Dust Seen Streaming Out of Namibia Into the Atlantic Ocean

Landsat 8 strikes again.

Landsat 8 is the United States Geological Survey’s most recently launched satellite, and it holds the powerful Operational Land Imager (OLI.) The OLI is a powerful multi-spectral imager with a wide dynamic range.

The OLI does a great job of keeping an eye on Earth, and now its captured images of winds in Namibia picking dust up and carrying it out over the Atlantic Ocean.

Continue reading “Dust Seen Streaming Out of Namibia Into the Atlantic Ocean”

A Region On Mars With Recent Water Is About To Get Major Attention

Credit: NASA/ JPL-Caltech

Striations exposed on the surface between Martian sand dunes (one pictured at top) in Lucaya Crater indicate fluctuating levels of salty groundwater. At “a” we see possible cross beds which are tilted layers of sand within larger layers deposited by wind or water. At b, dark and light strata are similar to that exposed in the dune at top and resemble the striations seen in the Namib Desert on Earth. The photo was taken by NASA’s Mars Reconnaissance Orbiter in infrared, red and blue light. Credit: NASA/JPL-Caltech

Researcher Dr. Mary Bourke from Trinity College Dublin have discovered a patch of land in an ancient valley in Mars’ Lucaya Crater that appears to have held water in the not-too-distant past, making it a prime target to search for past life forms on the Red Planet. Signs of water past and present pop up everywhere on Mars from now-dry, wriggly riverbeds snaking across arid plains to water ice exposed at the poles during the Martian summer.

A valley lined with sand dunes crosses the southern floor of the 21-mile-wide Lucaya Crater, located at latitude 11° south and longitude 52° east on Mars. Striations found between the dunes may have been created by recent water flows. The box shows the area pictured in the close up above. The 3.7-mile-long valley measures between 2,000 and 2,600 feet wide. Credit: NASA/JPL-Caltech with additions by the author

On Earth, Bourke had done previous studies of dunes in the Namib Desert near Walvis Bay, Namibia and noted “arctuate striations” — crusty arcs of sand cemented by water and minerals — on the surfaces of migrating sand dunes using photos taken by satellite. She subsequently assembled a team to check them out on the ground and discovered that the striations resulted when dune materials had been chemically cemented by salts left behind by evaporating groundwater.

“On Earth, desert dune fields are periodically flooded by water in areas of fluctuating groundwater, and where lakes, rivers and coasts are found in proximity,” said Bourke. These periodic floods leave tell-tale patterns behind them.” Once the material had been cemented, it hardens and remains behind as the dunes continue to migrate downwind.

Compare these cemented arctuate striations between dunes near Walvis Bay, Namibia with those in Lucaya Crater’s valley in the earlier image. White arrows highlight particularly prominent examples. Photos in (b) and (c) were taken from the ground. The excavated pit in (c) shows that the dipping sediment layers below the surface match the protruding layers on the surface. Alternating light and dark layers have different salt composition and grain size. Credit: Google Earth (left) and Dr Mary Bourke, Trinity College Dublin

Next, Bourke and colleague Prof. Heather Viles, from the University of Oxford, examined close up images of Mars taken with the Mars Reconnaissance Orbiter (MRO) and experienced a flash of insight: “You can imagine our excitement when we scanned satellite images of an area on Mars and saw this same patterned calling card, suggesting that water had been present in the relatively recent past.”

Bourke examined similar arcuate striations exposed on the surface between dunes, indications of fluctuating levels of salty groundwater during a time when dunes were actively migrating down the valley.

A possible scenario: an asteroid impacts Mars, forming Lucaya Crater and unleashing water flows that created the crater valley and striations.

So where did the water come from to create the striations in the crater valley? Bourke and Viles propose that water may have been released by the impact that formed Lucaya Crater especially if the target area was rich in ice.

Extreme temperatures during the impact would have vaporized water but also possibly melted other ice to flow for a time as liquid water. Alternatively, the impact may have jump-started hydrothermal activity as hot springs-style underground flows.

