Scientists Find Elusive Waves In Sun's Corona

Source:

http://www.sciencedaily.com/releases/2007/08/070830150113.htm

Science Daily — Scientists for the first time have observed elusive oscillations in the Sun's corona, known as Alfvén waves, that transport energy outward from the surface of the Sun. The discovery is expected to give researchers more insight into the fundamental behavior of solar magnetic fields, eventually leading to a fuller understanding of how the Sun affects Earth and the solar system.

The research, led by Steve Tomczyk of the National Center for Atmospheric Research (NCAR), is being published this week in Science.
"Alfvén waves can provide us with a window into processes that are fundamental to the workings of the Sun and its impacts on Earth," says Tomczyk, a scientist with NCAR's High Altitude Observatory.
Alfvén waves are fast-moving perturbations that emanate outward from the Sun along magnetic field lines, transporting energy. Although they have been detected in the heliosphere outside the Sun, they have never before been viewed within the corona, which is the outer layer of the Sun's atmosphere. Alfvén waves are difficult to detect partly because, unlike other waves, they do not lead to large-intensity fluctuations in the corona. In addition, their velocity shifts are small and not easily spotted.
"Our observations allowed us to unambiguously identify these oscillations as Alfvén waves," says coauthor Scott McIntosh of the Southwest Research Institute in Boulder. "The waves are visible all the time and they occur all over the corona, which was initially surprising to us."
Insights into the Sun
By tracking the speed and direction of the waves, researchers will be able to infer basic properties of the solar atmosphere, such as the density and direction of magnetic fields. The waves may provide answers to questions that have puzzled physicists for generations, such as why the Sun's corona is hundreds of times hotter than its surface.
The research also can help scientists better predict solar storms that spew thousands of tons of magnetized matter into space, sometimes causing geomagnetic storms on Earth that disrupt sensitive telecommunications and power systems. By learning more about solar disruptions, scientists may be able to better protect astronauts from potentially dangerous levels of radiation in space.
"If we want to go to the moon and Mars, people need to know what's going to happen on the Sun," Tomczyk says.
A powerful instrument
To observe the waves, Tomczyk and his coauthors turned to an instrument developed at NCAR over the last few years. The coronal multichannel polarimeter, or CoMP, uses a telescope at the National Solar Observatory in Sacramento Peak, New Mexico, to gather and analyze light from the corona, which is much dimmer than the Sun itself. It tracks magnetic activity around the entire edge of the Sun and collects data with unusual speed, making a measurement as frequently as every 15 seconds.
The instrument enabled the research team to simultaneously capture intensity, velocity, and polarization images of the solar corona. Those images revealed propagating oscillations that moved in trajectories aligned with magnetic fields, and traveled as fast as nearly 2,500 miles per second.
In addition to Tomczyk and McIntosh, the research team included scientists from the National Solar Observatory, University of Notre Dame, Framingham High School in Massachusetts, University of Michigan, and NCAR.
Article: S. Tomczyk, S.W. McIntosh, S.L. Keil, P.G. Judge, T. Schad, D.H. Seeley, J. Edmondson, "Alfvén Waves in the Solar Corona", Science, August 31, 2007
Note: This story has been adapted from a news release issued by National Center for Atmospheric Research.

Fausto Intilla

www.oloscience.com

Mars Exploration Rovers Resume Driving

Source:

http://www.sciencedaily.com/releases/2007/08/070829170103.htm

Science Daily — After six weeks of hunkering down during raging dust storms that limited solar power, both of NASA's Mars Exploration Rovers, Spirit and Opportunity, have resumed driving.

