Posted: 15 Mar 2010 04:06 PM PDT
The sharpest images yet taken by the Mars Express spacecraft of Mars' tiny moon Phobos reveal features as small as 4.4 meters across, the European Space Agency announced March 15.
Some of the new images taken March 7 during one of several recent close flybys of the moon home in on the proposed landing site for a Russian mission, Phobos-Grunt (meaning Phobos soil), that is expected to touch down on the moon next year.
During the three flybys on March 7, 10 and 13, researchers measured the moon's tug on Mars Express by examining changes in the frequency of radio signals beamed by the spacecraft to Earth. The frequency shifts indicate that the craft has sped up or slowed down by a few millimeters per second due to the moon's gravity.
When combined with images, the gravity data may provide new clues about Phobos' composition and origin. According to one theory, Mars captured the moon from the nearby asteroid belt. Alternatively, Phobos may have formed where it now resides and could be a direct leftover from the planet-making era. With dimensions of 27 by 22 by 19 kilometers, the moon is the larger of Mars' two moons.
The Mars Express flybys, which happen every five months, may also determine if Phobos is a fragile pile of rocky fragments stuck together — what planetary scientists refer to as a rubble pile — or solid through and through, says Mars Express scientist Gerhard Neukum of the Free University of Berlin. He notes that due to orbital maneuvers that had to be performed on relatively short notice, scientists missed the opportunity to take even higher-resolution images with another camera on Mars Express, which would have revealed features on Phobos as small as a meter across.
The craft will make two more passes by Phobos before the end of March, but they will not come as close as the March 7 flyby.
Image: ESA/DLR/FU Berlin (G. Neukum)
Posted: 15 Mar 2010 02:21 PM PDT
The bacterial communities that live on human skin may form a bacterial fingerprint on the items that you touch.
In a new study led by microbiologists Rob Knight and Noah Fierer of the University of Colorado, Boulder, researchers swabbed three different keyboards and nine mice for bacteria, then compared the genomic variation between the communities to deduce whose hands had been touching what. The people were clearly identifiable from the bacterial communities they'd transferred to their computer input devices.
"The results demonstrate that bacterial DNA can be recovered from relatively small surfaces, that the composition of the keyboard-associated communities are distinct across the three keyboards, and that individuals leave unique bacterial 'fingerprints' on their keyboards," wrote Knight and his colleagues at the University of Colorado, Boulder in a new paper in the Proceedings of the National Academy of Sciences.
The results are the latest to show the variety and complexity of the bacterial communities living in a variety of different human ecosystems like the gut, saliva and skin. The Human Microbiome Project at the Institute for Genome Scientists is out to catalog and understand the relationships between our bacteria and ourselves. Early results suggest "our microbial partners may be essential for our survival as a species."
Microbiome science is just a few years old. It was only in the middle of the decade that sequencing and computational technology became available to do this kind of work. Already, the work is beginning to rewrite what it means to be a human.
"If humans are thought of as a composite of microbial and human cells, the human genetic landscape as an aggregate of the genes in the human genome and the microbiome, and human metabolic features as a blend of human and microbial traits, then the picture that emerges is one of a human 'supra-organism'," argued a 2007 Nature paper lead-authored by Peter Turnbaugh, a Harvard microbiologist.
Despite the excitement, we're just beginning to understand the bacterial community variations within a single body and between individuals. The new study adds a helpful plank of knowledge in pointing out that human skin microbiomes are diverse enough to allow researchers to distinguish between people. That's a bit surprising as a 2008 article had found "a low level of interpersonal variation" in skin microbiomes relative to studies performed on gut bacteria.
While the most obvious implication of the work might seem to be that the skin microbiome technique could be used in forensic settings, this technique is not coming to a courtroom near you, said Jacques Ravel, a microbiologist at the University of Maryland who works on both the human microbiome and more general forensic science.
"It's a nice piece of work but the forensic aspect as far as I'm concerned is the weakest," Ravel concluded.
The researchers will need a lot more evidence that human microbiomes don't change rapidly in time — and that bacterial communities transferred to keyboards endure with few changes.
Without that proof, Ravel said, the technique is unlikely to be used in real-world forensics, where evidence is often collected long after contact with a keyboard or other surface would have ceased.
Forensic scientists will also just need more data on variations in skin microbiomes to reduce the uncertainty associated with identifications.
"When we do a human genotyping for forensics, we can tell you this is the person and there is one chance in X billion that it is someone else," Ravel said. "Here, they don't have that power. They can't tell you that. The statistics support is still very weak. You can't bring that in the courtroom."
There is one forensic niche, though, where the microbiome could eventually come in handy: identical twins. A 2008 study found that identical twins showed substantial gut bacteria variation. Skin microbiomes could be similar.
"Even identical twins harbor substantially different microbial communities, suggesting that the collective genomes of our microbial symbionts may be more personally identifying than our own human genomes," the Colorado researchers conclude.
Citation: "Forensic identification using skin bacterial communities" in PNAS by Noah Fierer et al.
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