Probing the early Solar System

28 Presolar grains provide a new way to study various processes in the early Solar System. Whether measured directly or indirectly, both the absolute and relative concentrations of different presolar components are found to vary in different types of meteorites. The source of these differences probably lies in how and where the grains were processed—in the solar nebula and in asteroidal meteorite parent bodies.

29 Using the abundances of anomalous noble gases as tracers of presolar grain content, Gary Huss and Roy Lewis have found that the abundance of presolar grains progressively decreases as the metamorphic grade of meteorite increases. No presolar phases are found in meteorites of the highest metamorphic grades—undoubtedly because presolar material is destroyed in the asteroidal parent bodies of the meteorites. But even in meteorites of the same type and metamorphic grade, the quantity and characteristics of their presolar grains can differ. These differences could reflect grain processing in the solar nebula. For example, different size distributions of presolar SiC observed in different meteorites suggest pre-accretionary sorting by size.

30 Electron-beam mapping can be used to locate presolar grains in situ. Use of this technique avoids the undesirable destruction of diagnostic surface features by the harsh chemical treatments normally used to isolate presolar grains. To our surprise, with electron-beam mapping we have found that presolar SiC occurs as individual grains that lack the silicon oxide rims expected from exposure of SiC to the oxidizing nebula at high temperatures. We do not yet know whether this means that conditions in the solar nebula prevented the formation of silicon oxide rims or whether they were once present and were subsequently removed.

figure 5. oxygen isotopic ratios in presolar corundum (A1₂O₃) grains, compared with predictions made by Arnold Boothroyd and Irene-Juliana Sackmann for compositions resulting from dredge-up of main sequence nucleosynthesis products into the stellar envelope, as a function of stellar mass M and initial metallicity Z (2 is the mass fraction of atoms heavier than and including carbon). Grains of group 1 have oxygen compositions similar to those observed in oxygen-rich red giant stars. Group 3 grains have no observed stellar counterparts, but theory suggests that they (as well as group 2 grains) originated in low-mass red giants. The group 3 oxygen compositions indicate that when the parent stars of these grains were born, the average ¹⁷O and ¹⁸O abundances in the Galaxy were lower than when the Sun was born, reflecting Galactic chemical evolution. As described in the text, these compositions can be used to constrain the age of the Galaxy. Group 4 grains are of unknown origin. (Figure courtesy of Larry Nittler.)

IV Reading for General Understanding

A Check the comprehension of the text by choosing the answer, which you think is correct.

1. The path from dust grain to astrophysical insight is the subject of the article.

a) The subject of the article is the formation of the Solar System.

b) The formation of the Solar System is the subject of some other article.

c) It’s quite right.

2. Very few nuclides could have been produced in an initial “big bang” and that most element synthesis is in fact the result of nuclear reaction in stars.

- Most element synthesis is in fact the result of nuclear reaction in planets.

- Very few nuclides could not have been produced in an initial “big bang”.

- Most element synthesis could not be the result of nuclear reaction in planets and very gew nuclides could not have been produced in an initial “big bang”.

3. This eclectic process requires the work and insight of astronomers, theoretical astrophysicist and laboratory scientists.

a) Combined efforts of scientists from different branches of science will soon be crowned with success.

b) Since there is no joint opinion on the problem of ancient stardust, the results are difficult to achieve.

c) This eclectic process requires the work of theoretical astrophysicists only.

4. This discovery was the first identification of a specific carrier phase for a component of exotic noble gas.

a) This discovery was the first identification of a specific carrier phase for oxygen.

B) This discovery led to the identification of a common carrier gas.

c) It’s true. This was the identification of a specific carrier phase for a component of exotic noble gas.

B Pick out from the text all the word combinations with the following words (terms) and give their Russian equivalents.

Meteorite cloud pressure

Gas envelope component

Grain composition distribution

Material measurement(s) explosion

Star dust anomaly

V Reading for Detail and Language Study

1. Find in the text the English equivalents for the following wonds and phrases.

- звёздная пыль - красные гиганты

- взрывы - соотношение кремний-углерод

- метеорит - облачка

- кремниевый карбид - межзвёздная среда

- астрофизические знания - химические и физические свойства

- период полураспада - противоречить

- открытие - графит

- образцы - термодинамика

- растворитель - тот же вывод

- крупинки - поверхность звёзд

- удивительно большие значения - «большой взрыв»
- три порядка величины - прямое свидетельство

- молекулярное облако

2. Translate the following words and phrases:

Stardust, nuclides, tiny grains, abundance, outer envelopes of stars, “big bang”, individual grains of stardust, isotopic anomalies, well-understood processes, presolar grains, noble gases, enrichment, the age of Galaxy, carbonaceous, compelling evidence, deep convection, red giant parents, outgrowth, the life span of parent stars, to expel, direct evidence, supernova explosions, subtypes of stars in the Galaxy, to deepen, a lack of severe erosion, interstellar dust, refractory carbides, proportionally higher rates of mass loss, undesirable distraction of diagnostic surface features.

3. Translate the following phrases from the text:

1. These meteorite abundances turned out to be similar to those measured spectroscopically in the Sun.

2. This belief followed from the fact that closely similar isotopic ratios were measured in a wide variety of terrestrial and extraterrestrial samples, suggesting that all presolar solids had been vaporized when the Solar System formed.

3. Whether measured directly or indirectly, both the absolute and relative concentrations of different presolar components are found to vary in different types of meteorites.

4. Indeed, this is probably the only way ancient stardust can be distinguished from solids that formed within the Solar System.

5. One such separate, which was characterized by enrichments in both the heavy

and light isotopes of xenon, wasfound to consist primarily of nanodiamonds with a median grain size of 1-3 nm.

6. The oxygen isotopes in corundum grains are consistent with those predicted to result from the first dredge –up.

7. It turns out that the new laboratory data do not fit well with either the astronomical observations or the theory of dust in the diffuse interstellar medium.

8. One can then zero in on isotopically anomalous grains and perform detailed analyses, often on more than one chemical element.

9. Although a large SiC grain had been found in one of the residues, it proved to have a normal isotopic composition and was undoubtedly a terrestrial contaminant.

10.First, such stars are believed to be the sites of s-process nucleosynthesis.

4. Translate the microtext “Probing the early Solar System ” in written form.

VI Oral Practice

A Answer the following questions:

1. What is the subject of this article?

2. Does the stardust come from meteorites only?

3. What are the sources of anomalies?

4.What do presolar grains include?

Searching for Stardust

1. Why was the presence of presolar grains overlooked when the first measurements were made on gram-sized samples?

2. When were hydrogen isotopic anomalies measured in meteorites?

3. What is a halflife of radioactive ²²Na?