Big, hot and light years away – meet the exoplanets

Astronomers have started to obtain detailed information about the atmosphere of planets outside our solar system

An artist’s impression of the giant exoplanet HR 8799c orbiting its parent star 128 light years away

Less than 20 years after detecting the first planets in orbit around stars other than our own sun, astronomers are beginning to obtain detailed information about the atmosphere of some of these “exoplanets”. The most detailed atmospheric data are coming from a very young planetary system called HR 8799, 128 light years away. It is particularly suitable for analysis because its four gas giant planets are extremely large, hot and distant from their parent star – and therefore easier to observe than Earth-like bodies.

The vast majority of the 1,000 or so exoplanets identified so far have been detected indirectly through their gravitational or photonic effects on their planet star, either inducing a tiny wobble in the stellar orbit or periodically dimming its light by passing in front of it.

Direct imaging gives far more scientific information. Taking pictures of an exoplanet’s surface is beyond the capability of current telescopes but last week two scientific groups released direct spectroscopic observations of the HR 8799 system – chemical signatures of their atmospheres. The results are published in the Astrophysical Journal and Science.

One team used a new instrument attached to the Hale telescope at California’s Palomar Observatory to read the atmospheres of HR 8799’s four giant planets.

Each has a distinctly different composition, with varying amounts of simple molecules such as methane, ammonia, acetylene and carbon dioxide. The second team, using the W.M. Keck Observatory in Hawaii, focused on obtaining higher-resolution spectra from one planet in the system: HR 8799c, which is about seven times larger than Jupiter, the biggest member of the solar system.

HR 8799c has a cloudy atmosphere rich in carbon monoxide and water vapour. “With this level of detail, we can compare the amount of carbon to the amount of oxygen present in the planet’s atmosphere, and this chemical mix provides clues as to how the entire planetary system formed,” says Travis Barman of the Lowell Observatory in Arizona.

The analysis is consistent with the “core accretion” model of planetary formation, according to which the star HR 8799 was originally surrounded by a huge disk of gas and dust. As this cooled, grains of ice formed and started sticking together with dust into what became a planetary core.

“The results suggest the HR 8799 system is like a scaled-up solar system,” says a third member of the team, Quinn Konopacky of the University of Toronto. “So, in addition to the gas giants far from their parent star, it would not come as a surprise to find Earth-like planets closer in.”

Human brain cells make a smarter mouse

Human brain cells transplanted into mice turbocharged the animals’ learning and memory, in a remarkable experiment at the University of Rochester, New York.

The study focused on glial cells, and in particular a type of glia called astrocytes, which grow larger and more extensively in the human nervous system than in other animals. It is published in the journal Cell Stem Cell.

The researchers transplanted human “glial progenitors” – immature cells that develop into astrocytes – into newborn mice. As the animals grew up, human glia flourished in their brains alongside the normal neural network of a mouse.

“The human glial cells took over to the point where virtually all of the glial progenitor cells and a large proportion of the astrocytes in the mice were of human origin, and essentially developed and behaved as they would have in a person’s brain,” says Rochester neurologist Steven Goldman.

Measuring neural activity in the mature mice, the team found that their brainwaves travelled faster and appeared more similar to those in humans. Behavioural tests then showed that the transplanted mice learnt more quickly, for example when mastering a route through a maze and remembered locations, better than animals without human glial cells.

The study draws attention to the importance of glia, and astrocytes in particular, which researchers have rather neglected in favour of neurons. “In a fundamental sense we are different from lower species,” says Goldman. “Our advanced cognitive processing capabilities exist not only because of the size and complexity of our neural networks, but also because of the increase in functional capabilities and co-ordination afforded by human glia.”

Evolution: an end to roadkill?

An estimated 80 million birds die every year in collisions with vehicles on American highways – but research in Nebraska suggests that evolution may reduce the road kill, at least for some species in some places. Charles Brown of the University of Tulsa has been studying cliff swallows with colleagues at the University of Nebraska for 30 years. The species has colonised road bridges, underpasses and culverts, building clusters of thousands of mud nests on their walls.

Every year since 1982 the researchers have travelled the same roads at the same times to count nests and collect dead birds. This methodical survey shows a steady fall in road kill from 20 swallows a year at the beginning of the period to between two and four a year recently, although the total number of nests has increased from about 12,000 to 25,000 and traffic volume has risen too.

The proposed explanation is that natural selection has reduced the length of the swallows’ wings. “Longer-winged swallows sitting on a road probably can’t take off as quickly, or gain altitude as quickly, as shorter-winged birds, and thus the former are more likely to collide with an oncoming vehicle,” Brown explains.

The study, published in the journal Current Biology, shows a marked decline over three decades in the wing length of the cliff swallow population. Birds killed by traffic have significantly longer wings than average.

Although the researchers concede that other factors may also be at play – for example, the birds learning to avoid cars or the selective removal of risk-takers – they favour wing shortening.

“Evolution is an ongoing process, and all this – roads, SUVs, and all – is part of nature or ‘the wild’,” Brown says. “They exert selection pressures in a way we don’t usually think about.”

Gut reaction to a simulated stomach

A model gut, developed at the Institute of Food Research in Norwich to simulate digestion, is set for commercialisation on a wider scale. At the same time IFR will extend the capability of the Dynamic Gastric Model, as it is known, to simulate special situations where human studies are not possible, for example, of infant formula digestion or the interaction between drugs and alcohol.

The computer-controlled model carries out the mechanical and biochemical processes of a living stomach, digesting samples of real food. Although IFR already carries out some work for the food and pharmaceutical industries, this will be expanded by a collaborative agreement with Bioneer, a Danish biotechnology company.

Meanwhile a new £900,000 grant from the UK Biotechnology and Biological Sciences Research Council will help improve the gut, says IFR’s Peter Wilde: “We will clearly demonstrate how well the model simulates and predicts the availability of nutrients or drugs in humans, and refine the model so that it can be more widely used and therefore reduce the reliance on animal and human studies.”

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