Global Warming

        Politicians have legislated a reduction of air pollution in some places; and, politicians may be able to legislate a stop to the release of extra carbon dioxide as a greenhouse gas into the atmosphere that is warming the planet and may cause predicted consequences.  Unfortunately, politicians may not be able to legislate a reduction of the extra carbon dioxide in the atmosphere because politicians cannot completely legislate without the means to implement, which can be explained in the following.

 

 

Global Warming by The Numbers

or

Are We Terraforming a Planet

 

        Carbon as part of the carbon dioxide in the atmosphere is in a natural chemical cycle for example with the air, the water, the ground and with living and decaying matter.  The extra carbon dioxide that humans are reportedly releasing into the atmosphere is not quickly becoming part of Earth's natural carbon cycle.  Therefore, because carbon dioxide absorbs and emits some of the infrared electromagnetic radiation (heat) from the surface of the Earth back toward the surface of the Earth then the extra carbon dioxide that is not part of the natural carbon cycle and that remains in the atmosphere is reportedly making Earth's lower atmosphere warmer.
       Currently, the atmosphere is reported to have at least 400 ppmv (parts per million in volume) (http://co2unting.com) of carbon dioxide, which was first measured at that amount during March of 2015.  The amount of carbon dioxide in the atmosphere is usually measured either from ground stations or from NASA's Orbiting Carbon Observatory-2 (OCO-2).
       The mass of carbon in 1 ppmv of carbon dioxide in the atmosphere has been calculated to be 2.13 Gt (Giga or 109 metric tonnes).  Therefore the approximate mass of carbon in the carbon dioxide presently in the atmosphere is at least 852 Gt.  852 Gt is the mass of how much the carbon would weigh if the force of one Earth gravity pulls the carbon as a solid against the ground.
       Before the beginning of the first Industrial Revolution during the early 1700s, the concentration of carbon dioxide in the atmosphere was measured at 280 ppmv.  After the Second Industrial revolution around 1870, the concentration of carbon dioxide in the atmosphere was measured at around 290 ppmv.  280 ppmv of carbon dioxide calculates to approximately 600 Gt of carbon.  This makes an increase from before the beginning of the Industrial Age to March of 2015 to be 252 Gt of carbon.  Humans would perhaps need to build something very large or massive to remove this extra carbon from the atmosphere.  400 ppmv of the atmosphere is .04% of the volume of the atmosphere, which can appear to be a very small number that can be a reason why people do not believe that the extra carbon dioxide in the atmosphere is making the planet warmer.  Adding the mass of two oxygen atoms present in each carbon dioxide molecule calculates the current mass of the extra carbon dioxide in the atmosphere to be at least 924 Gt.

       Greenhouse gas is partly a misnomer.  Greenhouse gases do not warm the atmosphere in exactly the same way that a glass-enclosed greenhouse warms air inside a greenhouse.  Enclosed greenhouses retain most heated air due to a lack of air convection to the outside air.  The longer wavelengths of infrared light from the Sun cannot pass through the glass of a greenhouse.  However, some of the other solar radiation that enters a greenhouse and is absorbed on surfaces inside the greenhouse radiates as longer wavelengths of infrared heat.  The glass of a greenhouse 'reflects' and retains the longer wavelengths of infrared heat inside the greenhouse, making the air inside the greenhouse warmer.  Greenhouses keep heat in; and, greenhouse gases return heat down.  Eventually, all of the Sun's energy arriving on the surface of the Earth (including in greenhouses) will radiate into outer space, which is known as an energy balance that is based on a discovered law of thermodynamics that energy can neither be created nor destroyed.

       Without greenhouse gases warming Earth's atmosphere, the averaged global temperature was determined to be a little above -18 degrees Celsius or 0 degrees Fahrenheit, which is based on an average of solar light energy on the surface of the Earth to be, depending on the source, between 340-400 Watts/m2.  Direct sunlight has an energy on the upper atmosphere of Earth at around 1370 Watts/m2, and an estimated 200-990 Watts/m2 at ground level depending on how much sunlight is absorbed and reflected in the atmosphere.  Tangential sunlight energy on the surface of Earth can be as much as 70 Watts/m2 of naturally indirect and reflected sunlight.

