sexta-feira, 31 de maio de 2013

Cosmic Rays pose excessively high radiation risks to future human Mars missions

Measurements taken by NASA's Mars Science Laboratory (MSL) mission as it delivered the Curiosity rover to Mars in 2012 are providing NASA the information it needs to design systems to protect human explorers from radiation exposure on deep-space expeditions in the future.  MSL's Radiation Assessment Detector (RAD) is the first instrument to measure the radiation environment during a Mars cruise mission from inside a spacecraft that is similar to potential human exploration spacecraft. The findings will reduce uncertainty about the effectiveness of radiation shielding and provide vital information to space mission designers who will need to build in protection for spacecraft occupants in the future. The findings, which are published in the May 31 edition of the journal Science, indicate radiation exposure for human explorers could exceed NASA's career limit for astronauts if current propulsion systems are used.
Two forms of radiation pose potential health risks to astronauts in deep space. One is galactic cosmic rays (GCRs), particles caused by supernova explosions and other high-energy events outside the solar system. The other is solar energetic particles (SEPs) associated with solar flares and coronal mass ejections from the sun.
Galactic cosmic rays are one of the most important barriers standing in the way of plans for interplanetary travel by crewed spacecraft.
Cosmic rays are energetic particles originating from outer space that travel towards every direction and also impinge on Earth's atmosphere. Almost 90% of all the incoming cosmic ray particles are simple protons, with nearly 10% being helium nuclei (alpha particles), and slightly less than 1% is other heavier elements. Electrons (beta particles) or gamma ray photons with similar origin are also included under that denomination. The term ray is a historical accident, as cosmic rays were at first, and wrongly, thought to be mostly electromagnetic radiation. In modern common usage high-energy particles with intrinsic mass are known as "cosmic" rays, and photons, which are quanta of electromagnetic radiation (and so have no intrinsic mass) are known by their common names, such as “gamma rays” or “X-rays”, depending on their frequencies. Cosmic rays attract great interest practically, due to the damage they inflict on microelectronics and life outside the protection of an atmosphere and magnetic field, and scientifically, because the energies of the most energetic ultra-high-energy cosmic rays (UHECRs) have been observed to approach 3 × 1020 eV, about 40 million times the energy of particles accelerated by the Large Hadron Collider (LHC). At 50 Joules, the highest-energy ultra-high-energy cosmic rays have energies comparable to the kinetic energy of a 90-kilometre-per-hour (56 mph) baseball.
Galactic cosmic rays (GCRs) are one of the most important barriers standing in the way of plans for interplanetary travel by crewed spacecraft. Galactic cosmic rays are the high-energy particles that flow into our solar system from far away in the Galaxy. GCRs are mostly pieces of atoms: protons, electrons, and atomic nuclei which have had all of the surrounding electrons stripped during their high-speed (almost the speed of light, 299 792 458 m/s) passage through the Galaxy. Cosmic rays provide one of our few direct samples of matter from outside the solar system. The magnetic fields of the Galaxy, the solar system, and the Earth have scrambled the flight paths of these particles so much that we can no longer point back to their sources in the Galaxy. Cosmic rays also pose a threat to electronics placed aboard outgoing probes. In 2010, a malfunction aboard the Voyager 2 space probe was credited to a single flipped bit, probably caused by a cosmic ray. Strategies such as physical or magnetic shielding for spacecraft have been considered in order to minimize the damage to electronics and human beings caused by cosmic rays.
The second form of “radiation” to boost the levels of risk towards a Mars missions is represented by the Solar energetic particles (SEP). These are high-energy particles coming from the Sun. They consist of protons, electrons, and alpha particles helium ions, and HZE ions (which have an electric charge greater than +2) that are highly energetic. They are of particular interest and importance because they can endanger life in outer space. Solar energetic particles can originate from two processes: Particles accelerated at a solar-flare site or by shock waves associated with coronal mass ejections (CMEs). However, only about 1% of the CMEs produce strong SEP events.
Radiation exposure is measured in units of Sievert (Sv) or milisievert (one one-thousandth Sv). Long-term population studies have shown exposure to radiation increases a person's lifetime cancer risk. Exposure to a dose of 1 Sv, accumulated over time, is associated with a 5 percent increase in risk for developing fatal cancer.
NASA has established a 3 percent increased risk of fatal cancer as an acceptable career limit for its astronauts currently operating in low-Earth orbit. The RAD data showed the Curiosity rover was exposed to an average of 1.8 milisievert of GCR per day on its journey to Mars. Only about 5 percent of the radiation dose was associated with solar particles because of a relatively quiet solar cycle and the shielding provided by the spacecraft. “In terms of accumulated dose, it's like getting a whole-body CT scan once every five or six days," said Cary Zeitlin, a principal scientist at the Southwest Research Institute (SwRI) in San Antonio and lead author of the paper on the findings. "Understanding the radiation environment inside a spacecraft carrying humans to Mars or other deep space destinations is critical for planning future crewed missions.”
The RAD data will help inform current discussions in the United States medical community, which is working to establish exposure, limits for deep-space explorers in the future.

