菲莱的第二着陆点在“骷髅岭”找到了

Philae’s second touchdown site discovered at ‘skull-top’ ridge

After years of detective work, the second touchdown site of Rosetta’s Philae lander has been located on Comet 67P/Churyumov-Gerasimenko in a site that resembles the shape of a skull. Philae left its imprint in billions-of-years-old ice, revealing that the comet’s icy interior is softer than cappuccino froth.

经过多年的搜寻工作，罗塞塔彗星探测器的菲莱着陆器的第二个着陆点位于67P / 楚留莫夫－格拉希门克彗星上类似于头骨的位置。 菲莱在数十亿年前的冰块中留下了自己的烙印，这表明彗星的冰冷的内部比卡布奇诺上的泡沫更柔软。

Detective story

Philae descended to the surface of the comet on 12 November 2014. It rebounded from its initial touchdown site at Agilkia and embarked on a two-hour flight, during which it collided with a cliff edge and tumbled towards a second touchdown location. Philae eventually came to a halt at Abydos, in a sheltered spot that was only identified in Rosetta imagery 22 months later, a few weeks before the conclusion of the Rosetta mission.

搜寻故事

    菲莱于2014年11月12日降落到彗星的表面。它从最初在阿奇基亚（Agilkia）着陆时弹起，并继续飞行了两个小时，在此过程中，它与悬崖边缘相撞并向第二个着陆点坠落。 菲莱最终在阿拜多斯（Abydos）的一个阴暗的角落停下了脚步。22个月后，该地点在罗塞塔任务结束几周后才在罗塞塔影像中被发现。

•阿奇基亚：尼罗河中的小岛。

•阿拜多斯：古埃及城市遗址。位于尼罗河西岸的拜勒耶纳东南11公里。

ESA’s Laurence O’Rourke, who played the leading role in finding Philae in the first instance, was also determined to locate the previously undiscovered second touchdown site.

ESA的劳伦斯·奥罗克（Laurence O'Rourke）首先在寻找Philae方面发挥了领导作用，他还决心找到先前未发现的第二个着陆点。

“Philae had left us with one final mystery waiting to be solved,” says Laurence. “It was important to find the touchdown site because sensors on Philae indicated that it had dug into the surface, most likely exposing the primitive ice hidden underneath, which would give us invaluable access to billions-of-years-old ice.”

“菲莱给我们留下了最后的谜团，有待解决。” 劳伦斯说， “找到接地点很重要，因为Philae上的传感器表明它已经挖入了地面，很可能暴露出隐藏在其下的原始冰层，这将使我们获得数十亿年历史的冰层的宝贵价值。”

Together with a team of mission scientists and engineers, he set about pulling together data from both Rosetta and Philae instruments to find and confirm the ‘missing’ touchdown site.

   他与一个任务科学家和工程师团队一起，着手将罗塞塔和菲莱的仪器中的数据汇总在一起，以查找并确认“消失”的着陆点。

The star of the show

Although a bright patch of ‘sliced ice’ observed in high-resolution images from Rosetta’s OSIRIS camera proved crucial in confirming the location, it was Philae’s magnetometer boom, ROMAP, that turned out to be the star of the show. The instrument was designed to make magnetic field measurements in the comet’s local environment, but for the new analysis the team looked at changes recorded in the data that arose when the boom – which sticks out 48 cm from the lander – physically moved as it struck a surface. This created a characteristic set of spikes in the magnetic data as the boom moved relative to the lander body, which provided an estimate of the duration of Philae stamping into the ice. The data could also be used to constrain the acceleration of Philae during these contacts.

节目的明星

    尽管从罗塞塔的OSIRIS摄像机的高分辨率图像中观察到明亮的“切片冰”斑对确定位置至关重要，但事实证明，菲莱的磁力计动臂（ROMAP）才是节目的亮点。 该仪器是用来在彗星的局部环境中进行磁场测量，但是进一步分析后，该团队研究了当悬臂撞击到彗星（悬臂距着陆器48厘米）时发生的数据记录变化。 当悬臂撞击彗星表面时的位移会在磁数据中产生一组特征性的峰值，这提供了菲莱冲入冰层的持续时间的估算值。 在这些联系期间，数据还可以用于确定菲莱的加速度。

ROMAP’s data were cross-correlated with those collected by Rosetta’s RPC magnetometer at the same time to determine Philae’s attitude and exclude any influence from the background magnetic field of the plasma environment around the comet.

ROMAP的数据与罗塞塔的RPC磁力计所收集的数据相互关联，从而确定了菲莱的姿态并排除了彗星周围等离子体环境的背景磁场的任何影响。

“We weren’t able to make all the measurements we planned in 2014 with Philae, so it is really amazing to use the magnetometer like this, and to combine data from both Rosetta and Philae in a way that was never intended, to give us these wonderful results,” says Philip Heinisch, who led the analysis of the ROMAP data.

“我们无法使用Philae进行我们计划在2014年进行的所有测量，因此使用像这样的磁力计，并以从未想过的方式将Rosetta和Philae的数据合并在一起，真是太了不起了，这给了我们这些惊人的结果。”领导ROMAP数据分析的菲利普•海尼施说。

A reanalysis of the touchdown data found that Philae had spent nearly two full minutes at the second touchdown site, making at least four distinct surface contacts as it ploughed across it. One particularly notable imprint revealed in the images was created as Philae’s top surface sank 25 cm into the ice on the side of a crevice, leaving identifiable marks of its drill tower and sides. The spikes in the magnetic field data arising from the boom movement showed that it took Philae three seconds to make this particular depression.