Opportunity advanced 13.38 meters (44 feet) toward the edge of Victoria Crater on Aug. 21. Mission controllers were taking advantage of gradual clearing of dust from the sky while also taking precautions against buildup of dust settling onto the rover.
"Weather and power conditions continue to improve, although very slowly for both rovers," said John Callas of NASA's Jet Propulsion Laboratory, Pasadena, Calif, project manager for the rovers. With the improved energy supplies, both rovers are back on schedule to communicate daily. Opportunity had previously been conserving energy by going three or four days between communications.
No new storms have been lifting dust into the air near either solar-powered rover in the past two weeks. Skies are gradually brightening above both Spirit and Opportunity. "The clearing could take months," said rover Project Scientist Bruce Banerdt. "There is a lot of very fine material suspended high in the atmosphere."
As that material does settle out of the air, the powdery dust is accumulating on surfaces such as the rovers' solar panels and instruments. More dust on the solar panels lessens the panels' capacity for converting sunlight to electricity, even while more sunlight is getting through the clearer atmosphere.
Opportunity's daily supply of electricity from its solar panels reached nearly 300 watt-hours on Aug. 23. That is more than twice as much as five weeks ago, but still less than half as much as two months ago. It is enough to run a 100-watt bulb for three hours.
One reason the rover team chose to drive Opportunity closer to the crater rim was to be prepared, if the pace of dust accumulation on the solar panels increases, to drive onto the inner slope of the crater. This would give the rover a sun-facing tilt to maximize daily energy supplies. The drive was also designed to check performance of the rover's mobility system, so it included a turn in place and a short drive backwards.
The next day, a favorable wind removed some dust from Opportunity's solar panels, providing a boost of about 10 percent in electric output. This forestalled the need to hurry to a sun-facing slope. The team is still excited to get Opportunity inside Victoria Crater to examine science targets on the inner slope that were identified in June, shortly before dust storms curtailed rover activities. An estimate of how soon Opportunity will enter the crater will depend on assessments in coming days of how dust may be affecting the instruments and of how much energy will be available.
On Spirit, dust on the lens of the microscopic imager has slightly reduced image quality for that instrument, although image calibration can compensate for most of the contamination effects. The team is experimenting with ways to try dislodging the dust on the lens. Spirit's solar arrays are producing about 300 watt hours per day as dust accumulation on them offsets clearing skies. Spirit drove 42 centimeters (17 inches) backwards on Aug. 23 to get in position for taking images of a rock that it had examined with its Moessbauer spectrometer. The rover team is planning additional drives for Spirit to climb onto a platform informally named "Home Plate."
Note: This story has been adapted from a news release issued by NASA/Jet Propulsion Laboratory.

Fausto Intilla

www.oloscience.com

New Information On Geological And Volcanic Activity On The Moon

Source:

http://www.sciencedaily.com/releases/2007/08/070822132131.htm

Science Daily — Owing to SMART-1’s high resolution and favourable illumination conditions during the satellite’s scientific operations, data from Europe’s lunar orbiter is helping put together a story linking geological and volcanic activity on the Moon.

The combination of high-resolution data from SMART-1’s AMIE micro-camera and data from the US Clementine mission is helping scientists determine the tectonics of the Moon’s giant basins and the history of volcanic flooding of mid-sized craters, inside and around the lunar basins.
