It may sound like a plot of a sci-fi movie, but aliens might attack Earth to destroy humanity for the greater good of the rest of the Milky Way galaxy.

According to a study, titled Would Contact with Extraterrestrials Benefit or Harm Humanity? A Scenario Analysis, conducted by NASA and Pennsylvania State University scientists, our planet-polluting ways are not only threatening Earth, but also the intergalactic ecosystem, a reason which might offend extraterrestrial beings.

The team of scientists produced a list of plausible scenarios in which aliens could attack the Earth. With activities like destructing the ecosystem and emitting greenhouse gases into the atmosphere, distant aliens, who are possibly watching the changes in Earth's atmosphere, might consider us as a civilization growing out of control. Aliens might be worried that we might inflict the damage done to our plane on others, and to save the galaxy from the growing threat, they might attack Earth to exterminate us, scientists said.

These scenarios give us reason to limit our growth and reduce our impact on global ecosystems. It would be particularly important for us to limit our emissions of greenhouse gases, since atmospheric composition can be observed from other planets, the authors of the study wrote.

 Humanity may just now be entering the period in which its rapid civilizational expansion could be detected by an ETI (extraterrestrial intelligence) because our expansion is changing the composition of the Earth's atmosphere, via greenhouse gas emissions, the study said. A preemptive strike would be particularly likely in the early phases of our expansion because a civilization may become increasingly difficult to destroy as it continues to expand.

The authors of the study suggested that ETI might be an aggressive race, and therefore we shouldn't transmit too much information into space, Discovery News reported.

In particular, scientists warned against broadcasting information related to biological make-up. Scientists fear that this kind of information may help ETI to manufacture weapons that target humans.

However, the study also suggested that the encounter with aliens could turn in our favor also. As we continue the search for extraterrestrials into the future, perhaps our thinking about the different modes of contact will help human civilization to avoid collapse and achieve long-term survival, the study suggested.