1.      Radiation Measured by NASA's Curiosity on Voyage to Mars has Implications for Future Human Missions; Access: (accessed on: May 30, 2013);
2.       Cosmic ray; Access: (accessed on: May 31, 2013);
3.      Cosmic rays: What are cosmic rays?; Access:  (accessed on: May 31, 2013);
4.      HZE ions; Access:  (accessed on: May 31, 2013);
5.      Image: Access:  (accessed on: May 31, 2013)

quarta-feira, 4 de julho de 2012

A powerful sun storm could reach Earth by July 4

A solar flare is an explosion on the Sun that happens when energy stored in twisted magnetic fields (usually above sunspots) is suddenly released. Flares produce a burst of radiation across the electromagnetic spectrum, from radio waves to x-rays and gamma-rays. Scientists classify solar flares according to their x-ray brightness in the wavelength range 1 to 8 Angstroms. The amount of energy released is the equivalent of millions of 100-megaton hydrogen bombs exploding at the same time! The first solar flare recorded in astronomical literature was on September 1, 1859. Two scientists, Richard C. Carrington and Richard Hodgson, were independently observing sunspots at the time, when they viewed a large flare in white light.
There are 3 categories: X-class flares are big; they are major events that can trigger planet-wide radio blackouts and long-lasting radiation storms. M-class flares are medium-sized; they can cause brief radio blackouts that affect Earth's polar regions. Minor radiation storms sometimes follow an M-class flare. Compared to X- and M-class events, C-class flares are small with few noticeable consequences here on Earth. The sun has sent out a powerful giant solar flare on July 2 and is expected to sweep past Earth’s magnetic field on Wednesday, July 4. The start of a solar explosion on the Sun’s surface was for the first time viewed by the scientists at the Inter-University Centre for Astronomy and Astrophysics (IUCAA), in collaboration with University of Cambridge and Rice University, USA. A sun storm was noticed rising from a large sunspot called AR1515 that is now facing the Earth side of the sun. It released an extremely forceful solar flare at 6:43 a.m. EDT (1043 GMT) on July 2. The flare registered as a class M5.6 solar storm on the scale used by astronomers to measure the sun’s weather.
Astronomer Tony Phillips said the solar flare released a wave of charged plasma called a coronal mass ejection (CME), but the particles were not aimed directly at Earth.
According to Tony Phillips stated, “The eruption also hurled a CME into space, but not directly toward Earth. The south-traveling cloud could deliver a glancing blow to our planet’s magnetosphere on July 4th or 5th.”
The strength of the solar flare is classified by three primary classes – C-class flares, M-class flares and X-class flares. The weakest storms are the C-class flares, which cause little effect that can be felt on Earth. M-class flares are moderate solar storms that can supercharge the Earth’s northern lights display.
The most powerful X-class solar flares can threaten spacecraft and astronauts in orbit; affect satellite signals, as well as harm power lines and other infrastructure on the ground, when targeted towards earth.
Scientist Durgesh Tripathi said hot gases evolved during large solar explosions would travel towards the earth which could affect power grids and satellites.
Helen Mason of the University of Cambridge said active regions are now arising frequently across the Sun. The opportunity to study them is facilitated with solar spacecraft, such as Hinode and the Solar Dynamics Observatory.
The study about solar flares would help in forecasting such explosions and in taking needed precautions to avoid damage to power grids and satellites.


