This Island Earth

Dr. Cal Meacham (Rex Reason), a noted scientist and jet pilot, is sent an unusual substitute for electronic condensers that he ordered (after nearly crashing a Lockheed T-33 Shooting Star during a cross-country flight, prior to being saved by a mysterious green glow). Instead, he receives instructions and parts to build a complex communication device called an interocitor. Although neither Meacham nor his assistant Joe Wilson (Robert Nichols) have heard of such a device, they immediately begin construction. When they finish, a mysterious man named Exeter (Jeff Morrow) appears on the device's screen and tells Meacham he has passed the test. His ability to build the interocitor demonstrates that he is gifted enough to be part of Exeter's special research project.
Intrigued, Meacham is picked up at the airport by an unmanned, computer-controlled Douglas DC-3 aircraft with no windows. Landing in a remote area of Georgia, he finds an international group of top-flight scientists already present, including an old flame, Dr. Ruth Adams (Faith Domergue). Cal is confused by Ruth's failure to recognize him and suspicious of Brack (Lance Fuller) and other odd-looking men leading the project.
Cal and Ruth flee with a third scientist, Steve Carlson (Russell Johnson), but their car is attacked and Carlson is killed. When they take off in a Stinson 108 light aircraft, Cal and Ruth watch as the facility and all its inhabitants are incinerated. Then their aircraft is drawn up by a bright beam into a flying saucer. They learn that Exeter and his men are from the planet Metaluna, having come to Earth seeking uranium deposits as well as scientists to help defend their planet in a war against the Zagons. Exeter takes the Earthlings back to his world, sealing them in protective tubes to offset pressure differences between planets.
They land safely, but the Metalunans are under attack by Zagon starships guiding meteors as weapons against them. The planet is under bombardment and falling quickly to the enemy. Metaluna's leader, the Monitor (Douglas Spencer), reveals that the Metalunans intend to relocate to Earth, then insists that Meacham and Adams be subjected to a Thought Transference Chamber in order to subjugate their free will. Exeter believes this is immoral and misguided. Before the couple can be sent into the brain-reprogramming device, Exeter decides to help them escape.
Exeter is badly injured by a Mutant while he, Cal and Ruth flee from Metaluna in the saucer, with the planet's protective "ionization layer" becoming totally ineffective. Under the Zagon bombardment, Metaluna heats up and turns into a lifeless "radioactive sun." The Mutant has also boarded the saucer and attacks Ruth, but dies as a result of pressure differences on the journey back to Earth.
As they enter Earth's atmosphere, Exeter sends Cal and Ruth on their way in their aircraft, declining an invitation to join them. Exeter is dying and the ship's energy is nearly depleted. The saucer flies out over the ocean and rapidly accelerates until it is enclosed in a fireball, crashes into the water and explodes.

Question: Who are under attack by Zagon starships?
Answer: Metalunans; Metalunans