The moon of Jupiter –
Adrastea (XV) – was previously designated as S/1979
J1. It was discovered in 1979 by then graduate student D.C. Jewitt
and his professor E. Danielson.
The name of that moon is of mythological origin. Adrastea was a nymph of Crete to whose care Rhea entrusted the in fant Zeus to save him from being swallowed by his father
– Cronus.
The moon by this name is in almost circular prograde orbit (→eccentricity
e = 0.0018) with a →semimajor axis a = 129,000 km. At pericenter (closest to the planet) Adrastea is separated from the Jupiter a distance of q = 128,768 km. At apocenter (furthest from the planet) this moon is separated from the Jupiter a distance of Q = 129,232 km.
Its mass is so diminutive ~7.4933×1015 kg
, that it is comparable to a single Mount Giewont
!
An in teresting feature of that moon is that it revolves in side of the so called →Roche limit.
It is very small and must have a very rigid structure since the tidal forces of Jupiter haven't torn it apart yet! It also revolves slightly faster than Jupiter spins around its axis!
Its orbital period is only 0.3 day, which means that its mean celestial angular velocity in the sky is 1,208°
(over 3.33
revolutions).
The main obstacle in discovery of that moon was its small angular distance from
Jupiter and also its low brightness only 18.7m
(over 120.2 thousand times fainter than the faintest stars visible to the naked
eye). For comparison: Jupiter is about –2.7m,
so Adrastea is shining fainter by about 21.4m. It corresponds to a difference in brightness of
over 363 million times!
I have given some crucial data of Adrastea 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
|
Adrastea
|
|---|
| Mean distance from the planet [×103 km] |
129.0
|
| Mean distance from the planet [planetary R] |
1.8
|
| Orbital period [days] |
0.30
|
| Orbital eccentricity [e] |
0.0018
|
| Orbit inclination [degrees] |
0.1
|
| Mean diameter [km] |
16.4
|
| Main discoverer and year of the discovery |
D.C. Jewitt 1979
|
| Visual magnitude [mag] |
18.7
|
| Mass [kg] |
~7.4933 × 1015
|
Orbital Parameters |
Pericenter
[q] |
Apocenter
[Q] |
| Distance from the planet [×103 km] |
128.8
|
129.2
|
| Distance from the planet [planetary R] |
1.8
|
1.8
|
| Angular size of the moon's orbit observed from the Earth* [degrees] |
0°00'42.24''
|
0°00'42.39''
|
|
| Angular diameter of the planet's disc as observed from the moon [degrees] |
67°27'14.33''
|
67°10'45.38''
|
| Brightness of the planet as observed from the moon** [mag] |
–21.1
|
–21.1
|
| Diameter of the moon's disc as observed from the planet's "surface" [degrees] |
0°00'59.06''
|
0°00'58.59''
|
| Brightness of the moon as observed from the planet's "surface"** [mag] |
0.3
|
0.3
|
|
Orbital velocity [km/sec] |
31.39
|
31.28
|
* 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
– ADRASTEA
Views
of the Solar System – ADRASTEA – Photo
Archives
Solar
System Exploration – ADRASTEA
The
Nine Planets – ADRASTEA
The Astronomy Workshop – Satellite Viewer
Planetary Satellite Mean Orbital Parameters
Natural Satellite Physical Parameters
 |
