木卫四之谜

“伽利略”号木星探测器 1 995年 1 2月到达木星附近 ,开始对木星及其四颗“伽利略卫星”进行探测。这颗高度成功的飞行器对木星系统的探测使我们重新考虑我们原先的木星系统知识 ,尤为突出的是木卫四。“伽利略”号探测器对木卫四的观测给了我们一个巨大的惊奇 :木卫四内部似乎有水的海洋。木卫四的早期探测是“旅行者”飞船进行的。“旅行者”在 1 979年到达木星系统时 ,揭示出大量“伽利略卫星”知识 :木卫一的火山 ;木卫二年轻的 ,断裂的 ,多冰的表面 ;木卫三上各式各样的“地形”。对木卫四的认识它是这样描述的 :做着乏味的、料想中的…     

伽利略卫星的等势面和正常重力场

给出了轨道面接近赤道面的轨旋同步卫星的正常重力场在等势面上分布的展开式，并讨论了潮汐对其正常重力场的影响，利用这一方法，讨论了伽利略卫星正常重力场及其在等势面上的分布，以及木星的潮汐对伽利略卫星的正常重力场的影响，计算表明，潮汐对伽利略卫星的正常重力场影响不大，其径向的影响grt大约是10^-3-10^-5m/s^2的量级，与重力场在经度和纬度方向的分量接近，通过估算，月球的重力场所受到的潮汐影响要比绝大多数伽利略卫星受到的潮汐影响小。     

“伽利略”发现木星周围的岩石小卫星

当地基望远镜使木卫的数目达到60,并可能还会增加时,伽利略木星探测器拍摄到木星一些更小卫星的图像。在“伽利略”2002年11月飞掠木卫五期间,它的恒星跟踪器——飞船上用于瞄准某颗导航星为飞船定位的望远镜发现了9个亮闪光。飞掠期间恒星跟踪器     

第5届亚太地区天文奥赛观测试题

1、木星和它的四颗伽利略卫星。选择合适的目镜,将木星放到视场中央。把结果展示给考官看。尽可能详尽地把你所观测到的景象描绘下来。     

怎样辨认木星的伽利略卫星

怎样辨认木星的伽利略卫星杨超当我们用望远镜观测木星的时候，总会发现其附近有四颗较亮的小星，好似卫士一样在保卫着木星，它们就是木星的枷利略卫星。３８０多年来，它们一直吸引着无数的天文学家及爱好者去观测、探索它们。研究伽利略卫星对太阳系的演化及日心体系的...     

伽利略卫星食计时观测

木星的又一个可见期已经来临。 木星是太阳系中拥有众多卫星的行星之一(39颗)。三百多年前,伽利略用自制的望远镜看木星时,发现有四颗星星绕着木星运转,以后的天文学家便把这四颗星星称为“伽利略卫星”。这四颗卫星由内到外,分     

木卫五的身世之谜

地球和木星这样的行星是太阳形成时其周围的气体和尘埃盘构成的。类似地球的岩质行星形成于接近太阳的高温环境下,而像木星这样的气体巨行星形成于离太阳较远的寒冷区域。同样,木星,这颗太阳系中最大的行是可能也有自己的气体和尘埃盘。由伽利略发现的四颗木星卫星(木卫一、木卫二、木卫三和木卫四,合称伽利略     

木星伽利略卫星的“相互掩食”现象

木星绕太阳公转一圈约12年,每隔6年则过春分或秋分点一次。在此前后,对木星而言,太阳带着地球通过其赤道平面。也就是说,木星、运行轨道与木星赤道夹角小于0.5度的四颗伽利略卫星、地球以及太阳几乎在同一个平面,结果是伽利略卫星产生互相遮掩或将自己的阴影投射在另一颗卫星上的现象能被地球上     

国外空间探测器发展概览（下）

木星是太阳系八大行星中最大的一颗,并有很多天然卫星,很像是一个微型的太阳系,所以不少人认为探测木星有助于了解太阳系。第一批访问木星的是美国先驱者-1O和11,它们以行星际漫游的方式对木星进行了探测。1972年3月2日发射的先驱者-10于l973年12月在穿过木星云层时拍摄并发回了首批木星及其卫星的照片。     

太阳系究竟有多少颗卫星

自１６０９年伽利略首次用望远镜观测天象以来,人类开始不断发现太阳系其他行星周围的卫星。木星的４颗大卫星（木卫一至四）,其亮度在５１～６３星等之间,是太阳系内除月亮以外最亮的四颗卫星,用伽利略时代的小望远镜就能清晰地看到,因此是首批确认的卫星,称为...     

Internal Structure Models and Dynamical Parameters of the Galilean Satellites

Radio Doppler data generated by the Deep Space Network (DSN) from the recent encounters of the Galileo spacecraft with the Galilean satellites have been used to determine the mass (GM) and unnormalized quadruple gravity coefficients in the external gravitational fields of the Galilean satellites. Therefore, a series of internal structure models, which satisfy the given constraints for the mean density and the mean moment of inertia, can be presented by solving Emden equations. And some dynamical parameters can also be calculated based on the density distributions given by internal structure models.     

Cassini VIMS observations of the Galilean satellites including the VIMS calibration procedure

The Visual and Infrared Mapping Spectrometer (VIMS) observed the Galilean satellites during the Cassini spacecraft's 2000/2001 flyby of Jupiter, providing compositional and thermal information about their surfaces. The Cassini spacecraft approached the jovian system no closer than about 126 Jupiter radii, about 9 million kilometers, at a phase angle of <90°, resulting in only sub-pixel observations by VIMS of the Galilean satellites. Nevertheless, most of the spectral features discovered by the Near Infrared Mapping Spectrometer (NIMS) aboard the Galileo spacecraft during more than four years of observations have been identified in the VIMS data analyzed so far, including a possible ¹³C absorption. In addition, VIMS made observations in the visible part of the spectrum and at several new phase angles for all the Galilean satellites and the calculated phase functions are presented. In the process of analyzing these data, the VIMS radiometric and spectral calibrations were better determined in preparation for entry into the Saturn system. Treatment of these data is presented as an example of the VIMS data reduction, calibration and analysis process and a detailed explanation is given of the calibration process applied to the Jupiter data.     

