Could interstellar ice provide the answer to birth of DNA?

Researchers at the University of York have shown that molecules brought to earth in meteorite strikes could potentially be converted into the building blocks of DNA.

The building blocks of DNA could have come from space [Credit: iStock]

They found that organic compounds, called amino nitriles, the molecular precursors to amino acids, were able to use molecules present in interstellar ice to trigger the formation of the backbone molecule, 2-deoxy-D-ribose, of DNA.

It has long been assumed that amino acids were present on earth before DNA, and may have been responsible for the formation of one of the building blocks of DNA, but this new research throws fresh doubt on this theory.

Meteor shower

Dr Paul Clarke, from the University of York's Department of Chemistry, said: "The origin of important biological molecules is one of the key fundamental questions in science. The molecules that form the building blocks of DNA had to come from somewhere; either they were present on Earth when it formed or they came from space, hitting earth in a meteor shower.

"Scientists had already shown that there were particular molecules present in space that came to Earth in an ice comet; this made our team at York think about investigating whether they could be used to make one of the building blocks of DNA. If this was possible, then it could mean that a building block of DNA was present before amino acids."

Before life began

In order for cellular life to emerge and then evolve on earth, the fundamental building blocks of life needed to be synthesised from appropriate starting materials -- a process sometimes described as 'chemical evolution'.

The research team showed that amino nitriles could have been the catalyst for bringing together the interstellar molecules, formaldehyde, acetaldehyde, glycolaldehyde, before life on Earth began. Combined, these molecules produce carbohydrates, including 2-deoxy-D-ribose, the building blocks of DNA.

DNA is one of the most important molecules in living systems, yet the origin 2-deoxy-D-ribose, before life on earth began, has remained a mystery.

'One-pot'

Dr Clarke said: "We have demonstrated that the interstellar building blocks formaldehyde, acetaldehyde and glycolaldehyde can be converted in 'one-pot' to biologically relevant carbohydrates -- the ingredients for life.

"This research therefore outlines a plausible mechanism by which molecules present in interstellar space, brought to earth by meteorite strikes, could potentially be converted into 2-deoxy-D-ribose, a molecule vital for all living systems."

The research is published in the journal Chemical Communications.

Source: University of York [September 14, 2017]

Read More

Photosynthesis under light conditions different from the Earth

Researchers at the Astrobiology Center (ABC) of National Institutes of Natural Science (NINS) in Japan and their colleagues have proposed that Earth-like red-edge reflection patterns could be observed on exoplanets around M-dwarfs. They point out that the first oxygenic phototrophs are most likely to have evolved underwater to utilize visible light, as occurred in the primordial ocean on Earth.

Artists impressions of a habitable planet around M-dwarfs (left) and primordial Earth (right). The surface of M-dwarf 
planet is illuminated by visible light. On the other hand, similar light conditions are expected underwater, since only 
blue-green light can penetrate meters of water [Credit: Astrobiology Center]

M-dwarfs or red dwarfs are small (0.5-0.1 solar-masses) and cool ( ~3000 Kelvin) stars, and are abundant in universe. The sun-like stars are considered plausible targets for searching habitable exoplanets. However, nearby M-dwarfs are becoming the most extensive targets for habitable planet searches because they are the most abundant nearby stars and thus could be the first candidate for detecting biosignatures on exoplanets via transit or direct imaging observations in near future.

One of the most important exoplanetary biosignatures is a specific reflection pattern on the land surface called "red-edge," which is caused by vegetation such as forests and grasslands. On the Earth, red-edge appears between red and infrared (IR) wavelengths, since red light is absorbed for photosynthesis while IR radiation is reflected. In previous studies, it was predicted that red-edge position on exoplanets should be decided by the radiation spectrum of nearby stars. Around M-dwarfs, red-edge was expected to be shifted to a longer wavelength, since planets on the exoplanets use abundant IR radiation for photosynthesis.