       The rate of atmospheric cooling during and after sunsets indicates the possible rate at which infrared heat passes by or radiates from greenhouse gases into outer space.  Infrared radiates from greenhouse atoms and molecules in a spherical pattern.  Water vapor is 1.4 to 8 times more powerful as a greenhouse gas (1050,000 ppmv) than carbon dioxide, depending on the regional water content in the atmosphere.  Another source states that water vapor has a 66 to 85% of the total influence of greenhouse gases; and, carbon dioxide has a 9 to 26% of the total influence.  Some of the other greenhouse gases that are in lesser quantities are methane, nitrous oxide, ozone and chlorofluorocarbons.  A methane molecule can remain in the Earths atmosphere for up to 10 to 12 years after which the methane molecule oxidizes into the greenhouse gases of carbon dioxide and water vapor.  Methane concentration in the atmosphere has been varying during recent geological time from 320 to 770 ppbv (parts per billion in volume).
       The effect of water vapor on warming the atmosphere can vary greatly in less than 24 hours, as compared to the long term continuous effect of carbon dioxide.  The atmospheric temperature during a cloudy and humid night may decrease 5 degrees Fahrenheit or 3 degrees Celsius from the previous daytime high temperature; and, on the following night that is cloudless and dry, the atmospheric temperature can decrease 20-40 degrees Fahrenheit or 11-22 degrees Celsius.

       Science and engineering currently do not have an efficient method to separate carbon dioxide gas directly into pure carbon and pure oxygen.  If the carbon from the extra carbon dioxide in the atmosphere could be removed as amorphous carbon (non-crystallized as carbon dust) with an upper density for amorphous carbon at 2.1 grams/cm3 then the volume of the extra carbon in the atmosphere can be calculated.  For example, comparing the volume of extra carbon in the atmosphere to the height of Mt. Everest by measuring Mt. Everest from a base height of 2.711 km above sea level to the peak at 8.848 km above sea level as a right cone shaped pile of carbon with a base of radius equal to 3.5 km calculates to a volume of 78.73 cubic km.  The volume was not measured from sea level because part of the volume would be inside of Earth's crust.  The mass of amorphous carbon in a volume of 78.73 cubic km with a density of 2.1 grams/cm3, or a density of 2.1 Gt/km3, is approximately 165 Gt.  Therefore, the comparative volume of extra carbon in the atmosphere of 252 Gt at a height of Mt. Everest, ignoring compression densities, is 1.52 piles.  The political and environmental decisions can be what to do with this extra carbon.
       For an example on adding the sources of the extra carbon in the atmosphere, the percent of crude oil, or petroleum, or more specifically hydrocarbons that is used to manufacture burning fuels that emit carbon dioxide gas is around 80.3%.  The remaining crude oil is used to manufacture, for example, road asphalt, and synthetic materials such as fertilizers, greases, paints, rubbers, plastics, and other artificial additives.  Of the 80.3% of the mass of hydrocarbons that is burnt as fuels, 13.5% is the mass of hydrogen and 84.5% is the mass of carbon.  Therefore, 80.3% x 84.5% = about 68% of the mass of hydrocarbons is burned into carbon dioxide.  An unconfirmed estimate is that the oil industry has removed, from 1870 to 2009, 944 billion barrels of oil from the ground or 135 Gt.  (135 Gt were probably weighed at the force of one Earth gravity which is the same as mass.)  Of the 135 Gt, 135 x 68% = 91.8 Gt of carbon from hydrocarbons was burned into the atmosphere from 1870 to 2009.
       Burning coal also adds carbon dioxide into the atmosphere.  The approximated amount of coal burnt from 1900 to 2012 is 297 Gt as estimated from a graph of world coal production, and data from the United States Energy Information Administration.  The amount of carbon in most coal that is burned is from bituminous (44.14% US) and sub-bituminous (47.48% US) coals that varies in carbon content from 45% - 86% for bituminous and 35% - 45% for sub-bituminous.  Other coals burned are anthracite at .16% US containing 86 - 97% carbon and lignite at 7.21% US containing 25 - 35% carbon.  Using the averaged percent from each type of coal burnt is [(44.14% x 65.5%) + (47.48% x 40%) + (.16% x 91.5%) + (7.21% x 30%)] x 297 = 149.1 Gt of carbon from coal was burned into the atmosphere from 1900 to 2012.
       The amount of natural gas burnt from 1970 to 2011 is around 62 Gt, which is calculated from 1 cubic meter of natural gas containing .75 kg of natural gas.  75% of natural gas is carbon; therefore, from 1970 to 2011, burning natural gas put 62 Gt x 75% = 46.5 Gt of carbon into the atmosphere.
       Adding the rough estimates of carbon burned from crude oil, coal and natural gas into the atmosphere from the dates used is about 288 Gt, which is more than the amount of extra carbon that was measured in the atmosphere at 252 Gt.  A separate graph claims that the amount of carbon emitted from fossil fuels into the atmosphere from 1751 to 2007 is 337 Gt.  Much of the difference between 337 and 252 Gt was reportedly absorbed into the oceans.

