1
00:00:00,000 --> 00:00:01,716
[Music]

2
00:00:01,716 --> 00:00:03,350
Our solar system is home

3
00:00:03,350 --> 00:00:06,350
to eight planets
and nearly 300 known moons,

4
00:00:06,683 --> 00:00:11,283
but of those many worlds, only
two are shaped by an active rain cycle:

5
00:00:11,766 --> 00:00:14,833
Earth and Saturn's largest moon, Titan.

6
00:00:15,550 --> 00:00:20,300
Now, NASA's James Webb Space
Telescope has discovered a new molecule

7
00:00:20,316 --> 00:00:24,183
in Titan's atmosphere, one
that may have implications for the future

8
00:00:24,250 --> 00:00:27,250
of this surprisingly Earthlike world.

9
00:00:27,250 --> 00:00:28,816
[Music]

10
00:00:28,816 --> 00:00:32,616
From space, Titan appears to be a
featureless, orange globe,

11
00:00:32,616 --> 00:00:36,550
with its lower atmosphere
and its surface hidden by an organic haze.

12
00:00:37,116 --> 00:00:40,366
But when we look at the moon in
infrared, its features emerge:

13
00:00:40,966 --> 00:00:43,550
dark dune fields, circling the equator,

14
00:00:43,550 --> 00:00:47,550
vast plains in the mid-latitudes,
and in the far north,

15
00:00:47,750 --> 00:00:51,433
lakes and seas rivaling
the Great Lakes of North America.

16
00:00:52,366 --> 00:00:56,833
Unlike Earth, these bodies are not made
of liquid water, but of hydrocarbons

17
00:00:56,833 --> 00:00:59,933
like methane and ethane chilled
to cryogenic temperatures.

18
00:01:00,700 --> 00:01:04,750
From 2022 to 2023, my colleagues
and I studied Titan

19
00:01:04,750 --> 00:01:08,516
with the Webb Telescope and
the Keck Observatory on Mauna Kea.

20
00:01:08,850 --> 00:01:11,866
Their powerful infrared vision
cut through Titan's haze

21
00:01:11,983 --> 00:01:14,983
to reveal its northern hemisphere
during late summer.

22
00:01:15,383 --> 00:01:18,900
What we saw were
two broad areas of methane cloud cover

23
00:01:18,933 --> 00:01:22,616
around 55 degrees north, close
to the largest lakes and seas.

24
00:01:23,333 --> 00:01:28,450
In 2004, NASA's Cassini orbiter
made its first close encounter with Titan

25
00:01:28,583 --> 00:01:32,450
while the southern hemisphere was in
summer. Cassini witnessed rain clouds

26
00:01:32,450 --> 00:01:36,916
forming in the drier south polar regions
due to seasonal heating and evaporation.

27
00:01:37,583 --> 00:01:41,783
Climate models predicted that as Titan's
northern hemisphere entered summer

28
00:01:41,883 --> 00:01:46,383
beginning in 2017, methane would evaporate
from its large lakes and seas,

29
00:01:46,516 --> 00:01:49,516
rising into the lower
atmosphere to form rain clouds.

30
00:01:50,233 --> 00:01:54,733
Now, our study has confirmed that
when Titan's northern hemisphere warms up,

31
00:01:54,783 --> 00:01:57,933
it also undergoes
a seasonal cycle of cloud formation.

32
00:01:57,933 --> 00:01:59,733
[Music]

33
00:01:59,733 --> 00:02:01,883
In addition to taking pictures of Titan,

34
00:02:01,883 --> 00:02:04,933
we used the Webb Telescope’s
Mid-Infrared Instrument,

35
00:02:05,116 --> 00:02:08,116
or MIRI, to study
the makeup of its atmosphere.

36
00:02:08,216 --> 00:02:10,733
MIRI has both a camera and
a spectrometer:

37
00:02:10,733 --> 00:02:12,616
it can break apart
the light from an object

38
00:02:12,616 --> 00:02:15,383
to determine its chemical composition.

39
00:02:15,383 --> 00:02:19,250
Like Earth, Titan's
atmosphere is made primarily of nitrogen,

40
00:02:19,516 --> 00:02:21,933
but it also has
a substantial amount of methane,

41
00:02:21,933 --> 00:02:24,916
which plays a similar role
to Earth's water vapor.

