July 08 – Adrastea

Adrastea, the second moon out from the “surface” of Jupiter, was discovered by analysis of Voyager 2 images in 1979 by David C Jewitt and G Edward Danielson.  A subsequent photograph is available (the Voyager one was of a tiny speck) taken by the Galileo spacecraft, and here it is, looking more like an out-of-focus lemon than a moon . . . .

Adrastea (image credit: NASA)

Adrastea (image credit: NASA)

Adrastea is like the Earth’s Moon, in that it always keeps one face pointing towards the parent planet, but it has an unusual orbital period of 7 hours 9 minutes, which is about two hours less than one Jovian day, even though Jupiter has the fastest rotation of all the planets (which accounts for its easily visible bulge).  Only a very few moons do this (three are known, the others being Metis and Mars’ moon Phobos).  As I mentioned two days ago, we can tell without looking it up that Adrastea will have a prograde orbit, because it ends with an “a”.

Metis and Adrastea share another unusual fact in common.  They orbit too close for comfort to their parent, meaning that at some point in the future they will impact the planet.

In Greek mythology, Adrasteia was the nymph who had to nurse Zeus and hide him from his father, Kronos.  Her name means “inescapable”.


1695   –   Death of Christian Huygens.


1959   –   Launch of Explorer 6.


2011   –   Final launch of shuttle Atlantis (flight number STS-135).


Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s