The Yellowstone caldera formed 640,000 years ago in an explosion of magma more than 1000 times greater than the Mount St Helens eruption in 1980. While it is common knowledge that the caldera floor rises and falls, the source of the motion remains uncertain. According to a previous popular theory, the accumulation and release of fluid not far beneath the surface is driving the cycles, but Dzurisin, of the David A. Johnston Cascades Volcano Observatory in Vancouver, Washington, and his colleagues say a deeper source best explains their latest findings.

The team, led by Charles Wicks of the US Geological Survey in Menlo Park, California, used a series of satellite measurements to determine the fluctuations in elevation - up to 120 millimetres - over a seven-year period.

Although the floor of the caldera began subsiding in 1997, the researchers uncovered a new region of activity beneath the north rim of the caldera that continued to swell from 1995 until 2002. Models incorporating the measurements indicate that the source of the upward push was 10 to 16 kilometres beneath the surface in the basaltic magma layer, well below the level of the fluid suggested as the source of the motion (Nature, vol 440, p 72).

The picture is one of magma flow driving the undulation of the surface, flowing upward from beneath the caldera floor towards the northern rim and then down and out from beneath the rim. Seismic activity near the exit acts as a valve, suggests Wicks, blocking or releasing the magma outflow. This explains why the rim and floor can swell and sink at different times.

The idea also explains the rise in thermal activity in the rim area in 2003, Wicks says, when some trails had to be closed because of increased steam releases and a rise in surface temperatures. The swelling magma could have cracked the crust, creating new avenues for steam to escape to the surface, he says.

From issue 2541 of New Scientist magazine, 01 March 2006, page 11

Eberhard Sauter of the Alfred Wegener Institute for Polar and Marine Research in Bremerhaven, Germany, and his colleagues found a huge column of gas bubbles rising to the surface from Håkon Mosby. They used an echo sounder to get acoustic images of the plume. Meanwhile, a remote-controlled robot dived down and videotaped the bubbles while a probe sampled the water and took temperature and depth readings.

The gas inside the bubbles turned out to be methane, which was protected from oxidation by a tough skin around the bubbles. "We found that a gas hydrate membrane enabled them to rise for around 800 metres," says Sauter. The bubbles eventually dissolved in surface waters, much of it probably ending up in the atmosphere (Earth and Planetary Science Letters, DOI: 10.1016/j.epsl.2006.01.041).

"We estimate that several hundred tonnes of methane are being released from this location every year," says Sauter. The atmospheric methane budget is around 600 gigatonnes per year, so this won't make a huge difference. However, if every deep-sea volcano turned out to release a similar amount, it would be a different matter.

No one really knows how many of these volcanoes there are. Estimates vary from thousands to tens of thousands, and it is unlikely that they are all active at the same time. "I'm not sure if it's time to say that deep sea methane is a significant source of atmospheric methane," says Alexei Milkov, a petroleum systems analyst for BP America in Houston, Texas. "The jury is still out."

The result could be carnage. An outbreak of H7N7 bird flu in Dutch poultry in 2003 required the slaughter of some 30 million birds - half the country's poultry. If, as seems inevitable, H5N1 strikes in a big way the result will be similar devastation.

Yet culling alone may not stop H5N1 spreading. Scientists contacted by New Scientist in the past few days say that the growth of intensive poultry farming and vaccine development have made the EU's policy outdated. Farms in the Netherlands and elsewhere are now so crowded that the old methods of controlling outbreaks are likely to fail. In these areas, they say, the most susceptible birds should be vaccinated now, before the disease hits. Only this, they say, will stop outbreaks in these regions from spiralling out of control.

Last week the EU relaxed its policy and allowed some farmers to vaccinate free-range birds. The ruling applies only to the Netherlands and three western departments in France where free-range ducks and geese are used for foie gras production and wetland areas are used by migrating wild birds. Apart from these few exceptions, vaccination remains prohibited.

In most EU countries, the strategy has been to order poultry to be kept indoors. This is supposed to limit their exposure to wild birds infected with the virus, but success is far from guaranteed. When turkeys kept indoors in eastern France started dying of H5N1, Ilaria Capua of Italy's national reference lab for bird flu wasn't surprised. "You can infect turkeys by stepping in infected bird poo and tracking it into the barn," she says. French investigators suspect the virus probably came in on bales of straw used as turkey bedding.

When such outbreaks occur, the standard response is to slaughter the infected birds and all other poultry within a certain radius. The tactic appears to have worked in eastern France, where 11,000 turkeys at the infected farm were slaughtered, but this part of France was lucky in having relatively few poultry farms. In high-density areas it could be a different story, says Arjan Stegeman of Utrecht University in the Netherlands. When Stegeman and his team analysed what happened during the 2003 Dutch outbreak, they found that such measures were barely able to contain the virus in areas of high poultry density. The country's poultry industry was hit hard as a result, and is only just recovering now.

With the recent arrival of H5N1, several other parts of Europe that have poultry densities on a par with those in the Netherlands are similarly threatened. These include the German states of Schleswig-Holstein, where infected wild birds have been found, and Lower Saxony. "If a non-vaccinated flock is infected in such a region, the probability of an outbreak similar to 2003 is very, very large," Stegeman says. There are a many such regions across Europe (see Map).

A mass outbreak in any of these regions will not only affect poultry. The vast amounts of virus that will be shed by the affected birds will put people at risk of infection with the often lethal disease, and increase the chances of the virus mutating to a form that can readily pass from person to person.

Stegeman is one of those who believe the EU's decision not to vaccinate birds before an outbreak is wrong. The EU has not ruled out "ring-vaccination" of poultry to slow or prevent spread of the virus around the source of an outbreak, but Stegeman says this is useless for flu. It takes two doses of vaccine and four weeks to protect birds, and this is far too long to be effective in an emergency.

So if the case for pre-emptive vaccination is so strong, why do the authorities refuse to consider it? One objection has been that it allows the virus to circulate undetected in vaccinated animals, as such animals show no obvious symptoms. This poses a constant risk to unvaccinated animals and, for viruses like H5N1, to humans.

Moreover, virus circulating in vaccinated chickens can mutate into potentially more dangerous forms. This is known to have happened to H5N2 bird flu in Mexico, and may have encouraged the emergence of the lethal "Z genotype" of H5N1 in China.

Supporters of vaccination argue that this would not happen in Europe. Vaccinated chickens would be regularly tested, and culled if they tested positive. Key to this is the use of a marker vaccine that triggers the production of a slightly different set of antibodies to those induced by the wild virus. Antibody tests can then distinguish between infected birds and those that have simply been vaccinated.

These scientists cite the experience of the intensive poultry-rearing region near Verona in northern Italy, which after suffering repeated outbreaks of bird flu has been vaccinating high-risk flocks against H5 and H7 bird flu for more than a year. It has worked. The outbreaks have stopped and Italy now exports the meat. Animals are routinely tested for signs of infection and are safe to eat.

The reason for this success is twofold. First, vaccinated birds are harder to infect. "If you can infect unvaccinated turkeys by tracking one poo into the barn, you need to track in 100 to infect vaccinated ones," Capua says. Secondly, if infection does occur, the birds produce and shed far less virus, so it doesn't spread as readily, giving authorities precious time to identify and stop an outbreak in its tracks.

The birds most in need of vaccination are turkeys, which are particularly sensitive to the virus. Laying hens are also at risk as egg trays and trucks collecting the eggs move from farm to farm. Free-range poultry are also at constant risk from exposure to infected wild birds. Broiler chickens raised indoors have far less contact with the outside world, and should not need vaccinating, says Capua. Nor should poultry in low-density areas, where classic culling may stop an outbreak spreading.

Vaccination is not without its problems. If Europe decided to vaccinate all its high-risk birds tomorrow, it would be hard to find enough vaccine. And because no one knows how long H5N1 is likely to persist in resistant resident wild birds such as mallards vaccination might have to continue for years.

Nor would Europe be the only buyer seeking vaccine. UN agencies are already vaccinating poultry in Nigeria, where the virus is spreading out of control, and other countries are likely to follow. "There definitely won't be enough vaccine available," Capua says. "Because there has been so little demand, companies have not invested in the capacity to make more."

Europe should start building a vaccine stockpile now, before the return of another wave of infected birds from nesting grounds in Siberia next winter makes things even worse, she says. "We'll really be blind if we don't start getting ready now. It could be the destruction of Europe's poultry industry."

From issue 2541 of New Scientist magazine, 04 March 2006, page 8

He adds: "We're more likely to be hit between now and then by an object that we don't know about."

On 23 February, new observations allowed researchers to more accurately calculate the orbit of the asteroid, named 2004 VD17, which was originally detected by the Massachusetts Institute of Technology's LINEAR project. Since the improvement did not rule out a potential collision with the Earth on 4 May 2102, they increased the asteroid's rating to level 2 on the Torino Scale, a relatively rare event.
Degrees of danger

The Torino Scale, adopted in 1999, is akin to a Richter scale for asteroid impacts. The vast majority of the 4000 or so near-Earth objects (NEOs) detected so far have been assigned to level zero on the Torino scale, meaning they have "no likely consequences".

Level 1, colour-coded green, suggests a possible impact that "merits careful monitoring". Beyond that, the risk continues to rise along the scale – levels 2, 3 and 4 are yellow; 5, 6 and 7 are orange; while 8, 9 and 10 earn red.

The highest level ever reached by an asteroid was level 4 by Apophis (2004 MN4) in December 2004, but subsequent calculations downgraded that concern to a level 1. So VD17 currently claims the top spot on NASA's online list of potential asteroid impacts.

Despite the rarity of the yellow designation, Yeomans says "Torino 2 is not very alarming." He notes that the scale does not take account of how soon an impact may occur, unlike its rival, the Palermo Scale.

Based on current observations, he says the asteroid has a 1 in 1600 chance of striking the Earth in 2102 and a 1 in 500,000 chance of hitting two years later. But further observations will soon refine the orbit calculation for VD17 – and hopefully ease minds.

NEO hunter, Andrea Milani Comparetti of the University of Pisa, Italy, says VD17 "is a serious problem, but not for our generation". He also notes that VD17 is dim and distant and is not projected to pass close by the Earth before 2102. "You will need fairly powerful telescopes to see it before it arrives," he told New Scientist.
Smaller threats

Since 1998, NASA has had a US Congressional mandate to locate 90% of all NEOs of 1 kilometre or larger by 2008. Yeomans says that 830 out of a predicted 1100 have been found so far, along with thousands of smaller objects.

In the NASA Authorization Act of 2005, Congress directed the space agency to study and report back on the best way to cost-effectively locate 90% of all asteroids down to a diameter of just 140 metres. Yeomans says there are likely to be about 100,000 such NEOs.

Yeomans and Bill Bottke of the Southwest Research Institute in Boulder, Colorado, were both members of a team that reported in 2003 that a survey to locate such small asteroids would be cost-effective, considering the damage an impact could cause. Bottke says the group found that to find 90% of the remaining hazard would cost roughly $300 million.

2004 VD17 is estimated to have a diameter of about 580 metres. An asteroid of that size would produce an impact crater about 10 kilometres wide and an earthquake of magnitude 7.4 if it struck land.

To most people, that would sound eccentric at the very least. It looked as if the idea would quietly wither on the vine. Then in January this year, it turned out that Louis's theory is still alive and kicking, and soon to roll off the press in a reputable peer-reviewed journal. I sent a preprint to several researchers, who despite voicing mixed opinions almost all agreed about one thing: the red particles Louis describes look biological.

"If they're not living cells, I don't know what they are," said Milton Wainwright, a microbiologist at the University of Sheffield, UK. "Maybe this is the beginning of something amazing." Another scientist simply commented: "Sounds like bullshit to me." That was it - I could resist this weird and controversial story no longer.

The saga dates back to 25 July 2001, when red rain fell in a district of Kerala called Kottayam. Over the following two months, red rain fell sporadically there and in other Kerala districts, gradually tailing off over time. The local newspapers buzzed with eyewitness reports. People found their clothes stained by red raindrops. Although these usually had a mild red tint, sometimes the colour was so strong that witnesses compared it to blood. Usually, the red rain would fall for less than 20 minutes.

Louis, a solid-state physicist at Mahatma Gandhi University in Kottayam, was intrigued and decided to study the rain with his student Santhosh Kumar. The pair compiled more than 120 reports of the rain from local newspapers and other sources, and gathered samples of the red rain from spots more than 100 kilometres apart (see Map).

Under the microscope, they could see red particles 4 to 10 micrometres wide with an average density of about 9 million particles per millilitre. When they dried the samples they found that each cubic metre of rainwater contained about 100 grams of the red stuff. Louis suggests 5 millimetres of red rain would typically have fallen over a square-kilometre area during each of about 100 downpours. That would make 500,000 cubic metres of water in total, containing a staggering 50 tonnes of red particles.

What could they be? One possibility was that fine red sand had blown over Kerala from some distant desert. Sand can travel amazingly far. In July 1968, for instance, fine grit in raindrops left parts of southern England coloured rusty red. The sand had blown from the Sahara inside a massive high-pressure system before falling in a rain shower.

