We have chosen to work with Triton, the moon of the Neptune. The name Triton comes from Roman mythology, where Triton was a god of the occasion, born by Neptune and Amfitrite. He is often depicted as a half-man, half-fish and with his famous seashell with which he could create and calm storms.

In 1846 astronomers found a moon orbiting the newly discovered planet Neptune. Neptune got its name from the sea-god Neptune, so the newly discovered moon got its name from Neptune’s son, Triton.

But it wasn’t until a 100 years after the discovery of Triton that the scientists started to observe the moon more closely and the name was publicly accepted. When astronomers started to study the moon they discovered that it had a highly inclined retrograde orbit. Which makes Triton one of the most fascinating objects in our solar system.

Tritons surface can tell us a lot about its violent beginning and many theories suggests an equally cataclysmic end.

These were the reasons that gave us inspiration to work with Triton and sign up for the "Catch a Star!" competition.

Origin and evolution of Triton

The origin and evolution of Triton are not that well known. However from the distinctiveness of both its orbit and its surface, we can derive that this moon has undergone significant remodelling during ages past. There are two theories regarding the origin of Triton. The first is that it was formed within the Neptune system as an equatorial satellite to Neptune, developing at its current orbit. The other one suggests that triton itself was formed as a protoplanet to the sun, and was then captured by Neptune's gravity when crossing its orbit. The latter of these is the commonly most accepted. This because it explains how the extraordinary surface features and strange inclined orbit of the moon have come to be. If this is indeed how it came to pass, then almost all of Tritons interior would have been forced upward towards the surface of the moon by the immense tidal forces exerted on the moon by Neptune. Once on the surface, the molten materials were condensed by the differences in temperature between the hot interior of the moon and the almost atmosphere-free environment on the moon’s surface. This led to the forming of a mantle of water ice.

Also, the heavy tidal forces exerted on Triton by Neptune constantly melts large masses of methane and water ices, which are then transported upwards to the surface were they form powerful geysers that rise straight up for several kilometres an then turn very abruptly towards the south-west. The particles thrown up into the atmosphere by these geysers then fall down on the southern hemisphere as methane and nitrogen snow. This phenomenon may help us to explain why the surface of this particular moon is so smooth compared to almost all of the other moons in our solar system. Because if Triton, once captured by Neptune's gravitational pull, was affected by these powers to such a degree that geothermal processes occurred in its interior and caused massive geysers to form, these would then have covered almost the entire planets surface with methane and nitrogen snow, subsequently flattening it out. On the surface of the moon can also be seen the results of geological activities similar to those we believe occur on Pluto. The icecap on Triton rests upon layer of liquid "magma" believed to consist of Ammonium, methane and water. This "magma" is kept in a liquid state by both the pressure from the icecap above and by the tidal forces from Neptune. On the bottom of this layer Triton is believed to have a solid rock core.

  The Future of Triton   The Future of Triton   

The future of Triton is almost as uncertain as its origin. What we do know is that the circular orbit with its high inclination brings Triton closer to Neptune with each passing moment and will ultimately come to close to close to its enormous parent. However the ending scenes are played out is utterly determined by one fact, the overall density of the moon itself. Because if the density is to low, the moon will be torn apart by Neptune's gravity and form a ring of debris around the planet. But if the density of the moon is to high, it will continue to fall towards the planet, without breaking up, and after a while the moon will crash into Neptune with catastrophic consequences for them both. There isn’t very much to say about the death and downfall about this giant amongst moons since we haven’t actually visited this moon, and our largest source of knowledge about it comes from Voyager 2, as it passed through the Neptune system in august 1989 .


   Discovery and Observation   

The discoverer of Triton, William Lassell, was born in Bolton on the 18th of June, 1799. He became a successful brewer, and devoted all his leisure time to Astronomy. He made his own telescope mirrors, beginning in 1820 with a 17.8-cm mirror, and in 1844 he began constructing a telescope with a 61-cm mirror. Neptune was discovered on the 23rd of September, 1846, and the news about the discovery reached London on the 30th of September. On the 1st of October, John Herschel wrote a letter to Lassell in which he asked him to look for any satellites "with all possible expedition". Lassell, who lost no time, began looking for possible satellites with his new 61-cm reflector on the 2nd of October, and discovered Triton on the 10th. Furthermore, his observations led him to suspect that Neptune had a ring, but since the actual rings of Neptune are extremely thin and dark, this observation was probably due to an illusion. In 1847, Lassell wrote this in the Monthly Notices of the Royal Astronomical Society (and for some reason he writes about himself in third person):

"The observations of the satellite have been more successful: it has been seen repeatedly in the course of the year, and the non-existence of any star in the places successively occupied by it frequently ascertained. From the mean of his observations, Mr. Lassell concludes that the satellite revolves about the planet in 5 hours 21 minutes nearly, and that its greatest elongation is about 18 seconds of arc. The orbit which it appears to describe has a minor axis differing little from the diameter of the planet."

Lassell was correct about the elongation, but the orbital period of Triton is 5 days, 21 hours and 3 minutes. Even though the properties of Tritons orbit was established fairly accurately during the 19th century, that was just about everything that was known about the moon until the flyby of Voyager 2 in August, 1989. The first attempt to measure the diameter of Triton accurately took place in 1954, when the great Dutch planetary scientist Gerard Kuiper used the 200-inch Hale reflector at Palomar to obtain a value of 3,800 km. Because the apparent brightness of Triton is relatively high (even if one takes its large distance into account), it means that it must be either highly reflective, extremely large by satellite standards or both. During the years following 1954, several attempts to measure the diameter of Triton was made and the results varied between 6,000 and 2,500 km. The generally accepted value of Tritons diameter during the pre-Voyager years was something around 3,500 km


Discovered by

William Lassell

Date of discovery


Mass (kg)


Mass (Earth = 1)


Equatorial radius (km)


Equatorial radius (Earth = 1)


Mean density (gm/cm^3)


Mean distance from Neptune (km)


Rotational period (days)


Orbital period (days)


Mean orbital velocity (km/sec)


Orbital eccentricity


Orbital inclination (degrees)


Escape velocity (km/sec)


Visual geometric albedo


Magnitude (Vo)


Mean surface temperature



Our practical experiment

We decided to get our own ccd pictures of Triton with the Tycho Brahe Observatory in Oxie, Sweden. This was to happen on the 7 th of October 2002, yet the weather in Oxie was very cloudy and thus no pictures could be taken. As the weather remained cloudy the following days, our experiment could not been completed. Our supervisor was Peter Linde, a reader at the University of Lund.




Triton compared to Charon


As our knowledge of these two world are quite limited we can only try to make guesses at their origins. However, we do know that Charon and Triton both have a similarly high albedo, which suggests a similar chemical composition. This also supports the theory on how triton evolved as a protoplanet, and was captured by Neptune.



This report was made by:

Anders Nyholm

Kenneth Swedlund

Christoffer Johnsson