Nasa probe flew by 'snow globe' comet

Analysis of the data gathered by Nasa's Deep Impact probe at Comet Hartley reveals the object is surrounded by a huge cloud of fluffy ice particles.

The space mission's chief scientist Dr Mike A'Hearn told reporters some of these "snowballs" were very large.

"We think the biggest ones are at least the size of a golf-ball and possibly up to the size of a basketball," he said.

Deep Impact swept past the comet on 4 November, getting as close as 700km to the 1.5km-long, peanut-shaped object.

The probe's visible wavelength and infrared instruments returned a wealth of pictures and other data that should give scientists further insight into the diverse properties and behaviours of what are some of the Solar System's most remarkable objects.

The assessment of the cloud of material surrounding Hartley suggests the presence of a wide range of particle sizes. For every 25cm particle, there might be a thousand 2.5cm-sized particles, said Dr Pete Schulz, a mission scientist from Brown University.

"To me this whole thing looks like a 'snow globe' that you've just simply shaken," was how he described the environment around the comet's nucleus.

But the team stressed these particles were not solid chunks of ice in the sense most people might understand them. Rather, they are collections of small grains.

"We know that the ice [grains] on a fundamental level can't be bigger than somewhere between one and 10 microns in size," explained Dr Jessica Sunshine, the mission's deputy principal investigator.

"That's about the thickness of our hair. What that means is that the snowballs are not what we thought to begin with - we're not seeing hail-sized particles. What we're seeing are fluffy aggregates of very small pieces of ice. They're akin more to a dandelion puff than an ice cube."

Since 4 November, the science team has had a chance to consider the different look and activity occurring at the rough ends of the comet compared with its smooth middle.

Data shows the flat terrain is where water is evaporating below the surface and percolating out through the comet's dust covering. The jagged regions, on the other hand, are where carbon dioxide jets are ripping ice and dust particles out of the comet.

Deep Impact is on an extended mission, having been re-tasked to visit Hartley following its successful flyby of Comet Tempel 1 in 2005.

On that primary mission, the spacecraft released an impactor that crashed into Tempel's nucleus kicking up thousands of tonnes of icy debris.

Comets are thought to contain materials that have remained largely unchanged since the formation of the Solar System. They incorporate compounds that are rich in carbon, hydrogen, oxygen and nitrogen.

Intriguingly these are the elements that make up nucleic and amino acids, the essential ingredients for life as we know it; and there are some who believe comet impacts in the early years of the Solar System could have seeded the Earth with the right chemical precursors for biology.

As well as Tempel 1, spacecraft had previously visited comets Borrelly, Wild 2, Halley and Grigg-Skjellerup (although no close pictures were taken of Grigg-Skjellerup). All are bigger than Hartley.

Deep Impact's rendezvous with Comet Hartley occurred about 23 million km from Earth. The pair are now rapidly retreating from each other, although the probe continues to image Hartley.

The observation campaign will continue until late next week, by which time Deep Impact will have acquired some 122,000 pictures in total.

"That represents about 22GB of data, so this undoubtedly gives us an exhaustive view of this comet - more than we've been able to return from any other comet," said Tim Larson, the mission's project manager.

"After that, we'll do a final calibration on the instruments and the spacecraft will be [put] in a fairly quiet mode in December awaiting further instructions."

Nasa has requested ideas for what to do with Deep Impact next. Whatever that might be, it will not include another comet flyby. There is now insufficient fuel onboard to make major corrections to its trajectory.

Read more >>

Antimatter atom trapped !!!

Antimatter atoms have been trapped for the first time, scientists say.

Researchers at Cern, home of the Large Hadron Collider, have held 38 antihydrogen atoms in place, each for a fraction of a second.

Antihydrogen has been produced before but it was instantly destroyed when it encountered normal matter.

The team, reporting in Nature, says the ability to study such antimatter atoms will allow previously impossible tests of fundamental tenets of physics.

The current "standard model" of physics holds that each particle - protons, electrons, neutrons and a zoo of more exotic particles - has its mirror image antiparticle.

The antiparticle of the electron, for example, is the positron, and is used in an imaging technique of growing popularity known as positron emission tomography.

However, one of the great mysteries in physics is why our world is made up overwhelmingly of matter, rather than antimatter; the laws of physics make no distinction between the two and equal amounts should have been created at the Universe's birth.

Slowing anti-atoms

Producing antimatter particles like positrons and antiprotons has become commonplace in the laboratory, but assembling the particles into antimatter atoms is far more tricky.

That was first accomplished by two groups in 2002. But handling the "antihydrogen" - bound atoms made up of an antiproton and a positron - is trickier still because it must not come into contact with anything else.

While trapping of charged normal atoms can be done with electric or magnetic fields, trapping antihydrogen atoms in this "hands-off" way requires a very particular type of field.

"Atoms are neutral - they have no net charge - but they have a little magnetic character," explained Jeff Hangst of Aarhus University in Denmark, one of the collaborators on the Alpha antihydrogen trapping project.

"You can think of them as small compass needles, so they can be deflected using magnetic fields. We build a strong 'magnetic bottle' around where we produce the antihydrogen and, if they're not moving too quickly, they are trapped," he told BBC News.

Such sculpted magnetic fields that make up the magnetic bottle are not particularly strong, so the trick was to make antihydrogen atoms that didn't have much energy - that is, they were slow-moving.

The team proved that among their 10 million antiprotons and 700 million positrons, 38 stable atoms of antihydrogen were formed, lasting about two tenths of a second each.

Early days

Next, the task is to produce more of the atoms, lasting longer in the trap, in order to study them more closely.

"What we'd like to do is see if there's some difference that we don't understand yet between matter and antimatter," Professor Hangst said.

"That difference may be more fundamental; that may have to do with very high-energy things that happened at the beginning of the universe.

"That's why holding on to them is so important - we need time to study them."

Gerald Gabrielse of Harvard University led one of the groups that in 2002 first produced antihydrogen, and first proposed that the "magnetic bottle" approach was the way to trap the atoms.

"I'm delighted that it worked as we said it should," Professor Gabrielse told BBC News.

"We have a long way to go yet; these are atoms that don't live long enough to do anything with them. So we need a lot more atoms and a lot longer times before it's really useful - but one has to crawl before you sprint.

Professor Gabrielse's group is taking a different tack to prepare more of the antihydrogen atoms, but said that progress in the field is "exciting".

"It shows that the dream from many years ago is not completely crazy."

More information on anti-matter click: The Ultimate Bomb

Read more >>