Hubble’s Neptune Anniversary Pictures

Today, Neptune has arrived at the same location in space where it was discovered nearly 165 years ago. To commemorate the event, NASA’s Hubble Space Telescope has taken these “anniversary pictures” of the blue-green giant planet.

Neptune is the most distant major planet in our solar system. German astronomer Johann Galle discovered the planet on September 23, 1846. At the time, the discovery doubled the size of the known solar system. The planet is 2.8 billion miles (4.5 billion kilometers) from the Sun, 30 times farther than Earth. Under the Sun’s weak pull at that distance, Neptune plods along in its huge orbit, slowly completing one revolution approximately every 165 years.

These four Hubble images of Neptune were taken with the Wide Field Camera 3 on June 25-26, during the planet’s 16-hour rotation. The snapshots were taken at roughly four-hour intervals, offering a full view of the planet. The images reveal high-altitude clouds in the northern and southern hemispheres. The clouds are composed of methane ice crystals.

The giant planet experiences seasons just as Earth does, because it is tilted 29 degrees, similar to Earth’s 23-degree-tilt. Instead of lasting a few months, each of Neptune’s seasons continues for about 40 years.

The snapshots show that Neptune has more clouds than a few years ago, when most of the clouds were in the southern hemisphere. These Hubble views reveal that the cloud activity is shifting to the northern hemisphere. It is early summer in the southern hemisphere and winter in the northern hemisphere.

In the Hubble images, absorption of red light by methane in Neptune’s atmosphere gives the planet its distinctive aqua color. The clouds are tinted pink because they are reflecting near-infrared light.

A faint, dark band near the bottom of the southern hemisphere is probably caused by a decrease in the hazes in the atmosphere that scatter blue light. The band was imaged by NASA’s Voyager 2 spacecraft in 1989, and may be tied to circumpolar circulation created by high-velocity winds in that region.

The temperature difference between Neptune’s strong internal heat source and its frigid cloud tops, about minus 260 degrees Fahrenheit, might trigger instabilities in the atmosphere that drive large-scale weather changes.

This illustration is a composite of numerous separate Hubble WFC3 images. A color image composed of exposures made through three color filters shows the disk of Neptune, revealing clouds in its atmosphere. 48 separate images from a single filter were brightened to reveal the very faint moons. The white dots are Neptune's inner moons moving along their orbits during Hubble's observations. The solid green lines trace the full orbit of each moon. The spacing of the moon images follows the timing of each Hubble exposure. About 30 moons are known to orbit Neptune, most of which are too faint or orbit too far away to appear in these images. Illustration credit: NASA, ESA, and Z. Levay (STScI)

Neptune has an intriguing history….. Continue reading Hubble’s Neptune Anniversary Pictures

Neptune’s first orbit: a turning point in astronomy

As Neptune nears a historic orbit around the Sun, Robin McKie recalls the dramatic story of how the icy world was discovered

Neptune rising: although discovered in 1846, we didn’t get a glimpse of this alien world until Voyager 2 swept past in 1989

Astronomers will celebrate a remarkable event on 11 July. It will be exactly one year since the planet Neptune was discovered. Readers should note a caveat, however. That year is a Neptunian one. The great icy world was first pinpointed 164.79 years ago – on 23 September 1846. And as Neptune takes 164.79 Earthly years to circle the sun, it is only now completing its first full orbit since its detection by humans. Hence those anniversary celebrations.

And there is much to commemorate – for Neptune’s discovery marked a turning point in astronomy. Its existence was revealed, not through a serendipitous observation by an astronomer but by the careful work of mathematicians. They calculated that perturbations in the orbit of Uranus, then thought to be the sun’s most distant planet, could only be explained by the existence of another, even remoter world whose gravity was affecting Uranus’s path….. Continue reading Neptune’s first orbit: a turning point in astronomy

Where Did Triton Come From?

Space scientists want to send a mission to Neptune and beyond. But they need a better plan than the one they’ve come up with
One of the puzzles over Neptune’s moon Triton is its retrograde orbit: it moves in the opposite direction to the mother planet’s rotation.
Many of the small outer moons of Jupiter, Saturn and Uranus also have retrograde orbits, almost certainly because they are captured objects.
But Triton is different. It is the seventh largest moon in the Solar System, bigger even than Pluto. So explaining its origin is not as simple as saying it must be a rock that flew too close. And yet that’s what many planetary geologists believe.
The one good look we’ve had of Triton came in 1989 during the Voyager 2 flyby. It turns out that Triton is an icy body, probably with a metallic core. And it has a thin nitrogen atmosphere
It is also geologically active. One of Voyager 2’s most astounding discoveries were nitrogen geysers erupting from Triton’s surface. This surface is also relatively smooth, meaning the craters must be have been covered relatively recently.
The current thinking is that Triton was not a rock but probably a Kuiper Belt object that was somehow pushed Neptune’s way. But since we don’t really know what Kuiper Belt objects look like, it’s hard to tell.
So Bruno Christophe at ONERA – The French Aerospace Lab in Chatillon and a few amis want to go and have a look. Their plan is to send a spacecraft to fly past Neptune, take a good look at Triton, and then fly on to find a Kuiper Belt object to study. If they look remotely similar, then that’ll back up the idea that Triton really is from the Kuiper Belt.
That’s not a bad problem to solve in a single mission (although the choice of Kuiper Belt object will obviously be crucial)..
At the same time, Christophe and co want to use the mission to study gravity at great distances from the Sun. Their idea is to throw some light on the possibility that gravity is somehow different at large distances from the Sun, something that various theories predict and that the Pioneer space probes seem to have experienced, in an effect called the Pioneer anomaly.
That’s an ambitious medium sized mission (about 500 kg) .Christophe and co proposed their Outer Solar System Mission to ESA last year in the hope that it would also attract funding from NASA and launch in the 2020 timeframe.
Sadly it seems to have missed the cut this time. ESA announced its medium-sized mission candidates in February and OSS wasn’t in it. That’s understandable given the similarities to Pluto Express, which is currently en route for a fly past with the dwarf planet and then heading to an as-yet-undetermined Kuiper belt object.
But a journey to Neptune ought to be on the cards at some point in the future. Triton is spiralling into its mother planet. Some 3.6 billion years from now, the giant moon is destined to be torn apart by Neptune’s tidal forces, and so will eventually forming a ring.
Which means ESA better get a move on.