“彗星”《自然》（20230727出版）一周论文导读

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编译 | 未玖

Nature, 27 July 2023, VOL 619, ISSUE 7971

《自然》2023年7月27日，第619卷，7971期

天文学Astronomy

Spectroscopic identification of water emission from a main-belt comet

主带彗星水辐射的光谱识别

▲ 作者：Michael S. P. Kelley, Henry H. Hsieh, Dennis Bodewits, Mohammad Saki, Geronimo L. Villanueva, Stefanie N. Milam, et al.

▲ 链接：

https://www.nature.com/articles/s41586-023-06152-y

▲ 摘要：

主带彗星是位于小行星带的小型太阳系天体，在其近日点通道中反复表现出类似彗星的活动（即尘埃彗发或彗尾），强烈表明冰升华。虽然主带彗星的存在意味着小行星带中有尚存的水冰，但尽管用世界上最大的望远镜进行了严密探测，在这些天体周围仍未发现气体。

研究组展示了詹姆斯·韦伯太空望远镜的观测结果，它清楚地表明，主带彗星238P/Read有一个水蒸气彗发，但缺乏明显的二氧化碳气体彗发。该发现表明，Read彗星的活动是由水冰升华驱动的，这意味着主带彗星与普通彗星群有着根本的不同。

无论Read彗星是否经历了不同的形成环境或演化史，它都不太可能是最近才从外太阳系闯入小行星带的。根据这些结果，主带彗星似乎代表了一种挥发性物质样本，且这种物质目前在经典彗星的观测和陨石记录中没有代表性，这对于理解早期太阳系的挥发性物质及其随后演变非常重要。

▲ Abstract：

 Main-belt comets are small Solar System bodies located in the asteroid belt that repeatedly exhibit comet-like activity (that is, dust comae or tails) during their perihelion passages, strongly indicating ice sublimation. Although the existence of main-belt comets implies the presence of extant water ice in the asteroid belt, no gas has been detected around these objects despite intense scrutiny with the world’s largest telescopes. Here we present James Webb Space Telescope observations that clearly show that main-belt comet 238P/Read has a coma of water vapour, but lacks a significant CO2 gas coma. Our findings demonstrate that the activity of comet Read is driven by water–ice sublimation, and implies that main-belt comets are fundamentally different from the general cometary population. Whether or not comet Read experienced different formation circumstances or evolutionary history, it is unlikely to be a recent asteroid belt interloper from the outer Solar System. On the basis of these results, main-belt comets appear to represent a sample of volatile material that is currently unrepresented in observations of classical comets and the meteoritic record, making them important for understanding the early Solar System’s volatile inventory and its subsequent evolution.

物理学Physics

Femtosecond proton transfer in urea solutions probed by X-ray spectroscopy

X射线光谱学探测尿素溶液中的飞秒质子转移

▲ 作者：Zhong Yin, Yi-Ping Chang, Tadas Bal?iūnas, Yashoj Shakya, Aleksa Djorovi?, Geoffrey Gaulier, et al.

▲ 链接：

https://www.nature.com/articles/s41586-023-06182-6

▲ 摘要：

质子转移是水相化学中最基本的事件之一，也是超快电子和结构动力学耦合的典型范例。在飞秒时间尺度上解耦电子和核动力学仍是一项艰巨挑战，特别是在液相、生化过程的自然环境中。

研究组利用台式水窗X射线吸收光谱的独特特性来揭示水溶液中离子化尿素二聚体的飞秒质子转移动力学。借助于从头算量子力学和分子力学计算，利用X射线吸收光谱的元素特异性和位点选择性，研究组展示了除质子转移之外，尿素二聚体的后续重排和电子结构相关变化如何通过位点选择性来识别。

