Monday, December 3, 2007

Changes in Jupiter System 10.09.07

Pluto-Bound New Horizons Sees Changes in Jupiter System


The voyage of NASA's Pluto-bound New Horizons spacecraft through the Jupiter system earlier this year provided a bird's-eye view of a dynamic planet that has changed since the last close-up looks by NASA spacecraft.

Image right: This is a montage of New Horizons images of Jupiter and its volcanic moon Io, taken during the spacecraft’s Jupiter flyby in early 2007. The Jupiter image is an infrared color composite taken by the spacecraft’s near-infrared imaging spectrometer, the Linear Etalon Imaging Spectral Array (LEISA) at 1:40 UT on Feb. 28, 2007. The infrared wavelengths used (red: 1.59 µm, green: 1.94 µm, blue: 1.85 µm) highlight variations in the altitude of the Jovian cloud tops, with blue denoting high-altitude clouds and hazes, and red indicating deeper clouds. The prominent bluish-white oval is the Great Red Spot. The observation was made at a solar phase angle of 75 degrees but has been projected onto a crescent to remove distortion caused by Jupiter’s rotation during the scan. The Io image, taken at 00:25 UT on March 1st 2007, is an approximately true-color composite taken by the panchromatic Long-Range Reconnaissance Imager (LORRI), with color information provided by the 0.5 µm (“blue”) and 0.9 µm (“methane”) channels of the Multispectral Visible Imaging Camera (MVIC). The image shows a major eruption in progress on Io’s night side, at the northern volcano Tvashtar. Incandescent lava glows red beneath a 330-kilometer high volcanic plume, whose uppermost portions are illuminated by sunlight. The plume appears blue due to scattering of light by small particles in the plume. This montage appears on the cover of the Oct. 12, 2007 issue of Science magazine. Credit: NASA/JHU/APL.
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New Horizons passed Jupiter on Feb. 28, riding the planet’s gravity to boost its speed and shave three years off its trip to Pluto. It was the eighth spacecraft to visit Jupiter – but a combination of trajectory, timing and technology allowed it to explore details no probe had seen before, such as lightning near the planet’s poles, the life cycle of fresh ammonia clouds, boulder-size clumps speeding through the planet’s faint rings, the structure inside volcanic eruptions on its moon Io, and the path of charged particles traversing the previously unexplored length of the planet’s long magnetic tail.

“The Jupiter encounter was successful beyond our wildest dreams,” says New Horizons Principal Investigator Alan Stern, of NASA Headquarters, Washington. “Not only did it prove out our spacecraft and put it on course to reach Pluto in 2015, it was a chance for us to take sophisticated instruments to places in the Jovian system where other spacecraft couldn’t go, and to return important data that adds tremendously to our understanding of the solar system’s largest planet and its moons, rings and atmosphere.”

The New Horizons team presents its latest and most detailed analyses of that data today at the American Astronomical Society’s Division for Planetary Sciences meeting in Orlando, Fla., and in a special section of the Oct. 12 issue of the journal Science. The section includes nine technical papers written by New Horizons team members and collaborators.

From January through June, New Horizons’ seven science instruments made more than 700 separate observations of the Jovian system – twice the activity planned at Pluto – with most of them coming in the eight days around closest approach to Jupiter. “We carefully selected observations that complemented previous missions, so that we could focus on outstanding scientific issues that needed further investigation,” says New Horizons Jupiter Science Team Leader Jeff Moore, of NASA Ames Research Center, Moffett Field, Calif. “The Jupiter system is constantly changing and New Horizons was in the right place at the right time to see some exciting developments.”

Jovian weather was high on the list, as New Horizons’ visible light, infrared and ultraviolet remote-sensing instruments probed Jupiter’s atmosphere for data on cloud structure and composition. They saw clouds form from ammonia welling up from the lower atmosphere and heat-induced lighting strikes in the polar regions – the first polar lighting ever observed beyond Earth, demonstrating that heat moves through water clouds at virtually all latitudes across Jupiter. They made the most detailed size and speed measurements yet of “waves” that run the width of planet and indicate violent storm activity below. Additionally, New Horizons snapped the first close-up images of the Little Red Spot, a nascent storm about half the size of Jupiter’s larger Great Red Spot and about 70 percent of Earth’s diameter, gathering new information on storm dynamics.

Under a range of lighting and viewing angles, New Horizons also captured the clearest images ever of the tenuous Jovian ring system. In them, scientists spotted clumps of debris that may indicate a recent impact inside the rings, or some more exotic phenomenon; movies made from New Horizons images also offer an unprecedented look at ring dynamics, with the tiny inner moons Metis and Adrastea shepherding the materials around the rings. A search for smaller moons inside the rings – and possible new sources of the dusty material – found no bodies wider than a kilometer.

