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  Night Sky
 

Turn off or shield your outside lights downward. 
Unshielded, they ruin the night sky, annoy your neighbors, and don’t help with crime.
Keep the starry skies available to everyone.

December 2016 night sky

—Charlie Christmann

Mission to Mars

On Earth, we are blanketed with several layers of protection from radiation and meteorites: the magnetosphere, the ozone layer, and our atmosphere. In space, outside the protection of Mother Earth, life faces the threat of a thousand cuts. In this case, DNA damage to our cells one–by-one due to radiation, or by colliding with small chunks of space rocks floating out there. With NASA’s focus squarely on getting to Mars, and Space X pushing to place a colony there in the next few decades, the need to understand and engineer methods to protect the Mars-bound crew is urgent.

The probability of colliding with something in space is much more likely near Earth. Humans have polluted Earth’s orbit with space junk from previous space launches, derelict rockets, and debris from exploded or collided crafts. The International Space Station is always wary of space junk and has used its on-board rockets to move it out of the way. At other times, the crew will hunker down in the Soyuz capsules ready to abandon the station if there is a close call coming without time to move out of the way. Once on Mars, the thin atmosphere of the planet will provide little protection from meteors. Small space rocks that would burn up high in our atmosphere hit the Mars surface very hard.

Once outside the orbit of the geosynchronous satellites, collisions are much less likely—space between planets is big. But, the potential speeds are much higher and even a large dust particle is lethal unless the craft has ballistic shielding (like a bulletproof vest). This is where the radiation threat lies. And the surface of Mars is not much safer either—lacking a planetary magnetic field.

Radiation comes from two sources in space. Our sun is a nuclear reactor boiling off its atmosphere as charged particles, electrons, protons and alpha particles, known as “plasma.” Around five hundred million pounds of the sun’s atmosphere flows away into space each second. Accelerated by the strong magnetic fields, particles in the wind can reach speeds of 150 miles per second to over four hundred miles per second. Solar storms, called coronal mass ejections, can blast a trillion pounds of solar material into space. If the explosion is directed towards Earth, our magnetic field can bend and deflect most the of the storm, but some solar stuff loops around to the polar regions causing the northern and southern lights where the charged particles hit our atmosphere. The solar wind ebbs and flows along with the eleven-year solar cycle.

While the sun is a major concern, there are other radiation threats out there much deadlier. These come from outside our solar system. Cosmic rays are parts of atoms traveling near the speed of light. The source of these rays are not fully understood, but many are believed to come from super novae exploding around our galaxy. Others may come from the energetic heart of faraway galaxies called quasars.

While not all of the solar radiation can be stopped, it is much easier to stop than cosmic rays. Cosmic rays will break apart the chromosomes in our cell’s DNA and can lead to cancer and possibly, over years of exposure, brain and organ damage. A shield is available, but it is bulky and heavy. Doubling the shield thickness only provides about a ten percent decrease in radiation exposure. Surprisingly, one of the best shields is something we will need to take along with us anyway—water. Placing our water supplies around the outside of the ship may be a good solution to reducing exposure.

Another study by NASA’s DREAM2 team, lead by Principal Investigator William Farrell, suggests the best time to send humans into interplanetary space is during the most active part of the solar cycle. While solar particles are a threat, they are much less deadly than the extra solar cosmic rays.

According to DREAM2 team member Nathan Schwadron, of the University of New Hampshire at Durham, “The high energy of GCRs [galactic cosmic rays] allows these particles to penetrate nearly every material known to man, including shielding on space craft; when the cosmic rays penetrate that shielding, secondary particles are produced that can damage organs and lead to cancer.”

The solar wind forms a bubble around our solar system and deflects some of the cosmic rays from entering. During solar activity peaks, more cosmic rays are deflected. As the cycle reaches a minimum, more cosmic rays penetrate into the solar system.

Over the last few cycles, solar scientists have seen the peak of each cycle has been weaker. This may mean less solar radiation to contend with, but means more of the deadly cosmic rays are reaching both Earth and Mars. Currently, the sun is heading toward its solar cycle minimum, emerging from a mini-maximum. Astronomers are thinking the solar cycle peaks will be getting weaker over the next several cycles, exposing astronauts to higher risks both in interplanetary space and in Earth orbit.

“It is a bit ironic, but the reduced GCRs in solar maximum and possibly fewer SEP [solar energetic particles] events because of the trend of decreasing solar activity suggests that the next solar maximum may be one of the safest times to fly missions to deep space in the last eighty years,” said Schwadron.

The next solar minimum is expected to occur sometime in 2019 or 2020 when the number of sunspot numbers reach a minimum and the sun’s face may be spotless for weeks or months at a time.


 
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