The vastness of space and the puzzling nature of the cosmic objects that occupy it provides no shortage of material for astronomers to ponder.
To round up some of the most enduring mysteries in the field of astronomy, the journal Science enlisted help from science writers and members of the Board of Reviewing Editors to choose eight puzzling questions being asked by leading astronomers today.
As Robert Coontz, deputy news editor at Science, writes in his introduction to the series, the participants decided that, "true mysteries must have staying power," rather than being questions that might be resolved by research in the near future. In fact, while some of the topics discussed may one day be solved through astronomical observations, others may never be solved, he added.
In no particular order, here are eight of the most compelling mysteries of astronomy, as presented by the journal Science: