Did the Earth move for you?

Just as a forensic scientist can find out what happened at a crime scene so a forensic seismologist can fingerprint the Earth to pinpoint unidentified explosions.

Geoscientist Terry Wallace of the University of Arizona is using data from some 3600 seismic stations – that normally look for volcanic and earthquake activity – to spot sinking submarines, industrial explosions, nuclear weapons testing, landslides, and other unidentified phenomena that make the Earth move.

Terry Wallace (image courtesy of Wallace)

Terry Wallace (image courtesy of Wallace)

Seismological tools and theory can be used as constraints to tell when an accident occurs or something that’s not accidental, like a nuclear explosion, explains Wallace, We can then put behind that some ideas of how big an explosion might be, or if it’s a landslide, how big the landslide might have been, or how far the rocks have fallen, for example.

He and his colleagues have confirmed, for instance, the when and where of Indian and Pakistani nuclear testing in the late 1990s. They have also studied the claim that Iraq tested a nuclear weapon in 1989. The alleged test was reported to have been carried out beneath Lake Rezazza, approximately 100 km southwest of Baghdad at 10:30h on 19 September. Wallace and his colleagues examined the global earthquake catalogues produced by the International Seismic Center and the US Geological Survey and say they reveal no seismic disturbances at all in Iraq that day. Moreover, they say there has been no seismicity within 50 km of the reported test site for the years 1980 to 1999. One problem with the assertion that no weapons testing took place, they point out, is that the detection threshold for these global catalogues was just magnitude 4.0 in 1989 so a smaller magnitude event may have not been picked up by the sensors. Thankfully, national catalogues for Israel, Jordan and Iran reported no seismic event in the region on that date either (19 September 1989).

Nuclear tests (image courtesy of Wallace)

Nuclear tests (image courtesy of Wallace)

The lower detection limit of modern seismic testing is only limited by the natural noises of the Earth. However, comparisons between results from different stations will reveal very fine detail. Explosions and earthquakes both generate seismic waves, but they have distinctive frequency signatures much like the tones of a voice, Wallace told Spotlight, Just as most children’s voices can be distinguished from adults, seismograms can be used to identify if a disturbance was caused by an earthquake or an explosion.

Two explosions (image courtesy of Wallace)

Two explosions (image courtesy of Wallace)

Wallace and his team have also analysed the seismic activity that occurred on the day the Russian submarine Kursk sank north of the Kola Peninsula. There were two explosions on 12th August 2000 associated with reports of this vessel sinking. There was a gap of two minutes between the explosions, the second of which was much bigger. Seismometers detected both up to 4500 km away. Calculations that compare results from different seismometers revealed that the second explosion was the equivalent of five tonnes of TNT exploding, which Wallace suggests was a warhead detonating. Our findings were corroborated when the Russians released their report in July this year, says Wallace.

The Kursk sank on 12th August 2000, in the Barents Sea

The Kursk sank on 12th August 2000, in the Barents Sea

Wallace revealed the latest details of his Earthly forensics investigations at the 2002 American Geophysical Union meeting in San Francisco in December. He revealed that he and his colleagues are investigating the sinking of the USS Scorpion submarine near the mid-Atlantic ridge in 1968, the sinking of another Russian sub in the Baltic in 1989, and the sinking of a large oil derrick in the North Sea that produced a 3.5-magnitude earthquake when it hit the ocean floor.

Water seismometers, or hydrophones, are even more sensitive to water rumblings than are the land-based versions. Using a hydrophone in the water, we can see the explosion of one stick of dynamite anywhere in the world. That’s how quiet the oceans are. So if you are going to hide something, don’t do it in the water, Wallace says.

The whole research effort for my group is to develop as big a portfolio as possible. This way, when we see an industrial accident where a fireworks factory blows up or a gasoline tank blows up, we have all the different kinds of seismic records we can get from that and we have characterized them. Then the next time something like that happens we have some experience to draw from. We’ve got some fingerprints left over to help us understand what is happening, Wallace adds.

Further reading

Suggested searches

Seismology
Seismic waves

Starry, starry night

The heavens may be full of stars like our Sun complete with planetary systems just like ours, according to a new study by US astronomers. David Weintraub and Jeff Bary of Vanderbilt University in Nashville Tennessee have studied the planetary disks around T Tauri stars and reckon the astronomical received wisdom about them may be wrong. They suggest there may be a lot more planets circling stars like the Sun than current models of star and planet formation predict.

