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See Inside August 2009

Whatever Happened to the Mars Rovers?

Also: updates on stem cells from proteins, quasicrystals and a billion-year memory drive

Natural Quasicrystals
First cooked up in the lab in 1984, quasicrystals are unusual substances that lie somewhere between the crystalline and the amorphous. Specifically, they display ordered arrangements and symmetries but are not periodic—that is, they are not defined by a single unit cell (such as a cube) that repeats itself in three dimensions [see “Quasicrystals”; SciAm, August 1986].

After years of searching, Paul Steinhardt of Princeton University and his colleagues think they have finally found the first natural quasicrystal. They examined substances chemically similar to quasi­crystals that had already been lab-synthesized. That search led them to khatyrkite, a mineral reportedly found in the Koryak Mountains of Russia that consists of an aluminum alloy. A khatyrkite-bearing sample in Italy also contained similar granules of a similar alloy that fit the quasicrystal bill.

Still, some doubts persist concerning khatyrkite’s origin, because aluminum alloys do not form easily by natural processes. Steinhardt says that he will continue to consider the various processes that could have formed the sample. “As is often the case for minerals, it is a lot easier to identify and characterize the mineral than it is to explain how it formed,” he remarks. Steinhardt’s team’s work appears in the June 5 Science—John Matson

Really Long-Term Memory
Preserving information for future generations has prompted some concern for digital archivists [see “Ensuring the Longevity of Digital Documents”; SciAm, January 1995]. For instance, today’s memory cards, holding 10 to 100 gigabits per square inch, last only 10 to 30 years. A solution could lie with an experimental memory device based on an iron nanoparticle that travels inside a carbon nanotube between two electrical contacts; an applied voltage shuttles the nanoparticle between the contacts. The device, described in the June 10 Nano Letters, can hold one trillion bits per square inch, and theoretical calculations suggest that the system could remain thermodynamically stable for one billion years. Don’t bother with the extended warranty.

All-Protein Mix
Inducing adult cells to revert back to a stem cell state at first required the insertion of four genes, one of which was a cancer gene [see “Potent Alternative”; SciAm, February 2008]. Then scientists figured out a way to make these stem cells without the cancer gene. Now they have gotten adult mouse cells to pluripotency by using only the proteins encoded by the genes. Such a protein-only approach, described in the May 8 Cell Stem Cell, ensures that foreign DNA does not unexpectedly integrate into and modify the host cells.

Big Splash
The results of Mars rover Opportunity’s two-year exploration of Victoria Crater fills in details about the wet history of Mars [“The Red Planet’s Watery Past”; SciAm, December 2006]. In particular, the rover found little spheres of hematite, a form of iron oxide, in Victoria that resembled those found kilometers away. The finding suggests that the conditions that shaped the Martian terrain operated on a regional basis, conclude the researchers in the May 22 Science. Opportunity’s next target is a crater called Endeavour, nearly 14 kilometers from Victoria. Meanwhile its twin, Spirit, became trapped in soft, sandy soil on the other side of the planet in May. As of mid-June, scientists still had not figured out how to get the rover, which already had a broken wheel, moving again.

Note: This article was originally printed with the title, "Updates."

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