这些结果表明，平板射流、台式X射线吸收光谱在阐明生物分子系统中溶液相超快动力学方面具有相当大的潜力。

▲ Abstract：

Proton transfer is one of the most fundamental events in aqueous-phase chemistry and an emblematic case of coupled ultrafast electronic and structural dynamics. Disentangling electronic and nuclear dynamics on the femtosecond timescales remains a formidable challenge, especially in the liquid phase, the natural environment of biochemical processes. Here we exploit the unique features of table-top water-window X-ray absorption spectroscopy to reveal femtosecond proton-transfer dynamics in ionized urea dimers in aqueous solution. Harnessing the element specificity and the site selectivity of X-ray absorption spectroscopy with the aid of ab initio quantum-mechanical and molecular-mechanics calculations, we show how, in addition to the proton transfer, the subsequent rearrangement of the urea dimer and the associated change of the electronic structure can be identified with site selectivity. These results establish the considerable potential of flat-jet, table-top X-ray absorption spectroscopy in elucidating solution-phase ultrafast dynamics in biomolecular systems.

能源科学Energy Science

Accelerating the energy transition towards photovoltaic and wind in China

加速中国向光伏和风能的能源转型

▲ 作者：Yijing Wang, Rong Wang, Katsumasa Tanaka, Philippe Ciais, Josep Penuelas, Yves Balkanski, et al.

▲ 链接：

https://www.nature.com/articles/s41586-023-06180-8

▲ 摘要：

中国到2060年实现碳中和目标要求将光伏（PV）和风能的发电量从1 PWh/年增加至10~15 PWh/年。然而，根据可再生能源设备安装的历史速率，即最近的高分辨率能源系统模型和基于中国“十四五”能源发展（CFED）的预测，到2060年，发电量仅能达到5~9.5 PWh/年。

研究组表明，通过单独优化部署3844个新公用事业规模的PV和风电场，与超高压（UHV）输电和储能相协调，并考虑到电力负荷的灵活性和学习动态，PV和风电的发电量可以从9 PWh/年（对应CFED路径）增至15 PWh/年，伴随着平均减排成本从每吨二氧化碳（tCO2）97美元降至6美元。

为了实现这一目标，PV和风能的年化投资应从2020年的770亿美元（当前水平）增至21世纪20年代的1270亿美元，并在21世纪50年代进一步增至4260亿美元/年。PV和风能的大规模部署可实现共同获益，以增加最贫穷地区居民的收入。

该研究结果突出了通过建设储能、扩大输电能力和调整需求侧电力负荷来升级电力系统的重要性，以降低部署PV和风力发电来实现中国碳中和的经济成本。

▲ Abstract：

China’s goal to achieve carbon (C) neutrality by 2060 requires scaling up photovoltaic (PV) and wind power from 1 to 10–15PWh ?year?1. Following the historical rates of renewable installation, a recent high-resolution energy-system model and forecasts based on China’s 14th Five-year Energy Development (CFED), however, only indicate that the capacity will reach 5–9.5 PWh year?1 by 2060. Here we show that, by individually optimizing the deployment of 3,844 new utility-scale PV and wind power plants coordinated with ultra-high-voltage (UHV) transmission and energy storage and accounting for power-load flexibility and learning dynamics, the capacity of PV and wind power can be increased from 9 PWh year?1(corresponding to the CFED path) to 15 PWh year?1, accompanied by a reduction in the average abatement cost from US$97 to US$6 per tonne of carbon dioxide (tCO2). To achieve this, annualized investment in PV and wind power should ramp up from US$77 billion in 2020 (current level) to US$127 billion in the 2020s and further to US$426 billion year?1 in the 2050s. The large-scale deployment of PV and wind power increases income for residents in the poorest regions as co-benefits. Our results highlight the importance of upgrading power systems by building energy storage, expanding transmission capacity and adjusting power load at the demand side to reduce the economic cost of deploying PV and wind power to achieve carbon neutrality in China.

人工智能Artificial Intelligence

 Heat-assisted detection and ranging

热辅助探测和测距

▲ 作者：Fanglin Bao, Xueji Wang, Shree Hari Sureshbabu, Gautam Sreekumar, Liping Yang, Vaneet Aggarwal, et al.

