Sky and Telescope - July 2015 - 25

Key Phases of the Pluto Encounter

Hydra

16:00

Pluto-Earth
occultation

15:00

14:00

Charon
13:00

Charon-Sun
occultation

FRENZY OF ACTIVITY During its July 14th pass through
the Pluto system at 13.8 km (8.6 miles) per second, New
Horizons will execute a complex, preprogramed sequence
of twists and turns to record everything it can. None of
these observations will be radioed to Earth until the next
day, and mission scientists will have to wait more than a full
year to get all the data in uncompressed form.

Kerberos

Charon-Earth
occultation

Styx
Pluto

12:00
Pluto-Sun
occultation

11:00

Closest to
Charon
(28,800 km)

Sun
Earth

0.24

50,000 km
Closest to
Pluto
(12,500 km)

Nix

10:00

oriz

ons

traj

ect

30,000 miles

ory

9:00

S&T: GREGG DINDERMAN, SOURCE: NASA

Encounter phase

Dates

Starting range

LORRI's resolution

Approach Phase 1

Jan. 6 - April 4

226 ×

Approach Phase 2

April 4 - June 23

121 × 106 km

May 28: 281 km/px

Approach Phase 3

June 23 - July 13

26 × 106 km

July 1: 79 km/px

106

1,000 km/pixel

Major activities
LORRI shoots images for optical navigation; SWAP, PEPSSI, and
SDC measure environment unaﬀected by Pluto.
Previous activities continue; Ralph (MVIC) and LORRI map Pluto
to look for surface changes; LORRI searches for moonlets and rings.

July 12: 13 km/px

Previous activities continue; Ralph (LEISA) and Alice map
atmosphere and look for variability; LORRI and Ralph (MVIC) map
surface geology and search for hazes and clouds.
High-resolution imaging; measurement of escaping atmosphere;
REX and Alice record radio and solar occultations.

July 13-15

1.2 × 106 km

July 13: 4 km/px
July 14: 0.4 km/px

Departure Phase 1

July 15 - Aug. 4

1.2 × 106 km

July 15: 4 km/px

Departure Phase 2

Aug. 4 - Oct. 22

24 × 106 km

(no imaging)

SWAP, PEPSSI, and SDC activities continue.

119 ×

(no imaging)

SWAP, PEPSSI, and SDC activities continue.

Near Encounter Phase

Departure Phase 3

Oct. 22 - Jan. 1, 2016

106

vational schedule. As Pluto and Charon grow in apparent size, the spacecraft must begin shooting mosaics of
overlapping images to cover their globes.
About 4 hours before closest approach, four of the
Deep Space Network's giant radio dishes will begin to
broadcast a pure, unmodulated signal toward Pluto that
will race across space toward the retreating spacecraft.
Closest approach happens at 11:50 UT, when New Horizons will pass 12,500 km from Pluto's surface. Fourteen
minutes later the spacecraft comes its closest to Charon,
which will be almost exactly opposite Pluto from New
Horizons, 28,800 km away.
New Horizons will continue imaging as it begins to
speed away from Pluto. LORRI will look toward its limb,

LORRI and Ralph (MVIC) image crescents and search for rings;
SWAP and PEPSSI study magnetotail and pickup ions through
one solar rotation; REX measures nightside temperatures.

potentially photographing haze layers ﬂoating high
above Pluto's surface. By this time, the radio beam from
Earth will have caught up with the spacecraft, which will
record it as the signal strength begins to fade while passing through Pluto's atmosphere.
An hour after the ﬂyby, the faint light of the Sun will
brieﬂy go out as New Horizons enters Pluto's shadow;
a minute later, Pluto will block Earth as well. About 1½
hours later, New Horizons will experience a similar pair
of occultations at Charon.
These radio occultations will enable scientists to
sensitively probe the structure of Pluto's atmosphere
and Charon's (if one exists). The Alice spectrometer
will also watch the Sun wink out behind both bodies,
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Sky and Telescope - July 2015

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