[LINK] Two links on life under the ice

[rfmcdonald]

Over at Wired the article "Antarctic Lake Hides Bizarre Ecosystem", by Alexandra Nitze, points to the discovery of archaic-seeming stromatolite mats on the floor of an Antarcitc lake isolated by the ice from the wider ocean.

Bacteria slowly built the mounds, known as stromatolites, layer by layer on the lake bottom. The lumps, which look like oversize traffic cones, resemble similar structures that first appeared billions of years ago and remain in fossil form as one of the oldest widespread records of ancient life. The Antarctic discovery could thus help scientists better understand the conditions under which primitive life-forms thrived. “It’s like going back to early Earth,” says Dawn Sumner, a geobiologist at the University of California, Davis.

Sumner and her colleagues, led by Dale Andersen of the SETI Institute in Mountain View, California, describe the discovery in an upcoming issue of Geobiology. “These are just incredibly beautiful microbial landscapes,” she says.

Researchers have probed many Antarctic lakes to study the weird and wonderful microbes that live there. Andersen alone has dived into at least eight such lakes. But he says the discovery of the stromatolites rocketed East Antarctica’s Lake Untersee “to the top of my list.”

Researchers study fossil stromatolites, from 3 billion years ago or more, to understand how life got a foothold on Earth. Today, stromatolites actively form in only a few spots in the ocean, like off the western coast of Australia and in the Bahamas. They also grow in some freshwater environments, like super-salty lakes high in the Andes and in a few of Antarctica’s other freshwater lakes. But scientists have never seen anything like the size and shape of Untersee’s stromatolites.

[. . .]

Andersen was used to finding mats of bacterial growth in other Antarctic lakes, but nothing like the big mounds he saw when he dived under the ice at Untersee. Up to half-a-meter high, these purplish piles studded the lake’s bottom like barnacles clinging to a ship hull. “It totally blew us away,” Andersen says. “We had never seen anything like that.”

Much more exotically, Paul Gilster at Centauri Dreams examines the consequences for Europa if it has a thinner-than-previously-theorized layer of ice over its world-ocean. Hypothetical space probes could drill more easily into the ocean, but they could also contaminated the Europan ocean.

[Richard] Greenberg (Lunar and Planetary Laboratory, University of Arizona) is the author of Unmasking Europa (Springer, 2008), which sharply critiques the ‘thick ice’ assumption by pointing to many instances of Galileo imagery showing what appears to be young and constantly resurfacing ice. Cracking and melting of a thinner ice sheet could actually expose the ocean, and make the job of studying it far easier, while demanding considerable caution in terms of possible contamination from terrestrial organisms.

[. . . I]if we do determine that the Europan ocean is accessible, our mission focus shifts to exploiting the terrain to find the best place for surface operations. From the paper:

Rather than focusing on the daunting, perhaps impossible, task of drilling down to the ocean, we should consider how to take advantage of the biosphere’s natural accessibility. With the rapid resurfacing, almost any europan landing site might provide oceanic samples; the issue will be how to find the freshest ones. When chaotic terrain forms, it replaces a section of crust with frozen ocean. Ridge formation squeezes out ocean material. Fresh oceanic material may be exposed at the surface as gaps open up and create the dilational bands. Any of these processes could be laying out biological samples on the surface.

Thus the need, says Greenberg, to ‘land smart,’ picking the optimum landing site to avoid the need for drilling through the ice in the first place. Reassessing a Europa orbiter, then, should involve a key objective: Identifying the most likely sites where the underlying ocean may have been recently exposed. A lander integrated with the orbiter mission would have the chance of finding extraterrestrial life near or even on the surface, as the frozen remnants of materials that have been briefly exposed through surface shifting of the ice. Greenberg thinks such a strategy could give us an answer on Europan life within the lifetime of many adults living today, as opposed to pursuing what is essentially a holding strategy as we develop a thick ice drilling model.

An overriding concern is protecting Europa from life that has hitched a ride from Earth, a problem that looms large with the thin ice model, whereas with thick ice and an isolated ocean, the chances of contamination seemed more remote. The NRC Task Group on the Forward Contamination of Europa (2000) adopted a standard for protection that says the probability of contaminating a Europan ocean with a viable terrestrial organism must be less than 10-4 per mission, referencing a 1964 resolution that Carl Sagan had a hand in fashioning with regard to the exploration of Mars.

Greenberg thinks these protocols are insufficient.

Go, read.