1
00:00:02,000 --> 00:00:09,000
The holy grail of current exoplanet research is the detection of a rocky, Earth-like planet in the ‘habitable zone’,

2
00:00:09,000 --> 00:00:14,000
a region around the host star with the right conditions for water to be liquid on their surface.

3
00:00:15,000 --> 00:00:21,000
The latest result from the European Southern Observatory comes closer than ever to attaining these goals.

4
00:00:25,000 --> 00:00:27,000
This is the ESOcast!

5
00:00:27,000 --> 00:00:32,000
Cutting-edge science and life behind the scenes of ESO, the European Southern Observatory.

6
00:00:32,000 --> 00:00:40,000
Exploring the Universe’s ultimate frontier with our host Dr J, a.k.a. Dr Joe Liske.

7
00:00:42,000 --> 00:00:45,000
Hello and welcome to another episode of the ESOcast.

8
00:00:45,000 --> 00:00:48,000
This time we have some very exciting news for you.

9
00:00:48,000 --> 00:00:50,000
It’s another major ESO discovery.

10
00:00:50,000 --> 00:00:54,000
We’d like to tell you about the discovery of the smallest, or rather lightest,

11
00:00:54,000 --> 00:01:00,000
and possibly most Earth-like planet so far discovered outside of our own Solar System.

12
00:01:00,000 --> 00:01:04,000
We’d also like to report on yet another planet within the same system

13
00:01:04,000 --> 00:01:09,000
that has now been shown to lie within the habitable zone of its parent star,

14
00:01:09,000 --> 00:01:13,000
meaning that it could host liquid water and possibly even life.

15
00:01:13,000 --> 00:01:18,000
Gliese 581 is a seemingly inconspicuous red dwarf star

16
00:01:18,000 --> 00:01:24,000
located 20.5 light-years away in the constellation Libra, or “the Scales”.

17
00:01:24,000 --> 00:01:29,000
It is among the 100 closest stars to us and weighs only one third the mass of the Sun.

18
00:01:29,000 --> 00:01:36,000
Such red dwarfs are intrinsically at least 50 times fainter than the Sun and are the most common stars in our Galaxy.

19
00:01:36,000 --> 00:01:40,000
For astronomers studying exoplanets, red dwarfs are ideal targets

20
00:01:40,000 --> 00:01:44,000
for the search for low-mass planets where water could be liquid.

21
00:01:44,000 --> 00:01:50,000
Because such dwarfs emit less light, the habitable zone is much closer to them than it is around the Sun,

22
00:01:50,000 --> 00:01:53,000
which makes it easier to detect the planets.

23
00:01:54,000 --> 00:01:58,000
Professor Michel Mayor from the Geneva Observatory and his team of European astronomers

24
00:01:58,000 --> 00:02:05,000
have carefully observed Gliese 581 over the past four years using the world’s leading planet-hunting instrument,

25
00:02:05,000 --> 00:02:11,000
the HARPS spectrograph on the ESO 3.6-metre telescope at the La Silla Observatory in Chile.

26
00:02:12,000 --> 00:02:20,000
Now, what they found was that Gliese 581 is orbited by a planet that has only 1.9 times the mass of the Earth.

27
00:02:20,000 --> 00:02:23,000
This planet is known as Gliese 581 e

28
00:02:23,000 --> 00:02:28,000
and it is the lightest and most Earth-like planet so far discovered outside of our own Solar System.

29
00:02:29,000 --> 00:02:38,000
Now within the very same system, the team also refined the orbit of a previously known planet, called Gliese 581 d.

30
00:02:38,000 --> 00:02:43,000
What they found was that this planet is definitely within the habitable zone of its parent star.

31
00:02:43,000 --> 00:02:47,000
Now what that means is that the planet is just at the right distance from the star

32
00:02:47,000 --> 00:02:50,000
for any water that might be present at its surface to be liquid.

33
00:02:51,000 --> 00:02:56,000
If it were any closer, the radiation from the star would be too strong and the water would evaporate.

34
00:02:56,000 --> 00:03:00,000
If it were any further away, it would be too cold and the water would freeze.

35
00:03:01,000 --> 00:03:04,000
From previous observations — also done with the HARPS spectrograph

36
00:03:04,000 --> 00:03:08,000
at ESO’s La Silla Observatory and announced two years ago —

37
00:03:08,000 --> 00:03:13,000
this star was known to also harbour a system of three super-Earth planets.

38
00:03:13,000 --> 00:03:17,000
With Gliese 581 e the planetary system has four known planets,

39
00:03:17,000 --> 00:03:27,000
with masses of about 1.9 (planet e), 16 (planet b), 5 (planet c), and 7 Earth-masses (planet d).

40
00:03:28,000 --> 00:03:33,000
The planet with the largest orbit in this system is Gliese 581 d

41
00:03:33,000 --> 00:03:38,000
and it takes about 66.8 days for one round trip around its parent star.

42
00:03:38,000 --> 00:03:41,000
Now because it orbits within the habitable zone of its star,

43
00:03:41,000 --> 00:03:47,000
this planet could be covered in liquid oceans – making it the first serious 'water world' candidate.

44
00:03:48,000 --> 00:03:55,000
Thanks to Mayor and his team, we now know that the Gliese 581 system contains at least four exoplanets.

45
00:03:56,000 --> 00:04:01,000
These planets were discovered through the tiny wobble they cause to their host star as they move around

46
00:04:01,000 --> 00:04:06,000
only about 7 km/hour which equates to brisk walking speed.

47
00:04:07,000 --> 00:04:12,000
The discovery of Gliese 581 e and the refinement of Gliese 581 d’s orbit

48
00:04:12,000 --> 00:04:17,000
were possible only due to HARPS’s unique precision and stability.

49
00:04:18,000 --> 00:04:22,000
Using the HARPS spectrograph, Michel Mayor and his team of European exoplanet hunters

50
00:04:22,000 --> 00:04:29,000
are leading the way towards answering some of our most fundamental questions about life outside of our own Solar System.

51
00:04:29,000 --> 00:04:34,000
They are confident that in the not too distant future, a truly Earth-like planet will be discovered.

52
00:04:34,000 --> 00:04:36,000
So stay tuned!

53
00:04:36,000 --> 00:04:38,000
This is Dr J signing off for the ESOcast.

54
00:04:39,000 --> 00:04:42,000
Join us again next time for another cosmic adventure.

55
00:04:43,000 --> 00:04:46,000
ESOcast is produced by ESO, the European Southern Observatory. www.eso.org

56
00:04:46,000 --> 00:04:49,000
ESO, the European Southern Observatory, is the pre-eminent intergovernmental science and technology organisation in astronomy

57
00:04:49,000 --> 00:04:52,000
designing, constructing and operating the world's most advanced ground-based telescopes.

58
00:04:53,000 --> 00:04:56,000
Transcription by ESO ; translation by —