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Journey to the Center of the Board: Geopolitical Lessons from Mongolia 科技报告
来源:Center for Strategic & International Studies. 出版年: 2020
作者:  admin
收藏  |  浏览/下载:8/0  |  提交时间:2020/12/28
NSF approves funding for next stage of NCAR’s new solar observatory 新闻
来源平台:National Center of Atmospheric Research. 发布日期:2020
作者:  admin
收藏  |  浏览/下载:7/0  |  提交时间:2020/12/07
Measuring the true cost of conservation 新闻
来源平台:EurekAlert. 发布日期:2020
作者:  admin
收藏  |  浏览/下载:9/0  |  提交时间:2020/11/20
Ancient crocodiles' family tree reveals unexpected twists and turns 新闻
来源平台:EurekAlert. 发布日期:2020
作者:  admin
收藏  |  浏览/下载:0/0  |  提交时间:2020/11/09
Don’t Let China Greenwash Its Belt and Road 科技报告
来源:Center for Strategic & International Studies. 出版年: 2020
作者:  Jonathan E. Hillman
收藏  |  浏览/下载:34/0  |  提交时间:2020/10/12
Bolsonaro's Indigenous land mining policy a billion-dollar backfire 新闻
来源平台:EurekAlert. 发布日期:2020
作者:  admin
收藏  |  浏览/下载:0/0  |  提交时间:2020/09/22
A remnant planetary core in the hot-Neptune desert 期刊论文
NATURE, 2020, 583 (7814) : 39-+
作者:  David J. Armstrong;  Thé;  o A. Lopez;  Vardan Adibekyan;  Richard A. Booth;  Edward M. Bryant;  Karen A. Collins;  Magali Deleuil;  Alexandre Emsenhuber;  Chelsea X. Huang;  George W. King;  Jorge Lillo-Box;  Jack J. Lissauer;  Elisabeth Matthews;  Olivier Mousis;  Louise D. Nielsen;  Hugh Osborn;  Jon Otegi;  Nuno C. Santos;  ;  rgio G. Sousa;  Keivan G. Stassun;  Dimitri Veras;  Carl Ziegler;  Jack S. Acton;  Jose M. Almenara;  David R. Anderson;  David Barrado;  Susana C. C. Barros;  Daniel Bayliss;  Claudia Belardi;  Francois Bouchy;  ;  sar Briceñ;  o;  Matteo Brogi;  David J. A. Brown;  Matthew R. Burleigh;  Sarah L. Casewell;  Alexander Chaushev;  David R. Ciardi;  Kevin I. Collins;  Knicole D. Coló;  n;  Benjamin F. Cooke;  Ian J. M. Crossfield;  Rodrigo F. Dí;  az;  Elisa Delgado Mena;  Olivier D. S. Demangeon;  Caroline Dorn;  Xavier Dumusque;  Philipp Eigmü;  ller;  Michael Fausnaugh;  Pedro Figueira;  Tianjun Gan;  Siddharth Gandhi;  Samuel Gill;  Erica J. Gonzales;  Michael R. Goad;  Maximilian N. Gü;  nther;  Ravit Helled;  Saeed Hojjatpanah;  Steve B. Howell;  James Jackman;  James S. Jenkins;  Jon M. Jenkins;  Eric L. N. Jensen;  Grant M. Kennedy;  David W. Latham;  Nicholas Law;  Monika Lendl;  Michael Lozovsky;  Andrew W. Mann;  Maximiliano Moyano;  James McCormac;  Farzana Meru;  Christoph Mordasini;  Ares Osborn;  Don Pollacco;  Didier Queloz;  Liam Raynard;  George R. Ricker;  Pamela Rowden;  Alexandre Santerne;  Joshua E. Schlieder;  Sara Seager;  Lizhou Sha;  Thiam-Guan Tan;  Rosanna H. Tilbrook;  Eric Ting;  Sté;  phane Udry;  Roland Vanderspek;  Christopher A. Watson;  Richard G. West;  Paul A. Wilson;  Joshua N. Winn;  Peter Wheatley;  Jesus Noel Villasenor;  Jose I. Vines;  Zhuchang Zhan
收藏  |  浏览/下载:19/0  |  提交时间:2020/07/06

