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distant-traveller:


25 years ago, Voyager 2 captures images of Neptune







NASA’s Voyager 2 spacecraft gave humanity its first glimpse of Neptune and its moon Triton in the summer of 1989. This picture of Neptune was produced from the last whole planet images taken through the green and orange filters on the Voyager 2 narrow angle camera. The images were taken on Aug. 20, 1989, at a range of 4.4 million miles from the planet, 4 days and 20 hours before closest approach on Aug. 25. The picture shows the Great Dark Spot and its companion bright smudge; on the west limb the fast moving bright feature called “Scooter” and the little dark spot are visible. These clouds were seen to persist for as long as Voyager’s cameras could resolve them. North of these, a bright cloud band similar to the south polar streak may be seen.
In the summer of 2015, another NASA mission to the farthest zone of the solar system, New Horizons, will make a historic first close-up study of Pluto. Although a fast flyby, New Horizons’ Pluto encounter on July 14, 2015, will not be a replay of Voyager but more of a sequel and a reboot, with a new and more technologically advanced spacecraft and, more importantly, a new cast of characters. Those characters are Pluto and its family of five known moons, all of which will be seen up close for the first time next summer.

Image credit: NASA

distant-traveller:

25 years ago, Voyager 2 captures images of Neptune

NASA’s Voyager 2 spacecraft gave humanity its first glimpse of Neptune and its moon Triton in the summer of 1989. This picture of Neptune was produced from the last whole planet images taken through the green and orange filters on the Voyager 2 narrow angle camera. The images were taken on Aug. 20, 1989, at a range of 4.4 million miles from the planet, 4 days and 20 hours before closest approach on Aug. 25. The picture shows the Great Dark Spot and its companion bright smudge; on the west limb the fast moving bright feature called “Scooter” and the little dark spot are visible. These clouds were seen to persist for as long as Voyager’s cameras could resolve them. North of these, a bright cloud band similar to the south polar streak may be seen.

In the summer of 2015, another NASA mission to the farthest zone of the solar system, New Horizons, will make a historic first close-up study of Pluto. Although a fast flyby, New Horizons’ Pluto encounter on July 14, 2015, will not be a replay of Voyager but more of a sequel and a reboot, with a new and more technologically advanced spacecraft and, more importantly, a new cast of characters. Those characters are Pluto and its family of five known moons, all of which will be seen up close for the first time next summer.

Image credit: NASA

distant-traveller:

Giant geysers on Jupiter’s icy moon Europa mysteriously disappear



The huge plumes of water vapor erupting from Jupiter’s ice-covered moon Europa seem to have vanished, and scientists aren’t sure why.
In December 2013, researchers using NASA’s Hubble Space Telescope announced that they had spotted evidence of geysers blasting into space from Europa’s south polar region. The discovery sparked a great deal of excitement among space scientists, as it suggested that a robotic flyby probe might be able to sample Europa’s subsurface ocean of liquid water without even touching down.
However, follow-up Hubble observations in January and February of this year showed no signs of the plumes, which were estimated to reach about 125 miles (200 kilometers) into space.
There are several possible explanations, researchers said. For example, Europa’s geysers may be sporadic — more like volcanoes here on Earth than the plumes blasting pretty much constantly from the south pole of Saturn’s icy moon Enceladus, which harbors a subsurface ocean like Europa.
It’s also possible that Europa’s plumes are only visible to Hubble’s instruments at certain times.
"It could be just the way that we use the auroral emissions coming from those plumes at the UV [ultraviolet] wavelengths of light that we use with Hubble," discovery team member Kurt Retherford, of the Southwest Research Institute in San Antonio, told Space.com.
"These things depend on Jupiter’s plasma environment," Retherford added. "Maybe there were just a lot of particles, atoms, getting excited by electrons and ions in Europa’s atmosphere, more so than at other times, and [they] just lit up the plumes more than they usually do."
Further, the plumes may sometimes simply be too small to see, Retherford said. (Enceladus’ geysers have been observed relatively close-up by NASA’s Saturn-orbiting Cassini spacecraft, but scientists are relying on the Earth-orbiting Hubble to study the features on Europa.)
Another possibility is that the geysers don’t exist, that the detection by Hubble, which was based primarily on observations the telescope made in December 2012, was an artifact or misinterpretation of some sort. But Retherford stressed that this is unlikely.
"The best explanation still is plumes for that dataset, no doubt about it," he said.
Retherford and his colleagues are going to look for the plumes again soon. They’ll train Hubble on Europa from November through April, in a more comprehensive attempt to confirm the existence of the water-vapor geysers and to characterize their behavior.
"The question is the variability aspect of the plumes. Why do we see them in some observation sets and not others?" Retherford said.
Learning more about the plumes is a key priority for astrobiologists and for NASA, which is eyeing a mission to Europa in the mid-2020s. The leading candidate for that mission at the moment is probably a probe called the Europa Clipper, which would make multiple flybys of the icy satellite.
"This is the kind of thing that could have a profound impact on how we explore Europa," Curt Niebur, outer planets program scientist at NASA headquarters, said during a NASA planetary sciences subcommittee meeting Wednesday (Sept. 3).
"With an ocean that is tens of kilometers below the ice, most likely, if you can have a plume that’s possibly bringing material from that ocean up to orbit, well, that’s going to affect how you explore," Niebur added.

Image credit: NASA/ESA/K. Retherford/SWRI

distant-traveller:

Giant geysers on Jupiter’s icy moon Europa mysteriously disappear

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Nankeen Kestrel fledgling (Falco cenchroides) by © Patrick_K59
Two of the three fledglings raised in this hollow on the Mooloort Plains, Central Vic.

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Nankeen Kestrel fledgling (Falco cenchroides) by © Patrick_K59

Two of the three fledglings raised in this hollow on the Mooloort Plains, Central Vic.

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