That leaves open the possibility that microorganisms once populated our planetary neighbour and still might.
Thomas Zurbuchen, NASA's associate administrator for the Science Mission Directorate, said that these discoveries should be viewed as Mars "telling us to stay the course and keep searching for evidence of life".
But now new results from NASA's Curiosity rover, including the discovery of ancient organic material, have revived the hope of doing just that.
Scientists agree more powerful spacecraft - and, ideally, rocks returned to Earth from Mars - are needed to prove whether tiny organisms like bacteria ever existed on the red planet. Curiosity reports that methane levels on Mars go up and down in a predictable cycle. "Biological, geological and meteoritic sources are all possible", they wrote.More news: Simona Halep sweeps aside Garbine Muguruza to reach French Open final
Launched in 2011, Curiosity was created to assess whether Mars ever had an environment able to support small life forms called microbes.
A smaller discovery of organic matter by NASA's Curiosity rover was announced in 2012. Then the scientists sifted through the results to figure out what might be genuine Martian organics. "And what it does, it gives us a key to unlocking the mysteries associated with Mars methane because now we have something to test our models and our understanding against".
Questions remain, however, as to how the organic material was formed. "While we don't know the source of the material, the fantastic consistency of the results makes me think we have a slam-dunk signal for organics on Mars", Eigenbrode said. The Viking Project was the first U.S. mission to safely land spacecraft on the Martian surface, as well as send back images. When they did experiments in their laboratory on Earth to bake samples containing those three types of organic carbon, the readings were all consistent with what was detected on Mars. What the study has done, though, is to propel the search for life on Mars higher up the list of global space exploration priorities - giving space agencies ammunition to argue for a coordinated programme of missions to explore the Red Planet. This is the most compelling evidence yet that this dry planet once held lakes filled with carbon-based compounds capable of sustaining life.
Just a couple of weeks ago, NASA announced that Curiosity had successfully drilled a hole using this new technique, and its handlers were excited that the rover could get back to work.
The rover was able to heat the samples to between 932 and 1508 degrees Fahrenheit and study the organic molecules released through gas analysis.More news: United Kingdom transport minister orders inquiry, compensation into train cancellations
The new results represent the longest systematic record of atmospheric methane, with measurements taken regularly over five years.
"That is a good place for life to have lived if it ever existed on Mars", she said.
"The idea that best fits our data is the idea of sub-surface storage", he said. For example, scientists want to know if it has "Mars quakes".
The press conference is set to kick off at 2 p.m. EDT today, and while NASA obviously hasn't revealed exactly what it has in store, there's a few things we do know.More news: Late night shows slam Trump over canceled Eagles White House visit