对着陆数据的重新分析发现，Philae在第二个着陆点花费了近整整两分钟的时间，划过了至少四种不同的表面。 图片中显示的一个特别值得注意的痕迹是当Philae的顶部表面在缝隙一侧的冰层中下沉25厘米时钻塔和侧面在那留下了明显的痕迹。 悬臂运动引起的磁场数据峰值表明，菲莱花了三秒钟才做出这种特殊的下沉。

Skull face

“The shape of the boulders impacted by Philae reminded me of a skull when viewed from above, so I decided to nickname the region ‘skull-top ridge’ and to continue that theme for other features observed,” says Laurence.

骷髅脸

    劳伦斯说：“从上方观看时，受到菲莱撞击的巨石形状使我想起了一块头骨，因此我决定将这一区域称为“骷髅岭”，并继续使用该主题来称呼观察到的其他特征。”

“The right ‘eye’ of the ‘skull face’ was made by Philae’s top surface compressing the dust while the gap between the boulders is ‘skull-top crevice’, where Philae acted like a windmill to pass between them.”

“'骷髅脸'的右'眼'是由菲莱的顶面压缩灰尘而形成的，而巨石之间的缝隙是'骷髅顶缝'，菲莱就像风车一样在它们之间通过。”

Analysis of images and data from OSIRIS and Rosetta’s spectrometer VIRTIS confirmed that the bright exposure was water-ice covering an area of about 3.5 square metres. Although the ice was mostly in shadow at the time of the landing, the Sun was directly illuminating the area when the images were taken months later, lighting it up like a beacon to stand out against everything around it. The ice was brighter than the surrounds because it had not been previously exposed to the space environment and undergone space weathering.

分析来自OSIRIS和罗塞塔光谱仪的图像和数据后，证实明亮的曝光区域是冰水，覆盖约3.5平方米的区域。 尽管降落时的冰大部分都在阴影中，但是几个月后拍摄图像时，太阳直接照亮了该区域，像灯塔一样照亮了它，使其与周围的一切截然不同。 冰比周围的环境明亮，因为它以前没有暴露于太空环境中且没有经历过太空风化。

“It was a light shining in the darkness,” says Laurence, noting that it was located just 30 m away from where Philae was finally imaged on the comet surface.

    劳伦斯说：“这是一盏在黑暗中发光的光。”它位于距离菲莱最终在彗星表面被拍到的地方仅30 m。

Cappuccino froth

While an exciting conclusion in the search for the second touchdown site, the study also provides the first in situ measurement of the softness of the icy-dust interior of a boulder on a comet.

卡布奇诺泡沫

虽然在寻找第二个着陆点的过程中得出了令人兴奋的结论，而且该研究还提供了对彗星上巨石的冰尘内部柔软度的首次现场测量。

 “The simple action of Philae stamping into the side of the crevice allowed us to work out that this ancient, billions-of-years-old, icy-dust mixture is extraordinarily soft – fluffier than froth on a cappuccino, or the foam found in a bubble bath or on top of waves at the seashore,” adds Laurence.

“菲莱在缝隙侧面冲击的简单动作使我们能够得出结论，这种古老的，数十亿年历史的冰与粉尘的混合物非常柔软，甚至比卡布奇诺咖啡上的泡沫或泡泡浴或海边的海浪之上的泡沫还要蓬松柔软。”劳伦斯补充到。

The study also allowed an estimate of the boulder’s porosity – how much empty space exists between the ice-dust grains inside the boulder – of about 75%, which is in line with the value measured previously for the whole comet in a separate study. The same study showed that the comet is homogeneous anywhere in its interior on all size scales down to about one metre. This implies that the boulders represent the overall state of the comet’s interior when it formed some 4.5 billion years ago.

该研究还可以估算出巨石的孔隙率（巨石内部的冰尘颗粒之间存在多少空间）约为75％，这与之前在另一项研究中为整个彗星测得的值相符。 这项研究还表明，彗星在其内部的任何地方都是均匀的，所有尺度都可以缩小到大约一米。 这意味着巨石代表了大约45亿年前形成时彗星内部的整体状态。

“This is a fantastic multi-instrument result that not only fills in the gaps in the story of Philae’s bouncy journey, but also informs us about the nature of the comet,” says Matt Taylor, ESA’s Rosetta project scientist. “In particular, understanding the strength of a comet is critical for future lander missions. That the comet has such a fluffy interior is really valuable information in terms of how to design the landing mechanisms, and also for the mechanical processes that might be needed to retrieve samples.”

    “这是一种奇妙的多仪器共同得出的结果，不仅填补了菲莱弹跳之旅故事中的空白，而且使我们了解了彗星的性质。” ESA的罗塞塔项目科学家马特•泰勒说，“特别是，了解彗星的硬度对于未来的着陆任务至关重要。 彗星的内部如此蓬松，对于如何设计着陆机制以及获取样本所需的机械过程而言，确实是十分有价值的信息。”

ESA 2020/10/28 

http://www.esa.int/Science_Exploration/Space_Science/Rosetta/Philae_s_second_touchdown_site_discovered_at_skull-top_ridge