「物理」《自然》（20200430出版）一周论文导读 |美好，一直在身边|日本|冲电气工业|

编译 | 冯维维
Nature, 30 April 2020, Volume 580 Issue 7805
《自然》2020年4月30日，第580卷， 7805期

本文插图
物理学Physics
Nightside condensation of iron in an ultrahot giant exoplanet
铁元素在超热巨大系外行星夜间凝结
▲ 作者：David Ehrenreich, Christophe Lovis, Filippo Zerbi, etc.
▲ 链接：https://www.nature.com/articles/s41586-020-2107-1
▲ 摘要
超热的巨大系外行星接受的日照是地球的数千倍。它们的高温环境是研究极端行星气候和化学的理想实验室。
作者报告了在超热的外行星WASP-76b上探测到的非对称大气信号。他们使用高分散光谱学和一个大的光子收集区相结合的方法来解决这个信号。中性铁的吸收信号在尾缘以每秒- 11±0.7公里的速度发生蓝移，这可以用行星自转和白天吹来的热风的组合来解释。
相反，靠近晨光明暗界线的一侧没有信号，表明铁原子没有吸收那里的星光。作者由此得出结论，铁在穿越该行星背面的过程中必然会凝结。
▲ Abstract
Ultrahot giant exoplanets receive thousands of times Earth’s insolation. Their high-temperature atmospheres are ideal laboratories for studying extreme planetary climates and chemistry. Here we report the detection of an asymmetric atmospheric signature in the ultrahot exoplanet WASP-76b. We spectrally and temporally resolve this signature using a combination of high-dispersion spectroscopy with a large photon-collecting area. The absorption signal, attributed to neutral iron, is blueshifted by ?11 ± 0.7 kilometres per second on the trailing limb, which can be explained by a combination of planetary rotation and wind blowing from the hot dayside16. In contrast, no signal arises from the nightside close to the morning terminator, showing that atomic iron is not absorbing starlight there. We conclude that iron must therefore condense during its journey across the nightside.
Months-long thousand-kilometre-scale wobbling before great subduction earthquakes
大俯冲地震前长达数月的数千公里范围的抖动
▲ 作者：Jonathan R. Bedford, Marcos Moreno, Zhiguo Deng, Onno Oncken, Bernd Schurr, Timm John, Juan Carlos Báez, Michael Bevis
▲ 链接：https://www.nature.com/articles/s41586-020-2212-1
▲ 摘要
大推力地震是造成一些最具破坏性的自然灾害的原因。
作者使用一种最近开发的轨迹建模方法，该方法旨在将长期构造运动从每日GNSS时间序列中分离出来，来证明2010年智利的Maule地震（8.8级）和2011年日本的Tohoku-oki地震（9.0级）发生之前，地表位移发生了4~8毫米的逆转，这种逆转持续了几个月，跨越了数千公里。
日本东北部大地震前发生的地表位移反转模型显示，菲律宾海板块先是缓慢滑动，然后突然向下俯冲，其速度之快导致整个日本的粘弹性反弹。
因此，为了更好地理解即将发生的大地震，不仅要考虑板块界面摩擦过程的演化，还要考虑深部俯冲过程的动态边界条件，如亚稳态板块的突然致密化。
▲ Abstract
Megathrust earthquakes are responsible for some of the most devastating natural disasters. Here we use a recently developed trajectory modelling approach that is designed to isolate secular tectonic motions from the daily GNSS time series to show that the 2010 Maule, Chile (moment magnitude 8.8) and 2011 Tohoku-oki, Japan (moment magnitude 9.0) earthquakes were preceded by reversals of 4–8 millimetres in surface displacement that lasted several months and spanned thousands of kilometres. Modelling of the surface displacement reversal that occurred before the Tohoku-oki earthquake suggests an initial slow slip followed by a sudden pulldown of the Philippine Sea slab so rapid that it caused a viscoelastic rebound across the whole of Japan. Therefore, to understand better when large earthquakes are imminent, we must consider not only the evolution of plate interface frictional processes but also the dynamic boundary conditions from deeper subduction processes, such as sudden densification of metastable slab.