Key molecule discovered in Venus's atmosphere

Hydroxyl, an important but difficult-to-detect molecule, is made up of a hydrogen and oxygen atom each. It has been found in the upper reaches of the Venusian atmosphere, some 100 km above the surface, by Venus Express’s Visible and Infrared Thermal Imaging Spectrometer, VIRTIS. Credits: ESA (Image by C. Carreau)

Venus Express has detected the molecule hydroxyl on another planet for the first time. This detection gives scientists an important new tool to unlock the workings of Venus’s dense atmosphere.

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Hydroxyl, an important but difficult-to-detect molecule, is made up of a hydrogen and oxygen atom each. It has been found in the upper reaches of the Venusian atmosphere, some 100 km above the surface, by Venus Express’s Visible and Infrared Thermal Imaging Spectrometer, VIRTIS.

The elusive molecule was detected by turning the spacecraft away from the planet and looking along the faintly visible layer of atmosphere surrounding the planet’s disc. The instrument detected the hydroxyl molecules by measuring the amount of infrared light that they give off.

The band of atmosphere in which the glowing hydroxyl molecules are located is very narrow; it is only about 10 km wide. By looking at the limb of the planet, Venus Express looked along this faint atmospheric layer, increasing the signal strength by about 50.

Hydroxyl is thought to be important for any planet’s atmosphere because it is highly reactive. On Earth it has a key role in purging pollutants from the atmosphere and is thought to help stabilise the carbon dioxide in the martian atmosphere, preventing it from converting to carbon monoxide. On Mars it is also thought to play a vital role in sterilising the soil, making the top layers hostile to microbial life.
The reactive molecule has been seen around comets, but the method of production there is thought to be completely different from the way it forms in planetary atmospheres.

“Because the venusian atmosphere had not been studied extensively before Venus Express arrived on the scene, we have not been able to confirm much of what our models tell us by observing what is actually happening. This detection will help us refine our models and learn much more,” says one of the Principal Investigators of the VIRTIS experiment, Giuseppe Piccioni, from the Istituto di Astrofisica Spaziale e Fisica Cosmica in Rome, Italy.

On Earth, the glow of hydroxyl in the atmosphere has been shown to be closely linked to the abundance of ozone. From this study, the same is thought to be true at Venus. Now, scientists can set about estimating the amount of ozone in the planet’s atmosphere.

Venus Express has shown that the amount of hydroxyl at Venus is highly variable. It can change by 50% from one orbit to the next and this may be caused by differing amounts of ozone in the atmosphere.

“Ozone is an important molecule for any atmosphere, because it is a strong absorber of ultraviolet radiation from the Sun,” says Piccioni. The amount of the radiation absorbed is a key parameter driving the heating and dynamics of a planet’s atmosphere. On Earth, it heats the stratosphere (layer of the atmosphere) making it stable and protecting the biosphere from harmful ultraviolet rays.

Computer models will now be able to tell how this jump and drop in ozone levels over short intervals affects the restless atmosphere of that world.

“Venus Express has already shown us that Venus is much more Earth-like than once thought. The detection of hydroxyl brings it a step closer,” says Piccioni.

He and his colleagues are only reporting the initial detection from a few orbits in their latest paper. They are working on the analysis of data from about 50 other orbits and more observations will follow.

First detection of hydroxyl in the atmosphere of Venus by G. Piccioni et al. has been published in today's issue of Astronomy & Astrophysics Letters.
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Astronomers measure temperature of the early universe

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Carbon monoxide gas in distant galaxies imprints its signature on light from an even more distant quasar as it propagates towards Earth (Illustration: European Southern Observatory)

We cannot go back in time and stick a thermometer in the early universe, but astronomers have done the next best thing, using an indirect technique to find out what the universe's temperature was 11 billion years ago. It was a chilly 9 K (-264 °C) back then, which is still warmer than today's prevailing temperature of less than 3 K (-270 °C).