Free and forced obliquities of the Galilean satellites of Jupiter

The obliquity, or angular separation between orbit normal and spin pole, is an important parameter for the geodynamics of most Solar System bodies. Tidal dissipation has driven the obliquities of the Galilean satellites of Jupiter to small, but non-zero values. We present estimates of the free and forced obliquities of these satellites using a simple secular variation model for the orbits, and spin pole precession rate estimates based on gravity field parameters derived from Galileo spacecraft encounters. The free obliquity values are not well constrained by observations, but are presumed to be very small. The forced obliquity variations depend only on the orbital variations and the spin pole precession rate parameters, which are quite well known. These variations are large enough to influence spatial and temporal patterns of tidal dissipation and tidal stress.     

How fast do Galilean satellites spin?

Each of the Galilean satellites, as well as most other satellites whose initial rotations have been substantially altered by tidal dissipation, has been widely assumed to rotate synchronously with its orbital mean motion. Such rotation would require a small permanent asymmetry in the mass distribution in order to overcome the small mean tidal torque. Since Io and Europa may be substantially fluid, they may not have the strenght to support the required permanent asymmetry. Thus, each may rotate at the unknown but slightly nonsynchronous rate that corresponds to zero mean tidal torque. This behaviour may be observable by Galileo spacecraft imaging. It may help explain the longitudinal variation of volcanism on Io and the cracking of Europa's crust.     

Predictions of mutual phenomena of the Galilean satellites in 1985–1986

A thorough search covering more than 3 years shows that nearly 300 observable mutual eclipses and occultations of the Galilean satellites occur between May 1985 and April 1986, marking this apparition as a very favorable one. This paper tabulates quantities needed to obtain light curves of all events, excluding only those taking place either too close to Jupiter or with the planet too near the Sun. Since observations are relatively short and easy to incorporate into photometric programs, we urge an active campaign so as to provide the accurate astrometric data required to improve ephemerides (which are of immediate interest to the Galileo mission to Jupiter) and to look for tidal effects in the motion of Io.     

The Q Values of the Galilean Satellites and their Tidal Contributions to the Deceleration of Jupiter''''s Rotation

The relationship between the k2/Q of the Galilean satellites and the k2J/QJ of Jupiter is derived from energy and momentum considerations. Calculations suggest that the Galilean satellites can be divided into two classes according to their Q values: Io and Ganymede have values between 10 and 50, while Europa and Callisto have values ranging from 200 to 700. The tidal contributions of the Galilean satellites to Jupiter's rotation are estimated. The main deceleration of Jupiter, which is about 99.04% of the total, comes from Io.     

Equipotential surface and normal gravity of the Galilean satellites

In this article, expanded equations of normal gravity on the equipotential surface are proposed for a natural satellite whose orbital plane is close to its equatorial plane. Tidal effects on the normal gravity are also discussed. The authors apply these to the Galilean satellites. Calculations suggest that the tides raised by Jupiter weakly affect the Galilean satellites. The radial displacements of the gravity due to the tides are in the range between 10⁻³ and 10⁻⁵ m s⁻², which are similar to the latitudinal and longitudinal displacements. The variations along the latitude circle are larger than those along the longitude circle. We conclude that the tidal effects on most of the Galilean satellites are larger than those on the Moon.     

Observations at the inner edge of the Jovian current sheet: evidence for a dynamic magnetosphere

It is widely recognized that Io, the innermost of the Galilean satellites, releases matter into the rapidly-rotating Jovian magnetosphere at rates that may be as high as a ton per second. Following ionization, this iogenic, heavy-ion plasma dominates the dynamics of the Jovian magnetosphere. On average this plasma must be lost at a rate that balances its generation but we do not know whether this process is steady or intermittent. Measurements by the Galileo magnetometer suggest that this process is unsteady. By estimating the magnetic and particle stresses from these observations, we further can derive a mass density profile that is consistent with earlier measurements of the current sheet density and that is consistent with estimates of the radial transport of mass in the middle Jovian magnetosphere.     

Mutual occultations and eclipses of the Galilean satellites of Jupiter in 2002–2003: final astrometric results

The photometry of mutual occultations and eclipses of natural planetary satellites can be used to infer very accurate astrometric data. This can be achieved by processing the light curves of the satellites observed during international campaigns of photometric observations of these mutual events.
This work focuses on processing the complete data base of photometric observations of the mutual occultations and eclipses of the Galilean satellites made during the international campaign in 2002–2003. The final goal is to derive new accurate astrometric data.
We propose the most accurate photometric model of mutual events based on all the data available to date about the satellites, and develop the corresponding method for extracting astrometric data. This method is applied to derive astrometric data from photometric observations of mutual occultations and eclipses of the Galilean satellites.
We process the 371 light curves obtained during the international campaign of photometric observations of the Galilean satellites in 2002–2003. As compared with the theory, the rms 'O-C' residuals with respect to theory is equal to 0.055 and 0.064 arcsec in right ascension and declination, respectively, for the 274 best observations. Topocentric or heliocentric angular differences for satellite pairs are obtained for 119 time instants during the time period from 2002 October 10 to 2003 July 17.