Planetary science: Dry dust on Mars
Planetary science: Missions to Mars part 2
Neuroscience: Cigarette brain boost inseparable from addiction
Oncology: An amplified difference in melanoma cells
Neurobiology: What the retina doesn't tell the brain
Physics: Red light for photons
Population dynamics: Slow breeders need more space
Materials science: Doping nanocrystals
Palaeoclimatology: Atmospheric carbon dioxide record revisited
And finally… Sound analysis reveals didgeridoo secrets
 –  Planetary science: Dry dust on Mars (pp 44-69; N&V)
Six papers in Nature (7 July 2005 ) announce new analyses of scientific data from NASA's twin rovers, Spirit and Opportunity, which are still on active duty on Mars.
Matt Golombek and colleagues look at how well the characteristics of the rovers' landing sites were predicted by satellite and telescope surveys before they landed. The authors argue that the safety of the landing site was accurately predicted, but the geological assessment was less successful, which emphasises the inherent uncertainties in remotely sensed data, they say.
Jim Bell III and colleagues report the observation of solar transits by the martian moons Phobos and Deimos, the first time such an event has been recorded from the surface of another planet.
Alian Wang and colleagues found that the volcanic rocks at Spirit's landing site, Gusev crater, are coated with material rich in sulphur, bromine, chlorine and oxidized iron, suggesting that they might have interacted with acidic water, which then evaporated.
Albert Yen and colleagues report that martian dust particles are composed of similar material on opposite sides of the planet, suggesting that air-borne circulation distributes the dust far from its source. The presence of olivine — a mineral that reacts readily with water — indicates that the dust has not experienced a thorough soaking. Also, dark soil deposits at the two sites have similar compositions, indicating that they may reflect a global component, rather than being derived solely from local rocks.
Walter Goetz and colleagues also found olivine in atmospheric dust, as well as the iron mineral magnetite, which makes the dust magnetic.
Robert Sullivan and colleagues study wind-related features of the martian surface, including the origin of bright wind streaks formed during dust storms. Examining the distribution of grains in ripples at the Meridiani site, the authors conclude that some sand is more resistant to being carried by the wind than theory would predict.
"When you look at Mars as a small red speck in the night sky, it seems an incredible feat to land spacecraft on specific parts of it," comments David Catling in a related News and Views article.
Please note – the papers are listed in order of appearance in the journal, not in the order of their mentions above.
M. P. Golombek (California Institute of Technology, Pasadena, CA, USA)
Tel: +1 818 354 3883; E-mail: [email protected] Paper 
Albert S. Yen (California Institute of Technology, Pasadena, CA, USA)
Tel: +1 818 354 7101; E-mail: [email protected] Paper 
J. F. Bell III (Cornell University, Ithaca, NY, USA)
Tel: 607 255 5911; E-mail: [email protected] Paper 
R. Sullivan (Cornell University, Ithaca, NY, USA)
Tel: +1 607 255 9888; E-mail: [email protected] Paper 
Walter Goetz (Max-Planck-Institut für Sonnensystemforschung, Katlenburg-Lindau, Germany)
Tel: + 49 555 697 9347; E-mail: [email protected] Paper 
Alian Wang (Washington University in Saint Louis, MO, USA)
Tel: +1 314 935 5671; E-mail: [email protected] Paper 
David Catling (University of Bristol, UK)
Tel: +44 0117 954 5378; E-mail: [email protected] News and views author
 Planetary science: Missions to Mars part 2 (AOP)
In other Mars news, the most detailed map of minerals on the red planet's surface is unveiled in a paper published online this week by Nature. The rocks show a surprisingly complex volcanic history, and include a wide range of different types of magmas similar in variety to those found on Earth.
Phil Christensen and colleagues used infrared measurements from the orbiting Mars Odyssey probe to study rocks whose chemical make-up reveals lavas ranging from primitive mantle-derived basalts to highly differentiated silica-rich rocks which probably formed in magma chambers, following the re-melting of previously erupted rocks.
They also found volcanic basalts that contain more than 20 per cent olivine, a mineral that is quickly weathered by water. Similar layers of olivine-rich rocks were found in eroded canyon walls and ancient crater floors that date back to billions of years ago. This suggests that during each of the periods of history when the olivine layers were laid down, Mars did not have extensive water on its surface.
