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An old disk still capable of forming a planetary system



From the masses of the planets orbiting the Sun, and the abundance of elements relative to hydrogen, it is estimated that when the Solar System formed, the circumstellar disk must have had a minimum mass of around 0.01 solar masses within about 100 astronomical units of the star1,2,3,4. (One astronomical unit is the Earth–Sun distance.) The main constituent of the disk, gaseous molecular hydrogen, does not efficiently emit radiation from the disk mass reservoir5, and so the most common measure of the disk mass is dust thermal emission and lines of gaseous carbon monoxide6. Carbon monoxide emission generally indicates properties of the disk surface, and the conversion from dust emission to gas mass requires knowledge of the grain properties and the gas-to-dust mass ratio, which probably differ from their interstellar values7,8. As a result, mass estimates vary by orders of magnitude, as exemplified by the relatively old (3–10 million years) star TW Hydrae9,10, for which the range is 0.0005–0.06 solar masses11,12,13,14. Here we report the detection of the fundamental rotational transition of hydrogen deuteride from the direction of TW Hydrae. Hydrogen deuteride is a good tracer of disk gas because it follows the distribution of molecular hydrogen and its emission is sensitive to the total mass. The detection of hydrogen deuteride, combined with existing observations and detailed models, implies a disk mass of more than 0.05 solar masses, which is enough to form a planetary system like our own.

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Figure 1: Herschel detection of HD in the TW Hya protoplanetary disk.
Figure 2: Model of the physical structure and HD emission of the TW Hya circumstellar disk.


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Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. Support for this work was provided by NASA through an award issued by JPL/Caltech and by the US National Science Foundation under grant 1008800. This paper makes use of the following Atacama Large Millimeter/submillimeter Array (ALMA) data: ADS/JAO.ALMA#2011.0.00001.SV. ALMA is a partnership of ESO (representing its member states), the NSF (USA) and NINS (Japan), together with the NRC (Canada) and the NSC and ASIAA (Taiwan), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ.

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Authors and Affiliations



E.A.B., L.I.C., U.G. and K.Z. performed the detailed calculations used in the analysis. J.D.G. reduced the Herschel data. S.M.A. provided detailed disk physical models and U.G. provided thermochemical models, both developed specifically for TW Hya. E.A.B. wrote the manuscript with revisions by N.J.E. All authors were participants in the discussion of results, determination of the conclusions and revision of the manuscript.

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Correspondence to Edwin A. Bergin.

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The authors declare no competing financial interests.

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Bergin, E., Cleeves, L., Gorti, U. et al. An old disk still capable of forming a planetary system. Nature 493, 644–646 (2013).

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