The mission’s investigations of Jupiter’s four largest moons focused on Io, the closest to Jupiter and whose active volcanoes blast tons of material into the Jovian magnetosphere (and beyond). New Horizons spied 11 different volcanic plumes of varying size, three of which were seen for the first time and one – a spectacular 200-mile-high eruption rising above the volcano Tvashtar – that offered an unprecedented opportunity to trace the structure and motion of the plume as it condensed at high altitude and fell back to the moon’s surface. In addition, New Horizons spotted the infrared glow from at least 36 Io volcanoes, and measured lava temperatures up to 1,900 degrees Fahrenheit, similar to many terrestrial volcanoes.

New Horizons’ global map of Io’s surface backs the moon’s status as the solar system’s most active body, showing more than 20 geological changes since the Galileo Jupiter orbiter provided the last close-up look in 2001. The remote imagers also kept watch on Io in the darkness of Jupiter’s shadow, noting mysterious glowing gas clouds above dozens of volcanoes. Scientists suspect that this gas helps to resupply Io’s atmosphere.

New Horizons' flight down Jupiter's magnetotail gave it an unprecedented look at the vast region dominated by the planet's strong magnetic field. Looking specifically at the fluxes of charged particles that flow hundreds of millions of miles beyond the giant planet, the New Horizons particle detectors saw evidence that tons of material from Io’s volcanoes move down the tail in large, dense, slow-moving blobs. By analyzing the observed variations in particle fluxes over a wide range of energies and scales, New Horizons scientists are exploring how the volcanic gases from Io are ionized, trapped and energized by Jupiter's magnetic field, then ultimately ejected from the system.

Designed, built and operated by the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., New Horizons lifted off from Cape Canaveral Air Force Station, Fla., in January 2006. The fastest spacecraft ever launched, it needed just 13 months to reach Jupiter. New Horizons is now about halfway between the orbits of Jupiter and Saturn, more than 743 million miles (1.19 billion kilometers) from Earth. It will fly past Pluto and its moons in July 2015 before heading deeper into the Kuiper belt of icy rocky objects on the planetary frontier.

New Horizons is the first mission in NASA’s New Frontiers Program of medium-class spacecraft exploration projects. Stern leads the mission and science team as principal investigator; APL manages the mission for NASA’s Science Mission Directorate. The mission team also includes Southwest Research Institute, Ball Aerospace Corporation, the Boeing Company, NASA Goddard Space Flight Center, NASA Jet Propulsion Laboratory, Stanford University, KinetX Inc. (navigation team), Lockheed Martin Corporation, University of Colorado, the U.S. Department of Energy, and a number of other firms, NASA centers, and university partners.

Surprises in the Heliosphere

Surprises from the Edge of the Solar System

Sept. 21, 2006: Almost every day, the great antennas of NASA's Deep Space Network turn to a blank patch of sky in the constellation Ophiuchus. Pointing at nothing, or so it seems, they invariably pick up a signal, faint but full of intelligence. The source is beyond Neptune, beyond Pluto, on the verge of the stars themselves.

It's Voyager 1. The spacecraft left Earth in 1977 on a mission to visit Jupiter and Saturn. Almost 30 years later, with the gas giants long ago seen and done, Voyager 1 is still going and encountering some strange things.

"We've entered a totally new region of space," says Ed Stone, Voyager project scientist and the former director of JPL. "And the spacecraft is beaming back surprising new information."

Before we reveal the surprises, let us discuss exactly where Voyager 1 is:

Our entire solar system—planets and all—sits inside a gargantuan bubble of gas about four times wider than the orbit of Neptune. The sun is responsible. It blows the bubble by means of the solar wind. Astronomers call the bubble itself "the heliosphere" and its outer membrane "the heliosheath." [diagram]

Voyager 1 is about 10 billion miles from Earth, inside the heliosheath.

"You can simulate the heliosheath in your kitchen sink," says Stone. "Turn on the faucet so that a thin stream of water pours into the sink. Look down into the basin. Where the stream hits bottom, that's the sun. From there, water flows outward in a thin, perfectly radial sheet. That's the solar wind. As the water (or solar wind) expands, it gets thinner and thinner, and it can't push as hard. Abruptly, a sluggish, turbulent ring forms. That ring is the heliosheath."

Right: A simulated heliosheath in your kitchen sink. Image credit: Tony Phillips.

"The heliosheath is important to humans," continues Stone. "It helps protect us from galactic cosmic rays." Galactic cosmic rays are subatomic particles accelerated to nearly light speed by supernovas and black holes. Astronauts out in space are exposed to the particles—and that's not a good thing. Cosmic rays can penetrate flesh and damage DNA. Fortunately, the heliosheath deflects many cosmic rays before they ever reach the inner solar system. "Magnetic turbulence in the heliosheath scatters the particles harmlessly away."

Note: We have many shields against cosmic rays from the thin walls of spaceships to massive planetary atmospheres. But the heliosheath is our first line of defense, and that makes it special.

Because of its role as Solar System Protector, "we need to learn as much as we can about the heliosheath," says Stone. "Voyager 1 is giving us our first look inside."