Phil Christensen (Arizona State University, Tempe, AZ, USA)
Tel: +1 480 965 7105; E-mail: [email protected]
 Neuroscience: Cigarette brain boost inseparable from addiction (pp 99-106; N&V)
Nicotine gives the brain a stimulating boost, but its addictiveness means that it is set to kill 100 million people this century. New research in mice shows that the same brain system is involved in both stimulation and addiction, meaning that the two are unlikely to be separable.
Both effects are mediated by a subunit of a cell-surface protein called the nicotinic acetylcholine receptor, in a brain region called the ventral tegmental area (VTA), report Jean-Pierre Changeux and his colleagues in Nature (7 July 2005). They made the discovery by breeding mice to lack this molecule and then re-injecting it specifically into this brain area.
In behavioural tests, mice with restored receptor function in the VTA were more likely to seek out nicotine than those lacking the receptor. Furthermore, when their activities were monitored, the injected mice showed greater levels of inquisitive behaviours.
Jean-Pierre Changeux (CNRS/Institut Pasteur, Paris, France)
Tel: +33 1 45 68 88 05; E-mail: [email protected]
Julia A. Kauer (Brown University, Providence, RI, USA)
Tel: +1 401 863 9803; E-mail: [email protected]
 Oncology: An amplified difference in melanoma cells (pp 116-121; N&V)
Scientists have made steps towards understanding the genetic changes found in various types of tumour. William R. Sellers and colleagues report a significant advance in this area in Nature (7 July 2005). The researchers used DNA chips that allow ultra-high resolution genetic analyses. This helped them to find a distinct amplification of the gene encoding MITF (microphthalmia-associated transcription factor) in melanoma cells.
They also found that increased amounts of this master regulatory protein could explain why these cancerous cells show such high resistance to conventional melanoma chemotherapy. The authors believe that targeting MITF could offer new options to treat cancer, and other experts agree.
"Over-reliance on lineage-defining factors such as MITF could be a weak link in an otherwise unbreakable chain, providing an opportunity well worth exploiting therapeutically," writes Glenn Merlino in an accompanying News and Views article.
William R Sellers Dana Farber Cancer Institute, Boston, MA, USA)
Tel: +1 617 632 5261; E-mail: [email protected]
Glenn Merlino (National Cancer Institute, National Institutes of Health, Bethesda, MD, USA)
Tel: +1 301 496 4270; E-mail: [email protected]
 Neurobiology: What the retina doesn't tell the brain (pp 70-76)
The retina’s main task is to convert visual images into neural signals and transmit them, via the optic nerve, to the brain. Now, in a new study appearing in this week’s Nature, Markus Meister and his colleagues report that the retina is capable of a form of 'adaptive coding' of a type previously thought to occur only in the cortex of the brain.
Using an array of electrodes to record from retinae of both salamanders and rabbits, the authors report that ganglion cells in the retina appear to suppress the predictable features of a scene. For example, in an environment dominated by features with vertical orientation, the retina becomes significantly more sensitive to horizontal signals. The authors argue that the retina's sensitivity to unpredictable aspects is an adaptive feature that optimizes visual processing.
Markus Meister (Harvard University, Cambridge, MA, USA)
Tel: +1 617 496 8301; E-mail: [email protected]
 Physics: Red light for photons (pp 86-89)
Single-electron transport in an electronic chip can be controlled using the ‘Coulomb blockade’ effect, where the presence of an excess electron on a small island blocks the flow of further electrons. Now the same effect has been observed for photons of light, according to a Letter by Jeff Kimble and colleagues in Nature (7 July 2005).
Photon blockade has been the object of theoretical attention for nearly a decade, but it is technically challenging to create in the laboratory because photons do not interact directly with each other. However, the effect can be achieved using a single atom held in an optical cavity, tuned so as to allow the reversible exchange of photons between the atom and the surrounding field. The atom can absorb one photon to energize it to its first excited state, but subsequent photons cannot be absorbed because they don’t have the precise atomic transition energy needed to push the atom into its second excited state. As a signature of the effect, Kimble and colleagues saw that the transmitted photons arrived more regularly than would be expected for a classical beam of light. The experiment advances optical physics into a new regime characterized by the quantum effects of individual particles.
Jeff. Kimble (California Institute of Technology, Pasadena, CA, USA)
Tel: +1 626 395 8340; E-mail: [email protected]
 Population dynamics: Slow breeders need more space (pp 98-101)
Bird populations are more likely to be reduced by overcrowding in species that take a long time to breed, according to a new analysis in Nature. The study also shows that these birds are more susceptible to transient shifts in population age structure — a discovery that could help to judge species' extinction risks.
