In September 2015, a team of astronomers from the National Astronomical Observatory of Japan, University of Michigan, Kyoto Sangyo University, Rikkyo University and the University of Tokyo successfully observed the entire hydrogen coma of the comet 67P/Churyumov-Gerasimenko, using the LAICA telescope onboard the PROCYON spacecraft. They also succeeded in obtaining the absolute rate of water discharge from the comet.
This comet was the target of ESA’s Rosetta mission in 2015. Because the Rosetta spacecraft was actually inside the cometary coma, it couldn’t observe the overall coma structure. There were bad observing conditions during the time the comet could be observed from Earth, so through our observations, we were able to test the coma models for the comet for the first time.
Comet observation by the PROCYON spacecraft had not been scheduled in the original mission plan. Thanks to the efforts of the spacecraft and telescope operation teams, observations were conducted shortly after we started discussing the possibility, producing results of great scientific importance.
该结果是微型航天器在深空探索中的第一个科学成就。此外，这提供了一个理想的例子，其中低成本任务（例如，Procyon任务）的观察支持了大型任务（例如Rosetta Mission）的精确观察。我们希望这将成为微型航天器观察以支持大型任务的模型案例。
The Rosetta mission and its limits
The 2015 apparition (appearance) of the comet 67P/Churyumov-Gerasimenko was a target of ESA’s Rosetta mission. In the Rosetta mission, precise observations of the comet were carried out from close to the surface of the nucleus for more than two years including when the comet passed perihelion (closest approach to the Sun) on August 13, 2015. However, observation of the entire coma was difficult because the Rosetta spacecraft was located in the cometary coma.
为了推断罗塞塔（Rosetta）对特定区域的观察，并估计每秒彗星释放的水总量（水生产率），我们需要昏迷的模型。但是水生产率很大程度上取决于我们使用的昏迷模型。为了测试昏迷模型，我们必须将基于Rosetta的结果和各种昏迷模型的预测得出的绝对水生产率与预测。因此，用另一颗卫星观察远离彗星的整个昏迷很有用。
通常，SOHO航天器上的天鹅望远镜经常用于观察此类目标。不幸的是，彗星搬到了一个恒星后面的区域，由于天鹅望远镜的低空间分辨率，它无法将彗星与背景恒星区分开。
Our observations with the PROCYON spacecraft
PROCYON is the smallest spacecraft for deep space exploration, with a weight of ~65 kg, developed by the University of Tokyo and others. LAICA, which observed the comet, is a telescope which can observe emissions from hydrogen atoms and its development was led by Rikkyo University. The main objective of the LAICA telescope was wide-field-of-view imaging observations from deep space of the complete view of the 42 year-old geocorona and geotail (a layer of hydrogen gas expanding away from the Earth) left over from Apollo 16 in 1972. Despite its small size, the LAICA telescope has high spatial resolution (more than 10 times that of the SWAN telescope), so the LAICA telescope could distinguish the comet from the background stars. The PROCYON spacecraft was launched together with the Hayabusa2 spacecraft in December 2014.
大部分彗星昏迷中的氢原子的形式from water molecules ejected from the cometary nucleus which are then broken apart by solar UV radiation (photo-dissociation). By using coma models based on these mechanisms, we can estimate the water release rate from a brightness map of the hydrogen atoms.
由于水是彗星冰中最丰富的分子，因此不仅要理解彗星活动水平，而且对于理解在早期太阳系中形成的分子中掺入分子中的过程。
We performed imaging observations of the entire hydrogen coma of the comet and derived the absolute water production rates near the perihelion in 2015. Based on our results, we could test the coma models for the comet. Combined with Rosetta’s results, such as water production rates at different distances from the Sun and chemical composition, we could accurately estimate the total ejected mass of the comet in the 2015 apparition.
Laica望远镜对彗星观察的故事和未来的含义，尽管对Procyon航天器的原始任务计划没有安排对彗星的观察，但讨论了2015年5月Geocolona观察结束后开始观察彗星观察的可能性。通常，一块彗星在短时间内穿过太阳系，因此，航天器的观察条件（例如方向和亮度）每天都会改变。我们能够进行67p/c-g的观察结果，并在短时间内获得了科学显着的结果，这要归功于Laica望远镜的广泛视野和高空间分辨率，Procyon卫星的指向控制性能，以及Procyon卫星的指向控制性能，以及卫星和望远镜管理团队的努力工作。
该结果是微型航天器在深空探索中的第一个科学成就。Around the world, plans are progressing for more micro spacecraft like this. Moreover, this result is an ideal example of a low-cost mission supporting important parts that cannot be implement in a large mission. We hope this result will become a model case for micro spacecraft observations in support of large missions in the future.
Filed Under:Aerospace + defense