Most astronomers think planetary systems are common, Weintraub told Spotlight. However, this belief doesn’t match up well to the combination of astronomical measurements, as interpreted up to this time, and planet formation theory. The measurements indicate the disks out of which planets would form disappear in only a few million years. The astronomers who make these measurements and interpretations still tend to think planets are common; however, they are not sufficiently well aware that the timescale for the dispersal of the disks, as interpreted by them, is too short as compared to the timescale required by theory for the formation of planets.

David Weintraub

David Weintraub

The assumption is based on observations of T Tauri stars, stellar adolescents just a few million years old, which resemble the young Sun. The classic T Tauri star – less than 3 million years old – usually has a thick protoplanetary disk of dust and gas, which glows brightly in the infra-red region of the spectrum. Their older T Tauri siblings show no signs of encircling disks. This has led astronomers to assume the disk is gone in five million years; but, says Weintraub, the astronomers making this assumption don’t follow that to the logical conclusion that this is before planets form. He believes this is because modern theory of planet formation is simply not well known. Nevertheless, he adds, it is true that, based on the best current theories, the disks disappear in less time than is needed for the planets to form.

However, Weintraub and Bary argue that instead of the basic planetary building blocks being lost from around the star, the material may simply be evolving in ways that makes it invisible to Earthly telescopes. These stars are labelled as naked or weak line T Tauri stars. The Vanderbilt team has already begun gathering evidence that suggests planetary systems similar to our own may be relatively commonplace. The team published its preliminary findings in September in the journal Astrophysical Letters and will publish the full evidence in support of their hypothesis in The Astrophysical Journal later this year.

Jeff Bary inspecting the historic 6-inch telescope used by Edward Barnard in the 1880s (Photo by Daniel Dubois)

Jeff Bary inspecting the historic 6-inch telescope used by Edward Barnard in the 1880s (Photo by Daniel Dubois)

Weintraub is not happy with the conventional wisdom: Approaching it from a planetary evolution point of view, I have not been comfortable with some of the underlying assumptions, he says. Current models do not take the evolution of protoplanetary disks into account. Over time, the disk material should begin agglomerating into solid objects called planetesimals. As the planetesimals grow, an increasing amount of the mass in the disk becomes trapped inside these solid objects where it cannot emit light directly into space. So, Weintraub suggests this prevents astronomers on Earth from seeing any infra-red glow from the disk. Rather than the disk material dissipating, explains Bary, It may simply become invisible to our instruments.

Starry night

Starry night

The team has looked instead for the presence of molecular hydrogen around adolescent T Tauri stars, this material would be the main constituent of a protoplanetary disk and the characteristic spectral signal should persist even when dust grains and carbon monoxide, the other major constituents are locked out of site. T Tauri stars are strong X-ray sources and this, the astronomers reasoned, should provide enough energy to stimulate any molecular hydrogen around the star so that astronomers could detect its faint glow. When they pointed the four-metre National Optical Astronomical Observatory telescope in Kitt Peak, Arizona at their prime targets – naked T Tauri stars such as the one known as DoAr21 – they saw the faint signal of molecular hydrogen.

The T Tauri Star Forming System (Credit : C. & F. Roddier (IfA, Hawaii), CFHT)

The T Tauri Star Forming System (Credit : C. & F. Roddier (IfA, Hawaii), CFHT)

Weintraub and Bary admit that they have more work to do to in order to convince their colleagues to adopt their theory. They have been allocated time on a larger telescope, the eight-metre Gemini South in Chile and plan to survey 50 more naked T Tauri stars to see how many of them produce the same molecular hydrogen emissions. If a large number of them do, it will indicate that they have discovered a general mechanism involved in the planetary formation process.

Coincident with the publication of Weintraub’s results a team at Washington University has cast doubt on the assumption that it takes millions of years to form gas giant planets. Thomas Quinn and his colleagues reckon that if gas giants don’t form quickly they won’t form at all. Moreover, when he says quickly he means quickly – a few hundred years rather than the statelier multi-million-year pace associated with astronomy.

