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Happy birthday Neptune!

Neptune

Neptune, the eighth planet from the Sun, has now completed one 165-Earth-year-long orbit of the Sun since it's discovery in 1846.

THE EIGHTH PLANET is celebrating today, having completed one orbit around the Sun since its discovery in 1846. Neptune’s year is 164.8 Earth years long, so it has taken until now for it to make one full circle of the Solar System.

Neptune was the first planet to be found via a mathematical prediction. Astronomers had noted that Uranus—the next planet inwards to the Sun—was not following its predicted path, and the gravitational pull of an as-yet-undiscovered planet was thought to the culprit.

Predictions were made for where in the sky this mystery planet might be found, and sure enough, there it was—Neptune.

The story of the prediction and discovery has lots of twists and turns—read more about it here.

And the story of how the planet then got its name is equally complex—and you can read more about that here.

Neptune orbits the Sun at an average distance of 30.1 AU (one AU being the distance between Earth and Sun), or about 4.5 billion kilometres.

The following video (courtesy NASA, ESA, G. Bacon, and Z. Levay (STScI)) shows a speeded up view of Neptune rotating, using images taken every four hours by the Hubble Space Telescope:

Neptune is the fourth-largest planet, with a radius at the equator of 24,764 kilometres—about four times wider than Earth.

The giant blue world is the most distant Solar System body visited by a spacecraft. NASA’s Voyager 2 probe flew past Neptune in 1989.

Here’s a fascinating video (courtesy NASA, ESA, and G. Bacon and M. Estacion (STScI)) which puts that one Neptunian orbit into an Earth timeline perspective:

Story by Jonathan Nally. Images courtesy NASA.

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Voyager – the journey continues

AFTER 33 YEARS, NASA’s twin Voyager spacecraft are still going strong and still sending home information. This video features highlights of the Voyager journeys to the outer planets, and looks at their current status, at the edge of our Solar System, poised to cross over into interstellar space.

Adapted from information issued by NASA / JPL.

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Uranus fly-by – 25 years ago today

True- and false-colour images of Uranus

Two views of Uranus—one in true colour (left) and the other in false colour—were compiled from images returned Jan. 17, 1986, by the narrow-angle camera of Voyager 2. The spacecraft was 9.1 million kilometres from the planet, and several days from closest approach.

AS NASA’S VOYAGER 2 spacecraft made the only close approach to date of our mysterious seventh planet Uranus 25 years ago, Project Scientist Ed Stone and the Voyager team gathered at NASA’s Jet Propulsion Laboratory, Pasadena, California, to pore over the data coming in.

Images of the small, icy Uranus moon Miranda were particularly surprising. Since small moons tend to cool and freeze over rapidly after their formation, scientists had expected a boring, ancient surface, pockmarked by crater-upon-weathered-crater.

Instead they saw grooved terrain with linear valleys and ridges cutting through the older terrain and sometimes coming together in chevron shapes. They also saw dramatic fault scarps, or cliffs. All of this indicated that periods of tectonic and thermal activity had rocked Miranda’s surface in the past.

Surface of Miranda

A section of the surface of Miranda, innermost of Uranus' large satellites, as seen by Voyager 2 from 36,000 kilometres away. A complex topography of high and low terrain, craters and scarps can be seen.

The scientists were also shocked by data showing that Uranus’s magnetic north and south poles were not closely aligned with the north-south axis of the planet’s rotation. Instead, the planet’s magnetic field poles were closer to the Uranian equator. This suggested that the material flows in the planet’s interior that are generating the magnetic field are closer to the surface of Uranus than the flows inside Earth, Jupiter and Saturn are to their respective surfaces.

“Voyager 2’s visit to Uranus expanded our knowledge of the unexpected diversity of bodies that share the solar system with Earth,” said Stone, who is based at the California Institute of Technology in Pasadena. “Even though similar in many ways, the worlds we encounter can still surprise us.”

Here’s NASA’s pre-encounter video from the 1980s, showing how Voyager 2 sped past the planet while collecting its data:

A host of new discoveries

Voyager 2 was launched on August 20, 1977, 16 days before its twin, Voyager 1. After completing its prime mission of flying by Jupiter and Saturn, Voyager 2 was sent on the right flight path to visit Uranus, which is about 3 billion kilometres away from the Sun. Voyager 2 made its closest approach—within 81,500 kilometres of the Uranian cloud tops—on January 24, 1986.

Before Voyager 2’s visit, scientists had to learn about Uranus by using Earth-based and airborne telescopes. By observing dips in starlight as a star passed behind Uranus, scientists knew Uranus had nine narrow rings.

But it wasn’t until the Voyager 2 flyby that scientists were able to capture for the first time images of the rings and the tiny shepherding moons that sculpted them. Unlike Saturn’s icy rings, they found Uranus’ rings to be dark grey, reflecting only a few percent of the incident sunlight.

