[meteorite-list] Gullies on Mars Show Tantalizing Signs of Recent Water Activity

[Erik Fisler]

Thanks Ron! I needed this artical for my curent astronomy event in my astronomy class.
Can anyone give me an opinion on this for me to quote?
 
[Erik]


> From: baalke at zagami.jpl.nasa.gov

> To: meteorite-list at meteoritecentral.com

> Date: Mon, 2 Mar 2009 14:40:47 -0800

> Subject: [meteorite-list] Gullies on Mars Show Tantalizing Signs of Recent Water Activity

> 

> 

> 

> Media Relations

> Brown University

> 

> Contact:

> Richard Lewis, (401) 863-3766

> 

> March 2, 2009

> 

> Gullies on Mars Show Tantalizing Signs of Recent Water Activity

> 

> Brown planetary geologists have located a gully system that appears to have

> been carved by melt water that originated in nearby snow and ice deposits.

> The gullies, which the team determined to be about 1.25 million years old,

> may represent the most recent period when water flowed on the planet. The

> findings appear on the cover of the March issue of Geology.

> 

> PROVIDENCE, R.I. -- Planetary geologists at Brown University have found a

> gully fan system on Mars that formed about 1.25 million years ago. The fan

> offers compelling evidence that it was formed by melt water that originated

> in nearby snow and ice deposits and may stand as the most recent period when

> water flowed on the planet.

> 

> Gullies are known to be young surface features on Mars. But scientists

> studying the planet have struggled with locating gullies they can

> conclusively date. In a paper that appears on the cover of the March issue

> of Geology, the Brown geologists were able to date the gully system and

> hypothesize what water was doing there.

> 

> The gully system shows four intervals where water-borne sediments were

> carried down the steep slopes of nearby alcoves and deposited in alluvial

> fans, said Samuel Schon, a Brown graduate student and the paper's lead

> author.

> 

> "You never end up with a pond that you can put goldfish in," Schon said,

> "but you have transient melt water. You had ice that typically sublimates.

> But in these instances it melted, transported, and deposited sediment in the

> fan. It didn't last long, but it happened."

> 

> The finding comes on the heels of discoveries of water-bearing minerals such

> as opals and carbonates, the latter of which was announced by Brown graduate

> student Bethany Ehlmann in a paper in Science in December. Those discoveries

> build on evidence that Mars was occasionally wet far longer than many had

> believed, and that the planet may have hosted a warm, wet environment in

> some places during its long history.

> 

> However, the finding of a gully system, even an isolated one, that supported

> running water as recently as 1.25 million years ago greatly extends the time

> that water may have been active on Mars. It also adds to evidence of a

> recent ice age on the planet when polar ice is believed to have been

> transported towards the equator and settled in mid-latitude deposits, said

> James Head III, professor of geological sciences at Brown, who first

> approximated the span of the martian ice age in a Nature paper in 2003.

> 

> "We think there was recent water on Mars," said Head, who with Brown

> postdoctoral researcher Caleb Fassett is a contributing author on the paper.

> "This is a big step in the direction to proving that."

> 

> The gully system is located on the inside of a crater in Promethei Terra, an

> area of cratered highlands in the southern mid-latitudes. The eastern and

> western channels of the gully each run less than a kilometer from their

> alcove sources to the fan deposit.

> 

> Viewed from afar, the fan appears as one entity several hundred meters wide.

> But by zooming in with the HiRISE camera aboard the Mars Reconnaissance

> Orbiter, Schon was able to distinguish four individual lobes in the fan, and

> determine that each lobe was deposited separately. Moreover, Schon was able

> to identify the oldest lobe, because it was pockmarked with small craters,

> while the other lobes were unblemished, meaning they had to be younger.

> 

> Next came the task of trying to date the secondary craters in the fan. Schon

> linked the craters on the oldest lobe to a rayed crater more than 80

> kilometers to the southwest. Using well-established techniques, Schon dated

> the rayed crater at about 1.25 million years, and so established a maximum

> age for the younger, superimposed lobes of the fan.

> 

> The team determined that ice and snow deposits formed in the alcoves at a

> time when Mars had a high obliquity (its most recent ice age) and ice was

> accumulating in the mid-latitude regions. Sometime around a half-million

> years ago, the planet's obliquity changed, and the ice in the mid-latitudes

> began to melt or, in most instances, changed directly to vapor. Mars has

> been in a low-obliquity cycle ever since, which explains why no exposed ice

> has been found beyond the poles.

> 

> The team tested other theories of what the water may have been doing in the

> gully system. The scientists ruled out groundwater bubbling to the surface,

> Schon said, because it seemed unlikely to have occurred multiple times in

> the planet's recent history. They also don't think the gullies were formed

> by dry mass wasting, a process by which a slope fails as in a rockslide. The

> best explanation, Schon said, was the melting of snow and ice deposits that

> created "modest" flows and formed the fan.

> 

> NASA funded the research.

> 

> IMAGE CAPTIONS:

> 

> [IMAGE 1:

> http://news.brown.edu/files/article_images/Schon%20Mars%20gullies%20Zoom%20in.jpg

> (1.2MB)]

> The gully system in the Promethei Terra region of Mars appears to have been

> carved by melt water and may be the most recent period when water was active

> on the planet. Credit: NASA/JPL/University of Arizona

> 

> [IMAGE 2:

> http://news.brown.edu/node/10408]

> The gully system shows four distinct lobes. Credit: NASA/JPL/University of

> Arizona

> 

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