▲ 链接：

https://www.nature.com/articles/s41586-023-06174-6

▲ 摘要：

机器感知使用先进的传感器来收集周围场景的信息，以实现态势感知。当智能代理数量增加时，使用主动声纳、雷达和激光雷达来增强相机视觉的最先进机器感知面临诸多困难。利用无处不在的热信号，有望扩展感知的新前沿。

然而，物体及其环境不断地发射和散射热辐射，导致了被称为“重影效应”的无纹理图像。因此，热视觉不受信息丢失的特异性限制，而对导航至关重要的热测距即使与人工智能（AI）相结合，也很难实现。

研究组提出并实验证明了热辅助探测和测距（HADAR）可克服重影这一公开挑战，并将其针对AI增强的热感测进行了基准测试。HADAR不仅能在黑暗中像白天一样看到纹理和深度，还能感知到RGB或热视觉之外的纷杂物理属性，这为完全被动和物理感知的机器感知奠定了基础。

研究组开发了HADAR估计理论，并解决了其光子散粒噪声极限，该极限描述了基于HADAR的AI性能的信息理论边界。HADAR在夜间的测距优于热测距，其精度可与白天的RGB立体视觉相媲美。

该自动化HADAR热成像技术在温度精度上达到了Cramér–Rao界限，超越了现有的热成像技术。该研究工作带来了一种颠覆性技术，可通过基于HADAR的自主导航和人机社交来加速第四次工业革命（工业4.0）。

▲ Abstract：

Machine perception uses advanced sensors to collect information about the surrounding scene for situational awareness. State-of-the-art machine perception using active sonar, radar and LiDAR to enhance camera vision faces difficulties when the number of intelligent agents scales up. Exploiting omnipresent heat signal could be a new frontier for scalable perception. However, objects and their environment constantly emit and scatter thermal radiation, leading to textureless images famously known as the ‘ghosting effect’. Thermal vision thus has no specificity limited by information loss, whereas thermal ranging—crucial for navigation—has been elusive even when combined with artificial intelligence (AI). Here we propose and experimentally demonstrate heat-assisted detection and ranging (HADAR) overcoming this open challenge of ghosting and benchmark it against AI-enhanced thermal sensing. HADAR not only sees texture and depth through the darkness as if it were day but also perceives decluttered physical attributes beyond RGB or thermal vision, paving the way to fully passive and physics-aware machine perception. We develop HADAR estimation theory and address its photonic shot-noise limits depicting information-theoretic bounds to HADAR-based AI performance. HADAR ranging at night beats thermal ranging and shows an accuracy comparable with RGB stereovision in daylight. Our automated HADAR thermography reaches the Cramér–Rao bound on temperature accuracy, beating existing thermography techniques. Our work leads to a disruptive technology that can accelerate the Fourth Industrial Revolution (Industry 4.0) with HADAR-based autonomous navigation and human–robot social interactions.

地球科学Earth Science

Increased occurrences of consecutive La Ni?a events under global warming

全球变暖下连续拉尼娜事件频率增加

▲ 作者：Tao Geng, Fan Jia, Wenju Cai, Lixin Wu, Bolan Gan, Zhao Jing, et al.

▲ 链接：

https://www.nature.com/articles/s41586-023-06236-9

▲ 摘要：

大多数厄尔尼诺事件都是偶发性的，并在一个冬季达到峰值，而拉尼娜往往在厄尔尼诺之后发展，并持续两年或更长时间。相对于单年拉尼娜，连续拉尼娜的特点是经向东风范围更广，因此赤道太平洋的热量补给速度较慢，使寒冷异常现象持续存在，这对全球气候、生态系统和农业产生长期影响。持续多年拉尼娜事件的未来变化仍然未知。

利用未来温室气体强迫下的气候模型，研究组发现连续拉尼娜事件的频率增加，范围从低排放情景下的19±11%增至高排放情景下的33±13%，并得出高排放情景下频率更强的模型间共识。

在温室变暖的情况下，副热带东北太平洋的均态变暖最大值增强了针对扰动的区域热力学响应，产生了比20世纪响应厄尔尼诺温暖异常更北的异常东风。赤道东太平洋的一个变暖极大值进一步增加了向北更广异常模式的敏感性。

