Will space debris ever become so abundant that space flight will become economically or logistically impossible?

In 2007 China successfully destroyed one of their own aging polar-orbiting weather satellites just so they could prove they could. Debris from the destroyed satellite collided with Russia’s BLITS satellite in 2013, resulting in thousands of pieces of new space debris and is considered the most prolific and severe fragmentation in the course of five decades of space operations. Thanks China.

Now all we need is for North Korea to get their hands on that technology.

Still, space is a pretty big place and the pieces of junk are known and plotted so we can stay away from them, including little nuts and bolts travelling many times faster than a bullet.

Ever see the movie Gravity? Flaws in the science, but it was all about space junk taking out everything up there.
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Are there objects in the solar system revolving around the sun that do not lie on the planetary plane? How would we know, except in the rare coincident that our paths intersect?

Yes, of course. One example rarely considered is the Oort Cloud, pictured below. The Oort cloud is thought to contain objects that occasionally become dislodged to become long-period comets. It surrounds us like a giant sphere, well beyond Neptune and any known planets.

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How do I explain how we can see the moon during the day to my teacher?

How can you explain how we see the moon during the day to your teacher? The moon is visible in daytime because the apparent brightness (m) of reflected sunlight off the surface of the moon essentially exceeds the brightness of the blue sky, unlike the stars. That’s your simple answer.

Apparent brightness is the brightness we perceive after light passes through our atmosphere to our eyes.

Our sun and objects that reflect our sun’s rays are very bright in comparison with their surroundings. Any magnitude below -4 cannot be seen in daytime (the lower the number the brighter the object). Our sun is -26 and the full moon is -12.5, well above the magnitude necessary to see in daytime, -4. The brightest star has a magnitude of -1, dimmer than the required -4 magnitude required to be seen in daylight. All other stars are dimmer still.

Make sense?

Within 10 years, how can we live in space for approximately 1 year and on Mars for about 2 years, which is the time needed to catch the bus back home, which will take another approximately 1 year back home?

If you are wanting to think outside the box you might want to look at the Chinese space plans to launch a manned mission to Mars by 2020, at least according to CNN. If true, China will be the first ones to put footprints on Mars.