北大研究团队研究水星时有重大发现
北大研究团队研究水星时有重大发现，北京大学地球与空间科学学院的宗秋刚教授团队关于水星存在磁暴与环电流的文章，日前正式发表。北大研究团队研究水星时有重大发现。
北京大学地球与空间科学学院宗秋刚教授研究团队发现水星存在磁暴与环电流，破解了近半个世纪的谜题。相关研究成果于17日分别发表在国际学术期刊《自然·通讯》（Nature Communications）和《中国科学：技术科学》（Sci China Tech Sci）上。
磁暴是太阳风与磁层相互作用所引发的磁场扰动，是众多空间天气事件中最具危害性的一种。目前，土星、木星磁层中的数千到数十万电子伏特的捕获离子所组成的环电流的存在已在观测中得到证实。因此，与之相关的磁暴现象能否发生在太阳系乃至整个宇宙中其他行星的磁层，成为目前极具研究价值的课题之一。
在太阳系中，水星是距离太阳最近也是最小的行星，拥有和地球类似的内禀磁场，可抵御太阳风冲击并形成磁层。然而，由于水星的磁场强度不到地球磁场的百分之一，它所支撑的磁层在空间尺度上要比地球磁层小数十倍。此外，水星的大气层近乎逃逸殆尽，无法提供显著电离层。此前，学界普遍认为，水星磁层过小，无法容纳被稳定捕获的能量粒子，因此倾向于认为水星不存在环电流和磁暴。
宗秋刚团队综合分析了美国国家航空航天局信使号（MESSENGER）水星探测器为期5年的观测数据。观测显示，水星的环电流在向阳面呈分叉状，与地球的赤道环电流在形态上有很大差异，这一形态与试验粒子模拟结果高度吻合。这主要是在强太阳风压缩水星磁层的条件下，质子经历Shabansky轨道导致的。这些观测结果为水星磁层中存在环电流提供了确凿证据。研究显示，水星磁层中存在类似地球磁层中的环电流，并引发水星磁暴。研究结果对理解太阳系行星演化有重要启示。
北京大学地球与空间科学学院的宗秋刚教授团队关于水星存在磁暴与环电流的文章，日前分别被国际学术期刊《自然.通讯》 (Nature Communications) 和《中国科学：技术科学》英文刊（Sci China Tech Sci）正式发表。
磁暴是最具危害性的空间天气事件，一直以来磁暴这一现象是否仅发生在地球磁层是空间科学领域最受关注的问题之一。近期，北京大学宗秋刚教授团队的观测研究显示，水星磁层中也会存在类似地球磁层中的环电流，并引发水星磁暴，终结了长达近半个世纪的谜题。这是第一次在地球之外的行星发现存在磁暴现象，对于理解太阳系行星演化有重要的启示。
磁暴是太阳风与磁层相互作用所引发的磁场扰动，它是众多空间天气事件中最具危害性的一种。一场大规模的磁暴（如1859年的卡灵顿事件）会对人类现代科技文明，包括航天器、供电线路、输油管道以及通讯系统，造成数以万亿计的损失。最近，今年2月初（2月3-5日）， 一次地球磁暴过程使得SpaceX 发射的49颗卫星中的40颗卫星毁坏。Chapman和Ferraro最早对这一现象做出物理上的解释：引发磁暴的是空间中的环电流，它由环绕地球运动的高能带电粒子所驱动。目前，部分行星（土星、木星）磁层中的数千到数十万电子伏特的捕获离子所组成的环电流的.存在已经在观测中得到了证实。因此，与之相关的磁暴现象能否发生在太阳系、乃至整个宇宙中其他行星的磁层中成为目前极具研究价值的课题。
那么，水星磁层是否存在环电流和磁暴呢？水星作为太阳系中距离太阳最近也是最小的一颗行星，拥有和地球类似的内禀磁场，可以抵御太阳风的冲击并形成磁层。然而，由于水星的磁场强度只有不到地球磁场的百分之一，它所支撑的磁层在空间尺度上要比地球磁层小数十倍。此外，水星的大气层在太阳的炙烤之下也近乎逃逸殆尽，无法提供显著的电离层。悬殊的尺度差异以及电离层的缺失使得水星在比较行星研究中具有独特的地位。
图1 水星磁层示意图
尽管水星磁层中存在着诸多与地球磁层极为相似的动力学过程，如磁层亚暴、磁尾粒子向内磁层的注入等。此前，学界普遍认为水星磁层过小，无法容纳被稳定捕获的能量粒子，因此倾向于认为水星不存在环电流和磁暴。近期，北京大学地球与空间科学学院宗秋刚教授团队，综合分析了美国国家航空航天局信使号（MESSENGER）飞船为期五年的观测数据。得益于信使号飞船优越的仪器设备、轨道设计和调整规划，水星磁层中的能量粒子具有高时空覆盖率，有利于研究水星能量粒子的全空间分布特征。统计结果清晰地呈现出环电流这一结构。观测显示，水星的环电流在向阳面呈分叉状（即环电流在向阳面出现在中高纬区域而非赤道处，如图1所示），与地球的赤道环电流在形态上有很大差异。这一奇特的形态与试验粒子模拟结果高度吻合。这主要是由于在强太阳风压缩水星磁层的条件下，质子经历Shabansky轨道导致的（如图1所示）。这些观测结果为水星磁层中环电流的存在提供了确凿证据，终结了持续半个多世纪的谜题。
