Question: In the DC Comics universe, why didn’t the Green Lantern Corps do something about the destruction of Krypton?
Short Answer: They did.
The full answer to this question is an interesting window into comic book publishing history and the practice of retconing after mergers during the Silver Age of comic books.
The first Green Lantern, Alan Scott, was created by a company separate from DC (All-American Publications, Inc.) in All -American Comics #16 (Jul 1940).* Superman was originally published by National Allied Publications, Inc. in Action Comics #1 (Jun 1938) and the destruction of Krypton was first depicted in Superman #1 (Summer 1939).
National acquired All-American in 1944 and Detective Comics, Inc. acquired National in 1946,* thus creating the foundations of the DC Universe. The first official merging of their characters after acquisition was in All Star Comics #36 (Aug 1947).** However, the Green Lantern Corps and the Guardians of the Universe (who formed and control the GL Corps) had not been conceived of at this point. Green Lantern’s solo title was eventually canceled after issue #38 (May-Jun 1949) and he last appeared in All Star Comics #57 (Mar 1951).
The Green Lantern Corps we know of today did not exist until the introduction of Hal Jordan as the new Green Lantern in Showcase #22 (Sep 1959). The Guardians of the Universe were not introduced until a year later in Green Lantern Vol. 2 #1 (Jul 1960) – a full 21 years after the first mention of Krypton’s destruction in 1939. This means that some serious reconing was required to explain why the Corps and the Guardians would allow Krypton to be destroyed. DC finally addressed this 12 years later in Superman #257 (Oct 1972).
Tomar-Re, Green Lantern of Sector 2813 (where Krypton is located), tried to save Krypton when he learned about it’s impending doom. However, the Guardians of the Universe had a sort of “prime directive” rule that prevented direct interference when a civilization’s collapse was entirely self-inflicted (as opposed to a single rogue group or outside threat). Thus, Tomar-Re was forced to work entirely in secret. It may have further complicated matters that Kryptonian society was extremely xenophobic.
Tomar-Re scoured the galaxy in search of enough of a rare compound called stellarium to stabilize Krypton’s tectonic plates. However, while he was en route to Krypton to secretly employ the stellarium solution, a yellow solar flare blinded him and caused him to lose his grip on the stellarium, flinging it into space. While temporarily blinded, he recovered what scattered stellarium he could, but the delay caused him to arrive at Krypton in her last moments. The destruction of Krypton was the first thing he saw with his slowly recovering sight.
On a side note, prior to the destruction of Krypton, the Guardians of the Universe had planned to recruit Kal-El to the corps (after having previously considered both his mother, Lara, and father, Jor-El they figured their offspring was certain to be Corps material). Krypton’s destruction prior to Kal-El coming into adulthood interfered with their plan. Later, after watching Kal-El grow up to become Superman on Earth the Guardians concluded this made him more than enough of a hero and he did not need a power ring or Corps membership to be useful.
To make matters more interesting, according to Superman Vol. 2 #147 (Aug 1999) Jor-El had considered sending Kal-El to Oa (probability scenario three-one-one) but ultimately chose Earth instead because he disliked the Guardians’ isolation (being too similar to Kryptonians’ isolation, a cycle he was trying to break).
* It is interesting to note that in addition to Green Lantern, many characters taken for granted as DC Comics characters were originally created by All-American Publications including Flash, Hawkman, and Red Tornado. They formed the core of the Justice Society of America in All Star Comics #3 (Winter 1940–41) along with a few characters borrowed from National,*** nearly 20 years before the first appearance of the Justice League of America in The Brave and the Bold #28 (Mar 1960). Other notable All-American characters (and occasional JSA members) are Black Canary, Atom, Mr. Terrific, Wildcat, and Doctor Mid-Nite. All-American also introduced the world to Wonder Woman.****
** Detective Comics, Inc. (est. 1937) and National Allied Publications Inc. (est. 1934) were founded by the same person, Major Malcolm Wheeler-Nicholson. He was forced out of both companies shortly after founding each. The two companies officially merged on September 30, 1946 to form National Comics Publications. Although they were branded as DC Comics much earlier (some report that the brand Superman-DC first appeared in 1940) they did not officially change their name to DC Comics, Inc. until 1977.
*** Superman and Batman, while still owned by separate companies, appeared as guest stars in All-Star Comics #7 (Oct 1941) and #8 (Dec 1941) as “honorary members” of the Justice Society of America and were mentioned in issue #11 (Apr 1942). They would not officially appear again until All-Star Comics #36 (Aug 1947). The JSA also borrowed Hourman, Spectre, Doctor Fate, Sandman and Johnny Thunder from National and those characters appeared regularly.
**** A fun piece of trivia about the holy trinity of Superman, Batman, and Wonder Woman is that they were each originally properties of the three core publishing companies that came together to eventually form DC Comics, Inc. Superman was introduced by National Allied Publications, Inc. in 1938, Batman was introduced by Detective Comics, Inc. in 1939 and Wonder Woman was introduced by All American Publications, Inc. in 1941.