  1. Truthdrive ;
  2. ;
Sarvodaya ;

sexta-feira, 29 de junho de 2012

Hidden Portals in Earth's Magnetic Field
June 29, 2012: A favorite theme of science fiction is "the portal"--an extraordinary opening in space or time that connects travelers to distant realms.  A good portal is a shortcut, a guide, a door into the unknown. If only they actually existed....

It turns out that they do, sort of, and a NASA-funded researcher at the University of Iowa has figured out how to find them.

"We call them X-points or electron diffusion regions," explains plasma physicist Jack Scudder of the University of Iowa.  "They're places where the magnetic field of Earth connects to the magnetic field of the Sun, creating an uninterrupted path leading from our own planet to the sun's atmosphere 93 million miles away."
Observations by NASA's THEMIS spacecraft and Europe's Cluster probes suggest that these magnetic portals open and close dozens of times each day.  They're typically located a few tens of thousands of kilometers from Earth where the geomagnetic field meets the onrushing solar wind.  Most portals are small and short-lived; others are yawning, vast, and sustained.  Tons of energetic particles can flow through the openings, heating Earth's upper atmosphere, sparking geomagnetic storms, and igniting bright polar auroras.

NASA is planning a mission called "MMS," short for Magnetospheric Multiscale Mission, due to launch in 2014, to study the phenomenon. Bristling with energetic particle detectors and magnetic sensors, the four spacecraft of MMS will spread out in Earth's magnetosphere and surround the portals to observe how they work.

Just one problem:  Finding them.  Magnetic portals are invisible, unstable, and elusive.  They open and close without warning "and there are no signposts to guide us in," notes Scudder. 

Data from NASA's Polar spacecraft, circa 1998, provided crucial clues to finding magnetic X-points.
Actually, there are signposts, and Scudder has found them.

Portals form via the process of magnetic reconnection.  Mingling lines of magnetic force from the sun and Earth criss-cross and join to create the openings. "X-points" are where the criss-cross takes place.  The sudden joining of magnetic fields can propel jets of charged particles from the X-point, creating an "electron diffusion region."

To learn how to pinpoint these events, Scudder looked at data from a space probe that orbited Earth more than 10 years ago.

"In the late 1990s, NASA's Polar spacecraft spent years in Earth's magnetosphere," explains Scudder, "and it encountered many X-points during its mission."

Because Polar carried sensors similar to those of MMS, Scudder decided to see how an X-point looked to Polar. "Using Polar data, we have found five simple combinations of magnetic field and energetic particle measurements that tell us when we've come across an X-point or an electron diffusion region. A single spacecraft, properly instrumented, can make these measurements."

This means that single member of the MMS constellation using the diagnostics can find a portal and alert other members of the constellation. Mission planners long thought that MMS might have to spend a year or so learning to find portals before it could study them.  Scudder's work short cuts the process, allowing MMS to get to work without delay.

It's a shortcut worthy of the best portals of fiction, only this time the portals are real. And with the new "signposts" we know how to find them.

The work of Scudder and colleagues is described in complete detail in the June 1 issue of the Physical Review Letters.

