1
00:00:01,171 --> 00:00:04,434
Are there rivers and lakes on other worlds?

2
00:00:06,172 --> 00:00:07,863
NASA.

3
00:00:07,863 --> 00:00:09,635
We Asked a NASA Scientist.

4
00:00:09,843 --> 00:00:11,978
The answer, surprisingly, is yes.

5
00:00:11,978 --> 00:00:14,047
Titan, which is the largest moon of Saturn,

6
00:00:14,080 --> 00:00:16,316
has lakes and rivers on its surface.

7
00:00:16,383 --> 00:00:19,519
Unlike Earth, the rivers and lakes and streams on Titan

8
00:00:19,519 --> 00:00:22,722
are made out of methane
and ethane. But very much like Earth,

9
00:00:22,756 --> 00:00:24,724
there's what we call a hydrologic cycle.

10
00:00:24,724 --> 00:00:28,528
So methane can move back and forth
between the surface and the atmosphere.

11
00:00:28,561 --> 00:00:32,032
That means that we don't just have lakes
and streams and rivers.

12
00:00:32,065 --> 00:00:34,567
We also have rain and clouds.

13
00:00:34,735 --> 00:00:37,170
And Titan is one of the only places in the solar system

14
00:00:37,170 --> 00:00:39,239
where it might be possible to see a rainbow.

15
00:00:39,239 --> 00:00:43,109
At other points in solar system history,
we do think that other worlds

16
00:00:43,143 --> 00:00:44,778
also had lakes and streams.

17
00:00:44,920 --> 00:00:49,883
Mars, for example, we know, had a lot of liquid water on its surface earlier in its history.

18
00:00:49,916 --> 00:00:53,086
But today there's only two places
in our solar system

19
00:00:53,086 --> 00:00:56,689
that currently have liquid on their surface — Earth and Titan.

20
00:00:56,990 --> 00:00:59,534
So, are there rivers and lakes on other worlds?

21
00:00:59,862 --> 00:01:02,262
In our solar system, the answer is definitely yes,

22
00:01:02,262 --> 00:01:04,130
but we also know that there's more to be discovered

23
00:01:04,130 --> 00:01:07,133
as we start to learn
more about planets around other stars.