目前观测到的水星环电流质子总能量的动态范围为焦耳到焦耳，巨大的变化幅度足以支持磁暴活动的发生。根据推算，环电流所导致的地磁场下降在0.2 nT 到 3.5 nT之间，同比例相当于地球上Dst(Disturbance storm time, Dst)为约30 nT 到500 nT的大磁暴。此外，信使号在临近任务结束、撞击水星之前，为水星磁暴的存在提供了关键性的磁场观测证据。这一阶段的卫星轨道距离水星表面足够近，为探测地球以外的磁暴现象提供了绝佳的机会。在一次日冕物质抛射事件经过水星期间，利用一套成熟的天基地磁扰动指数算法分析了水星磁场在此期间的演化过程。这一演化过程与地球上的磁暴高度相似，包含了磁场突然下降的主相以及磁场缓慢增长回归到正常水平的恢复相。主相期间的磁场下降峰值超过60 nT，接近水星内禀磁场的三分之一。这一观测说明，尽管水星磁层与地球磁层之间存在着极大的差异，与地球上相似、甚至更为剧烈的磁暴现象依然可以在水星上发生。
北京大学地球与空间科学学院空间物理与应用技术研究所博士生赵玖桐为文章Zhao et al. (2022)的第一作者，北京大学宗秋刚教授与乐超研究员为文章的共同通讯作者。北京大学宗秋刚教授与中国极地研究所刘建军研究员为文章Zong et al. (2022)的第一作者和通讯作者。北京大学傅绥燕教授与宗秋刚教授为上述文章写了论评。这项工作得到了国家重点研发计划“变革性技术关键科学问题”重点专项、民用航天技术预先研究项目、国家自然科学基金委的经费支持。
加利福尼亚大学的三位研究人员发现，有证据表明，月球上的冰层比想象的要多得多。在他们发表在《 自然地球科学》 杂志上的论文中，利奥·鲁班科，雅纳维·文卡特拉曼和大卫·佩吉比较研究了水星上的冰和月球上的阴影区域以及它们发现的相似之处。
以前的研究人员使用来自阿雷西博天文台和美国宇航局的信使号太空船的数据发现，水星的两极上有一些陨石坑区域，这些区域看起来像月球一样。来自月球勘测轨道飞行器的数据显示在阴影陨石坑中有数米厚的冰沉积物，证明曾经有水和冰存在。研究还表明，冰块能够在陨石坑中持续存在，因为它们被遮挡，防止它被阳光分解。在这项新的努力中，研究人员调查了月球上看起来相似的区域也可能存在冰的可能性。
三位科学家开始注意到月球和水星的环境有些相似。他们还注意到水星和月亮都有阴影陨石坑，因为陨石坑内的物质堆积均有褪色的迹象。在水星上，先前的研究表明，材料的堆积部分是由冰构成的。为了确定月球是否也是如此，研究人员接下来研究对比了水星上2000个阴影陨石坑和月球上12000个类似阴影的陨石坑。
为了确定含有冰的相似性，研究人员将它们的直径与深度比率相互比较。在此过程中，他们注意到水星上阴影陨石坑的变浅与月球上阴影陨石坑的变化非常相似。他们认为，证据表明了在月球浅坑中收集的物质也可能是冰。如果他们的想法被证明是正确的，那就意味着月球表面上有数百万吨冰，远远超过大多数月球科学家的想法。
水星是太阳系八大行星中最小和最靠近太阳的行星，尽管如此，它有着八大行星中最大的离心率，轨道周期是87.969 地球日。由于大气层极为稀薄，无法有效保存热量，水星表面昼夜温差极大，为太阳系行星之最。白天时赤道地区温度可达430°C，夜间可降至-170°C。极区气温则终年维持在-170°C以下。
The San Jose Mercury News is an American daily newspaper, published in San Jose, California. It is owned by Media News Group. The Mercury News encompasses all other Bay Area newspapers owned by Media News Group, including the Oakland Tribune, Contra Costa Times, Marin Independent Journal, San Mateo County Times, Santa Cruz Sentinel, and 10 other local daily newspapers, each of which are branded as "an edition of the San Jose Mercury News," which accounts for the newspaper's high circulation.
