1st images of elusive auroras on Neptune revealed by James Webb Space Telescope

詹姆斯·韦伯太空望远镜首次揭示了海王星上难以捉摸的极光图像

For the first time, astronomers have captured direct images of Neptune's elusive auroras.

天文学家首次捉取到了海王星难以捉摸的极光的直接图像。

Scientists have long suspected that the distant ice giant hosts shimmering light displays, based on fleeting hints from the Voyager 2 probe's flyby and observations of similar activity on Jupiter, Saturn and Uranus. Capturing images of Neptune's auroras had remained out of reach until the James Webb Space Telescope (JWST or Webb) turned its powerful eye towards the icy planet.

科学家们长期以来一直怀疑这颗遥远的冰巨星存在璀璨的光芒显示，这一推测基于“旅行者2号”探测器飞越时获得的零星线索，以及对木星、土星和天王星上类似活动的观测。直到詹姆斯·韦伯空间望远镜（JWST 或韦伯望远镜）将强大的视线转向这颗冰冻行星，才终于成功捕捉到海王星极光的影像。

"Turns out, actually imaging the auroral activity on Neptune was only possible with Webb's near-infrared sensitivity," said Henrik Melin of Northumbria University, who conducted the research while at the University of Leicester, in a statement accompanying the photos. "It was so stunning to not just see the auroras, but the detail and clarity of the signature really shocked me."

北安普顿大学的亨里克·梅林（Henrik Melin）在随照片发布的声明中说道。：“事实证明，实际上只有借助韦伯望远镜的近红外敏感度，才能观测到海王星的极光活动，“他在莱斯特大学任职期间开展了这项研究。”不仅能看到极光，而且极光特征的细节和清晰度真的让我震惊。”

Even more significant is the unique nature of Neptune's aurora, which scientists say differs from those seen on Earth, Jupiter, and Saturn, where auroras are typically confined to the poles. This is because their magnetic fields are relatively well aligned with their rotation axes, guiding charged particles from the solar wind toward the polar regions.

更值得注意的是海王星极光的独特性，科学家表示，其极光与地球、木星和土星上的极光存在显著差异。在地球、木星和土星上，极光通常仅限于两极地区。这是因为这些行星的磁场与自转轴相对应，能够引导太阳风中的带电粒子向两极区域聚集。

Neptune, on the other hand, has a highly tilted and offset magnetic field, which means its auroras appear at unexpected locations, such as the planet's mid latitudes.

另一方面，海王星拥有一个高度倾斜且偏移的磁场，这意味着其极光会出现在意想不到的位置，例如该行星的中纬度地区。

These observations were made possible by the James Webb Space Telescope's Near-Infrared Spectrograph (NIRSpec), an instrument that analyzes the light absorbed or emitted by celestial objects. By breaking down the different wavelenghts of this light, scientists can determine key physical properties, such as temperature, mass and chemical composition.

这些观测结果得益于詹姆斯·韦伯空间望远镜的近红外光谱仪（NIRSpec），该仪器能够分析天体吸收或发出的光线。通过分解这些光线的不同波长，科学家可以确定关键的物理属性，例如温度、质量和化学组成。

In this case, NIRSpec captured detailed images of Neptune's ionosphere — the electrically charged layer of its upper atmosphere, similar to Earth's ionosphere, where auroras form. Excitingly, Webb's data revealed emissions of trihydrogen cation (H₃⁺), one of the most abundant ions in the universe. This discovery is significant because H₃⁺ plays a crucial role in planetary auroras, glowing in response to interactions between planets' atmospheres and charged particles from the solar wind.

在这种情况下，NIRSpec 捕获了海王星电离层的详细图像——这是其高层大气中带电的层，与地球的电离层类似，是极光形成的地方。令人兴奋的是，韦伯望远镜的数据揭示了三氢阳离子（H₃⁺）的发射，这是宇宙中最为丰富的离子之一。这一发现具有重要意义，因为H₃⁺在行星极光中扮演着关键角色，其发光现象源于行星大气与太阳风携带的带电粒子之间的相互作用。

"H3+ has a been a clear signifier on all the gas giants — Jupiter, Saturn, and Uranus — of auroral activity, and we expected to see the same on Neptune as we investigated the planet over the years with the best ground-based facilities available," explained JWST scientist Heidi Hammel. "Only with a machine-like Webb have we finally gotten that confirmation."

“H3+一直是木星、土星和天王星等气态巨行星上极光活动的明确标志，我们原本预计在海王星上也能观察到类似现象，因为多年来我们一直利用地面上最先进的观测设备对这颗行星进行研究，JWST科学家海蒂·哈梅尔解释道，”只有借助韦伯望远镜这种精密仪器，我们才最终获得了这一确认。”

The team was also able to take a temperature reading of Neptune, something that hasn't been done since Voyager 2's flyby in August, 1989. "I was astonished [by the results]," Melin said. "Neptune's upper atmosphere has cooled by several hundreds of degrees [in that time]. In fact, the temperature in 2023 was just over half of that in 1989."

该团队还成功测量了海王星的温度，这是自1989年8月旅行者2号飞越海王星以来首次实现的。 “我对结果感到震惊，”梅林说，"海王星的上层大气在过去几十年间冷却了数百摄氏度。事实上,2023年的温度仅为1989年的不到一半。”

The dip in planetary temperature may help explain why the aurora have been so difficult to view. This is because auroras occur when charged particles excite atmospheric gases, causing them to emit light. Higher temperatures generally mean more energetic particles and a higher rate of collisions, leading to brighter auroras. A substantially colder temperature would reduce the density of energetic ions, leading to weaker emissions that are harder to detect.

行星温度的下降可能有助于解释为何极光如此难以观测。这是因为极光的形成是由于带电粒子激发大气中的气体，使其发出光线。较高的温度通常意味着更具活力的粒子和更高的碰撞率，从而产生更明亮的极光。而显著较低的温度会降低高能离子的密度，导致发光强度减弱，从而更难被探测到。

Astronomers will continue to study Neptune using the JWST, hoping to gain a deeper understanding of our solar system's strangest planet.

天文学家将继续使用JWST研究海王星，希望更深入地了解太阳系最奇怪的行星。

"As we look ahead and dream of future missions to Uranus and Neptune, we now know how important it will be to have instruments tuned to the wavelengths of infrared light to continue to study the auroras," added Leigh Fletcher of Leicester University, co-author on the paper. "This observatory has finally opened the window onto this last, previously hidden ionosphere of the giant planets."

“当我们展望未来，憧憬着对天王星和海王星的探测任务时，我们现在已经清楚地认识到，拥有能够捕捉红外光波长的仪器对于继续研究极光是多么重要，“莱斯特大学的莱恩·弗莱彻（Leigh Fletcher）补充道，他是该论文的合著者。”这座天文台终于为我们打开了一扇通往巨行星最后一个、此前未被探测到的电离层的窗口。”