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Radio observations of Jupiter-family comets

机译：木星家庭彗星的无线电观测

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Radio observations from decimetric to submillimetric wavelengths are now a basic tool for the investigation of comets. Spectroscopic observations allow us: (ⅰ) to monitor the gas production rate of the comets, by directly observing the water molecule, or by observing secondary products (e.g., the OH radical) or minor species (e.g., HCN); (ⅱ) to investigate the chemical composition of comets; (ⅲ) to probe the physical conditions of cometary atmospheres: kinetic temperature and expansion velocity. Continuum observations probe large-size dust particles and (for the largest objects) cometary nuclei.rnComets are classified from their orbital characteristics into two separate classes: (ⅰ) nearly isotropic, mainly long-period comets and (ⅱ) ecliptic, short-period comets, the so-called Jupiter-family comets (JFCs). These two classes apparently come from two different reservoirs, respectively, the Oort cloud and the trans-Neptunian scattered disc. Due to their different history and-possibly-their different origin, they may have different chemical and physical properties that are worth being investigated.rnThe present article reviews the contribution of radio observations to our knowledge of the JFCs. The difficulty of such a study is the commonly low gas and dust productions of these comets. Long-period, nearly isotropic comets from the Oort cloud are better known from Earth-based observations. On the other hand, JFCs are more easily accessed by space missions. However, unique opportunities to observe JFCs are offered when these objects come by chance close to the Earth (like 73P/Schwassmann-Wachmann 3 in 2006), or when they exhibit unexpected outbursts (as did 17P/Holmes in 2007).rnAbout a dozen JFCs were successfully observed by radio techniques up to now. Four to ten molecules were detected in five of them. No obvious evidence for different properties between JFCs and other families of comets is found, as far as radio observations are concerned.
机译：从分光波长到亚毫米波长的无线电观测现已成为研究彗星的基本工具。光谱观察使我们：（ⅰ）通过直接观察水分子或观察副产物（例如OH自由基）或次要物种（例如HCN）来监测彗星的产气率； （ⅱ）调查彗星的化学成分； （ⅲ）探讨彗星大气的物理条件：动力学温度和膨胀速度。连续观测发现了大的尘埃粒子和（对于最大的物体而言）彗核。彗星从其轨道特征分为两类：（ⅰ）近乎各向同性的，主要是长周期彗星和（ⅱ）黄道，短周期的彗星。彗星，即所谓的木星家庭彗星（JFCs）。这两个类别显然来自两个不同的储集层，分别是奥尔特云和海王星散盘。由于它们的历史不同以及可能它们的起源不同，它们可能具有不同的化学和物理性质，值得研究。本文综述了无线电观测对我们对JFC知识的贡献。这项研究的困难在于这些彗星的气体和粉尘产生通常较低。奥尔特云的长周期，近乎各向同性的彗星在基于地球的观测中更为人所知。另一方面，太空飞行任务更容易获得JFC。但是，当这些物体偶然靠近地球时（例如2006年的73P / Schwassmann-Wachmann 3），或者它们出现意想不到的爆发（如2007年的17P / Holmes），都提供了观察JFC的独特机会。迄今为止，通过无线电技术已经成功地观测到了JFC。其中五个检测到四到十个分子。就无线电观测而言，没有发现JFC和其他彗星家族之间具有不同性质的明显证据。

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