Contents
[hide]
1 History
2 Coverage
3 Awards
4 Controversies
5 See also
6 References
7 External links
History[edit]
Mercury News headquarters (1967-2014)
Sections vary by day of the week, but Business, Sports, and The Valley are standard daily fare.
The San Jose Mercury was founded in 1851 as the San Jose Weekly Visitor, while the San Jose News was founded in 1883. In 1942, the Mercury purchased the News and continued publishing both newspapers, with the Mercury as the morning paper and theNews as the evening paper. In 1983, the newspapers were merged into the San Jose Mercury News, with morning and afternoon editions. The afternoon edition was later abandoned.
The paper says that the name "Mercury" refers to the importance of the mercuryindustry during the California Gold Rush, when the city's New Almaden Mines (nowAlmaden Quicksilver County Park) were the largest producer of mercury in North America. The name has a dual meaning, as Mercury is the Roman messenger of the gods as well as the god of commerce and thieves, known for his swiftness, and the nameMercury is commonly used for newspapers without the quicksilver association.
Because of its location in Silicon Valley, the Mercury News has covered many of the key events in the history of computing.
Ridder bought the Mercury and News in 1952. Ridder merged with Knight to form Knight Ridder in 1974.
On March 13, 2006 The McClatchy Company announced their agreement to purchase Knight Ridder. McClatchy decided that it would be expedient to explore the immediate resale of the Mercury News.[3]
On April 26, 2006 it was announced that Denver-based MediaNews Group would buy the Mercury News.[4] However, on June 12, 2006, federal regulators from the U.S. Department of Justice asked for more time to review the purchase, citing possible anti-trust concerns over MediaNews' ownership of other newspapers in the region. Although approval by regulators and completion of MediaNews' acquisition was announced on August 2, 2006, a lawsuit claiming antitrust violations by MediaNews and the Hearst Corporation had also been filed in July 2006.[5]
The suit, which sought to undo the purchase of both the Mercury News and the Contra Costa Times, was scheduled to go to trial on April 30, 2007. While extending until that date a preliminary injunction which prevented collaboration of local distribution and national advertising sales by the two media conglomerates, U.S. District Judge Susan Illston on December 19, 2006 expressed doubt over the legality of the purchase.[6] On April 25, 2007, days before the trial was scheduled to begin, the parties reached a settlement in which MediaNews preserved its acquisitions.[7]
In September 2014 the Mercury News moved to downtown San Jose, leaving its purpose-built headquarters that opened in 1967. Cited as reasons for the move were that the printing presses were no longer on site and the staff reductions that had occurred over the years.[8]
Coverage[edit]
The paper's local coverage and circulation is concentrated on the entire Bay Area, plus Santa Cruz County and excluding San Francisco and Sonoma County.
Awards[edit]
The newspaper has earned several awards, including two Pulitzer Prizes, one in 1986 for reporting regarding political corruption in the Ferdinand Marcosadministration in the Philippines, and one in 1990 for their comprehensive coverage of the 1989 Loma Prieta earthquake. Assistant managing editor David Yarnoldwas also a Pulitzer Prize finalist in 2004 for a local corruption investigation.[9] The Mercury News was also named one of the five best-designed newspapers in the world by the Society for News Design for work done in 2001.
Controversies[edit]
In August 1996 the Mercury News published "Dark Alliance," a series of investigative articles by reporter Gary Webb. The series claimed that members of the Nicaraguan Contras, an anti-government group organized with the help of the Central Intelligence Agency, had been involved in smuggling cocaine into America to support their struggle, and as a result had played a major role in creating the crack-cocaine epidemic of the 1980s. The series sparked three federal investigations, but other newspapers such as the Los Angeles Times later published articles suggesting that the series claims were overstated. Executive editor Jerry Ceppos, who had approved the series, eventually published a column that acknowledged shortcomings in the series reporting, editing, and production, while maintaining the story was correct "on many important points."[10]
See also[edit]
List of newspapers in California