Researchers at the Astrobiology Center (ABC) of National Institutes of Natural Science (NINS) and their colleagues have proposed an alternative prediction that red-edge could be observed as on the Earth even on exoplanets around M-dwarfs in the online journal Scientific Reports. They point out that the first oxygenic phototrophs are most likely to have evolved underwater to utilize visible light just as in the primordial ocean on the Earth. They examined light adaptation mechanisms of visible and IR radiation-using phototrophs required for adapting to land habitats and found that IR-using phototrophs struggle to adapt to changing light condition at the boundary of water and land. Kenji Takizawa, read author of the study, said "It is too risky to utilize IR-radiation during water-to-land evolution."

Source: National Astronomical Observatory of Japan [September 12, 2017]

Read More

Are we being watched? Tens of other worlds could spot the Earth

A group of scientists from Queen's University Belfast and the Max Planck Institute for solar system Research in Germany have turned exoplanet-hunting on its head, in a study that instead looks at how an alien observer might be able to detect Earth using our own methods. They find that at least nine exoplanets are ideally placed to observe transits of Earth, in a new work published in the journal Monthly Notices of the Royal Astronomical Society.

Image showing where transits of our Solar System planets can be observed. Each line represents where one of the 
planets could be seen to transit, with the blue line representing Earth; an observer located here could detect us 
[Credit: 2MASS/A. Mellinger/R. Wells]

Thanks to facilities and missions such as SuperWASP and Kepler, we have now discovered thousands of planets orbiting stars other than our sun, worlds known as 'exoplanets'. The vast majority of these are found when the planets cross in front of their host stars in what are known as 'transits', which allow astronomers to see light from the host star dim slightly at regular intervals every time the planet passes between us and the distant star.

In the new study, the authors reverse this concept and ask, "How would an alien observer see the solar system?" They identified parts of the distant sky from where various planets in our solar system could be seen to pass in front of the sun – so-called 'transit zones'—concluding that the terrestrial planets (Mercury, Venus, Earth, and Mars) are actually much more likely to be spotted than the more distant 'Jovian' planets (Jupiter, Saturn, Uranus, and Neptune), despite their much larger size.

"Larger planets would naturally block out more light as they pass in front of their star", commented lead author Robert Wells, a PhD student at Queen's University Belfast. "However the more important factor is actually how close the planet is to its parent star – since the terrestrial planets are much closer to the sun than the gas giants, they'll be more likely to be seen in transit."

To look for worlds where civilisations would have the best chance of spotting our solar system, the astronomers looked for parts of the sky from which more than one planet could be seen crossing the face of the sun. They found that three planets at most could be observed from anywhere outside of the solar system, and that not all combinations of three planets are possible.

Diagram of a planet (e.g. the Earth, blue) transiting in front of its host star (e.g. the Sun, yellow). Left: The lower black 
curve shows the brightness of the star noticeably dimming over the transit event, when the planet is blocking some of the 
light from the star. Right: How the transit zone of a Solar System planet is projected out from the Sun. The observer on 
the green exoplanet is situated in the transit zone and can therefore see transits of the Earth [Credit: R. Wells]

Katja Poppenhaeger, a co-author of the study, adds, "We estimate that a randomly positioned observer would have roughly a 1 in 40 chance of observing at least one planet. The probability of detecting at least two planets would be about ten times lower, and to detect three would be a further ten times smaller than this."

Of the thousands of known exoplanets, the team identified sixty-eight worlds where observers would see one or more of the planets in our solar system transit the sun. Nine of these planets are ideally placed to observe transits of Earth, although none of the worlds are deemed to be habitable.

In addition, the team estimate that there should be approximately ten (currently undiscovered) worlds which are favourably located to detect the Earth and are capable of sustaining life as we know it. To date however, no habitable planets have been discovered from which a civilisation could detect the Earth with our current level of technology.

The ongoing K2 mission of NASA's Kepler spacecraft is to continue to hunt for exoplanets in different regions of the sky for a few months at a time. These regions are centred close to the plane of Earth's orbit, which means that there are many target stars located in the transit zones of the solar system planets. The team's plans for future work include targeting these transit zones to search for exoplanets, hopefully finding some which could be habitable.

Source: Royal Astronomical Society [September 08, 2017]

Read More