Mars Rover Yielding New Clues While Lodged In Martian Soil

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ScienceDaily (June 28, 2009) — NASA's Mars rover Spirit, lodged in Martian soil that is causing traction trouble, is taking advantage of the situation by learning more about the Red Planet's environmental history.

In April, Spirit entered an area composed of three or more layers of soil with differing pastel hues hiding beneath a darker sand blanket. Scientists dubbed the site "Troy." Spirit's rotating wheels dug themselves more than hub deep at the site. The rover team has spent weeks studying Spirit's situation and preparing a simulation of this Martian driving dilemma to test escape maneuvers using an engineering test rover at NASA's Jet Propulsion Laboratory in Pasadena, Calif.
A rock seen beneath Spirit in images from the camera on the end of the rover's arm may be touching Spirit's belly. Scientists believe it appears to be a loose rock not bearing the rover's weight. While Spirit awaits extraction instructions, the rover is keeping busy examining Troy, which is next to a low plateau called Home Plate, approximately 3.2 kilometers (2 miles) southeast of where Spirit landed in January 2004.
"By serendipity, Troy is one of the most interesting places Spirit has been," said Ray Arvidson of Washington University in St. Louis. Arvidson is deputy principal investigator for the science payloads on Spirit and its twin rover, Opportunity. "We are able here to study each layer, each different color of the interesting soils exposed by the wheels."
One of the rover's wheels tore into the site, exposing colored sandy materials and a miniature cliff of cemented sands. Some disturbed material cascaded down, evidence of the looseness that will be a challenge for getting Spirit out. But at the edge of the disturbed patch, the soil is cohesive enough to hold its shape as a steep cross-section.
Spirit has been using tools on its robotic arm to examine tan, yellow, white and dark-red sandy soil at Troy. Stretched-color images from the panoramic camera show the tints best.
"The layers have basaltic sand, sulfate-rich sand and areas with the addition of silica-rich materials, possibly sorted by wind and cemented by the action of thin films of water. We're still at a stage of multiple working hypotheses," said Arvidson. "This may be evidence of much more recent processes than the formation of Home Plate...or is Home Plate being slowly stripped back by wind, and we happened to stir up a deposit from billions of years ago before the wind got to it?"
Team members from NASA's Johnson Space Center in Houston feel initial readings suggest that iron is mostly present in an oxidized form as ferric sulfate and that some of the differences in tints at Troy observed by the panoramic camera may come from differences in the hydration states of iron sulfates.
While extraction plans for the rover are developed and tested during the coming weeks, the team plans to have Spirit further analyze the soil from different depths. This research benefits from having time and power. In April and May, winds blew away most of the dust that had accumulated on Spirit's solar panels.
"The exceptional amount of power available from cleaning of Spirit's solar arrays by the wind enables full use of all of the rover's science instruments," said Richard Moddis of the Johnson team. "If your rover is going to get bogged down, it's nice to have it be at a location so scientifically interesting."
The rover team has developed a soil mix for testing purposes that has physical properties similar to those of the soil under Spirit at Troy. This soil recipe combines diatomaceous earth, powdered clay and play sand. A crew is shaping a few tons of that mix this week into contours matching Troy's. The test rover will be commanded through various combinations of maneuvers during the next few weeks to validate the safest way to proceed on Mars.
Spirit's right-front wheel has been immobile for more than three years, magnifying the challenge. While acknowledging a possibility that Spirit might not be able to leave Troy, the rover team remains optimistic. Diagnostic tests on Spirit in early June provided encouragement that the left-middle wheel remains useable despite an earlier stall.
"With the improved power situation, we have the time to explore all the possibilities to get Spirit out," said JPL's John Callas, project manager for Spirit and Opportunity. "We are optimistic. The last time Spirit spun its wheels, it was still making progress. The ground testing will help us avoid doing things that could make Spirit's situation worse."
Images and further information about Spirit and Opportunity are available at: http://marsrovers.jpl.nasa.gov and http://www.nasa.gov/rovers .
Adapted from materials provided by NASA/Jet Propulsion Laboratory.

Mystery Of The Missing Sunspots Solved?

