3I/ATLAS（C/2025 N1）：在“宇宙正午”时期对可能的行星形成遗迹进行直接航天器探测
3I/ATLAS (C/2025 N1): Direct Spacecraft Exploration of a Possible Relic of Planetary Formation at "Cosmic Noon"
AI总结：
本文提出利用已发射的Psyche、火星航天器阵列、Juice等探测器对第三个已知星际天体3I/ATLAS进行近距离观测，以检验其来自银河系厚盘及“宇宙正午”时期的运动学推断，弥补地面观测因太阳距角过小而无法开展的不足。
摘要：
星际天体3I/ATLAS（亦称为C/2025 N1 (ATLAS)，以下简称3I）由ATLAS智利望远镜于2025年7月1日发现，并迅速被确认为穿越太阳系的第三个已知星际天体（ISO），其无穷远处入射速度为57.9763 ± 0.0044 km s⁻¹。对3I相遇前运动学的分析表明，它很可能来自银河系厚盘，因此是银河系约90亿至130亿年前“宇宙正午”剧烈恒星形成时期的遗迹。将3I在运动学上归属于厚盘的这一判断，可在3I穿越太阳系期间通过观测加以检验。对地面观测者而言不利的是，3I的近日点将发生在地球视角下太阳的另一侧，太阳距角为12.80度，这使得从地球（或近地空间望远镜）进行观测十分困难甚至不可能。由于3I具有倾角为175.114度的逆行轨道（仅偏离黄道面4.886度），且其轨迹穿过火星轨道内侧，它将相对接近若干已发射的行星际航天器。我们发现存在强有力的科学理由，在以下接近时段进行观测：Psyche航天器于2025年9月4日以0.302 AU的距离接近，火星航天器阵列于2025年10月3日接近，以及Juice航天器于2025年11月4日接近。此外，Europa Clipper、Hera乃至更远的Lucy航天器可能在3I过近日点后的时期内穿过其彗尾，从而有可能直接观测那里的条件和成分。在可能的范围内，航天器观测可为3I近日点通过期间提供唯一的光谱和成像数据来源。
英文摘要：
The interstellar object 3I/ATLAS (also C/2025 N1 (ATLAS), henceforth, 3I), discovered by the ATLAS Chile telescope on 2025 July 1, was rapidly revealed to be the third known interstellar object (ISO) transiting the solar system, with an incoming velocity at infinity of 57.9763 $\pm$ 0.0044 km s$^{-1}$. An examination of 3I's pre-encounter kinematics shows that it is likely to be an object from the galactic thick disk, and thus a remnant of the Galaxy's ``cosmic noon'' period of intense star formation $\sim$9 - 13 gigayears ago. This kinematic assignment of 3I to the thick disk can be tested observationally in the transit of 3I through the solar system. Unfortunately for terrestrial observers, the 3I perihelion will happen when it is on the other side of the Sun as seen from Earth, at a solar elongation of 12.80 degrees, rendering observation from Earth (or near-Earth space telescopes) hard or impossible. With a retrograde orbit inclined 175.114 degrees (only 4.886 degrees from the ecliptic plane), and a trajectory passing inside the orbit of Mars, 3I will pass relatively close to a number of already launched interplanetary spacecraft. We find a strong science case for observations in the periods of the close approaches of the Psyche spacecraft on 2025 September 4, at 0.302 AU, the martian spacecraft array on 2025 October 3, and the Juice spacecraft on 2025 November 4. In addition, the Europa Clipper, Hera and even the more distant Lucy spacecraft may pass through 3I's cometary tail in the period after its perihelion passage, potentially directly observing the conditions and composition there. Spacecraft observations could, to the extent they are possible, provide the only source of spectral and imaging data during the 3I perihelion passage.
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