Pouring 1 billion liters of water on Mars would have several significant effects on the planet, although it is important to note that this hypothetical scenario would require a colossal amount of water that is not currently available on Mars. Nevertheless, let's consider the potential consequences:
Temporary liquid water: The water would initially exist as liquid due to the low atmospheric pressure and low temperatures on Mars. However, without ongoing atmospheric pressure maintenance and the absence of a dense atmosphere, the water would quickly evaporate or freeze.
Atmosphere alteration: The vaporization of such a massive amount of water could temporarily increase the atmospheric humidity. The increased water vapor might contribute to a transient rise in atmospheric pressure, although this effect would likely be short-lived as the water molecules would eventually dissociate and escape into space due to Mars' limited gravity.
Albedo changes: Water on the surface of Mars would change the reflectivity, or albedo, of the planet. The presence of water ice or liquid water could cause more sunlight to be reflected back into space, potentially affecting the climate and energy balance of the planet.
Geological processes: The sudden introduction of a large amount of water could trigger localized geological changes. The water could erode the surface, leading to the formation of new channels, valleys, or impact craters. It could also seep into the ground and interact with subsurface minerals, potentially altering the composition of the Martian soil.
Habitability considerations: While liquid water is a crucial ingredient for life as we know it, the introduction of water alone would not make Mars habitable for complex organisms. Mars lacks a thick atmosphere and a magnetosphere to shield against harmful solar radiation. The surface conditions, such as low temperatures and thin atmosphere, are still inhospitable to life as we understand it.
It's worth noting that the long-term sustainability of liquid water on Mars would depend on several factors, such as temperature, pressure, and the availability of ongoing water sources. A sustainable presence of liquid water would likely require significant alterations to the Martian environment, such as terraforming or establishing a controlled and contained habitat.
Overall, while pouring a billion liters of water on Mars would have notable effects, the challenges of making Mars habitable extend beyond simply introducing water to the planet's surface.