By Paul Rincon
Science reporter, BBC News
Nasa's New Horizons spacecraft has returned stunning views of the Jupiter system captured during a recent flyby.
They include huge volcanic eruptions on the surface of the Io moon, as well as the first close-up look at a burgeoning red storm in Jupiter's atmosphere.
The probe passed within 2.3 million km of Jupiter in a gravity kick manoeuvre to pick up speed as it dashes towards its ultimate target of Pluto.
New Horizons was already the fastest space mission ever launched.
"We collected a very diverse and rich data set through this encounter," said Alan Stern, associate administrator with Nasa's science mission directorate and chief scientist on the mission.
Dr Stern, along with colleagues on the mission, were discussing the observations at a news briefing at Nasa's headquarters in Washington DC.
The flyby yielded the first close-up images of the Little Red Spot, an Earth-sized storm twisting and churning in Jupiter's atmosphere.
This feature formed from the merger of three smaller storms between 1998 and 2000. Its "big brother", a gigantic tempest known as the Great Red Spot, has existed on Jupiter for centuries.
New Horizons was lucky to catch the Tvashtar plume
Referring to a colour image of the Little Red Spot, project scientist Hal Weaver said: "It is reminiscent of Van Gogh's Starry Night painting; but this is the real deal, not someone's imagination."
The Nasa probe also took new images of Jupiter's four largest moons: Io, Europa, Ganymede and Callisto.
Luckily, it arrived in the Jupiter system during an enormous eruption on Io. This moon is the most geologically active body in the Solar System.
Data from the Galileo spacecraft, which reached Jupiter in 1995, suggested Io's volcanoes were much hotter than those on Earth - a hypothesis New Horizon's scientists will aim to test.
When New Horizons made its flyby in February, Io's Tvashtar volcano was spewing dust 320km (200 miles) above the moon's surface. The umbrella-shaped volcanic plume rose so high it became illuminated by sunlight, rendering it clearly visible to the spacecraft.
"Galileo was orbiting Jupiter for six years, taking pictures of Io over that period but it never saw a plume like that," said John Spencer, a mission scientist from the Southwest Research Institute in Boulder, US.
By comparing the latest Io images with those from Galileo, team members were able to identify a previously unknown volcano in the moon's south polar region. They spotted many bright lava flows and - possibly - the birth of a new volcano.
Ganymede is the Solar System's largest moon
In some places, gas released by the eruptions was illuminated by electrical currents as Io moves through Jupiter's magnetic field. This generates aurorae like the northern and southern lights on Earth.
The spacecraft captured the clearest images yet of Jupiter's faint ring system, including two tiny "shepherd" moons - Metis and Adrastea - that keep the hoops of rock and dust in check.
The red spot resembles Starry Night by Van Gogh, says Hal Weaver
The scientists spotted unexpected clumps of dust in the rings. They suggest this could be the aftermath of an impact into the rings in the "last several months".
This could have been caused by a comet travelling at 10-15km/s and hitting a ring particle measuring tens of metres across or more.
"We caught another amazing temporary event in the jovian system. Most things in that system are constantly changing; very few things are eternal," explained Jeff Moore from Nasa's Ames Research Center in California.
Into the groove
New Horizons was also able to take images of the network of circular troughs carved on Jupiter's icy moon Europa. This icy moon is of considerable interest to planetary scientists because it is thought to harbour a relatively warm ocean under an outer crust of ice.
"This trough system may tell us something about the thickness of the ice crust which covers the global ocean. The location and placement of the troughs may tell us something about the evolution of the ice crust and whether it is moving," said Jeff Moore.
"This information will help us constrain the possibility we could openly communicate with the ocean, perhaps on some Nasa mission in the future."
The $700m (£350m) New Horizons probe was launched in January last year to gather information on Pluto and its moons.
The Jupiter pass was needed to accelerate the spacecraft away from the Sun by an additional 14,500km/h (9,000mph), pushing it past 84,000km/h (52,000 mph). This shortens the journey time to Pluto by four years.