较慢的热量补给与向北更广的偏东异常有关，使得第一年拉尼娜的寒冷异常一直持续到第二年拉尼娜。因此，在史上连续拉尼娜事件中出现的极端气候可能在21世纪会更频繁地发生。

▲ Abstract：

Most El Ni?o events occur sporadically and peak in a single winter, whereas La Ni?a tends to develop after an El Ni?o and last for two years or longer. Relative to single-year La Ni?a, consecutive La Ni?a features meridionally broader easterly winds and hence a slower heat recharge of the equatorial Pacific, enabling the cold anomalies to persist, exerting prolonged impacts on global climate, ecosystems and agriculture. Future changes to multi-year-long La Ni?a events remain unknown. Here, using climate models under future greenhouse-gas forcings, we find an increased frequency of consecutive La Ni?a ranging from 19 ± 11% in a low-emission scenario to 33 ± 13% in a high-emission scenario, supported by an inter-model consensus stronger in higher-emission scenarios. Under greenhouse warming, a mean-state warming maximum in the subtropical northeastern Pacific enhances the regional thermodynamic response to perturbations, generating anomalous easterlies that are further northward than in the twentieth century in response to El Ni?o warm anomalies. The sensitivity of the northward-broadened anomaly pattern is further increased by a warming maximum in the equatorial eastern Pacific. The slower heat recharge associated with the northward-broadened easterly anomalies facilitates the cold anomalies of the first-year La Ni?a to persist into a second-year La Ni?a. Thus, climate extremes as seen during historical consecutive La Ni?a episodes probably occur more frequently in the twenty-first century.

The social value of offsets

碳减排补偿的社会价值

▲ 作者：Ben Groom & Frank Venmans

▲ 链接：

https://www.nature.com/articles/s41586-023-06153-x

▲ 摘要：

目前尚不清楚为了补偿一吨二氧化碳的排放，应当在临时和有风险的补偿中储存多少碳。研究组将补偿社会价值（SVO）作为反映补偿持续时间以及非额外性和失败风险的碳社会成本的一个明确部分，其中SVO按照避免的经济损失来衡量。

SVO反映了临时储存的价值，并克服了先前气候科学和经济学的短板。SVO与政策相关。如果SVO/成本比超过替代方案的效益/成本比，则有效的净零政策将包括补偿。SVO提供了一个指标，通过SVO与碳社会成本之比来衡量补偿与永久碳储存的等效性。

研究组为不同的风险、持久性和气候情景提供了等效因子矩阵。经估算得出一个经验法则：在50年的时间里，每补偿封存1吨碳，就相当于永久封存0.33~0.5吨碳。

等效策略提供了一种用更简单、易于监督的短期合同取代永久补偿合同的方法，可用于碳生命周期分析和碳债务估值，并可作为比较自愿和合规市场中不同质量补偿的基础。

▲ Abstract：

It is unclear how much carbon should be stored in temporary and risky offsets to compensate one ton of CO2 emissions. Here we cast the social value of an offset (SVO), measured in terms of economic damages avoided, as a well-defined fraction of the social cost of carbon reflecting offset duration, and risks of non-additionality and failure. The SVO reflects the value of temporary storage, and overcomes shortcomings in the climate science and economics of previous contributions. The SVO is policy relevant. An efficient net-zero policy will consist of offsets if their SVO/cost ratio exceeds the benefit/cost ratio of alternatives. The SVO yields an indicator of the equivalence of offsets to permanent carbon storage measured by the ratio of the SVO to the social cost of carbon. We provide a matrix of equivalence factors for different risks, permanence and climate scenarios. Estimation yields a rule of thumb: one offset sequestering one ton for 50 years is equivalent to between 0.33 and 0.5 tons permanently locked away. Equivalence offers a means of replacing perpetual offset contracts by simpler, easy to monitor short-term contracts, has applications to carbon life cycle analysis and the valuation of carbon debts, and can be the basis of comparing offsets of different qualities in the voluntary and compliance markets.

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