Assignment:
Create an outline of your proposed paper.
Remember the topic is Methane and the possibility of life on Mars and Titan. You can limit the topic to, say, just one place, one aspect of methane, or the possibility of life on Mars or of life on Titan.
Use Roman Numbers (I,II,III,IV,...) to indicate the paragraphs/topics.
The first paragraph will be the Introduction. For this part of the outline you want to create a sentence that is the one main idea you want your reader to come away with.
The next 3-5 paragraphs will be evidence to support your main idea. Give each paragraph a title (after the Roman Numeral) and then a numbered list of facts related to that title.
The last paragraph is the conclusion. It's numbered list is key ideas that support your take-away idea from the introduction.