But under the microscope, the red particles that rained on Kerala were clearly not sand. Electron micrographs show that they are shaped like biological cells. "They don't look anything like sand, they look biological," says Monica Grady, a meteorite expert at the UK's Open University in Milton Keynes. The cells, if that's what they are, are mostly cup-shaped and have a thick wall.

One type of analysis shows their chemical make-up is about 50 per cent carbon and 45 per cent oxygen by weight, along with traces of other elements such as sodium and iron. That's consistent with the components of a biological cell, according to Jeffrey Walker, a molecular biologist from the University of Colorado in Boulder. But although many of the cells have some kind of detached inner capsule, there is no visible cell nucleus, and tests for DNA that Louis carried out came back negative.

Louis rules out a distant terrestrial source for the mysterious particles, because the red rain was concentrated over Kerala for two months despite changes in climate and wind patterns. Could the cells instead be local pollen or fungal spores washed off trees and houses by the rain? Louis says no, because red rain was collected in buckets placed in wide-open spaces. Equally, he says, the red particles can't be pollen or spores from the ground that accumulated in the atmosphere, because the rain would then have been red at the start of a shower; often the colour came later.

Instead, he links the coloured rain to a meteor airburst. During the early hours of 25 July 2001, just hours before the first red rain fell, several people in the Kottayam district heard a loud sonic boom that made their houses rattle. Louis has interviewed some of those who heard it, and concluded that it was too loud to have been an ordinary thunderclap. It's possible that an incoming meteor exploded in the atmosphere.

Louis then takes a large leap and suggests the meteor was a fragment of a comet harbouring microbes from space. He thinks that is the only explanation for the red rain pattern. The meteor flew over Kerala from north to south, he suggests, shedding fragments and alien microbes in the upper atmosphere, before finally exploding over Kottayam district. There, some of the red microbes mixed with rain clouds and fell fairly quickly, while the rest gradually settled into the clouds and fell in rain over the following weeks.

"Yes, it is an extraordinary claim, but I have to report what I observe," says Louis. "We are not able to explain it by assuming a terrestrial object." The red particles look like biological cells, he stresses, but contain no DNA. They could therefore be exotic, alien life forms unknown to science.

Far-fetched? Certainly sounds it. But the idea would undoubtedly have appealed to the late University of Cambridge astronomer Fred Hoyle, champion of the "panspermia" theory. With Chandra Wickramasinghe of Cardiff University, UK, Hoyle developed the idea that life on Earth evolved from microbes that fell to its surface on a comet. In this picture, primitive life forms could be ubiquitous throughout the universe, peppered among the planets and the stars.

Philosophically, panspermia has a certain appeal. It could resolve the genuine puzzle about why life arose on Earth so fast. The solar system began its life some 4.5 billion years ago as a hostile interplanetary war zone, with rocky missiles pelting everything in sight. Around 3.9 billion years ago, the Earth suffered a particularly violent bombardment that pulverised its crust. Yet carbon isotopes in ancient rocks hint that primitive microbes were thriving just 50,000 years later - a blink of an eye in evolutionary terms. Panspermia allows off-the-shelf microbes to arrive on the newly hospitable Earth. This waves away the apparent paradox that the Earth is the only place in the entire cosmos where we've found signs of life. From experience, astronomers assume that if something has occurred once in the universe, it's probably occurred many more times - we just haven't seen it yet.

Panspermia developed a touch of giggle-factor when Hoyle and Wickramasinghe blamed extraterrestrial viruses for flu epidemics. But it has come back into fashion of late, and proponents argue there's plenty of evidence for it. Experiments have shown that some tough bacteria can survive for years in space, despite the extreme cold and high levels of radiation. Others have proved that some of these bugs could survive the high-speed collisions that they would experience if they slammed into the Earth on a comet.

The idea of primitive microbes flying around the solar system in its early days is not as wild as it seems. "Most of the rocks near the surface of the Earth are shot through with microbial life. It would be a fairly simple thing for a little piece of the crust to be ejected and life survive and land somewhere else," says Walker. On balance, he says, he'd bet that life began here on Earth. But he wouldn't be that surprised if evidence emerged that life started somewhere else and was delivered to Earth by a hunk of space rock.
Extraordinary claims

In 1996, Martian meteorite ALH 84001 caused a furore when some scientists claimed that it harboured fossil bugs. The case was never proved. "But the most interesting information that we gathered from that meteorite was that when the rock was ejected from Mars and travelled to the Earth, the temperature of the interior never exceeded something like 50 °C," says Walker. "Plenty of microbes can survive that, especially spores."

