Philips Atlas of the Universe

THE SOLAR SYSTEM

migrates towards the upper part of the crust, the pressure
will be relaxed, and the nitrogen will explode in a shower
of ice and gas, travelling up the nozzle of the geyser-like
vent at a rate of up to 150 metres (500 feet) per second –
fast enough to send the material up for many kilometres
before it falls back. The outrush sweeps dark debris along
with it, and this debris is wafted downwind, producing
plumes of dark material such as Viviane Macula and
Namazu Macula. Some of these plumes are over 70 kilo-
metres (40 miles) long.
Monad Regio is part smooth and in part hummocky,
with walled plains or ‘lakes’ such as Tuonela and Ruach;
these have flat floors, and water must be the main material
from which they were formed, because nitrogen ice and
methane ice are not rigid enough to maintain surface relief
over long periods. Bubembe Regio is characterized by the
so-called ‘cantaloupe terrain’, a name given because of
the superficial resemblance to a melon-skin. Fissures
cross the surface, meeting in huge X or Y junctions, and
there are subdued circular pits with diameters of around
30 kilometres (19 miles).
It may well be that there will be marked changes in
Triton’s surface over the coming decades, because the sea-
sons there are very long indeed, and the pink snow may
migrate across to the opposite pole – which was in darkness
during the Voyager pass. Unfortunately we cannot hope
for another space mission before southern midsummer on
Neptune and Triton, which is not due until the year 2006.

Name Dist. from Orbital Orbital Orbital Diameter, Mag.

Neptune, km period, days incl.,° eccentricity km

Naiad 48,000 0.296 4.5 0 54 26

Thalassa 50,000 0.312 0 0 80 24

Despina 52,500 0.333 0 0 180 23

Galatea 62,000 0.429 0 0 150 23

Larissa 73,500 0.544 0 0 192 21

Proteus 117,600 1.121 0 0 416 20

Triton 354,800 5.877 159.9 0.0002 2705 13.6

Nereid 1,345,500– 360.15 27.2 0.749 240 18.7

9,688,500

Three more outer satellites were discovered in 2002. All are over 20 million km from Neptune, and are less than 50 km in diameter.

 Triton photomosaic

made up of Voyager 2

images – the light south-

polar cap lies at the bottom.

SATELLITES OF NEPTUNE SELECTED FEATURES ON TRITON

Name Lat. ° Long. E °

Abatos Planum 35–8S 35–81

Akupara Maculae 24–31S 61–65

Bin Sulci 28–48S 351–14

Boyenne Sulci 18–4S 351–14

Bubembe Regio 25–43S 285–25

Medamothi Planitia 16S–17N 50–90

Monad Regio 30S–45N 330–90

Namazu Macula 24–28S 12–16

Ob Sulci 19–14N 325–37

Ruach Planitia 24–31S 20–28

Ryugu Planitia 3–7S 25–29

Tuonela Planitia 36–42N 7–19

Uhlanga Regio 60–0S 285–0

Viviane Macula 30–32S 34–38

Zin Maculae 21–27S 65–72

Map of Triton showing

the main features recorded

from Voyager.

Planetary orbit

Triton

Nereid

Orbits of Triton and

Nereid.Triton has an almost

circular orbit, with retrograde

motion; Nereid has direct

motion but a highly eccentric

orbit. All the six satellites

discovered from Voyager 2

are closer-in than Triton;

all have direct motion.

North

40

30

20

10

0

–10

–20

–30

–40

–50

300 320 340 0 20 40 60 80