       The oceans are absorbing up to about half of the increasing carbon dioxide from the atmosphere, thus slowing down global warming.  As atmospheric warming warms the surface of the oceans, the oceans absorb less carbon dioxide; and, the oceans can release additional carbon dioxide from when the ocean waters were cooler and capable of absorbing a higher concentration of carbon dioxide.  When the rate of carbon dioxide that is absorbed into the oceans slows or returns to a balanced exchange with the atmosphere is unknown.
       Reportedly, Earth does not presently have enough "reducing agents" or "sinks" to quickly remove the extra carbon dioxide from the atmosphere.  The ocean water is one reducing agent for absorbing carbon dioxide, where the water in the oceans is part of the process that chemically transforms the absorbed carbon dioxide into carbonate sediments.

       Differences in water temperatures is one parameter that causes differences in water densities; and, gravity will pull the denser cooler water down around and past the less denser warmer water, while pushing the warmer water up toward a level of equal density with the warmer water.  This is one of the few processes that move ocean currents.  If the temperature and therefore the density differences are greater than the possibility is that ocean currents can move faster.  If global warming causes the ocean temperatures to be more uniform then the possibility is that ocean currents can slow down, especially if less cold water is melting from less Arctic ice.
       Since 1870, the rising or falling of ocean levels occurred on an averaged cycle every 2.5 years.  The cumulative long term change in ocean levels since 1870 was a continuous averaged rise to around 20 cm at present.

       If water temperatures at all depths in the oceans rise 2 degrees Celsius then the warmer water will expand, raising the ocean level by around 5 ft. or 1.5 meters.  Because ocean water is cooler at the North and South Poles and warmer around the equator, the ocean level around the equator is slightly higher than the level of the oceans at the Poles.  Gravity pulls the higher warmer water downhill along the surface of cooler denser water and toward the Poles, causing some ocean currents to flow from the equator toward the Poles.  The rotation of the Earth has a stronger effect than gravity on ocean currents.  The rotation of the Earth spins the currents as gyres around and back toward the equator.  If the cooler waters at the North and South Poles become warmer and closer in temperatures and levels to the waters around the equator then less water could be flowing in these currents.

       Whenever Earth's atmosphere rises 1 degree Celsius, the atmosphere absorbs 5.95 x 1021 Joules (kg x m2 / s2) of energy.  Joules is a unit of measurement for relating energy to work.  Transferring Joules into units of work for example, 5.95 x 1021 Joules that is a rise of 1 degree Celsius in 5 minutes can supply the work of 2.66 x 1016 mechanical horsepower (hp).  One mechanical horsepower is the work used to move 550 pounds of mass to a distance of one foot in one second (550 lbs. x ft. / s), or for one metric horsepower to move (or lift) 75 kg of mass to a distance of 1 meter in 1 second (75 kg x m / s) against an opposing force equal to one Earth gravity.  Air horsepower is sometimes measured as mechanical horsepower.  Earth has about 509 million km2 of surface area witch calculates from a rise of 1 degree Celsius in 5 minutes to an increased averaged supply for 5.2 x 107 mechanical horsepower above each square kilometer.  For example, the flow of increasing thermal infrared energy as kinetic energy into cooler air can increase the convection of air circulation and turbulence in an air mass and therefore can cause more violent weather, which is one reason why cooling air masses during sunsets weaken storms.

       Politicians, especially local politicians, are permitting the use of alternative energy sources.  For example, Earth reportedly radiates 100 million gigawatts of infrared heat energy into outer space.  Heat in the atmosphere can also be used to make electricity using for example a thermoelectric generator, in which heat flowing between two conductors at different temperatures causes charged particles to flow.  However, the efficiency of current thermoelectric generators is reportedly 5 to 8%, as compared to a water turbine for a hydroelectric plant that has an efficiency of near 90%.  Where to build hydroelectric plants and what and who to flood can be a political problem.  Also, denying potable and irrigational water rights for hydroelectric generation can also be a political problem.

