RAS: Pluto Has Carbon Monoxide in Its Atmosphere

[bystander]

NAM 18: Pluto has carbon monoxide in its atmosphere
Royal Astronomical Society | National Astronomy Meeting | 2011 Apr 19

Artist's impression of Pluto's huge atmosphere of carbon monoxide. [i]Credit: P.A.S. Cruickshank[/i]

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A British-based team of astronomers has discovered carbon monoxide gas in the atmosphere of Pluto, after a worldwide search lasting for nearly two decades. Team leader Dr Jane Greaves of the University of St Andrews will present the new discovery in her talk on Wednesday 20 April at the National Astronomy Meeting in Venue Cymru, Llandudno, Wales.

Pluto was discovered in 1930 and then considered as the Sun's smallest and most distant planet. Since 2006 it has been regarded by astronomers as a 'dwarf planet', one of a handful of such bodies with sizes of hundreds of kilometres that orbit in the distant reaches of the Solar System, out beyond Neptune. Pluto is the only dwarf planet known to have an atmosphere, found in 1988 when it dimmed the light of a distant star before Pluto passed in front of it.

The new results, obtained at the 15-metre James Clerk Maxwell Telescope in Hawaii, show a strong signal of carbon monoxide gas. Previously the atmosphere was known to be over a hundred kilometres thick, but the new data raise this height to more than 3000 kilometres - a quarter of the way out to Pluto's largest moon, Charon. The gas is extremely cold, about -220 degrees Centigrade. A big surprise for the team was that the signal is more than twice as strong as an upper limit obtained by another group, who used the IRAM 30-metre telescope in Spain in 2000.

"It was thrilling to see the signal gradually emerge as we added in many nights of data", said Dr Jane Greaves, the team leader from the University of St Andrews, "The change in brightness over the last decade is startling. We think the atmosphere may have grown in size, or the carbon monoxide abundance may have been boosted." Such changes have been seen before but only in the lower atmosphere, where methane - the only other gas ever positively identified - has also been seen to vary.

In 1989 Pluto made its closest approach to the Sun, a comparatively recent event given that it takes 248 years to complete each orbit. The gases probably result from solar heating of surface ice, which evaporates as a consequence of the slightly higher temperatures during this period. The resulting atmosphere is probably the most fragile in the Solar System, with the top layers blowing away into space.

"The height to which we see the carbon monoxide agrees well with models of how the solar wind strips Pluto's atmosphere" commented team member Dr Christiane Helling, also of the University of St Andrews.

Unlike the greenhouse gas carbon dioxide, carbon monoxide acts as a coolant, while methane absorbs sunlight and so produces heating. The balance between the two gases, which are just trace elements in what is thought to be a nitrogen-dominated atmosphere, is critical for its fate during the many-decades long seasons. The newly discovered carbon monoxide may hold the key to slowing loss of the atmosphere - but if the chilling effect is too great, it could result in nitrogen snowfalls and all the gases freezing out onto the ground. "Seeing such an example of extra-terrestrial climate-change is fascinating", says Dr Greaves. "This cold simple atmosphere that is strongly driven by the heat from the Sun could give us important clues to how some of the basic physics works, and act as a contrasting test-bed to help us better understand the Earth's atmosphere."

The data were obtained with the JCMT's 'receiver A', an instrument that has been in regular operation since the 1990s. Dr Per Friberg, who designed new observing modes and data analysis procedures for the team, commented "This shows how we can make the best use of telescopes and keep making unexpected discoveries." The JCMT is operated jointly by the UK, Canada and the Netherlands and is approaching its twenty-fifth anniversary. The team have another Pluto observing run scheduled at the JCMT for the end of April, and in the long-term, they hope to continue tracking the changes in the atmosphere at least up to the fly-by of NASA's New Horizons space probe in 2015.

Discovery of carbon monoxide in the upper atmosphere of Pluto - JS Greaves, Ch Helling, P Friberg

• Monthly Notices of the Royal Astronomical Society Letters (online 15 Apr 2011) DOI: 10.1111/j.1745-3933.2011.01052.x
  arXiv.org > astro-ph > arXiv:1104.3014 > 15 Apr 2011

[neufer]

MOPITT 2000 global carbon monoxide.