All in all, it seems that panspermia could work. Now Louis thinks the red rain of Kerala provides evidence that it actually does. His new report on the subject, which will appear in Astrophysics and Space Science in the next few months, is impressive in its detail, according to Wainwright. "Everything in the paper is done correctly, there's nothing wacky about it," he says. Grady says it is "very, very thorough indeed".

However, if scientists have a favourite quote, it's this one, popularised by Carl Sagan: "extraordinary claims require extraordinary evidence". I'm hearing it a lot in discussions about the red rain of Kerala. Grady thinks Louis and Kumar have jumped to the extraterrestrial conclusion far too quickly. "They seem to prefer the most bizarre explanation they could find," agrees Charles Cockell at the Open University, who studies the microbiology of extreme rocky environments.

What other explanations are there? Wainwright likens the red cells to spores from a rust fungus, or possibly pollen or algae. With Wickramasinghe and others, Wainwright has shown in balloon experiments that winds can carry microbes from the ground to high altitudes. Particles the size of those in the red rain could soar several kilometres above the Earth's surface. The dimpled shape could easily have arisen when the cells collapsed in the microscopy process. If that were true, he says, then the only mystery concerns the lack of DNA. "You wouldn't expect spores, microbes or algae not to have any DNA," he says. The simplest explanation is that Louis's experiments missed it, so Wainwright wants to repeat the tests. If the cells do turn out to contain DNA, then there is no great mystery. "I'd kind of relax if there was DNA there," says Wainwright.

If there is no DNA, Wainwright argues, the cells might be something extraordinary. He speculates, like Louis, that the lack of DNA might point to some kind of exotic life form, although he admits it would be paradoxical for cells without DNA to be classed as "living".

Cockell argues that there could be a simpler explanation - the red particles are actually blood. "They look like red blood cells to me," he says. The size fits just right; red blood cells are normally about 6 to 8 micrometres wide. They are naturally dimpled just like the red rain particles. What's more, mammalian red blood cells contain no DNA because they don't have a cell nucleus.

It's tough to explain, however, how 50 tonnes of mammal blood could have ended up in rain clouds. Cockell takes a wild guess that maybe a meteor explosion massacred a flock of bats, splattering their blood in all directions. India is home to around 100 species of bats, which sometimes fly to altitudes of 3 kilometres or more. "A giant flock of bats is actually a possibility - maybe a meteor airburst occurred during a bat migration," he says. "But one would have to wonder where the bat wings are."

Walker agrees that the particles in the red rain look uncannily like red blood cells. He says a simple test for haemoglobin could resolve this quickly. "If they believe they aren't red blood cells, then they need to explain how they've managed to eliminate that possibility," says Cockell. "I would have thought some more basic biochemical analysis of these cells would be worthwhile, and that should identify it, whatever it is."

"It's a pity that they don't realise this is interesting without all the extraterrestrial hype," Cockell adds. "How might you get blood into rain? I don't think anyone has observed an event where they've seen an animal ripped apart and its blood distributed in clouds. In some ways, that whole process is far more interesting than what Louis is trying to prove." For blood cells to survive would be astonishing: normally they would be destroyed within minutes if kept in rainwater, unless the salinity was the same as inside the blood cell.

In the next few weeks, the mystery of Kerala's red rain may finally be solved. Louis sent samples to Wickramasinghe's lab in Cardiff last month. As New Scientist went to press, he and Wainwright were still analysing them.

If they can't explain the origin of the samples, then the suggestion that they are alien life will gain credence. In that case, someone will have to verify an observation that Louis made which even he finds astonishing: that the cells replicate. In earlier unpublished papers, Louis says he cultured the red rain cells in unconventional nutrients, such as cedar wood oil, and showed that these DNA-devoid microbes divide happily at a temperature of 300 °C. Louis admits he left these claims out of his latest paper because he thought they would be considered "too extraordinary".

Extraordinary is an understatement: if the cells really do replicate we'll have found the first evidence of extraterrestrial life. In the end, though, I didn't find any scientist willing to bet that the red rain of Kerala contained aliens. But everyone agreed it's a cracking good story that's crying out for a proper explanation. "I think you've got to be intrigued," said Wainwright. "If you're not intrigued, then what are you doing in science?"

From issue 2541 of New Scientist magazine, 02 March 2006, page 34