Some of the coldest objects in the universe are gas clouds that fill the space between stars and galaxies. But even these are warmer than absolute zero, or 0 K. That is because they are heated by radiation leftover from the universe's earliest times.

Called the cosmic microwave background (CMB), this radiation was emitted by the hot plasma that filled the universe a mere 380,000 years after the big bang, which took place an estimated 13.7 billion years ago.

But as the universe expanded, the electromagnetic waves that comprise this radiation were stretched to longer wavelengths and lower energies, decreasing the radiation's temperature. Today, that temperature is just 2.7 K.

Now, a team led by Raghunathan Srianand of the Inter-University Centre for Astronomy and Astrophysics in Pune, India, has measured what the CMB temperature was 11 billion years ago, when the universe was just a fifth its current age.

Indirect route

They found it to be 9.15 K back then, with an uncertainty of 0.7 K in either direction. That is "in excellent agreement" with the 9.3 K temperature predicted in the big bang scenario, says team member Patrick Petitjean of the Institut d'Astrophysique in Paris, France.

The astronomers arrived at their figure by a very indirect route. What they actually measured was the temperature of carbon monoxide gas in a galaxy about 11 billion light years away.

The gas was detected by the way it intercepts light from an even more distant object called a quasar – a bright galaxy whose central black hole is consuming its surroundings.

The team used the Very Large Telescope (VLT) array in Paranal, Chile, to measure the wavelengths where the carbon monoxide absorbs the quasar's light. The wavelengths affected depend on the temperature of the galaxy's gas, whose heat is thought to come from the CMB.

Charles Bennett, chief scientist for NASA's Wilkinson Microwave Anisotropy Probe (WMAP) mission, which measures the CMB, says it is important to make such measurements to test scientists' expectations. "It's nice to see consistent things in different ways," he told New Scientist.

Journal reference: Astronomy & Astrophysics (vol 482, p L39)

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How to Escape From a Black Hole

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According to Einstein's theory of general relativity, black holes are regions of space where gravity is so strong that not even light can escape. And in the 1970's physicist Stephen Hawking asserted that any information sucked inside a black hole would be permanently lost. But now, researchers at Penn State have shown that information can be recovered from black holes.

A fundamental part of quantum physics is that information cannot be lost, so Hawking's claim has been debated. His idea was generally accepted by physicists until the late 1990s, when many began to doubt the assertion. Even Hawking himself renounced the idea in 2004. Yet no one, until now, has been able to provide a plausible mechanism for how information might escape from a black hole. A team of physicists led by Abhay Ashtekar, say their findings expand space-time beyond its assumed size, providing room for information to reappear.

Ashtekar used an analogy from Alice in Wonderland: "When the Cheshire cat disappears, his grin remains," he said. "We used to think it was the same way with black holes. Hawking's analysis suggested that at the end of a black hole's life, even after it has completely evaporated away, a singularity, or a final edge to space-time, is left behind, and this singularity serves as a sink for unrecoverable information."

But the Penn State team suggest that singularities do not exist in the real world. "Information only appears to be lost because we have been looking at a restricted part of the true quantum-mechanical space-time," said Ashtekar. "Once you consider quantum gravity, then space-time becomes much larger and there is room for information to reappear in the distant future on the other side of what was first thought to be the end of space-time."

According to Ashtekar, space-time is not a continuum as physicists once believed. Instead, it is made up of individual building blocks, just as a piece of fabric, though it appears to be continuous, is made up of individual threads. "Once we realized that the notion of space-time as a continuum is only an approximation of reality, it became clear to us that singularities are merely artifacts of our insistence that space-time should be described as a continuum."

To conduct their studies, the team used a two-dimensional model of black holes to investigate the quantum nature of real black holes, which exist in four dimensions. That's because two-dimensional systems are simpler to study mathematically. But because of the close similarities between two-dimensional black holes and spherical four-dimensional black holes, the team believes that this approach is a general mechanism that can be applied in four dimensions. The group now is pursuing methods for directly studying four-dimensional black holes.

The team's work will be published in the May 20, 2008 issue of the journal Physical Review Letters.

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