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<<Carbon monoxide (CO), also called carbonous oxide, is a colorless, odorless, and tasteless gas which is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal biological functions. Carbon monoxide is present in small amounts in the atmosphere, chiefly as a product of volcanic activity but also from natural and man-made fires (such as forest and bushfires, burning of crop residues, and sugarcane fire-cleaning). The burning of fossil fuels also contributes to carbon monoxide production. Carbon monoxide occurs dissolved in molten volcanic rock at high pressures in the Earth's mantle. Worldwide, the largest source of carbon monoxide is natural in origin, due to photochemical reactions in the troposphere which generate about 5 x 10¹² kilograms per year. Carbon monoxide is a nutrient for methanogenic bacteria, a building block for acetylcoenzyme A. This is the theme for the emerging field of bioorganometallic chemistry. Extremophile micro-organisms can thus metabolise carbon monoxide in such locations as the thermal vents of volcanoes.

Carbon monoxide has an indirect radiative forcing effect by elevating concentrations of methane and tropospheric ozone through chemical reactions with other atmospheric constituents (e.g., the hydroxyl radical, OH.) that would otherwise destroy them. Through natural processes in the atmosphere, it is eventually oxidized to carbon dioxide. Carbon monoxide concentrations are both short-lived in the atmosphere and spatially variable.

Carbon monoxide has been unknowingly used by humans since prehistoric times, for the smelting of iron and other metallic ores. The gas was used for executions by the Greek and Romans in Classical Antiquity, and was first described by the Spanish doctor Arnaldus de Villa Nova in the 11th century. In 1776, the French chemist de Lassone produced CO by heating zinc oxide with coke, but mistakenly concluded that the gaseous product was hydrogen as it burned with a blue flame. The gas was identified as a compound containing carbon and oxygen by the Scottish chemist William Cumberland Cruikshank in the year 1800. Its toxic properties on dogs were thoroughly investigated by Claude Bernard around 1846.

During World War II, a gas mixture including carbon monoxide was used to keep motor vehicles running in parts of the world where gasoline and diesel fuel was scarce. External charcoal or wood gas generators were fitted, and the mixture of atmospheric nitrogen, carbon monoxide and smaller amounts of other gasses produced by gasification was piped to a gas mixer. The gas mixture produced by this process is known as wood gas. Carbon monoxide was also reportedly used on a small scale during the Holocaust at some Nazi extermination camps. Carbon monoxide poisoning is the most common type of fatal air poisoning in many countries. Carbon monoxide is colorless, odorless, and tasteless, but highly toxic. It combines with hemoglobin to produce carboxyhemoglobin, which is ineffective for delivering oxygen to bodily tissues. Concentrations as low as 667 ppm may cause up to 50% of the body's hemoglobin to convert to carboxyhemoglobin. A level of 50% carboxyhemoglobin may result in seizure, coma, and fatality. In the United States, the OSHA limits long-term workplace exposure levels above 50 ppm.

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Carbon monoxide occurs in various natural and artificial environments.
Typical concentrations in parts per million are as follows:

Concentration 	Source

0.1 ppm 	Natural atmosphere level (MOPITT)
0.5 to 5 ppm 	Average level in homes
5 to 15 ppm 	Near properly adjusted gas stoves in homes, modern vehicle exhaust emissions
100 to 200 ppm 	Exhaust from automobiles in the Mexico City central area
5,000 ppm 	Exhaust from a home wood fire
7,000 ppm 	Undiluted warm car exhaust without a catalytic converter

The most common symptoms of carbon monoxide poisoning may resemble other types of poisonings and infections, including symptoms such as headache, nausea, vomiting, dizziness, fatigue and a feeling of weakness. Infants may be irritable and feed poorly. Neurological signs include confusion, disorientation, visual disturbance, syncope and seizures. Carbon monoxide binds to other molecules such as myoglobin and mitochondrial cytochrome oxidase. Exposures to carbon monoxide may cause significant damage to the heart and central nervous system, especially to the globus pallidus, often with long-term sequelae. Carbon monoxide may have severe adverse effects on the fetus of a pregnant woman.

Carbon monoxide is produced naturally by the human body as a signaling molecule. Thus, carbon monoxide may have a physiological role in the body, such as a neurotransmitter or a blood vessel relaxant. Because of carbon monoxide's role in the body, abnormalities in its metabolism have been linked to a variety of diseases, including neurodegenerations, hypertension, heart failure, and inflammation.>>