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.

經(jīng)過多年的搜尋工作，羅塞塔彗星探測器的菲萊著陸器的第二個著陸點位于67P / 楚留莫夫－格拉希門克彗星上類似于頭骨的位置。 菲萊在數(shù)十億年前的冰塊中留下了自己的烙印，這表明彗星的冰冷的內(nèi)部比卡布奇諾上的泡沫更柔軟。

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.

搜尋故事

? ? 菲萊于2014年11月12日降落到彗星的表面。它從最初在阿奇基亞（Agilkia）著陸時彈起，并繼續(xù)飛行了兩個小時，在此過程中，它與懸崖邊緣相撞并向第二個著陸點墜落。 菲萊最終在阿拜多斯（Abydos）的一個陰暗的角落停下了腳步。22個月后，該地點在羅塞塔任務(wù)結(jié)束幾周后才在羅塞塔影像中被發(fā)現(xiàn)。

?阿奇基亞：尼羅河中的小島。

?阿拜多斯：古埃及城市遺址。位于尼羅河西岸的拜勒耶納東南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的勞倫斯·奧羅克（Laurence O'Rourke）首先在尋找Philae方面發(fā)揮了領(lǐng)導(dǎo)作用，他還決心找到先前未發(fā)現(xiàn)的第二個著陸點。

“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.”

“菲萊給我們留下了最后的謎團，有待解決?！?勞倫斯說， “找到接地點很重要，因為Philae上的傳感器表明它已經(jīng)挖入了地面，很可能暴露出隱藏在其下的原始冰層，這將使我們獲得數(shù)十億年歷史的冰層的寶貴價值?！?/p>

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.

? ?他與一個任務(wù)科學(xué)家和工程師團隊一起，著手將羅塞塔和菲萊的儀器中的數(shù)據(jù)匯總在一起，以查找并確認(rèn)“消失”的著陸點。

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.

節(jié)目的明星

? ? 盡管從羅塞塔的OSIRIS攝像機的高分辨率圖像中觀察到明亮的“切片冰”斑對確定位置至關(guān)重要，但事實證明，菲萊的磁力計動臂（ROMAP）才是節(jié)目的亮點。 該儀器是用來在彗星的局部環(huán)境中進行磁場測量，但是進一步分析后，該團隊研究了當(dāng)懸臂撞擊到彗星（懸臂距著陸器48厘米）時發(fā)生的數(shù)據(jù)記錄變化。 當(dāng)懸臂撞擊彗星表面時的位移會在磁數(shù)據(jù)中產(chǎn)生一組特征性的峰值，這提供了菲萊沖入冰層的持續(xù)時間的估算值。 在這些聯(lián)系期間，數(shù)據(jù)還可以用于確定菲萊的加速度。

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的數(shù)據(jù)與羅塞塔的RPC磁力計所收集的數(shù)據(jù)相互關(guān)聯(lián)，從而確定了菲萊的姿態(tài)并排除了彗星周圍等離子體環(huán)境的背景磁場的任何影響。

“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.

“我們無法使用Philae進行我們計劃在2014年進行的所有測量，因此使用像這樣的磁力計，并以從未想過的方式將Rosetta和Philae的數(shù)據(jù)合并在一起，真是太了不起了，這給了我們這些驚人的結(jié)果?！鳖I(lǐng)導(dǎo)ROMAP數(shù)據(jù)分析的菲利普?海尼施說。

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.

對著陸數(shù)據(jù)的重新分析發(fā)現(xiàn)，Philae在第二個著陸點花費了近整整兩分鐘的時間，劃過了至少四種不同的表面。 圖片中顯示的一個特別值得注意的痕跡是當(dāng)Philae的頂部表面在縫隙一側(cè)的冰層中下沉25厘米時鉆塔和側(cè)面在那留下了明顯的痕跡。 懸臂運動引起的磁場數(shù)據(jù)峰值表明，菲萊花了三秒鐘才做出這種特殊的下沉。

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.

骷髏臉

? ? 勞倫斯說：“從上方觀看時，受到菲萊撞擊的巨石形狀使我想起了一塊頭骨，因此我決定將這一區(qū)域稱為“骷髏嶺”，并繼續(xù)使用該主題來稱呼觀察到的其他特征。”

“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.”

“'骷髏臉'的右'眼'是由菲萊的頂面壓縮灰塵而形成的，而巨石之間的縫隙是'骷髏頂縫'，菲萊就像風(fēng)車一樣在它們之間通過?！?/p>

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.

分析來自O(shè)SIRIS和羅塞塔光譜儀的圖像和數(shù)據(jù)后，證實明亮的曝光區(qū)域是冰水，覆蓋約3.5平方米的區(qū)域。 盡管降落時的冰大部分都在陰影中，但是幾個月后拍攝圖像時，太陽直接照亮了該區(qū)域，像燈塔一樣照亮了它，使其與周圍的一切截然不同。 冰比周圍的環(huán)境明亮，因為它以前沒有暴露于太空環(huán)境中且沒有經(jīng)歷過太空風(fēng)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.

? ? 勞倫斯說：“這是一盞在黑暗中發(fā)光的光?！彼挥诰嚯x菲萊最終在彗星表面被拍到的地方僅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.

卡布奇諾泡沫

雖然在尋找第二個著陸點的過程中得出了令人興奮的結(jié)論，而且該研究還提供了對彗星上巨石的冰塵內(nèi)部柔軟度的首次現(xiàn)場測量。

?“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.

“菲萊在縫隙側(cè)面沖擊的簡單動作使我們能夠得出結(jié)論，這種古老的，數(shù)十億年歷史的冰與粉塵的混合物非常柔軟，甚至比卡布奇諾咖啡上的泡沫或泡泡浴或海邊的海浪之上的泡沫還要蓬松柔軟?！眲趥愃寡a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.

該研究還可以估算出巨石的孔隙率（巨石內(nèi)部的冰塵顆粒之間存在多少空間）約為75％，這與之前在另一項研究中為整個彗星測得的值相符。 這項研究還表明，彗星在其內(nèi)部的任何地方都是均勻的，所有尺度都可以縮小到大約一米。 這意味著巨石代表了大約45億年前形成時彗星內(nèi)部的整體狀態(tài)。

“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.”

? ? “這是一種奇妙的多儀器共同得出的結(jié)果，不僅填補了菲萊彈跳之旅故事中的空白，而且使我們了解了彗星的性質(zhì)。” ESA的羅塞塔項目科學(xué)家馬特?泰勒說，“特別是，了解彗星的硬度對于未來的著陸任務(wù)至關(guān)重要。 彗星的內(nèi)部如此蓬松，對于如何設(shè)計著陸機制以及獲取樣本所需的機械過程而言，確實是十分有價值的信息。”

ESA 2020/10/28?

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