:51.144
And so what you have to do is, you have to actually
map it to the planet,

36
00:01:51.144 --> 00:01:53.179
and to its interaction with the solar wind.

37
00:01:53.179 --> 00:01:56.449
And then it starts to emerge that you have a drape situation,

38
00:01:56.449 --> 00:02:01.254
where the magnetic field of the solar wind encounters the planet
and it starts to wrap around it.

39
00:02:01.254 --> 00:02:05.191
And the reason it wraps around the planet is those electric
currents that we were seeing.

40
00:02:05.758 --> 00:02:08.661
[David Brain]
The magnetic field in the solar wind is straight lines,

41
00:02:08.661 --> 00:02:11.097
you can think of straight spaghetti noodles,

42
00:02:11.097 --> 00:02:14.167
and it’s flowing towards the planet and those spaghetti noodles

43
00:02:14.167 --> 00:02:17.704
wrap around this basketball-shaped planet.

44
00:02:17.704 --> 00:02:19.506
And that’s indeed what we saw in the data –

45
00:02:19.506 --> 00:02:23.443
the magnetic field lines draping around Mars as a planet.

46
00:02:23.443 --> 00:02:27.213
One thing that wasn’t so expected was the
specific configuration

47
00:02:27.213 --> 00:02:31.017
of the electric currents that we derived from
the magnetic field data.

48
00:02:31.017 --> 00:02:35.121
If Mars is a ball here, it’s sort of this cup shape
on the dayside

49
00:02:35.121 --> 00:02:38.825
that loops back on itself, maybe something
that looks like this.

50
00:02:38.858 --> 00:02:42.629
What wasn’t so intuitive to me was the directions
of those currents,

51
00:02:42.629 --> 00:02:47.267
and the fact that it wraps continuously around
to the nightside,

52
00:02:47.267 --> 00:02:52.472
and it makes this marvelously complex current system
on the nightside as well.

53
00:02:53.373 --> 00:02:55.842
[Robin Ramstad]
This is the first time that we’ve been able to actually

54
00:02:55.842 --> 00:02:57.076
map out the currents,

55
00:02:57.076 --> 00:02:58.945
so we can see where the energy’s being transferred,

56
00:02:58.945 --> 00:03:02.715
we can see what actually forms the underlying mechanisms

57
00:03:02.715 --> 00:03:04.918
creating these induced magnetospheres that are

58
00:03:04.918 --> 00:03:08.488
not just common here in the solar system, they’re
fifty percent of the planets that have them –

59
00:03:08.488 --> 00:03:09.656
of the terrestrial planets.

60
00:03:09.656 --> 00:03:13.293
And if you want to understand how the atmospheres
of Mars and Venus,

61
00:03:13.293 --> 00:03:17.163
why they’re so different from the Earth,
and why they’re so different from each other

62
00:03:17.163 --> 00:03:19.132
despite both being non-magnetized,

63
00:03:19.132 --> 00:03:21.901
we need to understand their induced
magnetospheres first.

64
00:03:22.635 --> 00:03:26.439
[David Brain]
So, knowing how these global current systems are configured

65
00:03:26.439 --> 00:03:30.643
teaches us about how charged particles near the
planet are going to move –

66
00:03:30.643 --> 00:03:35.815
both charged particles in the solar wind,
and charged particles from the atmosphere itself

67
00:03:35.815 --> 00:03:38.751
that are in the process of escaping to space.

68
00:03:38.751 --> 00:03:42.188
So now we can understand better where those
particles came from,

69
00:03:42.188 --> 00:03:45.725
how they move near Mars, and where they’re
going to go next.

70
00:03:45.725 --> 00:03:49.562
That in turn teaches about atmospheric escape
from the planet,

71
00:03:49.562 --> 00:03:51.631
and the history of the atmosphere over time,

72
00:03:51.631 --> 00:03:54.400
how thick has it been, how much has been removed.

73
00:03:54.400 --> 00:04:04.944
♪♪♪