Dr. Tony Phillips| Production editor: Dr. Tony Phillips | Credit: Science@NASA

terça-feira, 27 de julho de 2010

The South Atlantic magnetic anomaly (SAMA) and signals of the Earth´s magnetic poles reversal

Important variations in the magnetic field, observed by satellites in certain areas of the globe, could herald an inversion of the poles. This phenomenon has already come about several times in the history of the planet. Is the Earth losing its compass? This is what a study by the Department of Geomagnetism and Paleomagnetism of the Paris Geophysical Institute (l’Institut de physique du globe de Paris [IPG]) would have us believe.
We are all contained by the Earth’s magnetic field without really noticing it. We become aware of it only when we use a compass to find our way. This is the most obvious manifestation of the Earth’s magnetism, which has existed for 3 billion years and is generated 3,000 kilo-meters under our feet by the stirring of our planet’s liquid iron core. This liquid iron core causes the Earth to act like a giant magnet; the magnetic lines are organized on a bipolar basis, more or less in alignment with the Earth’s rotational axis.
This bipolar configuration, however, is not permanent. It varies with the movement of the Earth’s liquid core, and in the past, the positions of the magnetic poles have been known to switch entirely. These phenomena were verified by paleomagnetic studies on ancient volcanic basalts. The latter contain magnetic grains that kept both the orientation and strength of the Earth’s magnetic field when they became solid.
The Earth’s magnetosphere is a close- to-spherical magnetic field that surrounds our planet. As a matter of fact, this magnetosphere shields us from the constant bombardment that our globe suffers as a consequence of t its exposition to the Sun. It is estimated that the Sun is blowing several radiation particles, in many directions, around 1 billion kilograms of electrons, protons and other forms of dense matter per second.
There is a spot in this magnetic shielding that actually plays as a hole letting the incoming solar wind to penetrate close to our ground and release a larger radiation dose comparatively to other areas where the magnetosphere shows a more uniform profile. That dip is said to be caused by the eccentric displacement of the center of the
magnetic field from the geographical center of the Earth as well as the displacement between the magnetic and geographic poles. This dip is dubbed the South Atlantic magnetic anomaly (SAMA). It is occupying the area between Southeast Brazil and South Africa.
The minimum value, of the total geomagnetic field F of about 22,850 nT is found around 26° South and 54° West, which agrees well with the International Geomagnetic Reference Field (IGRF) model for the year 2000. The F field strength within the radius of about 1000 km around the F minimum point is less than 23,000 nT. It can be noted that the anomaly is dynamic, the center of the anomaly, that is the area of F minimum, has traveled in the last century from near Rio de Janeiro (23°.0 S, 43°.0 W) to Rio Grande do Sul (29°.0 S, 54°.0 W). These locations are determined from a combination of the magnetic maps prepared by the Brazilian National Observatory, Ministry of Science and Technology, Rio de Janeiro and the IGRF models Marins (2002). The center of F minimum and location of magnetic equator both have undergone a large secular variation unseen elsewhere. It is thought that this westward drift of the center of the anomaly and magnetic equator may be related to the westward drift of the geomagnetic axis of the Earth. The present value of F at São Martinho da Serra (SMS) (29°.43 S, 53°.80 W) is 22,883 nT and it is decreasing at the rate of 28 nT/year.
If the South Atlantic magnetic anomaly (SAMA) is taken as signal of an imminent reversal of our planet´s magnetic poles, how imminent is the reversal occurrence?

quinta-feira, 22 de julho de 2010

The thermosphere

The thermosphere is the biggest of all the layers of the earth's atmosphere directly above the mesosphere and directly below the exosphere. Within this layer, ultraviolet radiation causes ionization. The International Space Station has a stable orbit within the middle of the thermosphere, between 320 and 380 kilometers (200 and 240 mi). Auroras also occur in the thermosphere.
Named from the Greek θερμός (thermos) for heat, the thermosphere begins about 80 kilometers (50 mi) above the earth. At these high altitudes, the residual atmospheric gases sort into strata according to molecular mass. Thermospheric temperatures increase with altitude due to absorption of highly energetic solar radiation by the small amount of residual oxygen still present. Temperatures are highly dependent on solar activity, and can rise to 1,500 °C (2,730 °F). Radiation causes the atmosphere particles in this layer to become electrically charged, enabling radio waves to bounce off and be received beyond the horizon. At the exosphere, beginning at 500 to 1,000 kilometers (310 to 620 mi) above the Earth's surface, the atmosphere turns into space.
The highly diluted gas in this layer can reach 2,500 °C (4,530 °F) during the day. Even though the temperature is so high, one would not feel warm in the thermosphere, because it is so near vacuum that there is not enough contact with the few atoms of gas to transfer much heat. A normal thermometer would read significantly below 0 °C (32 °F), due to the energy lost by thermal radiation overtaking the energy acquired from the atmospheric gas by direct contact.
The dynamics of the lower thermosphere (below approximately 120 kilometers (75 mi)) are dominated by atmospheric tide, which is driven, in part, by the very significant diurnal heating. The atmospheric tide dissipates above this level since molecular concentrations do not support the coherent motion needed for fluid flow.

