1
00:00:01,000 --> 00:00:03,000
Using the NASA / ESA
Hubble Space Telescope

2
00:00:03,000 --> 00:00:05,500
astronomers have found
the first clear evidence

3
00:00:05,500 --> 00:00:07,500
of high altitude haze or clouds

4
00:00:07,500 --> 00:00:10,000
in the atmosphere
of an extrasolar planet.

5
00:00:10,000 --> 00:00:12,500
This discovery reveals
a deeper understanding

6
00:00:12,500 --> 00:00:16,500
of the class of giant planets
that astronomers call 'hot Jupiters'.

7
00:00:41,000 --> 00:00:42,500
This is the Hubblecast.

8
00:00:42,500 --> 00:00:46,500
News and images from the
NASA / ESA Hubble Space Telescope.

9
00:00:46,500 --> 00:00:49,500
Travelling through time and space
with our host, Dr. J

10
00:00:49,500 --> 00:00:52,500
EPISODE 12: Murk
on a monster planet.
a.k.a. Dr. Joe Liske.

11
00:00:52,500 --> 00:00:54,500
Hello and welcome
to the Hubblecast.

12
00:00:55,000 --> 00:00:57,500
On the last fifteen years
astronomers have discovered

13
00:00:57,500 --> 00:01:01,500
more than 270 planets
around other stars.

14
00:01:02,000 --> 00:01:04,000
A burning question
is naturally:

15
00:01:04,000 --> 00:01:07,000
what are this so called
extrasolar planets like?

16
00:01:07,000 --> 00:01:11,500
Well, most of them are
actually giant gaseous worlds

17
00:01:11,500 --> 00:01:13,500
several times the size of Jupiter,

18
00:01:13,500 --> 00:01:16,500
which is our own
Solar System's largest planet.

19
00:01:16,500 --> 00:01:20,000
Others are smaller
rocky or icy worlds

20
00:01:20,000 --> 00:01:23,500
that are still several times larger
than our own home planet Earth.

21
00:01:24,000 --> 00:01:28,000
We have yet to discover a world
that is similar to our own planet.

22
00:01:30,500 --> 00:01:34,000
Using the Advanced Camera
for Surveys or ACS

23
00:01:34,000 --> 00:01:36,000
the Hubble Space Telescope
has recently observed

24
00:01:36,000 --> 00:01:42,000
a fascinating large gaseous planet
around the star HD 189733.

25
00:01:42,500 --> 00:01:46,000
Careful analysis of this very
high precision observation

26
00:01:46,000 --> 00:01:50,500
by a team lead by Frédéric Pont
from the Geneva University Observatory

27
00:01:50,500 --> 00:01:56,000
showed that this planet,
designated HD 189733b,

28
00:01:56,000 --> 00:01:59,500
possesses a murky haze layer
extending over an altitude range

29
00:01:59,500 --> 00:02:03,500
of about 1,000 kilometres
in the planet's upper atmosphere.

30
00:02:05,000 --> 00:02:07,000
The atmosphere
of this gaseous planet

31
00:02:07,000 --> 00:02:09,500
is at around 800 degrees Celsius.

32
00:02:10,000 --> 00:02:13,000
This is due to its proximity
to its parent star,

33
00:02:13,000 --> 00:02:16,000
and is the reason that astronomers
call this type of planet

34
00:02:16,000 --> 00:02:18,000
a 'hot Jupiter'.

35
00:02:19,500 --> 00:02:22,500
These hazes are probably made
of tiny condensed particles

36
00:02:22,500 --> 00:02:25,500
less than 1/1000th.
of a millimetre across,

37
00:02:25,500 --> 00:02:30,000
similar to those already known on
Venus and Saturn's moon Titan.

38
00:02:31,000 --> 00:02:35,500
Their presence means that
the sky over HD 189733b

39
00:02:35,500 --> 00:02:38,500
would look very much
like a red hazy sunset

40
00:02:38,500 --> 00:02:41,500
viewed from an industrially
polluted city on Earth.

41
00:02:44,500 --> 00:02:46,500
Today we have a special guest.

42
00:02:46,500 --> 00:02:48,500
This is Dr. Bob Fosbury,

43
00:02:48,500 --> 00:02:51,000
he's the leader
of the European Hubble effort.

44
00:02:51,500 --> 00:02:55,000
So tell me Bob what's so special about
this particular star and its planet?

45
00:02:55,500 --> 00:02:57,500
Well this is a rather
special planetary system

46
00:02:57,500 --> 00:03:00,000
because the star itself
is quite small,

47
00:03:00,000 --> 00:03:03,500
it's only about 75%
of the size of our Sun,

48
00:03:03,500 --> 00:03:06,500
and yet the planet itself
is larger than Jupiter.

49
00:03:06,500 --> 00:03:09,500
So when the planet transits
in front of the star

50
00:03:09,500 --> 00:03:13,000
it obscures quite a large
fraction of light from the star

51
00:03:13,000 --> 00:03:15,000
which enables a very
accurate measurement.

52
00:03:15,000 --> 00:03:18,000
So what exactly made
these observations so precise?

