A galaxy being stretched out of shape has been imaged by the NASA/ESA Hubble Space Telescope. Known as NGC 2146, it has been severely warped and deformed so that an immense dusty arm of glittering material now lies directly in front of the centre of the galaxy, as seen in the image.
NGC 2146 is classified as a barred spiral due to its shape, but the most distinctive feature is the dusty spiral arm that has looped in front of the galaxy’s core as seen from our perspective. The forces required to pull this structure out of its natural shape and twist it up to 45 degrees are colossal. The most likely explanation is that a neighbouring galaxy is gravitationally perturbing it and distorting the orbits of many of NGC 2146’s stars. It is probable that we are currently witnessing the end stages of a process which has been occurring for tens of millions of years.
Neptune has 13 moons, and the largest of them, Triton, has a rather unusual feature. It has a retrograde orbit – it orbits Neptune in the opposite direction to the planet’s spin, and it is the only large moon in our solar system to do so. It takes speedy 5.87 earth days for this rebel moon to complete an orbit around Neptune.
In addition to being the odd one out in terms of its orbit, Triton also has a surprising composition. Underneath its frozen nitrogen crust lies an icy mantle, which houses a core made of rock and metal. Triton’s density of 2.050 g per cubic cm (one of the most dense of the outer solar system satellites) suggests that is has a higher rock content than the other icy moons that orbit Saturn and Uranus. Overall, Triton’s composition is remarkably similar to that of dwarf planet and Kuiper Belt object, Pluto.
Triton’s unusual orbit, coupled with its unexpected composition, suggests that Triton was originally part of the Kuiper Belt. Instead of being formed at the same time as Neptune, Triton was instead captured by Neptune’s gravity and coaxed into orbit.
This geologically active moon, which spews out nitrogen gas, has an orbital eccentricity of almost zero; it is nearly a perfect circle. Tidal forces, caused by interactions between the two bodies’ gravitational fields, cause Triton’s orbit to decay. Currently, Triton orbits at a distance of 354,759 km from Neptune; this is closer than our moon orbits the Earth. In an estimated 3.6 billion years, it is thought that the moon may pass the Roche limit (the limit by which the moon’s gravity can no longer withstand the pull of Neptune and thus disintegrates) and be torn apart, creating a ring system similar to that of Saturn.
From the odd way it orbits Neptune, to vomiting nitrogen and eventually meeting a violent demise, Triton should definitely call it a night.