WEBVTT FILE

1
00:00:02.669 --> 00:00:04.437
OSIRIS-REx was designed to

2
00:00:04.437 --> 00:00:08.108
retrieve a sample from asteroid Bennu
and return it to Earth.

3
00:00:08.191 --> 00:00:10.910
So of the more than 1 million
known asteroids

4
00:00:10.910 --> 00:00:14.531
in our solar system, why Bennu?

5
00:00:14.597 --> 00:00:18.702
First, as a near-Earth asteroid,
Bennu is easy to reach.

6
00:00:18.768 --> 00:00:21.621
It takes about 14 months to orbit
the sun and comes

7
00:00:21.621 --> 00:00:25.158
close to earth once
every six years to get there.

8
00:00:25.225 --> 00:00:28.461
OSIRIS-REx was launched
in 2016 on an Atlas

9
00:00:28.461 --> 00:00:32.248
five rocket with a single booster
and a center upper stage.

10
00:00:32.332 --> 00:00:35.902
It also got a big assist from Earth's
gravity in 2017,

11
00:00:36.086 --> 00:00:38.838
allowing it to match Bennu's orbital tilt.

12
00:00:38.838 --> 00:00:42.842
The second reason that Bennu was
chosen was its size and spin rate.

13
00:00:42.926 --> 00:00:46.129
Bennu measures about half a kilometer
in diameter and rotates

14
00:00:46.129 --> 00:00:49.132
on its axis once every 4.3 hours,

15
00:00:49.282 --> 00:00:53.119
which is actually pretty slow
compared to many smaller asteroids.

16
00:00:53.369 --> 00:00:56.856
This allowed OSIRIS-REx to map
Bennu surface up close

17
00:00:56.940 --> 00:01:01.745
and to match its velocity briefly
touch down and collect a sample.

18
00:01:01.828 --> 00:01:06.032
Before OSIRIS-REx arrived, scientists
thought that Bennu's slow rotation

19
00:01:06.032 --> 00:01:09.869
meant a low risk of flinging away
most of its sample material.

20
00:01:09.953 --> 00:01:11.604
But shortly after arrival,

21
00:01:11.604 --> 00:01:15.508
Bennu was caught on camera,
ejecting hundreds of pebbles.

22
00:01:15.592 --> 00:01:20.180
It turns out that Bennu
regularly sheds small particles, but

23
00:01:20.180 --> 00:01:24.567
it still had plenty of loose material left
on its surface for sample collection.

24
00:01:24.651 --> 00:01:28.621
The third reason for choosing
Bennu was its composition.

25
00:01:28.705 --> 00:01:31.941
We don't know what ingredients
were present during the formation of life

26
00:01:31.941 --> 00:01:35.128
on Earth,
but primitive asteroids like Bennu serve

27
00:01:35.128 --> 00:01:40.116
as time capsules, preserving material
from the dawn of the solar system.

28
00:01:40.200 --> 00:01:41.267
Spectrometers on

29
00:01:41.267 --> 00:01:45.755
OSIRIS-REx confirmed that Bennu is rich
in carbon based molecules,

30
00:01:45.839 --> 00:01:49.476
including organics
that are the stuff of life.

31
00:01:49.559 --> 00:01:52.796
When the Bennu sample is analyzed,
it will help scientists to better

32
00:01:52.796 --> 00:01:57.817
understand the formation
of the solar system and our own origins.

33
00:01:57.901 --> 00:02:01.738
So why this particular asteroid proximity
to Earth?

34
00:02:01.821 --> 00:02:06.242
The right size and spin and a carbon
rich composition?

35
00:02:06.326 --> 00:02:08.294
That is why we chose Bennu.