       From an empirical observation, and ignoring long term positive and negative feedbacks in the behavior of the weather, past weather events that are no longer in effect are not a direct known cause for future weather.  A tropical cyclone that occurred last year is not a known cause for a tropical cyclone to occur next year.  However, past weather behavior has been a good indicator about the possible behavior of future weather.

       Many global warming numbers are averaged and do not indicate a constant global event.  A known past global warming is the Paleocene-Eocene thermal maximum (PETM) during which, according to geologists, extreme weather conditions and events were sporadic both time-wise and geographically, as is also claimed for today's global warming.  The average rise of worldwide temperature during the PETM was 5-8 degrees Celsius or 9-15 degrees Fahrenheit.  The first "pulse" of global warming during the PETM lasted a few thousand years.  The second "pulse" of global warming during the PETM lasted more than 200,000 years, after which the PETM atmospheric temperatures returned to the behavior of Eocene temperatures.  The pulses during the PETM were more gradual changes as compared to today's global warming that could have unknown consequences, such as the faster rise of carbonic acid in the waters that may not allow time for water-life to adapt.
       If the extra carbon dioxide being released into the atmosphere is stopped, scientists vary in their predictions about how long a current global warming weather will last from a few hundreds of years to a few thousands of years.  Perhaps, the best that we can do for the present is to measure the current and identify the cause.
       However, life reportedly survived very well during the PETM, perhaps, as imagined, with some adaptions and migrations.  Scientists predict that humans can survive a PETM-like event; but, many humans could experience more persistent hotter weather as uncomfortable, perhaps because humans evolved during relatively lower concentrations of carbon dioxide in the atmosphere than were present during the distant past; and, when humans walked out of Africa, many humans walked into cooler climates.

      The rise of carbonic acid (H2CO3) in the oceans is reportedly from the absorption of the rise of carbon dioxide in the atmosphere, either in the rain, land water or directly into the oceans (H2O + CO2 -> H2CO3).  Carbonic acid in the oceans is 'neutralized' from the weathering of magnesium oxide and calcium oxide flowing from rocks into the oceans.  The current rise of carbonic acid in the oceans is reportedly faster than the natural weathering of neutralizing agents into the oceans.  Carbonic acid lowers the pH in water.  The pH in the oceans has lowered from 8.25 from the beginning of the Industrial Age in 1751 to the averaged measurements of a little less than 8.08 in 2010, which is basic and non-acidic.  Acidic pH is less than 7.0 pH.  Because the pH scale is logarithmic, a change of 1 in the pH scale is a 10x concentration change.  Seasonal changes and the differences between local readings from other local readings of ocean pH have been larger than the averaged decrease in pH from 1751 to 2010.  Should politics wait to act when the oceans become too low in pH?

       C3 plant life (carbon dioxide is first made into carbon-3 compounds) reportedly begins to be stressed when the carbon dioxide in the atmosphere becomes less than 500 ppmv, which can decrease the biomass of a plant and crop yield.  When carbon dioxide concentration in the atmosphere decreases to 150 ppmv and less, C3 plants can begin to suffocate.  During the last ice ages, the amount carbon dioxide in the atmosphere was reportedly as low as 180 ppmv.  C3 plants are cool weather plants with an optimum growing range of 65-75 degrees Fahrenheit or 20-25 degrees Celsius.  C3 plants prefer moist soil.  Examples of C3 plants are wheat, rice, oats, apples, potatoes and woody trees.  C3 plants are about 85% of the plants.
       C4 plant life (carbon dioxide is first made into carbon-4 compounds) are more efficient than C3 plants for photosynthesizing, and can survive lower atmospheric carbon dioxide levels near 10 ppmv.  C4 plants are warm tropical plants that have an optimum growing range of 90-95 degrees Fahrenheit or 30-35 degrees Celsius, and can survive intense sunlight and arid conditions.  C4 plants as foraging plants can have less protein and more energy (sugar) than a C3 plant.  Examples of C4 plants are corn, sugarcane, summer annuals, tropical grasses, millet, papyrus and crabgrass.  C4 plants are 3% of the plants.
       CAM plants are the best at retaining water.  CAM plants can survive low atmospheric carbon dioxide levels near 5 ppmv, and can survive more extreme arid conditions than C4 plants.  Examples of CAM plants are cacti, pineapples and orchids.  CAM plants are 8% of the plants.
       Scientists are currently attempting to convert C3 rice into C4 rice.  Global warming has been predicted to cause more rain and more heat.  Perhaps C3, C4 and CAM plants can survive global warming, migrating by seed dispersion to different areas.