The interiors of giant planets remain poorly understood. Even for the planets in the Solar System, difficulties in observation lead to large uncertainties in the properties of planetary cores. Exoplanets that have undergone rare evolutionary processes provide a route to understanding planetary interiors. Planets found in and near the typically barren hot-Neptune '  desert'  (1,2)(a region in mass-radius space that contains few planets) have proved to be particularly valuable in this regard. These planets include HD149026b(3), which is thought to have an unusually massive core, and recent discoveries such as LTT9779b(4)and NGTS-4b(5), on which photoevaporation has removed a substantial part of their outer atmospheres. Here we report observations of the planet TOI-849b, which has a radius smaller than Neptune'  s but an anomalously large mass of39.1-2.6+2.7Earth masses and a density of5.2-0.8+0.7grams per cubic centimetre, similar to Earth'  s. Interior-structure models suggest that any gaseous envelope of pure hydrogen and helium consists of no more than3.9-0.9+0.8 per cent of the total planetary mass. The planet could have been a gas giant before undergoing extreme mass loss via thermal self-disruption or giant planet collisions, or it could have avoided substantial gas accretion, perhaps through gap opening or late formation(6). Although photoevaporation rates cannot account for the mass loss required to reduce a Jupiter-like gas giant, they can remove a small (a few Earth masses) hydrogen and helium envelope on timescales of several billion years, implying that any remaining atmosphere on TOI-849b is likely to be enriched by water or other volatiles from the planetary interior. We conclude that TOI-849b is the remnant core of a giant planet.


Observations of TOI-849b reveal a radius smaller than Neptune'  s but a large mass of about 40 Earth masses, indicating that the planet is the remnant core of a gas giant.


  
Scientists lament 'Humpty Dumpty' effect on world's spectacular, rare wildlife 新闻
来源平台:EurekAlert. 发布日期:2020
作者:  admin
收藏  |  浏览/下载:0/0  |  提交时间:2020/06/09
Scientists lament 'Humpty Dumpty' effect on world's spectacular, rare wildlife 新闻
来源平台:EurekAlert. 发布日期:2020
作者:  admin
收藏  |  浏览/下载:12/0  |  提交时间:2020/06/09
Hydrothermal (NN)-N-15-N-15 abundances constrain the origins of mantle nitrogen 期刊论文
NATURE, 2020, 580 (7803) : 367-+
作者:  Zhao, Steven;  Jang, Cholsoon;  Liu, Joyce;  Uehara, Kahealani;  Gilbert, Michael;  Izzo, Luke;  Zeng, Xianfeng;  Trefely, Sophie;  Fernandez, Sully;  Carrer, Alessandro;  Miller, Katelyn D.;  Schug, Zachary T.;  Snyder, Nathaniel W.;  Gade, Terence P.;  Titchenell, Paul M.;  Rabinowitz, Joshua D.;  Wellen, Kathryn E.
收藏  |  浏览/下载:14/0  |  提交时间:2020/05/13

Nitrogen is the main constituent of the Earth'  s atmosphere, but its provenance in the Earth'  s mantle remains uncertain. The relative contribution of primordial nitrogen inherited during the Earth'  s accretion versus that subducted from the Earth'  s surface is unclear(1-6). Here we show that the mantle may have retained remnants of such primordial nitrogen. We use the rare (NN)-N-15-N-15 isotopologue of N-2 as a new tracer of air contamination in volcanic gas effusions. By constraining air contamination in gases from Iceland, Eifel (Germany) and Yellowstone (USA), we derive estimates of mantle delta N-15 (the fractional difference in N-15/N-14 from air), N-2/Ar-36 and N-2/He-3. Our results show that negative delta N-15 values observed in gases, previously regarded as indicating a mantle origin for nitrogen(7-10), in fact represent dominantly air-derived N-2 that experienced N-15/N-14 fractionation in hydrothermal systems. Using two-component mixing models to correct for this effect, the (NN)-N-15-N-15 data allow extrapolations that characterize mantle endmember delta N-15, N-2/Ar-36 and N-2/He-3 values. We show that the Eifel region has slightly increased delta N-15 and N-2/Ar-36 values relative to estimates for the convective mantle provided by mid-ocean-ridge basalts(11), consistent with subducted nitrogen being added to the mantle source. In contrast, we find that whereas the Yellowstone plume has delta N-15 values substantially greater than that of the convective mantle, resembling surface components(12-15), its N-2/Ar-36 and N-2/He-3 ratios are indistinguishable from those of the convective mantle. This observation raises the possibility that the plume hosts a primordial component. We provide a test of the subduction hypothesis with a two-box model, describing the evolution of mantle and surface nitrogen through geological time. We show that the effect of subduction on the deep nitrogen cycle may be less important than has been suggested by previous investigations. We propose instead that high mid-ocean-ridge basalt and plume delta N-15 values may both be dominantly primordial features.