Strawberries in space

You’re speeding through the icy depths of space, millions of miles from Earth, when you realise you’d like a snack to remind you of the long summers of home. What do you do? Bizarrely, the answer might be as simple as going to pick some strawberries.

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

‘Sauna-like’ planet found orbiting distant star

A newly-discovered planet orbiting a distant star is covered by deep oceans, according to an international team of astronomers. The ‘water world’ is only a little larger than Earth, but it is much less dense, leading the astronomers to suggest it is exceptionally watery, with a small rocky core.

...but what good's an ocean without a beach? Image: Hypothesisnow

With a ‘surface’ temperature of 190^oC, the planet may also have a rather steamy, ‘sauna-like’, atmosphere.

The planet, named GJ 1214b, consists of almost 50% water: in comparison, only around 0.06% of the Earth’s mass is water, despite it being known as the ‘blue planet’. Astronomers inferred the existence of the planet from the way it dimmed the light of its parent star every time it passed in front of it – once every 1.6 days. It also causes the star to wobble slightly as it orbits – another tell-tale sign of an orbiting planet.

The amount of light-dimming and the wobble told astronomers the size and mass of GJ 1214b, which in turn allowed them to work out its density. GJ1214b is slightly larger than Earth (its radius is 2.68 times that of Earth) and much less dense (1.9 grams per centimetre³ compared to Earth’s 5.5 grams per cm³. The only plausible way a planet could be that big but weigh so little would be if it consisted of lots of water around a rocky core, perhaps with a thin atmosphere of hydrogen and helium.

The presence of liquid water is rather exciting because, as far as we know, water is one of the prerequisites of life, and finding inhabited planets is one of the long-term goals of astronomy. The new discovery also takes us one step closer to finding a truly Earth-like planet out there somewhere. NASA’s Kepler space telescope is sensitive enough to find exo-planets even smaller than GJ 1214b, so maybe one day we’ll find a home-from-home. The only tricky part then will be actually getting there…

Paper Reference: Charbonneau , D., et al, (2009). A super-Earth transiting a nearby low-mass star. Nature, 462, p891-894. doi:10.1038/nature08679

‘Buckets’ of water found on moon

NASA scientists have found large quantities of water in the debris thrown up by the LCROSS spacecraft, which was deliberately crashed into the moon last month.

The lunar south pole, perfect place for an (indoor) swimming pool? Image credit: NASA

The finding tells us much about our nearest neighbour, and its potential role in space exploration: the presence of water ice on the moon is vital for future lunar exploration. It could supply drinking water, oxygen and rocket fuel, which opens up the possibility of permanent lunar settlement.

LCROSS, which stands for Lunar CRater Observing and Sensing Satellite, slammed into the Cabeus crater at the moon’s south pole. The bottom of the crater never sees sunlight and is the ideal place to look for hidden water ice, which may have lain undisturbed for the past billion years. LCROSS hit the crater floor in two stages: the first was the expended upper stage rocket, called Centaur, used to get the spacecraft into position for its collision. Following close behind was LCROSS itself. LCROSS was loaded with cameras and spectrometers to record the results of the first impact before it too hit the lunar surface four minutes later.

Although it perhaps wasn’t the most elegant experiment ever conducted, it seems to have achieved all its designers hoped for. Data from spectrometers aboard LCROSS confirmed the presence of water in the material thrown up by the impact. Spectrometers look at the light emitted or absorbed by a substance, as this gives a clue as to what it is made of. The LCROSS data contained the unmistakable signature of water. And it wasn’t just a trace of water: the scientists believe the signal corresponds to around 100kg of water (or ‘a dozen two-gallon buckets’, according to one researcher on the BBC), suggesting there is more than the occasional frozen puddle to be found in the dark corners of the moon.

Many people were disappointed with the initial results of the LCROSS mission. The 2,200kg spacecraft was expected to create a plume of material around ten kilometres high and visible from Earth as it was illuminated by the sun. Instead, the plume was much smaller, only reaching one and a half kilometres above the lunar surface. This was still enough to advertise the presence of water to the cameras on LCROSS.

See the little grey blob? Thats the plume of dust and ice. Unimpressive, perhaps, until you notice the scale bar! Image credit: NASA

WIMPs to be found by scintillating bolometer!

Scientists from France and Spain have built a scintillating bolometer. The device is now running at close to -273.15^oC in an underground laboratory in Spain.

Look, it's a shiny blue crystal thingy! Image: IAS/SINC

Which is great, but does raise a few questions: what is a scintillating bolometer, and why is it kept at extremely low temperatures and buried beneath a mountain?

The answer is about as strange as you’d expect for a machine called a scintillating bolometer. It is a prototype device which has been created to detect something that barely interacts with the world we know, yet makes up about 22% of our universe – dark matter. Dark matter is one of the most enduring mysteries of modern physics: our best models of the universe predict its existence, and we can infer its presence from the effect its gravity has on normal matter, yet we have never actually seen it!

The difficulty is that the predicted particles of dark matter – aptly known as WIMPs, or Weakly Interacting Massive Particles – usually shoot straight through normal matter without leaving any sign of their passing. The scintillating bolometer picks up the tiny bursts of heat and light released when, very rarely, a WIMP slams into the nucleus of an atom within the unique detector crystal at the heart of the machine.

The heat released from such a collision raises the temperature of the crystal by a tiny, but measurable, fraction of a degree. At the same time, the tiny flash of light is absorbed by a separate metallic disc, which also heats up slightly. The combination of certain amounts of heat and light will show that a WIMP has failed to escape the scintillating bolometer, proving the existence of one of physics’ most elusive particles.

So what about the extremely low temperature and underground lab? The rock walls of the underground lab effectively shield the detector from any stray radiation, such as cosmic rays, which might trigger the detector and give a false reading; the frigid temperature ensures the tiny temperature change can actually be detected.

Paper Reference: doi:10.1016/j.optmat.2008.09.016