Do responses get cached even if there is no cache-control header?

Question

I'm trying to understand why this resource is being cached even though there is no cache-control header returned in the response.

How is it possible that this resource is being cached?

Answer 1

This is addressed in Section 4.2.2 of RFC 7234:

Since origin servers do not always provide explicit expiration times, a cache MAY assign a heuristic expiration time when an explicit time is not specified, employing algorithms that use other header field values (such as the Last-Modified time) to estimate a plausible expiration time.

And, indeed, browsers do this.