 

Modern plants grown during controlled experimental conditions for the same length of time.

 

       One measurement is that up to 30% of the sunlight on a plant is used for the plants metabolism.  Another source states that up to .5% of the total solar energy in most plants is stored as an energy source in the chemistry of plants.  Some of the solar energy in plants is converted into chemical energy to create chemical bonds of potential energy that are later released as energy for metabolism.  For example, warm blooded animals that eat plants release some of the earlier stored solar energy as heat to maintain a constant body temperature.  Are Carl Sagan and the existentialists correct? We are, "made of starstuff"; and, Earth happened to be at the right place for life to evolve.  Are we accidentals from nature; and, is abiotic nature not rational in that abiotic nature does not think about the now, the why and the how? Accidentals have a philosophical meaning that the parts have a presence that does not affect the true essence.  Therefore, a contradiction may exist about the rational as not intrinsic to nature.  The rational may need to decide what to do for the survival of nature.  The rational can supply, convey or sometimes arguably invent the reasons.

       Because extreme weather can be sporadic, the data for human deaths and the lost value of monetary property due to extreme storm damages had some sporadic behavior.  Special math may be needed to "see" or verify changes or trends in sporadic data, or to test for the statistically significant confidence, the randomness or the sampling error in the data.  Death rates from extreme weather in the US have been around 300 to 500 per year; and, the rate of worldwide deaths due to extreme weather has significantly decreased.  The lower worldwide death rate due to extreme weather is reportedly due to wider use of early communications about approaching extreme weather conditions, allowing people time to prepare, to cope with, and to adjust better to the extreme weather.
       The number of extreme weather events in the US is rising based on a fitted average to sporadic data (in math called curve fitting).  In the US, the approximated average of extreme weather events rose from 20 in the mid-1960s to near 80 around 2010.  Worldwide, the numbers for extreme weather events were increasing on an increasing rate from 23 during the 1950's to 354 during 2000-2008, which are the latest found published dates.
       The costs of extreme weather losses and damages in the US and worldwide are also rising, which include losses of homes, businesses, and fewer crops due to weather damage and shortened growing seasons.  The recent lower-cost years in the US have been rising slightly with sporadic peaks, which include increased political expenditures for repairing storm damages.  Worldwide the cost of extreme weather events in billions of US$ rose from around $50 in the late 1980's to around $140 by 2012, which appears to include emerging and spreading economies.

       Ending on a solemn note, some science predicts that all the carbon will be naturally removed from the atmosphere and buried underground after billions of years due to overlapping wind and water sedimentation, which includes dead animal and plant materials, and buried sedimentation under the ocean floor.  Buried carbon is recycled into the atmosphere usually through volcanism.  According to geological graphs, the amount of carbon dioxide in the atmosphere had been mostly decreasing from a little above 2000 ppmv since around the start of the Cretaceous Period at 146 million years ago, indicating that perhaps volcanism during this time period cannot recycle carbon from the ground into the atmosphere as carbon dioxide fast enough to sustain carbon-based life forms for the long term.  Geology claims that volcanism recycles carbon into the atmosphere after 100-200 million years in the ground.
       However, another prediction is that life on Earth will end after 600 million years from now after the increasing energy output from the Sun will erode by chemical weathering more minerals of the types that will subsequently increase the chemical absorption of more carbon dioxide from the atmosphere, and slowly, beginning with C3 plant life, suffocated plant life that breathes carbon dioxide; and, because plants exhale oxygen, the extinction of animal life that breathes oxygen will follow the extinction of plant life.  Also, the increasing intensity of sunlight will increase the weathering and burying rate of carbon-containing organics.  And, no life is expected to be surviving on the surface of Earth at 7.6 billion years from now when the Sun is at its maximum size of a red giant, swelling a little past the orbit of Earth.  The Sun does not have enough mass to nova.  The orbital friction on the Earth inside the Sun will supposedly spiral the Earth toward the center of the Sun, returning the elements of the Earth back into a type of star from which most of the elements were created.

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        For people who are not familiar, the house has solar shingles for generating electricity.

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        The obelisk on the left is the Washington Monument.  The obelisk on the right is an Egyptian monument.  Together the two obelisks represent a span of human history.

