Archive for the ‘Astrochemistry’ Category

The aromatic Universe

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The rich molecular structures of polycyclic aromatic hydrocarbons — essentially planar flakes of fused benzene rings — and their fullerene cousins are revealed through their vibrational and electronic spectra.

In this artistic impression, large polycyclic aromatic hydrocarbon (PAH) molecules exposed to the strong radiation field of a star first lose all their peripheral hydrogen atoms (white atoms, top right) and are transformed into small graphene flakes whose fragile, dangling carbon rings at the corners break off. That degradation is then followed by the loss of carbon atoms. The loss creates pentagons (red) in the dehydrogenated PAH molecule, which bends the structure out of the plane and culminates in the formation of a C60 fullerene

A. Candian, J. Zhen, A.G.G.M. Tielens
Over the past 20 years, ground- and space-based observations have revealed that the universe is filled with molecules. Astronomers have identified nearly 200 types of molecules in the interstellar medium (ISM) of our galaxy and in the atmospheres of planets; for the full list, see Molecules are abundant and pervasive, and they control the temperature of interstellar gas. Not surprisingly, they directly influence such key macroscopic processes as star formation and the evolution of galaxies.

Written by physicsgg

August 19, 2019 at 8:51 am

Quantum tunnelling enables ‘impossible’ space chemistry

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Accelerated chemistry in the reaction between the hydroxyl radical and methanol at interstellar temperatures facilitated by tunnelling
Robin J. Shannon, Mark A. Blitz, Andrew Goddard & Dwayne E. Heard
Understanding the abundances of molecules in dense interstellar clouds requires knowledge of the rates of gas-phase reactions between uncharged species.
However, because of the low temperatures within these clouds, reactions with an activation barrier were considered too slow to play an important role.
Here we show that, despite the presence of a barrier, the rate coefficient for the reaction between the hydroxyl radical (OH) and methanol—one of the most abundant organic molecules in space—is almost two orders of magnitude larger at 63 K than previously measured at ∼200 K.
We also observe the formation of the methoxy radical product, which was recently detected in space.
These results are interpreted by the formation of a hydrogen-bonded complex that is sufficiently long-lived to undergo quantum-mechanical tunnelling to form products.
We postulate that this tunnelling mechanism for the oxidation of organic molecules by OH is widespread in low-temperature interstellar environments…

Read also: Quantum mechanics enables ‘impossible’ space chemistry

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July 1, 2013 at 10:25 am

Mars Science Laboratory Time Lapse: Sol 0 – Sol 281

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This is a time lapse video from the Curiosity Rover, created with the Raw Images available at… .
Created from using only Full Data Product from the Front Left Hazcam and covers the period between Sol 0 (August 8th, 2012) and Sol 281 (May 21st, 2013).

Written by physicsgg

May 24, 2013 at 5:26 pm

Mars Rock Touched by NASA Curiosity has Surprises

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Target: Jake Matijevic Rock
This image shows where NASA’s Curiosity rover aimed two different instruments to study a rock known as “Jake Matijevic.” The red dots are where the Chemistry and Camera (ChemCam) instrument zapped it with its laser on Sept. 21, 2012, and Sept. 24, 2012, which were the 45th and 48th sol, or Martian day of operations. The circular black and white images were taken by ChemCam to look for the pits produced by the laser. The purple circles indicate where the Alpha Particle X-ray Spectrometer trained its view.

This image was obtained by Curiosity’s Mast Camera on Sept. 21, 2012 PDT (Sept. 22 UTC), or sol 46. An unannotated version of this image is also available.

Scientists white-balanced the color in this view to increase the inherent differences visible within the rock. (nasa)

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Written by physicsgg

October 12, 2012 at 6:24 am

Posted in ASTROBIOLOGY, Astrochemistry, SPACE

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How to Find a Meteorite in 5 Steps

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A chrondite meteorite in situ in Rub’ al Khali, Saudi Arabia.
Image: Creative Commons | Meteorite Recon

To start, get permission to keep what you find, find a barren spot like the Mojave Desert or Great Plains, and track down ‘dark flight trajectories’ from recent fireballs
By Natalie Wolchover and Life’s Little Mysteries
Earth is under constant bombardment by space rocks. When they crash and burn through the atmosphere, most of the debris gets lost to the oceans, while some is buried or gradually weathered away. Nonetheless, plenty of chunks of fallen meteors, or meteorites, are strewn across the accessible parts of the planet. So far, more than 40,000 meteorites have been found and catalogued, and countless more are still out there, waiting to be chanced upon.

If you need further incentive for finding something that was forged at the birth of our sun and contains secrets about the nature of our solar system, there’s this: Space rocks are worth as much as $1,000 per gram. The following tips will get you started on your search, but be warned: This extraterrestrial treasure hunt requires hard work and dedication.

Step 1. Get permission
Before you plan a meteorite hunt, make sure that if you find one, you’ll be allowed to keep it. Space rocks found in national parks belong to the federal government and cannot legally be kept, said David Kring, a meteorite scientist at the University of Arizona’s Lunar and Planetary Institute……

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Written by physicsgg

May 3, 2012 at 4:36 pm

Mars is too dry to support life on its surface…

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… but it could be lurking in the depths

New research has shown that life on the surface of Mars is unlikely given the nature of the soil

Scientists have virtually ruled out the possibility of life on Mars having revealed the planet experienced a 600 year water drought.

