Lada Terra is a major landmass near the south pole of Venus which is centered at 60°S and 20°E and has a diameter of . It is defined by the International Astronomical Union as one of the three "major landmasses," or terrae, of Venus. The term "landmass" is not analogous to the landmass on Earth, as there are no apparent oceans on Venus. The term here applies to a substantial portion of land that lies above the average planetary radius, and corresponds to highlands.
The broad region of Lada Terra contains massive coronae, rift zones, and volcanic plains 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.
Lada Terra is named after Lada, the Slavic goddess of love.
Features
Lada Terra is one of eight distinct regions on the surface of Venus. Ishtar Terra and Aphrodite Terra are the other significant terrae of the planet, located near the northern polar region and the equator, respectively.
Lada Terra has a diameter of . and covers most of the south pole region on Venus. The region consists of heavily deformed terrains indicating crustal deformation processes affecting the area in the past. The lowlands are much smoother terrain with very little deformation, which scientists postulate to be relatively young lava flow remnants. The most prominent region is the midlands, where gently sloping topography is disrupted by faults, fractures, and corona, making this area the most complex and studied region in Lada Terra.
Lada Rise
The western portion of Lada Terra contains a large dome-shaped structure about across termed, "the Lada Rise," which is the main highland of the region. It reaches an elevation of about and is dominated by one of the most massive corona in the solar system, the Quetzalpetlatl Corona, as well as two massive rift zones surround and partially intersect the rise. The high rises of Venus generally fall into the corona-dominated or rift-dominated categories, but the Lada Rise is unique in that it contains both of these features in relatively equal amounts. In 2007, data retrieved from the Venus Express mission using the Visible and Infrared Thermal Imaging Spectrometer revealed high emissivity anomalies which is interpreted by many scientists to be a hotspot analogous to the Hawaii hot spot on Earth. This, along with the positive gravity anomaly observed, implies a recently active region. Further evidence is observed in the Boala Corona (which lies inside, and postdates the Quetzalpetlatl Corona), where the grabens formed in the depression of the Corona are interpreted to be surface manifestations of terrestrial dikes. The mantle upwelling associated with hot spot tectonism appears to be the dominant process which formed and evolved the Lada Rise.
Alpha-Lada Extensional Belt
A rift about long and wide, named the Alpha-Lada extensional belt, spans the northwestern edge of Lada Terra separating the relatively high lands of Lada Terra from the broad lowlands of Lavinia Planitia. The Lavinia Planitia basin is suspected to be an area of mantle downwelling, where there are less thermal stresses on the lithosphere. Because the nearby Lada Rise is speculated to be an area of mantle upwelling, models predict this could create a zone of weakness between these two convection cells which stretches the lithosphere, thus creating the rift zone. Associated with the rift zone are large lava flow fields and corona. The bedding relationships between the rift zone and these volcanic structures indicate they were formed about the same time, which many interpret as lava finding a preferential route to the surface through these newly formed fractures.
Ammavuro–Quetzalpetlatl Extensional Belt
A second rift, named the Ammavuro–Quetzalpetlatl extensional belt, is a long and wide rift which lies in the northeast region of Lada Terra. These two massive rifts intersect in the northern region of Lada Terra, and the observed deformation of the two extensional belts seems to have occurred at the same time, although the larger Alpha-Lada rift most likely continued to be deformed for a longer period.