53
00:03:18,000 --> 00:03:20,000
Why was this
only possible now?

54
00:03:20,000 --> 00:03:21,500
Well we have to do
this from space

55
00:03:21,500 --> 00:03:23,500
because when we try to do
this from the ground

56
00:03:23,500 --> 00:03:28,000
the atmosphere makes very difficult
to make precise measurements of brightness,

57
00:03:28,000 --> 00:03:29,500
so we do it from space.

58
00:03:29,500 --> 00:03:32,000
And the special thing about
this particular observation

59
00:03:32,000 --> 00:03:36,500
is that the scientists spread the light
out over many pixels in the detector.

60
00:03:36,500 --> 00:03:39,000
So rather than just having
a little point of light

61
00:03:39,000 --> 00:03:41,500
representing the star
on the detector

62
00:03:41,500 --> 00:03:45,000
the starlight was spread out
into a spectrum

63
00:03:45,000 --> 00:03:48,500
using the so called 'grism mode'
of the Advanced Camera for Surveys.

64
00:03:49,000 --> 00:03:51,500
Now, that enables a very
precise measurement

65
00:03:51,500 --> 00:03:56,000
because you can measure over many,
many pixels, a large area of detector,

66
00:03:56,500 --> 00:04:01,000
but it also, by spreading out the colours,
it enables you to measure the brightness

67
00:04:01,000 --> 00:04:06,500
or the reduction in brightness
of the starlight over many colours.

68
00:04:07,000 --> 00:04:10,500
And having these different measurements
in different colours

69
00:04:10,500 --> 00:04:14,000
enables you to characterize
the nature of the atmosphere.

70
00:04:15,000 --> 00:04:17,500
To detect the hazes
astronomers actually had to do

71
00:04:17,500 --> 00:04:19,500
quite a bit of detective work.

72
00:04:19,500 --> 00:04:22,000
And the reason why this
work was possible at all

73
00:04:22,000 --> 00:04:27,500
is because from our vantage
point the orbit of HD 189733b

74
00:04:27,500 --> 00:04:30,000
is seen almost exactly edge on.

75
00:04:30,500 --> 00:04:33,500
Now what that means is
that every two days or so

76
00:04:33,500 --> 00:04:37,000
the planet actually moves across
the face of its parent star

77
00:04:37,000 --> 00:04:39,000
as seen from here.

78
00:04:39,500 --> 00:04:41,000
When that happens

79
00:04:41,000 --> 00:04:43,500
some small fraction
of the light from the star

80
00:04:43,500 --> 00:04:47,000
has to pass through the atmosphere
of the planet in front of it

81
00:04:47,000 --> 00:04:49,000
in order to reach Earth.

82
00:04:49,000 --> 00:04:51,000
Because of this process

83
00:04:51,000 --> 00:04:53,500
the composition of
the atmosphere of the planet

84
00:04:53,500 --> 00:04:57,000
is stamped onto the light
like a unique fingerprint.

85
00:04:57,500 --> 00:04:59,500
Astronomers can then
see this fingerprint

86
00:04:59,500 --> 00:05:02,000
in the spectrum
of the star's light.

87
00:05:04,000 --> 00:05:07,000
The astronomers were expecting
to see clear signatures

88
00:05:07,000 --> 00:05:10,500
of sodium, potassium and water
in the planet's atmosphere.

89
00:05:11,000 --> 00:05:14,000
The fact that these were not seen
led them to this conclusion

90
00:05:14,000 --> 00:05:18,000
that they were being masked by
red-coloured high clouds or haze.

91
00:05:18,500 --> 00:05:20,000
According to the scientists

92
00:05:20,000 --> 00:05:23,000
the haze probably
consists of tiny particles

93
00:05:23,000 --> 00:05:26,000
condensates of iron
and silicates.

94
00:05:30,000 --> 00:05:33,000
When extrasolar planets were first
discovered about 15 years ago,

95
00:05:33,500 --> 00:05:37,500
little did we know how quickly we
would begin to unravel the secrets.

96
00:05:38,000 --> 00:05:40,000
The new Hubble observations
are an important step

97
00:05:40,000 --> 00:05:42,500
towards a better understanding
of these amazing planets

98
00:05:42,500 --> 00:05:44,500
outside our own Solar System.

99
00:05:44,500 --> 00:05:47,000
Who knows what we will
discover in the next few years

100
00:05:47,000 --> 00:05:49,000
about these distant worlds.

101
00:05:49,500 --> 00:05:52,000
This is Dr. J
signing off for the Hubblecast.

102
00:05:52,000 --> 00:05:56,000
Once again, nature has surprised us
beyond our wildest imagination...

103
00:05:58,000 --> 00:06:00,000
Hubblecast is produced
by ESA / Hubble

104
00:06:00,000 --> 00:06:02,000
at the European
Southern Observatory in Germany.

105
00:06:03,000 --> 00:06:05,000
The Hubble mission is a project
of international cooperation

106
00:06:05,000 --> 00:06:07,000
between NASA and
the European Space Agency.