I just saw this stunning image on Phil Plait’s Bad Astronomy and I assumed it was a fancy bit of art… or a computer generated view of glacial Britain… or UK-shaped frosted cake. Nope, it’s the UK as it looks from space, right now.
The UK is experiencing record low temperatures and I just got off the phone to my mum to hear that Bristol (my hometown, somewhere in the south-west of England) hit a bone shattering -15°C low last night. Yikes! And here I am looking out of my office window feeling the heat of the Sun of a 24°C California day. Truth be told, I’m a little jealous, I haven’t felt sub zero cold for years. In fact, the last time I saw negative temperatures in double figures was when I lived in the Arctic in 2002.
For now, I’ll just have to enjoy the view from space and hope this cold spell doesn’t cause too much hassle for my family and friends. My advice: Stay indoors, only go outside if you have a warm local pub within walking distance.
Subliming ice from the crater edge (NASA/JPL/University of Arizona)
This image looks like the frosted top of an over-baked muffin, but it’s actually the side of a crater on Mars covered with ice. Taken by NASA’s Mars Reconnaissance Orbiter (MRO) High Resolution Imaging Science Experiment (HiRISE) over the Martian south pole, this example demonstrates an active process of weathering acting on the red landscape. According to the HiRISE site, the ice layer is approximately 3 km thick.
In regions situated closer to the equator, craters aren’t open to erosion by ice (not surface ice in any case), but in polar regions it’s a different story. Due to the Martian thin and cold atmosphere, water ice rarely melts into a liquid; it bypasses the liquid phase and turns straight into a gas. This process is known as sublimation. There are terrestrial examples of sublimation too, including frozen carbon dioxide (or “dry ice”) which sublimes at room temperature, generating a carbon dioxide vapour.
For this particular crater, it is obvious where there is a higher rate of sublimation than others. As the Sun illuminates the crater edge from the bottom right, the rim of the crater receives the most sunlight, heating up the darker regolith and causing more ice loss. The large cracked-like structure within the crater is most likely a combination of darker material under the ice receiving preferential heating and shrinkage of the subliming ice pack.
This seasonal freezing of water vapour and sublimation of water ice erodes the sides of these polar craters, wearing them down season after season.
I never tire of seeing HiRISE images of the Red Planet, especially when they include active atmospheric processes that continue to shape the landscape of this alien world.
In October 2008, Cassini flew very close to the surface of Saturn’s icy moon Enceladus. From a distance of only 50 km from the moon, the spacecraft was able to collect samples of a plume of ice. In an earlier “skeet shot”, Cassini captured detailed images of the cracked surface, revealing the source of geysers blasting the water into space. At the time, scientist were able to detect that it was in fact water ice, but little else would be known until the molecular weight of chemicals in the plume could be measured and analysed.
At the European Geophysical Union meeting in Vienna this week, new results from the October Enceladus flyby were presented. Frank Postberg and colleagues from the Max Planck Institute for Nuclear Physics have discovered traces of sodium salts and sodium bicarbonate in the plume for the first time.
It would appear that these chemicals originated in the rocky core of the moon and were leached from the core via liquid water. The water was then transported to the surface where it was ejected, under pressure, into space. Although scientists are aware that the chemical composition in the plume may have originated from an ancient, now frozen, sub-surface ocean, the freezing process would have isolated the salt far from the surface, preventing it from being released.
“It is easier to imagine that the salts are present in a liquid ocean below the surface,” said Julie Castillo of NASA’s Jet Propulsion Laboratory in Pasadena, California. “That’s why this detection, if confirmed, is very important.”
This is the best evidence yet that Enceladus does have a liquid ocean, bound to cause a stir amongst planetary scientists and re-ignite excitement for the search for life living in a salty sub-surface ocean.
MODIS images of Lake Eerie on Feb. 6th (left) and Feb. 8th (right). Arrow indicates the area of Crane Creek State Park, where the rescue was mounted. Thinning and breakage of ice floe is evident (MODIS/NASA)
On Saturday (February 7th), more than 130 fishermen were stranded off the Lake Eerie shoreline. Eerie is the fourth largest of the five Great Lakes, sandwiched between the Canadian province of Ontario and by the US States of Ohio, Pennsylvania, and New York. It is a freshwater lake, a very popular fishing destination. During winter, large areas of the lake freeze over, tempting fishermen to venture further from the coastline onto the ice floe.
However, over the weekend, tragedy struck when a large chunk of ice thinned and drifted from the Ohio coastline (along Crane Creek State Park). The ice floe broke away, carrying 135 fishermen into the lake. One 65 year old man fell into the freezing waters and died of a heart attack. The remaining 134 men had to be airlifted from the ice by the emergency services, some were stranded for several hours. For the full details of the rescue, read the Associated Press article.
A satellite image of Lake Eerie during summer (Google)
Local officials warned fishermen of the risks with venturing too far into the frozen lake, but it would appear the temptation was too great to find the best fishing spot. According to news sources, the ice was up to 2 feet thick, giving the illusion of safety. However, temperatures were rising and an offshore wind of 35 mph cracked the ice, isolating the fishermen.
Comparing two images (top), one from February 6th (the day before the ice floe breakage) and one from February 8th (the day after), it is clear there is significant thinning of the ice. In the Feb. 6th image, it is hard to see the lake at all, the ice blends very well with the surrounding land. On Feb. 8th, the blue of the lake water is highlighted signifying ice thinning and breakage.
It is striking how illustrative the MODIS photos are, providing valuable information about everything from snow cover to forest fires. This one example how a comparison between two dates of lake ice cover can be so valuable. I’ll be keeping a close eye on this Earth observing mission…
astroengine.com 