The moon of Jupiter – Lysithea (X) –
was discovered in 1938 by S. Nicholson. It is the second of four satellites discovered by this astronomer since its discovery came 24 years after he found
Sinope. In the year when Lysithea was discovered he also found
Carme. And in the years to come he was to discover Ananke.
The name of that moon is of mythological origin. Lysithea was daughter of Oceanus and one of many Zeus's lovers...
The moon by this name is in elliptical prograde orbit (→eccentricity
e = 0.1124) with a →semimajor axis a = 11,717,000 km. At pericenter (closest to the planet) Lysithea is separated from the Jupiter a distance of q = 10,400,009 km. At apocenter (furthest from the planet) this moon is separated from the Jupiter a distance of Q = 13,033,991 km. In future these parameters may vary due to a large orbital distance from Jupiter and the orbital motion being disturbed by the Sun and other factors. Perhaps it is a captured asteroid (with a diminutive mass: ~6.2944×1016 kg – it equals almost
9 mountains like Giewont
!),
and in future will possibly return to heliocentric orbit.
An in teresting feature of that moon is that being the in nermost
''irregular'' satellite of Jupiter (in a higly inclined elliptical orbit), it revolves in the same direction as the planet is spinning on its
axis.
Due to its similarity in semimajor axis to some of the other satellites of Jupiter, it is considered to be a member of a so called
Himalia (probably the remnants of a single large body).
The orbital period is over 2/3 earthly year, which means that the average speed of its celestial motion is only
1°23'20'' per day. When this motion was detected and compared to the changes in Jupiter's position, this body was classified as a true planetary satellite (and not a distant celestial body with its position projected near the planet).
Other obstacle in detecting this moon earlier was its brightness of only 18.3m
(over 83.1 thousand times fainter than the faintest stars visible to naked eye). For comparison: Jupiter's brightness is about
–2.7m,
so Lysithea is shining fainter by about 21.0m. The corresponding difference in brightness is over
251 million times!
I have given some crucial data of Lysithea below. Table one contains the basic
information. Whereas table two gives more detailed parametrs of its orbit (calculated using the following formulae).
Translated by Karol Pankowski
|
Lysithea
|
|---|
| Mean distance from the planet [×103 km] |
11,717.0
|
| Mean distance from the planet [planetary R] |
163.9
|
| Orbital period [days] |
259.20
|
| Orbital eccentricity [e] |
0.1124
|
| Orbit inclination [degrees] |
28.3
|
| Mean diameter [km] |
36.0
|
| Main discoverer and year of the discovery |
S. Nicholson 1938
|
| Visual magnitude [mag] |
18.3
|
| Mass [kg] |
~6.2944 × 1016
|
Orbital Parameters |
Pericenter
[q] |
Apocenter
[Q] |
| Distance from the planet [×103 km] |
10,400.0
|
13,034.0
|
| Distance from the planet [planetary R] |
145.5
|
182.3
|
| Angular size of the moon's orbit observed from the Earth* [degrees] |
0°56'51.88''
|
1°11'16.11''
|
|
| Angular diameter of the planet's disc as observed from the moon [degrees] |
0°47'15.85''
|
0°37'42.76''
|
| Brightness of the planet as observed from the moon** [mag] |
–11.6
|
–11.1
|
| Diameter of the moon's disc as observed from the planet's "surface" [degrees] |
0°00'00.72''
|
0°00'00.57''
|
| Brightness of the moon as observed from the planet's "surface"** [mag] |
9.3
|
9.8
|
|
Orbital velocity [km/sec] |
3.68
|
2.94
|
* This value is calculated for Jupiter at opposition (distance 628.8 million km = 4.2 AU)
** The given value of magnitude is not corrected for some decreasing factors (e.g. the changing phase of illumination)
|
See other related links:
Astronomy for every – Jupiter's moons
Monde
des Monats
– HIMALIAGRUPPE
Views
of the Solar System – LYSITHEA
Solar
System Exploration – LYSITHEA
The
Nine Planets – LYSITHEA
The Astronomy Workshop – Satellite Viewer
Planetary Satellite Mean Orbital Parameters
Natural Satellite Physical Parameters
 |