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ScienceDaily (June 19, 2009) — The sun is in the pits of a century-class solar minimum, and sunspots have been puzzlingly scarce for more than two years. Now, for the first time, solar physicists might understand why.

At an American Astronomical Society press conference in Boulder, Colorado, researchers announced that a jet stream deep inside the sun is migrating slower than usual through the star's interior, giving rise to the current lack of sunspots.
Rachel Howe and Frank Hill of the National Solar Observatory (NSO) in Tucson, Arizona, used a technique called helioseismology to detect and track the jet stream down to depths of 7,000 km below the surface of the sun. The sun generates new jet streams near its poles every 11 years, they explained. The streams migrate slowly from the poles to the equator and when a jet stream reaches the critical latitude of 22 degrees, new-cycle sunspots begin to appear.
Howe and Hill found that the stream associated with the next solar cycle has moved sluggishly, taking three years to cover a 10 degree range in latitude compared to only two years for the previous solar cycle.
The jet stream is now, finally, reaching the critical latitude, heralding a return of solar activity in the months and years ahead.
"It is exciting to see", says Hill, "that just as this sluggish stream reaches the usual active latitude of 22 degrees, a year late, we finally begin to see new groups of sunspots emerging."
The current solar minimum has been so long and deep, it prompted some scientists to speculate that the sun might enter a long period with no sunspot activity at all, akin to the Maunder Minimum of the 17th century. This new result dispells those concerns. The sun's internal magnetic dynamo is still operating, and the sunspot cycle is not "broken."
Because it flows beneath the surface of the sun, the jet stream is not directly visible. Hill and Howe tracked its hidden motions via helioseismology. Shifting masses inside the sun send pressure waves rippling through the stellar interior. So-called "p modes" (p for pressure) bounce around the interior and cause the sun to ring like an enormous bell. By studying the vibrations of the sun's surface, it is possible to figure out what is happening inside. Similar techniques are used by geologists to map the interior of our planet.
In this case, researchers combined data from GONG and SOHO. GONG, short for "Global Oscillation Network Group," is an NSO-led network of telescopes that measures solar vibrations from various locations around Earth. SOHO, the Solar and Heliospheric Observatory, makes similar measurements from space.
"This is an important discovery," says Dean Pesnell of NASA's Goddard Space Flight Center. "It shows how flows inside the sun are tied to the creation of sunspots and how jet streams can affect the timing of the solar cycle."
There is, however, much more to learn.
"We still don't understand exactly how jet streams trigger sunspot production," says Pesnell. "Nor do we fully understand how the jet streams themselves are generated."
To solve these mysteries, and others, NASA plans to launch the Solar Dynamics Observatory (SDO) later this year. SDO is equipped with sophisticated helioseismology sensors that will allow it to probe the solar interior better than ever before.
"The Helioseismic and Magnetic Imager (HMI) on SDO will improve our understanding of these jet streams and other internal flows by providing full disk images at ever-increasing depths in the sun," says Pesnell.
Continued tracking and study of solar jet streams could help researchers do something unprecedented--accurately predict the unfolding of future solar cycles.
Adapted from materials provided by http://science.nasa.gov/. Original article written by Dr. Tony Phillips.

Long-lost, Dangerous Asteroid Is Found Again

Source:

http://www.sciencedaily.com/releases/2007/10/071011213216.htm

Science Daily — Echoing the re-discovery of America by the Spanish long after an earlier Viking reconnaissance, astronomers have learned that a recently observed asteroid - one that could potentially hit the Earth - was actually first observed nearly a half-century ago. Researchers at the Minor Planet Center of the Smithsonian Astrophysical Observatory in Cambridge, MA have confirmed work by SETI Institute astronomer Peter Jenniskens that the recently discovered asteroid 2007 RR9 is in fact the long-lost object 6344 P-L.