Samples of soil found that the surface had been starved of any moisture that might enhance the view that there are living organisms on the red planet.

Researchers spent three years gathering the the specific particles, which they likened to the soil found on the Moon – where it is conclusive that no life exists.

Dr Tom Pike, who fronted the study, said: ‘We found that even though there is an abundance of ice, Mars has been experiencing a super-drought that may well have lasted hundreds of millions of years.

‘We think the Mars we know today contrasts sharply with its earlier history, which had warmer and wetter periods and which may have been more suited to life.

‘Future NASA and ESA (European Space Agency) missions that are planned for Mars will have to dig deeper to search for evidence of life, which may still be taking refuge underground.’

The sample was collected during Nasa’s 2008 mission to Mars and was extracted from the northern region of the planet.

Despite that area being arctic, separate studies revealed that the planet in its entirety is covered with the exact same substance.

The results noted that most Earth-like organisms would need to retreat underground to survive on Mars.

Below ground, there is sufficient pressure for water to be kept in a liquid state, which would enable microbes to thrive.

And while the surface temperature is not ideal for life, being an extremely chilly -65C, below ground it would be much warmer thanks to heat from the planet’s core.

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Written by physicsgg

February 5, 2012 at 4:38 pm

Posted in ASTROBIOLOGY, Astrochemistry

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Possible life in the Martian trenches?

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A team of scientists at the Planetary Science Institute in Tucson, Arizona, have drawn attention to a couple of small mineral-rich depressions on Mars that, perhaps relatively recently in the red planet’s history, could have been places for life.

The troughs were discovered at Noctis Labyrintus, also known as ‘the labyrinth of the night’ – a region that is noted for its system of deep, steep-walled valleys. “We discovered these locations that show many kinds of minerals that formed by water activity,” says Catherine Weitz, lead author of a paper featured in the journal Geology and a senior scientist at the Institute. “The clays we found, called iron/magnesium [Fe/Mg]-smectites, are much younger at Noctis Labyrinthus relative to those found in the ancient rocks on Mars, which indicates a different water environment in these depressions relative to what was happening elsewhere on Mars.”

A Viking 1 image of Noctis Labyrinthus. The canyons are filled with mist from frost sublimated by the early-morning Sun. South is toward the top

The smectites that Weitz speaks of are a silica and aluminum based type of clay also found to contain iron or magnesium. This specific substance, which readily expands or contracts under the influence of water, is formed from other silicate materials which have been altered in the presence of non-acidic water.

Along with her colleagues, Weitz investigated around 300 metres of rock, vertically exposed within two 30 to 40 kilometre depressions close to the western end of the Valles Marineris canyon system. With the help of high-resolution images from the High Resolution Imaging Science Experiment (HiRISE) camera and spectral data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on the Mars Reconnaissance Orbiter (MRO) spacecraft, combined with the assistance of Digital Terrain Models that enabled elevations and geometric relationships between areas to be determined, the team were able to map hydrated minerals. This in turn allowed them to understand how the water chemistry varied over time within each of the depressions, also referred to as troughs…… Read the rest of this entry »

Written by physicsgg

September 21, 2011 at 1:43 pm

Posted in ASTROBIOLOGY, Astrochemistry, SPACE

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The chemical history of molecules in circumstellar disks

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Schematic view of the history of H2O gas and ice throughout the disk. The main oxygen reservoir at t(acc) is indicated for each zone; the histories are described in the text. The percentages indicate the fraction of the disk mass contained in each zone. Note the disproportionality of the R and z axes. The colours have no specific meaning other than to distinguish the different zones

Context: The chemical composition of a molecular cloud changes dramatically as it collapses to form a low-mass protostar and circumstellar disk. Two-dimensional (2D) chemodynamical models are required to properly study this process.
Aims: The goal of this work is to follow, for the first time, the chemical evolution in two dimensions all the way from a pre-stellar core into a circumstellar disk. Of special interest is the question whether the chemical composition of the disk is a result of chemical processing during the collapse phase, or whether it is determined by in situ processing after the disk has formed.
Methods: Our model combines a semi-analytical method to get 2D axisymmetric density and velocity structures with detailed radiative transfer calculations to get temperature profiles and UV fluxes. Material is followed in from the core to the disk and a full gas-phase chemistry network — including freeze-out onto and evaporation from cold dust grains — is evolved along these trajectories. The abundances thus obtained are compared to the results from a static disk model and to observations of comets.
Results: The chemistry during the collapse phase is dominated by a few key processes, such as the evaporation of CO or the photodissociation of H2O. At the end of the collapse phase, the disk can be divided into zones with different chemical histories. The disk is not in chemical equilibrium at the end of the collapse, so care must be taken when choosing the initial abundances for stand-alone disk chemistry models. Our model results imply that comets must be formed from material with different chemical histories: some of it is strongly processed, some of it remains pristine. Variations between individual comets are possible if they formed at different positions or different times in the solar nebula.

Written by physicsgg

September 10, 2011 at 8:37 am

Posted in Astrochemistry