What doomed the Titanic is well known, at least in outline. On a moonless night in the North Atlantic, the liner hit an iceberg and disaster ensued, with 1,500 lives lost.

Hundreds of books, studies and official inquiries have addressed the deeper question of how a ship that was so costly and so well built — a ship declared to be unsinkable — could have ended so terribly. The theories vary widely, placing the blame on everything from inept sailors to flawed rivets.

Now, a century after the liner went down in the early hours of April 15, 1912, two new studies argue that rare states of nature played major roles in the catastrophe.

The first says Earth’s nearness to the Moon and the Sun — a proximity not matched in more than 1,000 years — resulted in record tides that help explain why the Titanic encountered so much ice, including the fatal iceberg....