6344 P-L was last seen in 1960, and ever since has had the peculiar distinction of being the only Potentially Hazardous Asteroid without a formal designation. "The object was long recognized to be dangerous, but we didn't know where it was," says Jenniskens. "Now it is no longer just out there."
A designation as Potentially Hazardous means that 2007 RR9 is one of 886 (not 887) known asteroids bigger than 150 m (500 ft) in diameter that come to within 0.05 astronomical units of Earth's orbit (roughly 7,480,000 km or 4,650,000 miles). The size is estimated on the basis of the object's observed brightness and an assumed reflectance of 13 percent.
Jenniskens believes that this object may not, in fact, be an asteroid. "This is a now-dormant comet nucleus, a fragment of a bigger object that, after breaking up in the not-so-distant past, may have caused the gamma Piscid shower of slow meteors (IAU #236) that is active in mid-October and early November," he says. 2007 RR9 moves in a 4.70-year orbit, nearly all the way out to the distance of Jupiter. Because of this elongated orbit, it has a Tisserand parameter of T = 2.94, which defines it dynamically as a Jupiter Family Comet (T = 2.0 - 3.0), not an asteroid (T > 3.0).
So far, this object has not yet been seen to be even weakly active, but the now dormant comet is still moving closer to the Sun. It is sliding rapidly toward visibility in the southern hemisphere, and is expected to brighten to magnitude +18.5 in mid-October. According to Gareth V. Williams of the Minor Planet Center, it will pass Earth around November 6 at 0.07 AU, when the minor planet is at high latitudes in southern skies.
The original designation of P-L stands for "Palomar-Leiden," the juxtaposition of two observatory names that reflect what was a very fruitful collaboration by the trio of pioneer asteroid searchers Tom Gehrels of the University of Arizona, and Ingrid van Houten-Groeneveld and her husband Cornelis Johannes van Houten. Gehrels made a sky survey using the 48-inch Schmidt Telescope at the famed Palomar Observatory, long before modern asteroid reconnaisances, and shipped the photographic plates to the van Houtens at Leiden Observatory in the Netherlands. There, Ingrid discovered 6344 P-L on four plates taken on September 24-28, 1960. The trio are jointly credited with several thousand asteroid discoveries, but only 6344 P-L is a potential danger to Earth.
Peter Jenniskens is a meteor astronomer with the SETI Institute and author of "Meteor Showers and their Parent Comets" published by Cambridge University Press (2006). He is also credited with the identification of the parent body of the Quadrantid meteor shower. As it happens, he graduated from Leiden Observatory in 1992, before joining the SETI Institute.
Note: This story has been adapted from material provided by SETI Institute.

Fausto Intilla

www.oloscience.com

Pluto-bound Spacecraft Sees Changes In Jupiter System

Source:

http://www.sciencedaily.com/releases/2007/10/071009164110.htm

Science Daily — 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.

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.
Note: This story has been adapted from material provided by Johns Hopkins University.

Fausto Intilla

www.oloscience.com

Exoplanet Offers Clues To Earth's Future

Source:

http://www.sciencedaily.com/releases/2007/09/070912130828.htm

Science Daily — An international team of astronomers that includes Steve Kawaler of Iowa State University has announced the first discovery of a planet orbiting a star near the end of its life.

The news provides a preliminary picture of what could be the Earth's destiny in four to five billion years. That's when the sun will exhaust its hydrogen fuel, expand enormously as a red giant and expel its outer layers in an explosive helium flash.
The planet discovered by the researchers, "V 391 Pegasi b," has survived all those changes to its sun.
The international research team was led by Roberto Silvotti from the INAF-Osservatorio Astronomico di Capodimonte in Naples, Italy. They discovered the planet orbiting "V 391 Pegasi," a faint star in the constellation of Pegasus.
"The exciting thing about finding a planet around this star is that it indicates that planetary systems can survive the giant phase and the helium flash of their parent star," said Kawaler, an Iowa State professor of physics and astronomy. "It bodes well for the survival of our own Earth in the distant future. Before V 391 Pegasi lost its outer regions at the helium flash, the planet orbited the star at about the same distance that the Earth orbits our sun."
But, Kawaler said, "We shouldn't take too much heart in this -- this planet is larger than Jupiter, so a smaller planet like the Earth could still be vulnerable."
Kawaler helped the 23-member research team make its discovery by coordinating observations during a 2003 run of the Whole Earth Telescope. Iowa State is a lead institution in the Whole Earth Telescope, a worldwide network of cooperating observatories that allow astronomers to take uninterrupted measurements of variable stars that change in brightness. The discovery of V 391 Pegasi b was made by detailed measurements of the clocklike variation of the star caused by the planet tugging on it.
Kawaler also advanced the project by doing theoretical calculations to make sure irregularities of the star's orbital motion were caused by the orbiting planet.
The astronomers found that at the present time, V 391 Pegasi b has an orbital distance 1.7 times the medium distance between the Earth and the sun. As stars age and reach their red giant phase, they undergo an enormous expansion (with their volume increasing by a factor of millions) that can easily reach and engulf their inner planets.
"The same will happen to the sun," Silvotti said. "As far as our planets are concerned, we expect Mercury and Venus to disappear in the sun's envelope, whereas Mars should survive. The fate of the Earth is less clear because its position is really at the limit: it appears more likely that the Earth will not survive the red giant expansion of the sun either, but it is not for sure."
As is the case for almost all planets beyond our solar system, V 391 Pegasi b cannot be seen directly. Silvotti said it took seven years of observations and calculations to confirm the existence of the planet.
The announcement, culminating seven years of research, will be published in the Sept. 13 issue of the journal Nature.
Note: This story has been adapted from a news release issued by Iowa State University.

Fausto Intilla

www.oloscience.com

Pioneering NASA Spacecraft Mark Thirty Years Of Flight

Source:

http://www.sciencedaily.com/releases/2007/08/070829170339.htm

Science Daily — NASA's two venerable Voyager spacecraft are celebrating three decades of flight as they head toward interstellar space. Their ongoing odysseys mark an unprecedented and historic accomplishment.

Voyager 2 launched on Aug. 20, 1977, and Voyager 1 launched on Sept. 5, 1977. They continue to return information from distances more than three times farther away than Pluto.
"The Voyager mission is a legend in the annals of space exploration. It opened our eyes to the scientific richness of the outer solar system, and it has pioneered the deepest exploration of the sun's domain ever conducted," said Alan Stern, associate administrator for NASA's Science Mission Directorate, Washington. "It's a testament to Voyager's designers, builders and operators that both spacecraft continue to deliver important findings more than 25 years after their primary mission to Jupiter and Saturn concluded."
During their first dozen years of flight, the Voyagers made detailed explorations of Jupiter, Saturn, and their moons, and conducted the first explorations of Uranus and Neptune. The Voyagers returned never-before-seen images and scientific data, making fundamental discoveries about the outer planets and their moons. The spacecraft revealed Jupiter's turbulent atmosphere, which includes dozens of interacting hurricane-like storm systems, and erupting volcanoes on Jupiter's moon Io. They also showed waves and fine structure in Saturn's icy rings from the tugs of nearby moons.
For the past 18 years, the twin Voyagers have been probing the sun's outer heliosphere and its boundary with interstellar space. Both Voyagers remain healthy and are returning scientific data 30 years after their launches.
Voyager 1 currently is the farthest human-made object, traveling at a distance from the sun of about 15.5 billion kilometers (9.7 billion miles). Voyager 2 is about 12.5 billion kilometers (7.8 billion miles) from the sun. Originally designed as a four-year mission to Jupiter and Saturn, the Voyager tours were extended because of their successful achievements and a rare planetary alignment. The two-planet mission eventually became a four-planet grand tour. After completing that extended mission, the two spacecraft began the task of exploring the outer heliosphere.
"The Voyager mission has opened up our solar system in a way not possible before the Space Age," said Edward Stone, Voyager project scientist at the California Institute of Technology, Pasadena, Calif. "It revealed our neighbors in the outer solar system and showed us how much there is to learn and how diverse the bodies are that share the solar system with our own planet Earth."
In December 2004, Voyager 1 began crossing the solar system's final frontier. Called the heliosheath, this turbulent area, approximately 14 billion kilometers (8.7 billion miles) from the sun, is where the solar wind slows as it crashes into the thin gas that fills the space between stars. Voyager 2 could reach this boundary later this year, putting both Voyagers on their final leg toward interstellar space.
Each spacecraft carries five fully functioning science instruments that study the solar wind, energetic particles, magnetic fields and radio waves as they cruise through this unexplored region of deep space. The spacecraft are too far from the sun to use solar power. They run on less than 300 watts, the amount of power needed to light up a bright light bulb. Their long-lived radioisotope thermoelectric generators provide the power.
"The continued operation of these spacecraft and the flow of data to the scientists is a testament to the skills and dedication of the small operations team," said Ed Massey, Voyager project manager at NASA's Jet Propulsion Laboratory in Pasadena, Calif. Massey oversees a team of nearly a dozen people in the day-to-day Voyager spacecraft operations.
The Voyagers call home via NASA's Deep Space Network, a system of antennas around the world. The spacecraft are so distant that commands from Earth, traveling at light speed, take 14 hours one-way to reach Voyager 1 and 12 hours to reach Voyager 2. Each Voyager logs approximately 1 million miles per day.
Each of the Voyagers carries a golden record that is a time capsule with greetings, images and sounds from Earth. The records also have directions on how to find Earth if the spacecraft is recovered by something or someone.
NASA's latest outer planet exploration mission is New Horizons, which is now well past Jupiter and headed for a historic exploration of the Pluto system in July 2015.
For a complete listing of Voyager discoveries and mission information, visit the Internet at:
http://www.nasa.gov/voyager and http://voyager.jpl.nasa.gov/
JPL manages the Voyager mission for NASA's Science Mission Directorate. NASA's Lewis Research Center (now Glenn Research Center) in Cleveland, Ohio, managed the launches of the Voyager spacecraft.
Note: This story has been adapted from a news release issued by NASA/Jet Propulsion Laboratory.