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        This post is an imaginative speculation about why the environment of outer space may not be safe for space travel at the speed of light speed or faster.

        The largest nearby obstacle to interstellar travel between the stars is the theorized existence of the Oort Cloud named after the astronomer named Jan Oort who theorized that the source of comets is from a cloud of icy objects.  The Oort Cloud may also contain a small number of asteroids and perhaps some dwarf planets.  The Oort Cloud may extend spherically in shape from beyond Pluto half way or more to the nearest star, Alpha Centauri, at 4.5 light years from the Sun.  The theory for the existence of the Oort Cloud is based partly on the fact that the outer edge of the orbits of some of the comets that orbit the Sun arrive from that far away in any direction.  The Oort Cloud is also theorized to extend to the distance of the Sun's gravitational influence.

 

Oort profile

Distance is drawn at 10x logarithmic scale.

 

Oort Cloud - 3D

 

        For example, Comet West has an orbital period around the Sun that calculated widely from 254,00 to 558,000 years because Comet West broke into four parts when orbiting near the Sun after the discovery in 1975.  The farthest orbit from the Sun of Comet West at aphelion was calculated at 70,000 AU (Astronomical Units, 1 AU is the average distance of the Earth from the Sun) or about 6.5 x 1012 miles or about 10.4 x 1012 km, which is about 1.1 light years or about 24% of the distance to Alpha Centauri.
        The amount of objects in the Oort Cloud was best estimated presently to be at least equal to the mass of five Earths, which indicates that the Oort Cloud is very sparse in the density of objects.  Other stars, including Alpha Centauri, may also have Oort Clouds that can present additional obstacles to space travel.  Therefore, if a straight line is drawn between the boundaries of the heliospheres of the Sun and a destination star then will this straight line never intersect an object at any time.  A possible solution could be to search for or to clear and maintain a clear path through the Oort Clouds in every direction of space travel, or to send space probes to map the locations and behaviors of the objects in the Oort Clouds, in concept creating space lanes.
        On April 17, 2000, NASA announced, "NASA's Cassini spacecraft, currently en route to Saturn, has successfully completed its passage through our solar system's asteroid belt between Mars and Jupiter.
        "This makes Cassini the seventh spacecraft ever to fly through the asteroid belt.  Before NASA's Pioneer 10 spacecraft successfully passed through the region in 1972, it was not known whether a spacecraft could survive the trip."
        The sizes of the asteroids range in size from about 600 km or 372 miles in length to the size of small particles or what the solar wind does not move out of the solar system.  The asteroid belt has one known dwarf planet named Ceres that has a length of 950 km or 590 miles.  However, the total mass of all the known asteroids is about 4% of the mass of Earth’s moon, indicating that the asteroid belt is also very sparse in density.  The exact number of asteroids in unknown.  Two known calculations for the average distance between asteroids that are larger than 1 km or about .62 miles in length are 2 million miles or about 3.8 million km, and 5 to 10 million miles or a little over 8 to 16 million km apart.
        A spaceship traveling through the asteroid belt reportedly has, "the chance of running into [an asteroid in the asteroid belt to be] almost vanishingly small - far less than one in one billion.  That means that if you want to actually come close enough to an asteroid to make detailed studies of it, you have to aim for a specific asteroid."

        Another possible problem for interstellar space travel is the existence of rogue planets in the Milky Way Galaxy that do not orbit a star and drift through space or may be orbiting the galactic core.  Some rogue planets were determined to be dwarf stars that are too small to start fusion.  One theory is that some dwarf stars may have “debris disks” that did not coalesce into planets.  Smaller rogue planets and their moons may exist; but, astronomers have no way presently to detect rogue planets that do not emit radiation, and are to small for detection through gravitational microlensing.  The estimates for the number of rogue planets in the Milky Way Galaxy vary from twice as many rogue planets as stars in the Milky Way Galaxy to 100,000 times as many rogue planets as stars in the Milky Way Galaxy.
        However, another estimate does not predict a reliable estimate for the number of rogue planets.  "Both gravitational microlensing and planetary transit observations indicate that there may be at least as many planets bound to stars as there are stars in the Milky Way, and microlensing measurements indicate that there are more rogue planets not bound to host stars than there are stars.  The Milky Way contains at least one planet per star, resulting in 100–400 billion planets, according to a January 2013 study of the five-planet star system Kepler-32 with the Kepler space observatory."  Also, a few people speculated that dark matter is not all exotic matter.
        Space between the stars is beginning to be read as less void than earlier thought, which could explain a reason why no one has presented any obvious evidence that aliens from other star systems have been on Earth.

