What exactly did the Mars rover Curiosity find on the red planet this week that had the chief scientist call the discovery "one for the history books."
"The biggest news that would come from this instrument is that they found organic molecules - organic matter," said Dr. Steve Ruff.
Ruff is a scientist at Arizona State University's Mars Space Flight facility who was heavily involved with the Mars exploration rovers which landed in January 2004.
He cautions people not to get too excited about the mysterious discovery.
"This could be something very interesting to scientists -- but chances are -- I guarantee you this is not evidence -- they haven't found evidence for life on Mars, I guarantee that."
The leading theory is that it detected some type of organic material -- potential indicators of life on Mars, but scientists want to make sure the results are valid before formally announcing them.
At ASU, there's a full sized model of the rover Curiosity and it's bigger than you might think -- it's about the size of a small sport utility vehicle. And its exploration on the red planet has only just begun.
That means we could be hearing about many more exciting discoveries, but Dr. Ruff believes scientists may wait a little longer in the future before leaking any information to reporters.