Fausto Intilla

www.oloscience.com

Saturn's Skewed Ring Current

Source:

http://www.sciencedaily.com/releases/2007/08/070824130101.htm

Science Daily — Images taken by Cassini’s Magnetospheric Imaging Instrument (MIMI) show that Saturn’s ring current is a warped disc that balloons out of the equatorial plane on the planet’s dayside and remains a thin disk that rises above the plane at larger distances on the nightside.

Dr Stamatios "Tom" Krimigis, the Principal Investigator for the instrument, who is presenting images at the European Planetary Science Congress in Potsdam on Thursday 23rd August, said, "Ring currents surround planets sort of like the brim of a hat.
Uniquely in Saturn’s case, that brim has been crushed at the front and tipped up at the back, so it’s pretty bent out of shape!"
The presence of a ring current around Saturn was first suggested in the early 1980s following magnetic anomalies observed by the Pioneer 11 and Voyager 1 and 2 spacecraft. Ring currents are also found around Earth and Jupiter. They are caused when plasma becomes trapped between mirror points on magnetic field lines, similar to the Van Allen radiation belts surrounding Earth, and gradually drifts around the planet. The aggregate motion of all of the hot ions distributed around the equator generates an electric current.
On Saturn, the source of the plasma is material from the rings and gas vented by geysers on the moon Enceladus, which is subsequently ionized and accelerated. The MIMI images show that the ring current occupies a region of the equatorial plane between 540 000 kilometres and 1 080 000 kilometres from the centre of Saturn. They also show that Saturn’s ring current is persistently asymmetric (unlike Earth’s), and that the asymmetry rotates nearly rigidly with Saturn.
MIMI, which was developed by an international team led by the Johns Hopkins University Applied Physics Laboratory (APL), Laurel, Maryland, has three distinct sensors that allow it to "visualize the invisible" and show the plasma and radiation belts in Saturn’s environment in an image. The MIMI instrument includes an Ion and Neutral Camera developed by APL, a spectrometer built by the University of Maryland, and a low energy particle detector developed by the Max-Planck-Institut fuer Sonnensystemforschung and a number of co-investigator institutions including CESR in Toulouse.
Ring currents
A ring current at Earth was proposed by Chapman and Ferraro in the 1930s to explain the decrease in the equatorial magnetic field during geomagnetic storms; the detailed nature in terms of composition and energy content was not determined until the mid-eighties by the Active Magnetospheric Particle Tracer Explorers (AMPTE) mission, a joint programme by the US, Germany and the UK. The Principal Investigator for the AMPTE mission was Dr Krimigis.
In the case of Earth, ionospheric sources dominate the formation of the ring current.
Jupiter’s ring current was first measured partially by Voyager. The Galileo mission to Jupiter added considerably to the understanding of Jupiter’s ring current, showing thatat Jupiter, Io’s volcanoes provide the gas that is subsequently ionized and accelerated
Note: This story has been adapted from a news release issued by European Planetology Network.