Voyager image of Uranus' rings and two moons

Voyager 2 discovered two "shepherd" moons associated with Uranus' thin rings.

Scientists had also determined an average temperature for Uranus—minus 214 degrees Celsius—before this encounter, but the distribution of that temperature came as a surprise. Voyager showed there was heat transport from pole to pole in Uranus’ atmosphere that maintained the same temperature at both poles, even though the Sun was shining directly for decades on one pole and not the other.

By the end of the Uranus encounter and science analysis, data from Voyager 2 enabled the discovery of 11 new moons and two new rings, and generated dozens of science papers about the quirky seventh planet.

Interstellar mission

Voyager 2 moved on to explore Neptune, the last planetary target, in August 1989. It is now hurtling toward interstellar space, which is the space between stars. It is about 14 billion kilometres away from the Sun.

Voyager 1, which explored only Jupiter and Saturn before heading on a faster track toward interstellar space, is about 17 billion kilometres away from the Sun.

“The Uranus encounter was one of a kind,” said Suzanne Dodd, Voyager project manager, based at JPL. “Voyager 2 was healthy and durable enough to make it to Uranus and then to Neptune.”

“Currently both Voyager spacecraft are on the cusp of leaving the Sun’s sphere of influence and once again blazing a trail of scientific discovery.”

The Voyagers were built by NASA’s Jet Propulsion Laboratory in Pasadena, California, which continues to operate both spacecraft.

Link: More information about the Voyager spacecraft

Adapted from information issued by NASA Jet Propulsion Laboratory.

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Voyager: the Greatest Journey of Discovery

  • Twin missions visited the outer planets
  • Discovered new moons and planetary rings
  • Voyager 1 is now the farthest manmade object

A “meditation on the nature and meaning of exploration itself, disguised as a chronicle of the life and times of a space mission,” is what the New York Times says of Arizona State University Professor Stephen Pyne’s new book, Voyager: Seeking Newer Worlds in the Third Great Age of Discovery.

It adds that Pyne’s book takes readers on the roller-coaster ride through time and space, offering “a rich mix of history, science and fine writing. Sometimes it seems as if Captain Cook and Prince Henry the Navigator themselves are aboard the busy spacecraft.”

Cover of Voyager: Seeking Newer Worlds in the Third Great Age of Discovery

Voyager: Seeking Newer Worlds in the Third Great Age of Discovery, traces the history and impact of the twin Voyager spacecraft.

The expeditions of the twin Voyager spacecraft, rank among the most amazing achievements of the space age…indeed, among any age. Launched in August and September 1977 respectively, Voyager 2 and Voyager 1 journeyed to the outer reaches of the Solar System. Voyager 1 flew past Jupiter and Saturn; Voyager 2 encountered Jupiter, Saturn, Uranus and Neptune.

Along the way they discovered numerous new moons, rings around Jupiter, Uranus and Neptune, volcanoes on Jupiter’s moon Io, lightning in Saturn’s atmosphere, as well as many more accomplishments.

Both spacecraft are now way out beyond the edge of the Solar System, slowly drifting through the region where the Sun’s influence ends and true interstellar space begins. In 1998, Voyager 1 overtook Pioneer 10 as the most distant manmade object from Earth—almost 70 times further from the Sun than Earth is.

Today, Voyager 1 is almost 114 times further than the Earth. Voyager 2, travelling in a different direction, is 93 times the Earth-Sun distance.

Voyager: a modern-day Magellan

Why Pyne’s focus on the Voyager mission? While discovery is a uniquely human activity, the Voyager missions stand as iconic testaments, “grand gestures.” Moments of exploring, Pyne says, “that more than any other capture the general imagination, that fuse place, time, discovery and yearning in ways that seem to speak to an era’s sense of itself.”

Artist's impression of Voyager 2 flying past Jupiter

Artist's impression of Voyager 2 flying past Jupiter.

Voyager, he argues, was of the same ilk as Magellan’s journey in the First Age of Discovery and Alexander von Humboldt’s cross-continental trek across South America in the Second Age of Discovery.

Voyager was a defining symbol of the Third Age of Discovery, the exploratory tale of which transcends time and weaves the thread of all human endeavour into the distant future.

Pyne’s work raises “fascinating questions about the human impulses embedded in the space program and about how Voyager’s journey may change our sense of who we are.”

Time Magazine says of Voyager: Seeking Newer Worlds in the Third Great Age of Discovery, “For space geeks, a sweet read; for everyone else, an eye-opener.”

Pyne is an award-winning environmental historian, and the author of three previous books: “Year of the Fires,” “The Ice,” and “How the Canyon Became Grand.”

You can get more details of Voyager: Seeking Newer Worlds in the Third Great Age of Discovery at the SpaceInfo shop.

Adapted from information issued by ASU / NASA / Wikipedia.

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