And now for the surprises:

Magnetic Potholes: Every now and then, Voyager 1 sails through a "magnetic pothole" where the magnetic field of the heliosheath almost vanishes, dropping from a typical value of 0.1 nanoTesla (nT) to 0.01 nT or less. There are also "magnetic speed bumps" where the field strength jumps to twice normal, from 0.1 nT to 0.2 nT. These speed bumps and potholes are an unexpected form of turbulence. What role do they play in scattering cosmic rays? "This is under investigation," says Stone.

Sluggish solar wind: The solar wind in the heliosheath is slower than anyone expected. "The solar wind is supposed to slow down out there, just as the water in your sink slowed down to make the 'sluggish ring,'" says Stone, "but not this slow." Before Voyager 1 arrived, computer models predicted a wind speed of 200,000 to 300,000 mph. Voyager 1 measured only about 34,000 mph. "This means our computer models need to be refined."

Anomalous Cosmic Rays: "This one takes a little explaining," he says. "While the heliosheath protects us from deep-space cosmic rays, at the same time it is busy producing some cosmic rays of its own. A shock wave at the inner boundary of the heliosheath imparts energy to subatomic particles which zip, cosmic-ray-like, into the inner solar system. "We call them 'anomalous cosmic rays.' They're not as dangerous as galactic cosmic rays because they are not so energetic."

Right: A schematic diagram of the sun's heliosphere. Anomalous cosmic rays are supposed to come from the Termination Shock--but Voyager 1 found otherwise. [More]

Researchers expected Voyager 1 to encounter the greatest number of anomalous cosmic rays at the inner boundary of the heliosheath "because that's where we thought anomalous cosmic rays were produced." Surprise: Voyager crossed the boundary in December 2004 and there was no spike in cosmic rays. Only now, 300+ million miles later, is the intensity beginning to grow.

"This is really puzzling," says Stone. "Where are these anomalous cosmic rays coming from?"

Voyager 1 may find the source--and who knows what else?--as it continues its journey. The heliosheath is 3 to 4 billion miles in thickness, and Voyager 1 will be inside it for another 10 years or so. That's a lot of new territory to explore and plenty of time for more surprises.

NASA: Light Show on Venus

NASA Scientist Confirms Light Show on Venus11.28.07 Venus is a hellish place of high temperatures and crushing air pressure. The European Space Agency's Venus Express mission adds into this mix the first confirmation that the Venusian atmosphere generates its own lightning. The discovery is part of the Venus Express science findings that appear in a special section of the Nov. 29 issue of the journal Nature.

"In addition to all the pressure and heat, we can confirm there is lightning on Venus -- maybe even more activity than there is here on Earth," said Christopher Russell, a NASA-sponsored scientist on Venus Express from the University of California, Los Angeles, and lead author of one of the Nature papers. "Not a very good place to vacation, that is for sure."

Image right: Artist concept of lightning on Venus.
Image credit: ESA
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The discovery puts Venus in elite planetary company. Scientists currently know of only three other planetary bodies in the entire universe that generate lightning -- Earth, Jupiter and Saturn. Lightning on Venus -- as well as on any other planet -- is an important discovery because the electrical discharges drive the chemistry of an atmosphere by breaking molecules into fragments that can then join with other fragments in unexpected ways. The lightning on Venus is unique from that found on Earth, Jupiter and Saturn in that it is the only lightning known that is not associated with water clouds. Instead, on Venus, the lightning is associated with clouds of sulfuric acid.

Any future missions to the second rock from the sun may have to take into account the electrical activity in the Venusian atmosphere.

The confirming measurements of the electrical discharges were made with data obtained by the Venus Express magnetometer instrument provided by the Space Research Institute in Graz, Austria. The measurements were taken once a day for two minutes, during a period when the spacecraft was closest to Venus. A Venusian day is about 117 days long.

With its primary mission completed, Venus Express will now embark upon its extended mission to watch Earth's nearest planetary neighbor for two more Venusian days. Among other things, it will look for the telltale infrared radiation from lava flows. In 2010, when a Japanese mission, Venus Climate Orbiter, also called Planet-C, arrives at Venus, scientists will be able to compare results from the two spacecraft.

More than 250 scientists and engineers across Europe are involved in the Venus Express mission, supported by their institutes and national space agencies. The mission also sees the contribution of scientists from Russia and Japan, as well as from NASA, which sponsors 15 American Venus Express scientists and provides support to the radio science investigation via its Deep Space Network antennas.

Related images and graphics are online at .

For information about NASA's contribution to Venus Express, visit . For information about NASA and agency programs, visit .

Media contact: DC Agle 818-393-9011
Jet Propulsion Laboratory, Pasadena, Calif.

Dwayne Brown 202-358-1726
NASA Headquarters, Washington

Monica Talevi 011-31-71-565-3223
European Space Agency, Noordwijk, The Netherlands.