“Thanks to low-elevation solar illumination on these high-resolution images”, says SMART-1 Project Scientist Bernard Foing, “it is now possible to study fine, small-scale geological features that went undetected earlier.”
The study provides new information on the thermal and tectonic history of the Moon and the processes following the formation of the large basins. There are approximately 50 recognizable lunar basins more than 300 km in diameter. They are believed to be created by the impact of asteroids or comets during the Lunar Late Heavy Bombardment period, 350-750 million years after the formation of the Moon. Some of these basins (mostly on the near side) were then filled in by lava originating from volcanic activity.
Combining information from SMART-1 and Clementine makes it possible to assess the link between fine geological structures, identified for the first time with AMIE’s high resolution, and the chemical composition of the study area.*
The Humorum basin is an ‘ideal’, circular, compact and moderately thick basin that was created by a simple impact event, showing a thin crust and mass concentration within a small area (from Clementine topography and gravity data).*
The Procellarum basin, or Oceanus Procellarum, is a large, extended, complex basin that is moderately thick and shows no mass concentration. It may have been formed by faulting associated with the formation of the adjacent Imbrium crater (3.84 thousand million years ago), rather than by a ‘gargantuan’ impact.*
The Humorum basin shows concentric graben, or elongated, trench-like erosional features around the edge of the basin. These are formed as the crust is deformed due to the presence of a mascon (mass concentration or ‘local overweight’).*
“Lunar crust is like a fragile skin, wrinkled due to local mascons or its thermal history”, says Bernard Foing, “as doctors, we searched for these skin-imprints but some may be masked underneath the last layers of basalt.”
For the first time, strike-slip faults have been observed with SMART-1 in the Humorum basin. These are faults where the rupture is vertical and one side slides past the other. An example is the San Andreas fault along the western United States. However, there is no multi-plate tectonic activity on the Moon.
Procellarum is an extended basin, where the crust is thin enough to allow magma to arise from under the surface, 4 to 2 thousand million years ago. SMART-1 images do not show geological faults, or surfaces where the rock ruptures due to differential movement, in the Procellarum basin.
Procellarum shows wrinkle ridges that are not distributed radially around the basin. Due to their location, they do not seem associated with mascon tectonics, but are mostly results of thermal and mechanical deformation resulting from volcanic activity - basalt extruded by the lava causes compression in the area. The Procellarum basin contains the youngest basalt found on the Moon so far, up to 2 thousand million years old.
Different ‘pulses’ of volcanic activity in lunar history created units of lava on the surface. The flooding of mid-sized craters with lava due to volcanic activity in the region is reflected in the mineralogical map. Differences in the mineralogical composition provide a tool to study the geological history of the region. Flooded as well as unflooded craters are found in the region, reflecting the evolution of volcanic activity with time.
“This analysis shows the potential of the AMIE camera”, says Jean-Luc Josset, Principal Investigator for the AMIE camera, “and we are still analysing other datasets that make use of the varying illumination conditions during the operation of SMART-1 over one and half years”.
The results reflected in the article appear in ‘Coupling between impacts and lunar volcanism for Humorum and Procellarum basins’ by S. Peters, B. Foing, D. Koschny, A. Rossi and the SMART-1 AMIE team, presented at the European Planetary Science Congress on 22 August 2007.
*Images: http://www.esa.int/esaSC/SEMCXRWZK5F_index_0.html
Note: This story has been adapted from a news release issued by European Space Agency.

