The new clue of oxygen isotope originates the solar system

Oxygen is the most abundant element on Earth, accounting for nearly half of the planet's mass. Of the three stable isotopes of oxygen, isotope oxygen 16 (the nucleus contains 8 neutrons) accounts for 99.762% of the oxygen ratio on Earth, while the oxygen isotope 17 (9 neutrons in the nucleus) accounts for only 0.038%, The heaviest isotope - the oxygen isotope 18 (10 neutrons) accounts for 0.2%.

But the minerals in the most primitive Thai solar system, including meteorite called carbon chondrite, contain a relatively different proportion of oxygen isotopes than Earth. Perhaps the rarer, heavier oxygen cohorts have been more prevalent at the early stages of the solar system.

Musahid (Musa) Ahmed - a scientist of molecular motion research at Berkeley Laboratory's Department of Chemical Science - said: 'For a chemist, the question for oxygen isotope ratios is The question helps us understand the origin of the solar system. Why is the ratio of oxygen isotopes in meteorites significantly different from those on earth - the question has been disturbing scientists for years'.

Many models have been set up to explain this difference through chemical cycles, including the hypothesis that the ratio of isotopes in our solar system is caused by a strange star, or in many different stars. Models through the chemical process according to Ahmed are ' ineffective ' , or more convincingly: chemical processes in the solar crystal itself increase the ratio of oxygen isotopes. A process in which is called a "self-contained isotope". The most abundant oxygen-bearing molecule in the solar nebula is carbon mono-oxide, CO. The process of self-defense is considered to be the key to explaining the large proportion of oxygen that forms when CO is separated under vacuum ultraviolet light, or VUV rays. VUV has a wavelength of about 200 to 10 nanometers.

It is possible to observe the self-blocking process in dust clouds in the universe. When strong VUV light from a nearby star enters the cloud, it will break down the carbon molecular structure into carbon and oxygen atoms. Different isotopes absorb photons of VUV with different energies, but near the edge of the cloud the most abundant oxygen-containing 16-oxygen CO atoms absorb the photons that the oxygen isotope 16 absorbs. OK. Therefore the 16-isotope oxygen is deeper into the cloud. But other 17 and 18 oxygen isotopes that are absorbing energy are not blocked. At that time inside the cloud, CO molecules carrying heavier isotopes are more fragmented, thus releasing heavier oxygen molecules.

It is perfectly reasonable to speculate that a similar process took place at the beginning of the solar system. The original sun then emits a VUV ray that impacts the CO located in a hot area nearby, or it may be in a cooler area in the distance. Will the process of blocking the VUV really happen under such conditions? If so, what is its effect on oxygen isotope ratios? There has never been an answer so far, and the hypotheses have never been tested.

Ahmed said: 'Mark Thiemens of the University of California, San Diego contacted us to use molecular mobility 9.0.2 in a live experiment. The Advanced Light Source (ALS) produces the photovoltaic VUV that can be precisely adjusted to different energy levels for CO separation.

Thiemens cosmologist has been seeking answers to questions about the oxygen isotope in the solar system for more than 30 years. He is a member of the science group of the Genesis spacecraft that brought the specimen in the returning solar wind. He believes that the solar system pathway formed and developed cannot be deduced from understanding the chemical properties of the universe.

Sun under ultraviolet light.When the solar system formed, the original sun was an extremely large source of ultraviolet light.(Photo: NASA)

Along with the photosynthesis process of CO in the original solar system, water is also a key factor in the process.Water and CO create confusing chemical properties, they bind heavier oxygen isotopes to minerals to form the oldest meteorites, thereby creating all the solar system.

Ahmed explains: 'The first step is the process of photosynthesis CO into carbon atoms and oxygen atoms. Oxygen is then combined with a hydrogen atom to form hydroxyl radical - OH - easily combined with another hydrogen atom to create water. All of these processes are likely to take place on a dust element. So the oxygen in the water converts its isotope signal into silicate. The various oxygen isotopes maintain through the above steps. Our experiment explored what happened in the first step. '

In the experiment, extremely high purity carbon mono-oxide was passed through the laboratory and exposed to the VUV photon beam emitted from a Xyncrotron with 4 different wavelengths respectively. Those four wavelengths are important for the self-defense hypothesis. Contact time for each wavelength is relatively long, from about 3 hours to nearly 16 hours.

When carbon atoms and oxygen atoms are separated, oxygen quickly recombines with the unburnt CO molecule to create carbon dioxide. Carbon dioxide is collected in refrigerated liquid nitrogen tubes. Subrata Chakraborty - postdoctoral in the group of Thiemens and the lead author of the paper published the results of the study - brought the samples to the University of California San Diego. Chakraborty has extracted oxygen from carbonic. He then determined the isotope ratio based on mass spectrometry to separate isotopes according to their mass.

Ahmed said: 'The results surprised us. We plan to demonstrate that the self-blocking VUV process is related to the ratio of oxygen isotopes that constitute the ancient objects in the solar system. But in the end, there is no need to use self-defense. '

The differences that the researchers found in the CO reaction for different wavelengths in the experiment are not the differences that the self-defense hypothesis predicts. In fact, these differences are related to the CO electric properties of the molecule unrelated to the barrier.

Only basic physicochemical properties are sufficient to produce a higher rate of heavier isotopes. That ratio is also very consistent with the ratio in the original solar system. The authors conclude that the cold regions in the actual solar nebula and the potential site to form oxygen storage with relatively large amounts of heavy isotopes do not rely on self-defense.

Ahmed said: 'We can see the isotope ratio that Genesis has brought, but it cannot tell us the path that made it. The isotope ratio itself does not explain why there is a difference in the ratio between the early and present universe. So much research is still needed in the laboratory. One of the next steps is to study the reaction between oxygen, water and silicate. They are formed in the first pieces of the solar system. That's the kind of experiment that the molecular pathway 9.0.2 is designed to perform. It helps to study chemical properties in the environment like our interstellar space, our Earth's environment, in the combustion engine and in the Earth's atmosphere. '

The research was funded by NASA and the US Department of Energy.

Refer:

Subrata Chakraborty, Musahid Ahmed, Teresa L. Jackson, and Mark H. Thiemens.Experimental Test of Self-Shielding in Vacuum Ultraviolet Photodissociation of CO.Science, 2008;321 (5894): 1328 DOI: 10.1126 / science.1159178