Final answer:
The 2015 discovery of water on Mars indicated the existence of liquid water and habitable environments in Mars' ancient past, despite current conditions where liquid water isn’t stable due to low surface temperatures and pressure. The presence of water in Mars' history enhances the possibility of past life on the planet and guides current scientific exploration to 'follow the water' in search of life forms.
Step-by-step explanation:
In 2015, the discovery about the presence of water on Mars was particularly significant because it proved that liquid water must exist in some form on Mars. This result was not surprising given the evidence of flowing water in Mars’ past and suggests the former existence of habitable environments. Mars' rover Curiosity confirmed the existence of habitable environments by analyzing mudstone and finding conditions that could have supported life in the ancient past. This finding opens up the possibility that Mars may have been home to oceans and perhaps even life on its surface.
Although the Viking landers in 1976 found no organic molecules or evidence of biological activity, later missions have reported water in the form of ice under Mars' surface and water vapor in its atmosphere. Current rovers continue to explore evidence of extensive surface water in the past on Mars. Despite the inhospitable conditions on Mars today, the 2015 discovery indicates potential for life in its distant past when liquid water was more abundant and conditions were more Earth-like.