There can only be a number of reasons why extraterrestrials may visit our planet, or it may be possible they are already inhabiting our planet, living in secret bases at remote parts of the world or even in the deepest parts of the Ocean which has yet to be fully explored. With so many types of UFOs being seen, and even alien beings, the evidence of more than one type of alien is overwhelming.  The fact is, if some of them were hostile, we would have faced certain doom since alien technology is obviously much more advanced than ours.  Why are they here?

Theories on why Extraterrestrials may be visiting our Planet

1. Genetic Manipulation
Though this can be one of the most misunderstood reasons, the fact is human DNA can be very valuable, and one of the best laboratories to gather new specimens is planet Earth itself.  Extraterrestrials are just like us in a way if this is their agenda.  Think about it, the human race is constantly trying to better itself through newer technologies and through genetic manipulation.  Sounds far fetched? No, the fact is scientists are already changing the very DNA that humans have to create humans with certain features, like eye or hair color, and things like intelligence are being changed.  Parents wanting offspring with certain attributes are within their grasp now with the technology we have today, along with stem cell research.  So its not odd to think Extraterrestrials are doing the same, Possibly gathering the best human specimens they can find with the attributes that are "perfect" and merging their own for a disease/virus resistant, intelligent super race.  But to do this, they would have grow countless generations of humans waiting for evolution to take place for the best specimens.  Fact is, Humans are evolving, constantly breaking records, getting smarter, faster, and more resistant to diseases and viruses.  These genes are valuable since they provide the "best" attributes possible for a species.  They could very well be breeding with us just so they could take over slowly without any of us knowing, or maybe they are using our DNA to create a hybrid that looks exactly a human (which is often reported in many abduction cases).  So, why grow humans when there is virtually a limitless supply on Earth itself.  Whether they are harvesting us or not, its obvious they don't want to harm us, yet at least.  Which brings us to the next possible alien agenda.

2. Extraterrestrials can't control us yet
Humans have a soul essence that gives us the ability to live beyond the physical shell of our bodies, which could be a threat to their species.  Human spirituality could be one of the most powerful things the human race has to protect us, a soul essence is something aliens just don't seem to have.  Although aliens have very strong minds (esp, psychic powers, telekinesis), but do they have a spirit?  When they pass, where do they go, could they possibly have a demonic origin/purpose?  The human spirit can be a powerful thing to have, which is one reason they could be cross breeding with us, or maybe...feeding off our spirits.  

3. Extraterrestrials feed off our emotions
With reports of abductions, almost all the aliens are characterized as being emotionless or like worker bees.  Like bees that eat/store honey to survive,  one theory is the aliens feed off human emotion such as pain, fear, sexual arousal to satisfy them.  They could also be feeding on body parts as well, could they just be doing this to have a taste of what its like to be human?  Emotions can be very powerful things to the mind, and aliens may feed on emotions for survival, study, or just pleasure.  Not all alien races can be emotionless and evil, there could be a race watching over us.

4. Extraterrestrials are here to protect us
Whether it be for our own good, or for their own benefit and gain, there has been some evidence of UFOs acting against military or even against each other.  There have been reports of entire U.S. Nuclear facilities and missiles being deactivated in by UFOs, and even space shuttles.  Could it be to protect themselves, or us instead?  Because there are so many types of UFOs, its hard not to think that there are certain species of aliens protecting us, not all of them can be good or bad.  What would happen if we were to go into a nuclear war with ourselves, everyone and everything would be obliterated, and we would in turn become useless, could they be protecting us from ourselves in turn for more harvesting?  Why would the government/military scramble fighter jets after a UFO, though if they are protecting us unless they suspect something else instead.  The fact is the government wants power over airspace, and to secure their "power" they need to either recover alien technology and study it for better weapons by shooting them down or through "deals" with certain races.  The country that is able to capture, study, and create alien-based technology can have a lot of power in the world.  This brings us to some compelling evidence of conspiracy in the government.  

5. Curiosity
One of the many reasons put forward as to why we are being visited is that it is just a simple case of curiosity. In a similar way as the first explorers of our planet discovered new lands and new civilizations (e.g. the Incas, Mayans and Indians), alien lifeforms who stumble across us in their exploration of space may find us an intriguing and interesting species in our own right.
This would tend to explain why there has been so many sightings of various types of craft. Alien races, once they had learned of our existence, would want to come and observe us in a similar way that other civilizations on Earth were observed. However, this simple curiosity theory does not explain some of the more 'disturbing' aspects of Alien encounters such as abduction experiments and mutilations. This problem can however be catered for by the fact that we are probably being visited by more than one race of alien civilization, each having their own agenda.Also, once an alien civilization had discovered us maybe various groups within that civilization started visiting us. A group of alien scientists would obviously have a different agenda to a group of alien 'tourists' or even alien 'joyriders'.

6. Mining Minerals
Another popular theory put forward is that the Earth may well contain certain minerals which are not present on the alien planet. There has been some evidence of this in various reports and claims of 'underground' alien bases and sightings of craft seemingly taking samples of earth, planet and even other lifeforms. However I feel that this is probably the weakest of all the theories as surely we would notice any great reduction in any of our more common minerals. However it may be the case that the aliens only require very sample amounts of a particular substance for their purposes.

- By Nick Long