Snowstorms in the rings of Saturn

The rings of Saturn are one of the most stunning sights in our solar system. Now, researchers have shown how the gigantic plumes of ice that erupt from the surface of Saturn’s moon Enceladus give one of the rings, the E ring, its distinctive structure.

See that tiny dot on the right? That's Enceladus. Image: NASA/JPL/Space Science Institute

Researchers have known since 1981 that the E ring was created by kilometre-high plumes of ice and water vapour erupting above hotspots on the icy-bound surface of Enceladus. The new study shows that the eight identified plumes on Enceladus contribute to thicker bands of particles within the vertical structure of the ring, and that some plumes are better at doing so than others.

However, even after the particles are blasted free from the moon they end up back there, trapped by the moon’s gravity often after only one or two orbits.

To make their discovery the researchers instructed the Cassini spacecraft currently in orbit around Saturn to dive through the E ring while analysing the particles it passed. The results revealed the unusual vertical stripes, and feeding the data into a computer model of the E ring and Enceladus showed how the plumes create the stripes.

The researchers also show that many of the particles thrown up by the plumes escape into the rings. The rest, particularly the largest particles, fall back to the moon’s surface if their speed is less than around 207 metres per second, although it does also depend on where on the surface of Enceladus the plume originates.

The results of the study could allow researchers to find less obvious plumes by looking closely at the ring structure. They also shed light on the creation of one of the most spectacular features of our corner of the universe.

The ice plumes at the south pole of Enceladus. What goes up... Image: NASA/JPL/Scace Science Institute

Paper Reference: Kempt, S., Beckmann, U. and Schmidt, J. (2010) How the Enceladus dust plume feeds Saturn’s E ring. Icarus, 206 (2), p446-457.doi:10.1016/j.icarus.2009.09.016

Stepping back in time

Our extinct ancestors walked just like us, according to American scientists. By studying ancient fossilised tracks the researchers found that our way of walking, on two feet and taking long strides with each step, evolved long before we did.

Spot the ancestral gait... Image: Raichlen et al/PLOSone

Ancient hominims – the group of primates including ourselves – could have walked in one of two ways; either they walked just like us, with long, striding steps, or with bent legs like a chimpanzee. Different gaits leave different shaped footprints, so the researchers could compare fossilised trackways at Laetoli, Tanzania, to the footprints left by modern volunteers to see how some of our ancestors moved.

The fossil footprints found at Laetoli in Tanzania have courted controversy ever since they were discovered thirty years ago. At 3.6 million years old, the tracks are the oldest direct fossil evidence of bipedalism in any of our ancestors, and this presents a problem. They could only have been left by one of our distant ancestors called Australopithecus afarensis, but their skeletons suggest they used a bent-legged gait like chimps, well adapted to life in the trees.

To solve the puzzle, the researchers asked volunteers to walk through sand normally, or imitating a chimpanzee, with bent knees and back. A laser scanner mapped the footprints they left behind, and the results showed clear differences between the two gaits – bent-knee gaits leave much deeper toe-prints, for example. With this data the researchers could then look at the Laetoli tracks.

Their results were quite conclusive: Laetoli toe-prints were shallower than their heel-prints, and in the same range as our modern gait, strongly supporting the idea that they walked much like we do today. Our way of walking is the most energy efficient way to get around on two legs, so the results also suggest walking on the ground, rather than in the trees, was an important part of the Australopithecine lifestyle – an important step towards the plains-striding apes that went on to conquer the world.

Paper Reference: Raichlen DA,  Gordon AD,  Harcourt-Smith WEH,  Foster AD,  Haas WR Jr,. (2010) Laetoli Footprints Preserve Earliest Direct Evidence of Human-Like Bipedal Biomechanics. PLoS ONE 5(3). e9769. doi:10.1371/journal.pone.0009769

Mind-reading machines shed light on human memory

Computers can read our minds! At least they can if we’re in an fMRI scanner and the computer just has to work out which of three videos we’re thinking about.

Can you tell what she's thinking? Image: NASA

The research, carried out by British scientists, examined brain activity in the hippocampus, an area of the brain responsible for recording ‘episodic’ memories. Episodic memories are quite complex, recording details of our everyday experiences, and this is the first time anyone has shown it is possible to ‘read’ them based on brain activity.

