Sol Marta (ソル・マルタ, Soru Maruta) is an artificial satellite stationed beyond the atmosphere, at even a higher altitude than the First Tower's Rinkernator. Because of the extreme altitude where it's stationed, the people can't reach it through conventional methods. It's also called the Heavens because being the place where the Goddess lives,
Its name means Motherly Light in Hymmnos, and its purpose is constantly emitting Dynamic D-Waves to preserve the structures that were created through it: the Drafters and the Second Tower. However, Sol Marta itself is no more than the system for doing so, while the one that actually crafted and sings the Song that created and maintains these structures is a Reyvateil Origin. This why said Singer, Frelia, was called the Goddess by the people of Metafalss. Frelia was originally sent to this region so she, together with Sol Marta, could create the continent of Metafalica. For more details, please read the History of Metafalss article.
Also, it has the secondary function of being a relay station for the First Tower of Ar tonelico, allowing it to expand its broadcast range even further, and allowing the Reyvateils from Sol Ciel to travel to Metafalss without any problems.
The Ar Ciel SphereEdit
This is the characteristic glass sphere chamber that is located in the heart of Sol Marta. This enormous glass sphere is called the Ar Ciel Sphere, and it's the place where Frelia sang and dance to, little by little, create the Tower. If you looked down from this area, the blue shine of the planet of Ar Ciel would be reflected in your eyes, while if you looked up, you would be able to see an entire sky filled with stars. This area is essentially empty, with the exception of a big crossroad without rails, and that was because this space was intended only for Frelia's singing. And well, given that the Ar Ciel Sphere is taken as part of Sol Marta when looked from the outside, this is the reason why it has the same shape as a Heart of the Land. From that, you would be able to guess that the Ar Ciel Sphere is the Heart of the Land of Sol Marta.
The Control of Sol MartaEdit
Sol Marta wasn't built by the people of Metafalss. Because of that, its administration and management was on the hands of the Elemians, the residents of the First Tower. And if an emergency occurred, they had another way of keeping Sol Marta under their control, in the form of the Maintenance Droid, Raki.
With the exception of the maintenance and administration of the systems, she was in charge of the provision and suspension of the flow of Dynamic D-Waves of Sol Marta, though she didn't have complete authority to interrupt said flow based on her own judgment, and her decisions actually were always left to the information she received from the First Tower.
The information that Raki received from the First Tower were divided in two categories: the first one was information that the humans sent her about specific events, and in normal conditions, while the other was information sent from an automatic manual, which was only sent in emergency situations. According to the instructions featured in the later one, which Raki could receive from any of the two Towers, if anything happened to Frelia, she would automatically counterattack the cause, and she also is able to lower the Symphonic Power output of Sol Marta.
The Greenness that Sprouted in Sol Marta: the Tree of MartaEdit
Because of the happening of the Grathnode Inferia on 3040 AD, the communications with the First Tower were permanently cut off, and Frelia, in her complete isolation, decided to enter into a Cold Sleep Pod. Said Pod was located in her room inside Sol Marta, farther deep inside than the Ar Ciel Sphere, and around it, with the passage of the long years and months, the plants began sprouting. In just a flash, they began overflowing around the Pod, and in a short time, one of them became a gigantic World Tree, which would be later on known as the Tree of Marta.
The Tree of Marta had as its heart the Pod where Frelia was sleeping, from where it began growing, and no one knew where it would stop, and after some time, it ended created a forest that was around five times the size of Sol Marta. This marvelous grassland that could be seen be looking up to the space was called Soragahara/Celestial Plains*. To be more exact, the green field that extended in front of Croix's group while they were climbing up the Tower to the Heavens in the current times was the Celestial Plains.
*The name is a pun on 高天原/Takamagahara (High Plains of the Heavens), which is the dwelling place of the Kami (Gods) in Japanese Mythology.