Phrases like "while" and "even though" belong to a category called subordinating conjunctions, which we use to create adverb clauses. Adverb clauses are used to add information about "how," "when," "why," and other adverbial characteristics to a sentence. You've done this here: While/even though astronomers have so far found no Earth-like planets, this does not mean that there are none. (= this is showing a natural contrast between one reality, which is that the scientists haven't found Earth-like planets, and a surprising or "conceded" reality or outcome, which is that there may still be some) We as native speakers usually put these subordinating conjunctions into different categories of meaning based on our understanding of them. They can add the following information to a sentence: 1. time 2. concession (as shown above) 3. contrast (also called "opposition" or "direct contrast") - used to contrast two completely opposing facts or characteristics 4. cause and effect 5. reason/result 6. condition "While" can belong to the time or contrast categories, as in: While John waited in the car, we bought the scuba gear. (time) While I love chocolate, my sister hates it. (contrast) The example sentence showing contrast is the one that most closely resembles your use of "while" above, which very technically speaking means your choice of "while" is incorrect. "Even though" belongs to the concession category, as in: Even though I love chocolate, I eat it all the time. (concession) Answer: If we are splitting hairs here, I believe that "even though" is your best choice. The problem here is that many of us as native speakers have used "while" as you did above, as a subordinating conjunction of concession and not contrast, which blurs the distinction between the two (they are similar fundamentally, as both show a discordance). Also, this may depend to a point on your interpretation of the sentence. If you strictly believe that the fact that there are planets out there, it could be argued that the two clauses (the adverb and the independent) in the sentence are in direct contrast with each other (dealing with existence versus non-existence) and therefore "while" is possible. My opinion is that this is a poor choice of sentence to illustrate the difference between subordinating clauses. A better choice of examples would be: (1) __ Zeke is a huge fan of pie-eating contests, his wife can't stand them. The clear answer here is "while," as we are talking about a direct contrast in tastes. (2) We're coming to your bachelorette party __we believe they are antiquated. Here "even though" is really the best choice, as we're conceding a surprising outcome vis-a-vis the reality of the situation. Hope this helps!! KE. 本文来源：https://www.wddqw.com/doc/884705649e314332396893cd.html