        Because some current types of active sensors on Earth cannot radiate a detection signal that is faster than the speed of light, will a spaceship traveling faster than the speed of light perhaps travel faster than a sensor signal from the spaceship and not be able to detect an obstacle soon enough to avoid a collision with the obstacle?  The speed of light in a vacuum is constant at about 6.7 x 108 miles/hr or 10.8 x 108 km/hr; and, the direction and the speed of the source of the light does not affect the speed of the light.

        Another obstacle to space travel outside the solar system may be the amount of collisions with dust particles, or more commonly known as being sand blasted.  The solar wind clears the solar system of most dust.  However, the amount and density of dust beyond the Sun's heliosphere is unknown.  A heliosphere is a region of space that contains the solar wind of a star.  The heliospheres are not believed to be perfectly spherical.  The space outside the heliospheres is called interstellar space.
        When a dust particle collides with a spaceship some part of the kinetic energies of both the spaceship and the dust particle may convert into energies of heat from friction, sound as in the spaceship and dust particle vibrating from the collision, and into energies for deformation and separation of atoms and molecules, as in the dust particles being pulverized, and perhaps surface damage on the spaceship.
        Kinetic energy at collisions is a function of both mass and velocity at the instant of impact.  As mass or velocity or both increases then kinetic energy increases (K.E. = mass x velocity2 / 2 J (Joules = kg x m2/sec2)).  Therefore, if a spaceship increases speed to the speed of light then an increase in the rate of change of kinetic energy including more kinetic energy can change into the collision energies of heat, vibration, deformation and separation.  For example, an automobile traveling at 90 km/hr (55.9 miles/hr) and weighing 1300 kg (2866 lb.) has a kinetic energy of 4.1 x 105 J; and, a traveling spaceship at the speed of light that has a weight of 100,000 kg (220,462 lb.) on Earth has a kinetic energy of 4.5 x 1021 J.  A traveling spaceship at the speed of light colliding with dust particles through ten light years distance of space of about 5.87 x 1013 miles or 9.46 x 1013 km could be a concern.

        Space radiation can be harmful to space travelers.  At sufficient exposures, some types of radiation in outer space from stars that can be harmful to living tissue, and that can damage electronic machinery, are cosmic rays, charged particles, and the electromagnetic radiations of ultraviolet, x-ray and gamma rays.  Cosmic rays are subatomic particles that consist mostly of high energy protons.  Two sources of cosmic rays are solar flares and novas.  Cosmic rays can split DNA helixes, causing cell damage and illness.  Damage from sufficient radiation can quickly develop into acute radiation poisoning, or develop into chronic cancers.  Other effects of excessive space radiation on people after sufficient time are cataracts and sterility.  A magnetic field, as does the magnetic field of Earth, can protect people from cosmic rays.  At present, the health risks to space radiation are mostly untested; and, NASA reportedly limits astronauts' exposures to space radiation.
        For example, NASA shielded the Juno spacecraft for its mission to Jupiter.  Jupiter and the moons orbiting Jupiter radiate, "high energy particles ... [of] electrons, protons and ions[, and] Juno's brain would get fried on the very first pass near Jupiter."  "...  the principal investigator [and] engineers at Lockheed Martin Space Systems designed and built a special radiation vault made of titanium for a centralized electronics hub.  ...  engineers chose titanium because lead is too soft to withstand the vibrations of launch,  ...  This titanium box -- about the size of an SUV's trunk – encloses Juno's command and data handling box (the spacecraft's brain), power and data distribution unit (its heart) and about 20 other electronic assemblies.  ...  In addition, engineers wrapped copper and stainless steel braids like chain mail around wires connecting the electronics to other parts of the spacecraft.  ...  'The centralized radiation vault is the first of its kind,' [the principal investigator] said.  'We basically designed it from the ground up.'"

        Material and energy shielding placed around or ahead of the direction of travel of a spaceship can be imagined that would pulverize, deflect or absorb the impacts of the dust particles, and repel radiation, for example, using electrostatic repulsion of charged radiation, which is known in science fiction as matter and energy deflector shields.

        Traveling in a spaceship at or faster than the speed of light between the stars can feel like traveling in a motor vehicle at top speed on a flat barren terrain, that was earlier seen as barren, at night and without any headlights.