Fausto Intilla

www.oloscience.com

Jupiter: Friend Or Foe?

Source:

http://www.sciencedaily.com/releases/2007/08/070824133636.htm

Science Daily — The traditional belief that Jupiter acts as a celestial shield, deflecting asteroids and comets away from the inner Solar System, has been challenged by the first in a series of studies evaluating the impact risk to the Earth posed by different groups of object.

On Friday 24th August at the European Planetary Science Congress in Potsdam, Dr Jonathan Horner presented a study of the impact hazard posed to Earth by the Centaurs, the parent population of the Jupiter Family of comets (JFCs). The results show that the presence of a Jupiter-like planet in the Solar System does not necessarily lead to a lower impact rate at the Earth.
Dr Horner, from the UK's Open University (OU), said, "The idea that a Jupiter-like planet plays an important role in lessening the impact risk on potentially habitable planets is a common belief but there has only really been one study done on this in the past, which looked at the hazard due to the Long Period Comets. We are carrying out an ongoing series of studies of the impact risks in planetary systems, starting off by looking at our own Solar System, since we know the most about it!"
The team at the OU developed a computer model that could track the paths of 100,000 Centaurs around the Solar System over 10 million years. The simulation was run five times: once with Jupiter at its current mass, once without a Jupiter, and then with planets of three-quarters, a half and a quarter the mass of Jupiter (for comparison, Saturn is about a third of the mass of Jupiter). The team found that the impact rate in a Solar System with a planet like our Jupiter is about comparable to the case where there is no Jupiter at all. However, when the mass of Jupiter was between these two extremes, the Earth suffered an increased number of impacts from the JFCs.
Dr Horner said, "We've found that if a planet about the mass of Saturn or a bit larger occupied Jupiter's place, then the number of impacts on Earth would increase. However if nothing was there at all, there wouldn't be any difference from our current impact rate. Rather than it being a clear cut case that Jupiter acts as a shield, it seems that Jupiter almost gives with one hand and takes away with the other!"
The study shows that if there is no giant planet present, the JFCs will not be diverted onto Earth-crossing orbits, so the impact rate at the Earth is low. A Saturn-mass planet would have the gravitational pull to inject objects onto Earth-crossing orbits, but would not be massive enough to easily eject objects from the Solar System. This means that there would be more objects on Earth-crossing orbits at any given time, and therefore more impacts.
However, a planet with Jupiter's vast mass can give objects the gravitational boost to eject them from the Solar System. Therefore, if Jupiter deflects JFCs to an Earth-crossing orbit, it may well later sweep them right out of the Solar System and off the collision course with the Earth.
The group is now assessing the impact risk posed to the Earth by the Asteroids and will go on to study the Long Period Comets, before examining the role of the position of Jupiter within our system.
Jupiter family of comets
The Jupiter Family of Comets (JFCs) are short period comets with an orbital period of less than 20 years. Their orbits are controlled by Jupiter and they are believed to originate from the Kuiper Belt, a vast population of small icy bodies that orbit just beyond Neptune. Famous JFCs include Comet 81P/Wild 2, which was encountered by the Stardust spacecraft in January 2004 and Comet Shoemaker Levy-9, which broke up and collided with Jupiter in July 1994.
Note: This story has been adapted from a news release issued by European Planetology Network.

Fausto Intilla

www.oloscience.com

Largest Transiting Extrasolar Planet Found Around A Distant

Source:

http://www.sciencedaily.com/releases/2007/08/070806121128.htm

Science Daily — An international team of astronomers with the Trans-atlantic Exoplanet Survey just announced the discovery of TrES-4, a new extrasolar planet in the constellation of Hercules. The new planet was identified by astronomers looking for transiting planets -- that is, planets that pass in front of their home star -- using a network of small automated telescopes in Arizona, California, and the Canary Islands.