Bernt-Erik Sæther and his colleagues analysed data from 23 bird species, and demonstrated that those with a longer generation time are more likely to show 'density dependence' in their numbers. Previously, researchers had not been able to spot such trends in bird populations, probably because, as the authors now show, they are apparent only on scales of several generations.
Bernt-Erik Sæther (Norwegian University of Science and Technology, Trondheim, Norway)
Tel: +47 905 785 44; E-mail: [email protected]
 Materials science: Doping nanocrystals (pp 90-93; N&V)
New research in Nature (7 July 2005) provides an explanation of how to intentionally incorporate impurities into semiconductor nanocrystals. The introduction of impurity atoms (a process called doping) is already used in bulk semiconductors in order to modify their properties but until now has had limited success in nanocrystals.
Conventional thinking is that impurities are naturally expelled by the nanocrystals, but Steven Erwin and colleagues argue that this is not the case. They show that doping efficiency depends on the initial adsorption of impurities on the nanocrystal surface, and close attention to growth conditions, namely surface morphology, crystal shape and surfactants. So ‘undopable’ nanocrystals may soon become ‘dopable’ for use in applications such as solar cells and spintronics.
Steven C. Erwin (Naval Research Laboratory, Washington DC, WA, USA)
Tel: +1 202 404 8630; E-mail: [email protected]
Giulia Galli (Lawrence Livermore National Laboratory, Livermore, CA, USA)
Tel: +1 925 423 4223; E-mail: [email protected]
 Palaeoclimatology: Atmospheric carbon dioxide record revisited (pp 39-40)
In a Brief Communication in Nature (7 July 2005), a team of scientists report the reconstruction of a carbon dioxide record from the Vostok ice core in Antarctica for the longest interglacial period of the past million years, which occurred 400,000 years ago and lasted for 30,000 years. They found that conditions were similar to those of today’s interglacial period, before the advent of industrial activity.
To obtain a complete record spanning the entire period, Dominique Raynaud and colleagues corrected for flow disturbances in the ice-core data. The new record shows that carbon dioxide levels during this time were stable and apparently unaffected by the reorganization of the oceanic carbonate system as coral reefs became established in the warm oceans. The interglacial period 400,000 years ago is thought to be our present climate's closest analogue, suggesting that without human interference, atmospheric carbon dioxide levels would probably have remained stable for another few thousand years.
Dominique Raynaud (CNRS, St Martin D'Heres, France)
Tel: +7 812 356 64 60 or + 7 921 970 2546; E-mail: [email protected]
 And finally… Sound analysis reveals didgeridoo secrets (pp 39)
Australian physicists have unravelled the secrets of skilled didgeridoo playing. It turns out that what separates an expert from a novice is the opening and closing of the vocal tract, which alters the acoustics of the mouth, producing a huge range of different sound qualities.
A skilled player subconsciously reduces the opening of the glottis — the part of the larynx that contains the vocal cords — to set up strong resonances at certain frequencies inside the mouth. The vocal cords mimic the positions used when producing vowel sounds, explain Joe Wolfe and his colleagues in a Brief Communication in Nature (7 July 2005). If the vocal tract remains open, as in normal breathing, the lungs absorb much of the sound.
The researchers used a small tube and microphone to detect the sound characteristics inside the players' mouths. Such measurements have previously been difficult to make, not least because sound levels inside the mouth cavity can reach 100 dB. The results suggest that didgeridoo playing may be similar to playing a brass instrument, in which changes to the vocal tract can also influence the quality of the sound produced.
Joe Wolfe (The University of New South Wales, Sydney, NSW, Australia)
Tel: +61 293 854 954; E-mail: [email protected]
ALSO IN THIS ISSUE (7 July 2005)...
 Breaking of Henry’s law for noble gas and CO2 solubility in silicate melt under pressure (pp 94-97)
 ATP is a mediator of chemosensory transduction in the central nervous system (pp 107-110)
 Angiotensin-converting enzyme 2 protects from severe acute lung failure (pp 111-115)
 Rac1b and reactive oxygen species mediate MMP-3-induced EMT and genomic instability (pp 122-126)
 Kinase-regulated quantal assemblies and kiss-and-run recycling of caveolae (pp 127-132)
 Molecular basis of photoprotection and control of photosynthetic light-harvesting (pp 133-136)
 X-ray structure of a tetranucleosome and its implications for the chromatin fibre (pp 137-140)
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