Lately, the current sheet has been flattening itself out, allowing cosmic rays more direct access to the inner solar system. The current sheet is important because cosmic rays tend to be guided by its folds. That is the "heliospheric current sheet," a vast transition zone where the polarity of the sun's magnetic field changes from plus (north) to minus (south). Imagine the sun wearing a ballerina's skirt as wide as the entire solar system with an electrical current flowing along the wavy folds. Solar wind speeds have dropped to very low levels in 20, making it easier than usual for a cosmic ray to proceed. Once a cosmic ray enters the solar system, it must "swim upstream" against the solar wind. "Measurements by the Ulysses spacecraft show that solar wind pressure is at a 50-year low," he continues, "so the magnetic bubble that protects the solar system is not being inflated as much as usual." A smaller bubble gives cosmic rays a shorter-shot into the solar system. The heliospheric current sheet is shaped like a ballerina's skirt.Ĭredit: J. "This record-low IMF undoubtedly contributes to the record-high cosmic ray fluxes." "There has been a sharp decline in the sun's interplanetary magnetic field (IMF) down to only 4 nanoTesla (nT) from typical values of 6 to 8 nT," he says. Mewaldt lists three aspects of the current solar minimum that are combining to create the perfect storm: "At times of low solar activity, this natural shielding is weakened, and more cosmic rays are able to reach the inner solar system," explains Pesnell. When a cosmic ray tries to enter the solar system, it must fight through the heliosphere's outer layers and if it makes it inside, there is a thicket of magnetic fields waiting to scatter and deflect the intruder. The entire solar system from Mercury to Pluto and beyond is surrounded by a bubble of solar magnetism called "the heliosphere." It springs from the sun's inner magnetic dynamo and is inflated to gargantuan proportions by the solar wind. The sun's magnetic field is our first line of defense against these highly-charged, energetic particles. Cosmic rays cause "air showers" of secondary particles when they hit Earth's atmosphere they pose a health hazard to astronauts and a single cosmic ray can disable a satellite if it hits an unlucky integrated circuit. They are subatomic particles-mainly protons but also some heavy nuclei-accelerated to almost light speed by distant supernova explosions. Galactic cosmic rays come from outside the solar system. "We're experiencing the deepest solar minimum in nearly a century," says Dean Pesnell of the Goddard Space Flight Center, "so it is no surprise that cosmic rays are at record levels for the Space Age." Right now solar activity is as weak as it has been in modern times, setting the stage for what Mewaldt calls "a perfect storm of cosmic rays." Researchers have long known that cosmic rays go up when solar activity goes down. The cause of the surge is solar minimum, a deep lull in solar activity that began around 2007 and continues today. "The increase is significant, and it could mean we need to re-think how much radiation shielding astronauts take with them on deep-space missions." "In 2009, cosmic ray intensities have increased 19% beyond anything we've seen in the past 50 years," says Richard Mewaldt of Caltech. According to sensors on NASA's ACE (Advanced Composition Explorer) spacecraft, galactic cosmic rays have just hit a Space Age high. Planning a trip to Mars? Take plenty of shielding. Energetic iron nuclei counted by the Cosmic Ray Isotope Spectrometer on NASA's Advanced Composition Explorer (ACE) spacecraft reveal that cosmic ray levels have jumped 19% above the previous Space Age high.Īn artist's concept of the heliosphere, a magnetic bubble that partially protects the solar system from cosmic rays.Ĭredit: Walt Feimer/NASA GSFC's Conceptual Image Lab
0 Comments
Leave a Reply. |