Fausto Intilla

www.oloscience.com

In Search Of Interstellar Dragon Fire

Source:

http://www.sciencedaily.com/releases/2007/08/070821172205.htm

Science Daily — Ancient explorers set sail expecting to encounter dragons on the world's unknown oceans. NASA's twin Voyager spacecraft are searching for dragons of a different sort as they enter the boundary of our solar system – cosmic "dragons" that breathe a strange fire of high-speed atomic fragments called cosmic rays.

Just as mythical dragons were expected to inhabit stormy seas, these cosmic dragons could be found among turbulent magnetic fields powered by the colliding winds of stars, including our sun. The winds clash at the edge of our solar system, and space physicists wonder if these dragons may be found there, or if they are even more distant in interstellar space.
"Does a great dragon, in the form of a cosmic-ray accelerator, lurk within the turbulent boundary of our solar system to breathe out the fire of cosmic rays, or do these rays arise from even more powerful dragons somewhere in deep space?" asks Dr. John Cooper of NASA's Goddard Space Flight Center in Greenbelt, Md.
Cosmic rays can cause cancer in unprotected astronauts, and a better understanding of where and how cosmic rays are accelerated will improve predictions of how many will be encountered as astronauts set sail on the new ocean of space.
This ocean is not empty. The sun exhales a thin, hot wind of electrically conducting gas, called plasma, into space at many hundreds of miles per second. This solar wind forms a large plasma bubble, called the heliosphere, in space around the Sun. Beyond the orbit of Pluto, the solar wind gradually slows as it interacts with inflowing neutral gases from interstellar space, and then abruptly drops in speed to about 30 miles per second (50 kilometers/second) at a thin, invisible boundary around our solar system called the termination shock.
A simple kitchen experiment illustrates how this shock forms. When water runs at high speed from a kitchen faucet down to the bottom surface of the sink, the water hitting this surface first flows quickly and smoothly away from the impact point, but then runs into a circular boundary with slower, more turbulent flow beyond this boundary.
In the kitchen sink experiment, the circular boundary is the termination shock. The turbulent region beyond the shock boundary corresponds to a layer in the outer heliosphere of turbulent plasma flows and magnetic fields called the heliosheath. The boundary of this turbulent layer with the interstellar plasma environment, not so easily seen in the kitchen sink experiment because of the turbulence, is called the heliopause.
Our solar system is engulfed in a "dragon fire" of cosmic rays with a wide range of energy levels (the faster the cosmic ray, the greater its energy). Some are from known dragons like explosive flares on the sun. Astronomers believe the rays with the highest energy come from the largest dragons in the universe, including exploding stars called supernova, fast-rotating collapsed objects called neutron stars with incredibly strong magnetic fields, the heaviest collapsed stars called black holes that voraciously feed on infalling matter and spit out accelerated particles, and huge magnetic shock structures ejected far into interstellar space from these stellar sources. The energy for cosmic ray acceleration in all these sources comes from twisting, writhing motions of lower-energy charged particles in turbulent magnetic fields.
Nearer our solar system, Cooper is seeking the smaller dragons that breathe out lower energy fire, the so-called "suprathermal" cosmic rays. This suprathermal zone of fire spans a huge range in energy between that of the flowing plasma and the higher-energy cosmic rays. These suprathermal cosmic rays have been measured within the known heliosphere and theoretically modeled by Dr. Len Fisk and his collaborators at the University of Michigan.
Cooper's new idea is that similar energy distributions of such particles may be found in interstellar space. If the Voyager spacecraft eventually cross the heliopause and find this same suprathermal fire in interstellar space, it would mean that the fire breathers live outside the heliosphere.
Most space plasma scientists had expected the termination shock, traversed by Voyager 1 on December 16, 2004, to be the primary energy source for these suprathermal cosmic rays, but nothing was found. "I propose that that the fabled dragon of the termination shock breathes no fire and is a kinder and gentler creature, more like Puff the Magic Dragon," said Cooper. "I believe that the suprathermal cosmic rays we see within our solar system instead arise from even more powerful 'dragons' somewhere in interstellar space."
Cooper suggests that the zone of fire extends higher in energy within interstellar space and that Voyager 1 measurements are gradually revealing this expanded energy range during outward movement through the heliosheath towards the heliopause. He recently presented a paper on his new theory at the 2007 International Cosmic Ray Conference at Merida, Mexico. This conference took place on the Yucatan peninsula where an asteroid impact ended the long earthy reign of real dragons, the dinosaurs, sixty-five million years ago.
Cooper's idea was surprising at first, because the magnetic field carried by the solar wind into the heliosheath was expected to deflect both the incoming interstellar plasma and the suprathermal cosmic rays away from the heliosphere on approach to the heliopause boundary. Current theory is that the suprathermal cosmic rays are found inside the solar system because they sneak across the heliopause into the heliosphere as electrically neutral atoms, which are not deflected by magnetic force. Once inside the solar system, they become electrically charged as the sun's radiation strips electrons off of them. Once charged, they feel magnetic force and are carried out of the solar system by the magnetic field embedded in the solar wind. When they reach the termination shock, they are accelerated by the clashing magnetic fields there and shot back into the solar system, where we detect them as suprathermal cosmic rays.
However, since Voyager 1 has not yet found fully definitive evidence that the termination shock accelerates cosmic rays, Cooper thinks that instead they come from interstellar space. "The magnetic 'shield' formed by the solar wind is probably not smooth. Instead, as the solar wind crashes into the plasma found in interstellar space, it may roll and billow like a cloud, distorting the magnetic field carried with it. I believe interstellar suprathermal cosmic rays can slip between these folds to enter our solar system."
Another possibility is that the dragon lies somewhere between the termination shock and interstellar space, in the vast, teardrop-shaped region around the solar system called the heliosheath. This is where the low-speed solar wind piles up against the interstellar plasma. It forms a teardrop shape as our solar system moves through the galaxy. "However, Voyager 1 has sailed through the heliosheath for two and a half years since crossing the termination shock, and no other local acceleration source has been detected," said Cooper.
Cooper's theory will be tested again soon as the second Voyager spacecraft crosses the termination shock. "If Voyager 2 also finds no evidence of local cosmic ray acceleration as it crosses the termination shock, it will strengthen the case for more remote dragons in interstellar space, perhaps very far beyond in the galaxy, as the source of suprathermal cosmic rays," said Cooper. The first direct traces of these fiercer dragons may be found when the two Voyager spacecraft eventually cross the heliopause into local interstellar space.
Note: This story has been adapted from a news release issued by National Aeronautics And Space Administration.

Fausto Intilla
www.oloscience.com