42
00:02:24,916 --> 00:02:30,066
Trace gases are present as well, including
heavier hydrocarbons like ethane.

43
00:02:30,266 --> 00:02:33,266
but the details of their formation
are murky.

44
00:02:33,333 --> 00:02:38,266
Now, Webb's MIRI instrument has shed
new light on how these hydrocarbons form.

45
00:02:38,750 --> 00:02:43,266
When MIRI measured Titan's spectrum,
it saw a previously undetected spike

46
00:02:43,400 --> 00:02:45,783
indicating the presence
of the methyl radical,

47
00:02:45,783 --> 00:02:48,366
the missing link to the heavier
hydrocarbons.

48
00:02:48,366 --> 00:02:51,966
Here's how the process works: in
Titan's upper atmosphere,

49
00:02:51,966 --> 00:02:55,333
UV radiation from the Sun and electrons
from Saturn

50
00:02:55,350 --> 00:02:59,066
break apart methane into hydrogen atoms
and methyl radicals.

51
00:02:59,383 --> 00:03:02,833
The hydrogen is lost to space,
while the short-lived methyl

52
00:03:02,833 --> 00:03:06,100
radicals recombine into heavier
molecules, like ethane.

53
00:03:06,666 --> 00:03:10,133
Ethane and methane
eventually condense into droplets and rain

54
00:03:10,133 --> 00:03:13,700
out of the atmosphere, replenishing
lakes and seas on the surface.

55
00:03:14,133 --> 00:03:17,333
Rainfall on Titan
has yet to be directly observed,

56
00:03:17,516 --> 00:03:21,266
but the discovery of methyl radicals
fills a gap in our observations,

57
00:03:21,500 --> 00:03:25,650
and it supports our understanding of
this surprisingly Earthlike world.

58
00:03:25,650 --> 00:03:27,216
[Music]

59
00:03:27,216 --> 00:03:30,050
Further discoveries will come in 2034,

60
00:03:30,050 --> 00:03:34,633
when NASA's Dragonfly mission touches down
near the equator during northern winter.

61
00:03:35,133 --> 00:03:39,683
Dragonfly will drill into the icy surface
to look for complex molecules

62
00:03:39,766 --> 00:03:43,250
made from Titan's abundant methane,
nitrogen and oxygen.

63
00:03:43,716 --> 00:03:46,833
Of particular interest to its search
are amino acids,

64
00:03:47,016 --> 00:03:50,033
the building blocks of proteins
that make up life on Earth.

65
00:03:50,966 --> 00:03:56,216
As spring slowly returns to the northern
hemisphere, in the late 2030’s, Dragonfly

66
00:03:56,216 --> 00:03:59,933
may also become the first mission
to witness rainfall on another world.

67
00:03:59,950 --> 00:04:02,050
[Music]

68
00:04:02,050 --> 00:04:05,116
Looking ahead to the far future,
our study hints

69
00:04:05,116 --> 00:04:08,700
at an intriguing possibility
for the evolution of Titan's climate.

70
00:04:09,266 --> 00:04:12,483
If the methane that is being broken apart
in the upper atmosphere

71
00:04:12,550 --> 00:04:14,766
is not replenished
from the moon's interior,

72
00:04:14,766 --> 00:04:17,766
it could eventually disappear
from the environment.

73
00:04:17,933 --> 00:04:22,066
Over tens of millions of years,
Titan's lakes and seas could dry up.

74
00:04:22,750 --> 00:04:26,200
Its shorelines could gradually give way
to the encroaching desert.

75
00:04:26,950 --> 00:04:30,966
Its rain clouds and organic haze
could vanish, leaving a dark blue sky.

76
00:04:31,716 --> 00:04:34,716
At last, Saturn would be
visible from Titan's surface,

77
00:04:34,883 --> 00:04:40,633
gazing down upon a world of dry lakebeds,
empty river channels, and endless dunes.

78
00:04:40,633 --> 00:04:43,483
[Dry wind blowing]
[Music]

79
00:04:43,733 --> 00:04:55,566
[Music]