quinta-feira, 4 de março de 2010

The day the solar wind disappeared

From May 10-12, 1999, the solar wind that blows constantly from the Sun virtually disappeared in the most drastic and longest-lasting decrease ever observed. Dropping to a fraction of its normal density and to half its normal speed, the solar wind died down enough to allow physicists to observe particles flowing directly from the Sun's corona to Earth. This severe change in the solar wind also drastically changed the shape of Earth's magnetic field and produced a rare auroral display at the North Pole.
Starting late on May 10 and continuing through the early hours of May 12, the density of the solar wind dropped by more than 98%. Because of the drop-off of the wind, energetic electrons from the Sun arrived at the Earth in narrow beams, known as the strahl. Under normal conditions, electrons from the Sun are diluted, mixed, and redirected in interplanetary space and by Earth's magnetic field (the magnetosphere). But in May 1999, several satellites detected electrons arriving at Earth with properties similar to those of electrons in the Sun's corona, suggesting that they were a direct sample of particles from the Sun.
"This event provides a window to see the Sun's corona directly," said Dr. Keith Ogilvie, project scientist for NASA's Wind spacecraft and a space physicist at Goddard Space Flight Center. "The beams from the corona do not get broken up or scattered as they do under normal circumstances, and the temperature of the electrons is very similar to their original state on the Sun."
"Normally, our view of the corona from Earth is like seeing the Sun on an overcast, cloudy day," said Dr. Jack Scudder, space physicist from the University of Iowa and principal investigator for the Hot Plasma Analyzer (HYDRA) on NASA's Polar spacecraft. "On May 11, the clouds broke and we could see clearly."
Scudder, Ogilvie, and other scientists affiliated with the International Solar-Terrestrial Physics program (ISTP) presented their findings at the Fall Meeting of the American Geophysical Union in San Francisco's Moscone Center. Researchers working with more than a dozen spacecraft observed various facets of this event…...

Mike Carlowicz, ISTP Science Writer, 301-286-6353
Bill Steigerwald, NASA GSFC Public Affairs, 301-286-5015,

quinta-feira, 25 de fevereiro de 2010

The Gregorian Calendar

The Gregorian calendar is the calendar that is used nearly everywhere in the world. A modification of the Julian calendar, it was first proposed by the Calabrian doctor Aloysius Lilius, and was decreed by Pope Gregory XIII, for whom it was named, on 24 February 1582 via the papal bull Inter gravissimas. Its years are numbered per the perceived birth year of Jesus Christ, which is labeled the "anno Domini" era. This era was created in the 6th century by Roman monk Dionysius Exiguus.
The number of days in a Gregorian year is the average number of days per year in the time interval of 400 years of the Gregorian calendar. The Gregorian calendar was established in 1582 by the Pope Gregorio XIII and replaced the Julian calendar established by the roman emperor Julius Caesar in the year 46 B.C.
The Gregorian calendar contains regular years (with 365 days each) and leap years (with 366 days each). The rule used to decide if a year is a regular year or a leap year is quite simple. The year is a leap year if it is a multiple of 4, the centennial years excluded. A centennial year will be a leap year if it is a multiple of 400. So the most recent leap years we had are 2000, 2004 and 2008. Note that 2000 is a leap year only because it is a multiple of 400. The year 1900 was not a leap year. The same can be said of the year 2100 (despite the fact they are multiples of 4). The next leap year will happen in 2012