Quinn has used a highly refined mathematical model to look at the formation of planets. His findings suggest that the protoplanetary disk begins to fragment after just a few spins around its star. As the disk fragments, clusters of matter begin to form quickly and start to draw in the gases that form vapour shrouds around gas giants. If these planets can’t form quickly, then they should be a relatively rare phenomenon, whereas if they form according to this mechanism they should be a relatively common phenomenon, said Quinn.

According to the present theory, it takes between 1 and 10 million years to form a gas giant, a Jupiter or a Saturn and even longer to form a rocky solid planet like the Earth or Mars. If they are forming this quickly then perhaps Weintraub and Bary’s sightings of molecular hydrogen are simply revealing the last traces of a protoplanetary disk lost to space or absorbed by the star. Otherwise, astronomers should be able to see the planets around the T Tauri already.

Further reading

Quinn et al, Science, 298, 1756 (2002)
http://www.sciencemag.org/cgi/content/short/298/5599/1756

David Weintraub
http://www.vanderbilt.edu/AnS/physics/cv/weintraub_cv/frontpage.html

Suggested searches

T Tauri stars
Extrasolar planets
Formation stars planets

Sweet pollution solution

Doughnut-shaped molecules could provide a sweet solution for extracting toxic and environmentally harmful compounds from industrial waste water.

According to Ashley Bibby and Louis Mercier of Laurentian University, in Sudbury, Ontario, Canada, the industrial remediation process can be improved by using a property of molecules with a central hole to act as hosts for smaller, poisonous guests. Cyclodextrins are made by certain bacteria but have found a range of uses in the chemical laboratory. These cyclic molecules are shaped rather like a doughnut with a central hole into which smaller molecules can sit.

Cyclodextrin - the molecule with a hole (illustration by David Bradley)

Cyclodextrin – the molecule with a hole (illustration by David Bradley)

The researchers have trapped the water-soluble cyclodextrin molecules inside a porous silica framework to provide a robust new material (CD-HMS) that can absorb a range of water-soluble materials, including nitrophenol, nitroaniline, chlorophenol and phenol itself. Phenols are common ingredients and by-products of industries as diverse as chemical manufacture, pharmaceutical and agrochemical production, textiles and electronics industries. The CD-HMS can selectively extract these phenolic molecules from water.

Bibby and Mercier have found that the preference of certain toxic waste molecules, such as aromatic hydrocarbons, for the interior of the cyclodextrin doughnut lends itself well to extracting such molecules from water. We can achieve efficient adsorption of organic molecules from water, explains Mercier, The supported reagents we use can be prepared in a quite environmentally friendly way and should be effective under the typically harsh conditions (above ambient temperature, low pH, presence of bacteria, etc) found in industrial and waste water treatment plants.

The researchers explain that the open-framework structure of the porous silica in which there are large numbers of cyclodextrins in each pore allows a large number of phenol and other molecules to quickly enter and be trapped in the central cavity of the cyclodextrins simply by mixing the CD-HMS with the contaminated water.

In practice, the CD-HMS would be incorporated into a filter device. The adsorbed contaminants could then be released from the cyclodextrin groups by exposing the loaded CD-HMS to ethanol (in which organic molecules are highly soluble), thereby regenerating the materials, explains Mercier, The phenols could then be safely disposed of (stored in containers, incinerated, chemically or biologically degraded, recycled for chemical syntheses).

The material might also be adapted for other molecules including pesticides, volatile organic compounds, such as toluene and benzene and even drug separations. CDs will bind with many organic compounds in water simply because of the hydrophobic cavity of the molecule, adds Mercier, Molecules that have a good fit inside the cavity, however, will bind more effectively in the cavity than other molecules. Small aromatic molecules like phenols have a good fit and therefore bind effectively with the materials.

A good example of this is the team’s recent results on pesticide removal using CD-HMS. They found that when treating solutions containing a mixture of various pesticides those with aromatic functionalities (DDT for example) can be completely removed, whereas other pesticides are not adsorbed as effectively. The material is therefore selective to certain groups of molecules, but not to specific individual molecules. These more recent results will be published later in the year.

Further reading

Green Chem., 2003, 5

DOI: 10.1039/b209251b

Suggested searches

Cyclodextrins
Phenols