They mean the same thing, although "to date" is more literary. In everyday usage, you would normally say "so far".

From the free online dictionary: "so far" means 1. Up to the present moment: "So far there's been no word from them." 2. To a limited extent: "You can go only so far on five dollars." "to date" Until now: "To date, only half of those invited have responded." So in these instances yes, they have the same meaning. So long as they are used as a time references then "to date" and "so far" would mean the same. I may be wrong, but it seems like "to date" works better at the beginning of the sentence because "to date" can also mean "to court someone romantically." (Doing things with your girlfriend/boyfriend/spouse) "She is going to date that boy." "He wants to date her too." And so reading the first part of the sentence "They are the best candidates found to date" seems like they are looking for a candidate as a romantic partner and it's not until "for habitable planets" that you realize it means something different and a person might get confused. So it would be better to say "To date, they are the best candidates found for habitable planets." I have definitely seen "found to date" in the middle of sentences though so perhaps it just depends. Feel free to post for a response if you are ever confused about which one to use.

sure! Got it! Bre Thanks! lol

They are not the same thing, actually. "To date" is similar to "at the moment" - which implies that something is known to be true right now, like a fact; it is like waiting for something to discredit it or make it no longer the known fact. EX: The school teacher has taught in 2 public schools and 1 private school, to date. (Yes, "to date" can be used ANYWHERE in a sentence - as an adverbial.) However, "so far" is used for on-going actions, thoughts, ideas; think of it like saying that you know something now but expect a change soon. EX: We're baking cookies for the show tonight and, so far, we have 12 cookies done; in 2 more minutes, we'll have 24. Hope this helps!