Flowing water would have created the valley and saturated the soils there with salty water. In dry periods, erosion from the wind would have picked away the water-eroded sands to create the striking pattern of repeating dunes we see to this day.

Water, water everywhere … once upon a time. Nanedi Valles, a roughly 500-mile-long (800 km) valley extending southwest-northeast and photographed by Mars Express. In this view, Nanedi Valles ranges from approximately 0.5 – 3 miles (0.8- to 5.0 km) wide and extends to a maximum of about 1,640 feet (500 meters) below the surrounding plains. The valley’s origins remain unclear, with scientists debating whether erosion caused by ground-water outflow, flow of liquid beneath an ice cover or collapse of the surface in association with liquid flow is responsible. In all cases, it’s clear that water was involved. Copyright ESA/DLR/FU Berlin (G. Neukum)

Carbonate rocks, which require liquid water to form are dissolved by the same, have been detected in the valley using spectroscopy and could have served as the cement to solidify sands between the moving dunes. That in concert with alternating dry and wet periods would create the striations seen in the MRO photos.

“These findings are hugely significant,” said Bourke. “Firstly, the Martian sand dunes show evidence that water may have been active near Mars’ equator — potentially in the not-too-distant past. And secondly, this location is now a potential geological target for detecting past life forms on the Red Planet, which is important to those involved in selecting sites for future missions.”

African Lake Has a Twin on Titan

Titan's Ontario Lacus is found to bear a striking resemblance to Namibia's Etosha Pan. (NASA/JPL/ESA)


A large lake on Saturn’s cloud-covered Titan seems very similar to the Etosha Pan, a salt-encrusted dry lakebed in northern Namibia that periodically fills with water. As it turns out, Titan’s “great lake” may also be temporary.

Ontario Lacus, so named because of its similarity both in shape and size to Lake Ontario here on Earth, was first discovered near the south pole of Titan by the Cassini spacecraft in 2009. Its smooth, dark appearance in radar images indicated a uniform and reflective surface, implying a large — although likely shallow — body of liquid.

Of course, on Titan the liquid isn’t water — it’s methane, which is the main ingredient of the hydrologic cycle found on the giant moon. That far from the Sun the temperatures at Titan’s poles fall to a frigid -300ºF (-185ºC), much too cold for water to exist as a liquid and so, on this world, methane has taken its place.

A research team led by Thomas Cornet of the Université de Nantes, France has taken a closer look at Cassini’s radar data of Ontario Lacus and found evidence of channels carved into the southern portion. According to the team, this likely indicates that the lakebed surface is exposed.

Cassini image of Ontario Lacus. (NASA/JPL/SSI)

“We conclude that the solid floor of Ontario Lacus is most probably exposed in those areas,” said Cornet.

In addition, sediment layers surrounding the lake suggest that the liquid level has varied.

All in all, this reveals a striking resemblance between Ontario Lacus and Namibia’s Etosha Pan — an “ephemeral lake” that is dry for much of the year, occasionally filling with a shallow layer of water which evaporates, leaving salty rings of sediment.

The inherent otherworldly nature of Etosha Pan is further underlined — and perhaps foreshadowed! — by its use as a backdrop in the 1968 sci-fi film 2001: A Space Odyssey.

Although Ontario Lacus was initially thought to be permanently filled with liquid hydrocarbons, the team’s findings draw a strong correlation with this well-known Earthly environment, suggesting a much more temporary nature and showing the value of comparative research.

Satellite image of Etosha Pan, acquired on April 28, 2012. (Chelys/EOSnap)

“These results emphasise the importance of comparative planetology in modern planetary sciences,” said Nicolas Altobelli, Cassini project scientist for ESA.”Finding familiar geological features on alien worlds like Titan allows us to test the theories explaining their formation.”

Read the press release from ESA here.

Image credits: Cassini radar image JPL/NASA. Envisat radar image ESA. Composite image: LPGNantes.