The scientists designed a computer algorithm to analyse fMRI images of brain activity in ten volunteers. The computer could tell which of three short videos the volunteer was thinking about more often than if it was randomly guessing, which suggests that memories are recorded in a regular pattern.

fMRI works by showing changes to blood flow in different areas of the brain. Changes in blood flow show changes in brain activity – as hard-working neurons need to be supplied with oxygen to keep them working. The pattern of blood flow in the volunteers’ brains changed as they recalled one of the video clips they had been shown earlier, each of which showed a woman performing a normal activity such as drinking coffee.

The results not only demonstrate that memories are predictable, they also show where in the hippocampus episodic memories are recorded, as three areas of the hippocampus were active in all of the volunteers tested. Unfortunately the precise roles of the three areas are still unclear, although scientists believe one of them is involved with our spatial memory.

Understanding how memories are formed, and where they are stored, could help us to understand how memories are lost as we age or through brain damage or illness. But is there a more sinister application to computer mind-reading? Very targeted advertising could be just the beginning…

Paper Reference:

Chadwick, M.J., Hassabis, D., Weiskopf, N., and Maguire, E.A., (2010). Decoding Individual Episodic Memory Traces in the Human Hippocampus. Current Biology, Published online: March 11, 2010. doi:10.1016/j.cub.2010.01.053

Dinosaur for dinner

Earlier this week, scientists announced the discovery of an extraordinary fossil. It contained the body of snake caught in the act of devouring newly-hatched sauropods! Dominant terrestrial predator they may have been, but the dinosaurs didn’t have it all their own way. Here, I take a look at a few of the beasts that could terrify even those terrible lizards!

Slithering hunter

Caught in the act - Sanajah devours a titanosaur. Image: Wilson et al/PLOS Biology

The early snake Sanajeh indicus could never have tackled an adult titanosaur: sauropods such as the titanosaurs were some of the largest animals ever to walk the earth. Fully grown titanosaurs could reach 25 metres long and weigh more than 38 tonnes and were almost completely immune to predators: but when young they were just as vulnerable as any other small animal.

Sanajeh took full advantage of this, hunting amongst the titanosaur nest fields littering the landscape of India 67.5 million years ago. Sanajeh wasn’t huge – around 3.5 metres long – and couldn’t expand its mouth to swallow large prey, unlike modern snakes. It did manage to devour 0.5 metre long baby sauropods, however, and one unlucky snake was frozen in time as both it and its prey were engulfed by a landslide. The fossil not only tells us about the hazards facing newly-hatched dinosaurs, it also gives us an insight into the evolution of snakes, with their amazing expandable skulls.

Amphibian Ambush

You may want to show a bit more respect to the frogs in your garden pond. Small and slimy they may be, but their ancestors were willing to go up against the toughest of them. Lurking in the late Cretaceous undergrowth of Madagascar, Beelzebufo ampinga was waiting for small dinosaurs to put a foot wrong…

Beelzebufo was a 40-centimetre-long ambush predator. It sat, perfectly camouflaged, waiting for its prey to come along before striking with its immensely powerful jaws. Sadly, there’s no direct evidence that it dined on small dinosaurs, but its size, and the location it inhabited, do suggest dinosaur was part of this primitive frogs’ diet.

Feisty Furball

Psittacosaurus - a tasty snack for a rodent? Image: bumblesweet/Flickr

The Cretaceous period wasn’t just the age of the reptiles. One small furry group – the mammals – was making its presence felt in smaller ways, even managing occasionally to drag down one of the mighty reptiles that ruled the land. A few years ago, Chinese and American scientists unearthed Repenomamus giganticus, a giant fossil rodent from 139 million years ago. Incredibly they found the remains of a young ceratopsian dinosaur in the rodent’s stomach.

Repenomamus had sharp, pointed teeth, which hint at its carnivorous habits, and weighed around 13kg. This may be small compared to today’s mammals but it was a giant amongst the mammals alive at the same time. This obviously gave it the muscle, and courage, required to hunt juvenile Psittacosaurus, a distant relative of the more-famous Triceratops armed with a fearsome hooked beak.

Paper References:

Wilson J., Mohabey D., Peters S., Head J., (2010) Predation upon Hatchling Dinosaurs by a New Snake from the Late Cretaceous of India. PLoS Biology 8(3): e1000322. doi:10.1371/journal.pbio.1000322

Hu Y, Meng J, Wang Y, Li C (2005) Large Mesozoic mammals fed on young dinosaurs. Nature 433: 149–152.

Evans, S., Jones, M., and Krause, D., (2005) A giant frog with South American affinities from the Late Cretaceous of Madagascar. PNAS 105:2951-2956; doi:10.1073/pnas.0707599105