NASA sets sights on Neptune moon Triton
By Amanda Jermyn

Neptune, the farthest known planet in our solar system, is thirty times the distance of the Earth from the Sun. It is orbited by fourteen moons, the largest of which is Triton. In Greek mythology Triton was a sea god, so it seems fitting that this moon is now thought to harbor an ocean.

Triton orbits in the opposite direction from Neptune’s rotation, which makes it unlikely that it was formed along with Neptune. The current thinking is that it was originally a minor planet in the Kuiper belt, a ring of small icy objects just beyond Neptune, and that it was captured by Neptune’s gravity billions of years ago.

The last mission to visit Triton was the Voyager 2 spacecraft, which took the first and only close-up photos of Neptune and its moons during a brief flyby back in 1989. Recently, NASA’s Jet Propulsion Laboratory proposed sending a spacecraft named Trident to explore Triton. At much lower cost than other outer solar system missions such as Cassini, the proposal was presented under NASA’s Discovery program for missions costing under $500 million.

Triton is a particularly intriguing place to explore because it is known to be geologically active, with cryovolcanoes spewing liquid ammonia and nitrogen gas up to five miles high. In addition, its surface has deposits of tholins, organic compounds that could be precursors to life.

Data from the Voyager 2 flyby shows possible plumes of water being ejected from its interior, and Triton is now thought to harbor a liquid water ocean beneath its frozen surface. This ocean is most likely kept liquid by heat generated by the decay of internal radioactive elements. In addition, in the past, Triton had a highly elliptical orbit, so, as the distance from Neptune changed, the planet’s gravity continually stretched and squeezed Triton, heating its interior through friction. The presence of organic compounds and a liquid ocean could mean that Triton is capable of harboring life.

According to Dr. Amanda Hendrix of the Planetary Science Institute in Tucson, Arizona, Triton is a particularly compelling target “because you can visit the Neptune system, visit this interesting ocean world, and also visit a Kuiper belt object without having to go all the way out there.”

Scientists would also like to observe the changes that occur on Triton with the change of season. When one hemisphere experiences summer the frozen nitrogen, methane and carbon monoxide on its surface sublimate to form a gas, thickening the atmosphere. With the arrival of winter the gas freezes and forms ice on the surface again.

The proposed mission to Triton would carry instruments to detect oceans and to analyze its atmosphere. It would aim to photograph Triton in its entirety. If approved, it would launch by 2026 to take advantage of a gravity assist from Jupiter and to reach Triton during an opportune time in its orbit. This timing would allow Trident to view the plume activity previously observed by Voyager 2 and to observe the changes that occur every forty years as the seasons change.

It used to be thought that worlds beyond Mars could not support life because they were too far from the heat of the Sun, but our understanding of the internal heating of some moons and planets has changed all that. And there is now evidence that Jupiter’s moon, Europa, and Saturn’s moons, Enceladus and Titan, have water oceans under ice that could harbor life. If an ocean beneath Triton were confirmed, this would expand the range of places within the solar system that might support life.

As technology has improved exponentially since Voyager 2 was launched back in 1977, the proposed Trident mission has the potential to resolve some of the many unanswered questions about the outer solar system. Perhaps the most tantalizing among them is whether distant Triton might be capable of harboring life.

Join the Springfield Stars Club on Tuesday, May 28th at 7:00pm at the Springfield Science Museum for a talk celebrating the upcoming 50th anniversary of Neil Armstrong’s first step on the moon. Richard Sanderson and Ed Faits will give a talk on “Apollo 11: A Look Back at Humanity’s Greatest Achievement.” In addition to describing the mission’s historical significance, the talk will address its relevance for the future of manned space exploration. Refreshments will be served, and the public is welcome. The meeting is free of charge for members, with a suggested donation of $2 per non-member.