TrES-4 was discovered less than half a degree (about the size of the full Moon) from the team's third planet, TrES-3."TrES-4 is the largest known exoplanet," said Georgi Mandushev, Lowell Observatory astronomer and the lead author of the paper announcing the discovery. "It is about 70 percent bigger than Jupiter, the Solar System's largest planet, but less massive, making it a planet of extremely low density. Its mean density is only about 0.2 grams per cubic centimeter, or about the density of balsa wood! And because of the planet's relatively weak pull on its upper atmosphere, some of the atmosphere probably escapes in a comet-like tail." The new planet TrES-4 was first noticed by Lowell Observatory's Planet Search Survey Telescope (PSST), set up and operated by Edward Dunham and Georgi Mandushev. The Sleuth telescope, maintained by David Charbonneau (CfA) and Francis O'Donovan (Caltech), at Caltech's Palomar Observatory also observed transits of TrES-4, confirming the initial detections. TrES-4 is about 1400 light years away and orbits its host star in three and a half days. Being only about 4.5 million miles from its home star, the planet is also very hot, about 1,600 Kelvin or 2,300 degrees Fahrenheit."TrES-4 appears to be something of a theoretical problem," said Edward Dunham, Lowell Observatory Instrument Scientist. "It is larger relative to its mass than current models of superheated giant planets can presently explain. Problems are good, though, since we learn new things by solving them." "We continue to be surprised by how relatively large these giant planets can be," adds Francis O'Donovan, a graduate student in astronomy at the California Institute of Technology who operates one of the TrES telescopes. "But if we can explain the sizes of these bloated planets in their harsh environments, it may help us understand better our own Solar System planets and their formation."By definition, a transiting planet passes directly between the Earth and the star, blocking some of the star's light and causing a slight drop in its brightness. To look for transits, the small telescopes are automated to take wide-field timed exposures of the clear skies on as many nights as possible. When observations are completed for a particular field -- usually over an approximate two-month period -- astronomers measure very precisely the light from every star in the field in order to detect the possible signature of a transiting planet. "TrES-4 blocks off about one percent of the light of the star as it passes in front of it," said Mandushev. "With our telescopes and observing techniques, we can measure this tiny drop in the star's brightness and deduce the presence of a planet there." Not only is the planet TrES-4 mysterious and intriguing, but so is its host star cataloged as GSC 02620-00648. Georgi Mandushev explains: "The host star of TrES-4 appears to be about the same age as our Sun, but because it is more massive, it has evolved much faster. It has become what astronomers call a 'subgiant', or a star that has exhausted all of its hydrogen fuel in the core and is on its way of becoming a 'red giant', a huge, cool red star like Arcturus or Aldebaran."In order to help confirm they had found a planet, Gáspár Bakos of the Hungarian Automated Telescope Network (HATNet) and Harvard's Guillermo Torres switched from the 10-centimeter TrES telescopes to one of the 10-meter telescopes at the W. M. Keck Observatory on the summit of Mauna Kea, Hawaii. Using this giant telescope, they confirmed that the TrES team had indeed found a new planet. In order to measure accurately the size and other properties of TrES-4, astronomers also made follow up observations with bigger telescopes at Lowell Observatory and Fred L. Whipple Observatory in Arizona. The authors of the paper "TrES-4: A Transiting Hot Jupiter of Very Low Density", accepted for publication in the Astrophysical Journal, are: Georgi Mandushev and Edward Dunham of Lowell Observatory; Francis T. O'Donovan and Lynne Hillenbrand of the California Institute of Technology; David Charbonneau, Guillermo Torres, David Latham, Gáspár Bakos, Alessandro Sozzetti, and José Fernández of the Harvard-Smithsonian Center for Astrophysics; Mark Everett and Gilbert Esquerdo of the Planetary Science Institute; Markus Rabus and Juan Belmonte of Instituto de Astrofísica de Canarias in Tenerife, Spain; and Timothy Brown of the Las Cumbres Observatory Global Telescope.This research is funded by NASA through the Origins of Solar Systems Program.

Note: This story has been adapted from a news release issued by Lowell Observatory.

Fausto Intilla

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