History of Solar System formation and evolution hypotheses with Uranus having a 98° tilt. The Moon being relatively large with respect to the Earth and other moons which are in irregular orbits with respect to their planet is yet another issue. It is now believed these observations are explained by events which happened after the initial formation of the Solar System. Attempts to isolate the physical source of the Sun's energy, and thus determine when and how it might ultimately run out, began in the 19th century. At that time, the prevailing scientific view on the source of the Sun's heat was that it was generated by gravitational
Lada Terra as well as many other features that scientists use to attempt to piece together the history of this complex planet. The distinctive cross-cutting relationships found in the bedding of Lada Terra have been important in realizing relative ages of the extensional belts and coronae, as well as the complex tesserae features present planet-wide. In 1990 the Venus Radar Mapper revealed the largest outflow channel system on the planet located in the northern region of Lada Terra. Although Lada Terra is generally considered a highland of Venus, the topography is much lower-lying than its northern counterparts Ishtar Terra and Aphrodite Terra.