Mars Images Reveal Evidence of Ancient Lakes

Matt_dk writes "Spectacular satellite images suggest that Mars was warm enough to sustain lakes three billion years ago, a period that was previously thought to be too cold and arid to sustain water on the surface, according to research published today in the journal Geology. Earlier research had suggested that Mars had a warm and wet early history but that between 4 billion and 3.8 billion years ago, before the Hesperian Epoch, the planet lost most of its atmosphere and became cold and dry. In the new study, the researchers analysed detailed images from NASA’s Mars Reconnaissance Orbiter, which is currently circling the red planet, and concluded that there were later episodes where Mars experienced warm and wet periods."

Comments

Re:How do they determine those dates?

[locallyunscene]

FTFA:

The researchers determined the age of the lakes by counting crater impacts, a method originally developed by NASA scientists to determine the age of geological features on the moon. More craters around a geological feature indicate that an area is older than a region with fewer meteorite impacts. In the study, the scientists counted more than 35,000 crater impacts in the region around the lakes, and determined that the lakes formed approximately three billion years ago. The scientists are unsure how long the warm and wet periods lasted during the Hesperian epoch or how long the lakes sustained liquid water in them.

So to answer your question the moon is the reference point.

It has large error bars, but it's the best we have until we can send radiometric dating to these areas. [Crater Counting]

Re:How do they determine those dates?

[Ephemeriis]

How are these dates determined?

Basically, they're counting craters.

The idea is that everything in the solar system is being steadily bombarded by random bits of debris. More craters means that something has been exposed to the elements for a longer amount of time.

In this case... If you have a once-lakebed that's now covered with craters, it must have been a while since there was water in it.

No, it isn't perfect. But it isn't too horrible either.

And, of course, the numbers will be refined as more/better data and measurements become available.