February 2002 Sky from Keeble Observatory
One of our spacecraft is going to be missing … no, make that retired. We're not talking about another Mars fiasco, rather an extremely successful Jupiter probe, which has worked superbly three times longer than it was designed to do. Galileo has been orbiting Jupiter for six years, measuring radiation levels and magnetic fields, and returning images across the spectrum from ultraviolet through visible. But, the aging spacecraft is nearly out of attitude control fuel and reaction propellant for adjusting its course. Time for an honorable discharge!
But, first, a few more important observations! On 2002 January 18 Galileo passed Io for the closest observations yet, a mere 100 kilometers (about 60 miles) above the volcanically active surface. Indeed, Io is the most active moon or planet in our solar system. Stressed by tidal forces, the moon boasts dozens of active volcanic vents at any one time. The surface is renewed constantly as Io literally turns inside out every 10 million years or so. Io's gravity has nudged the spacecraft into an orbit which also allow the first close up observations of tiny Amalthea, one of the inner satellites which is a source for Jupiter's ring material, blasted from its surface by meteoroid impacts. That encounter will take place in November. Galileo will also continue observations of Jupiter itself. The Io flyby has placed the spacecraft on a ballistic trajectory towards its final "retirement." Galileo will plunge into the atmosphere of Jupiter and burn up in September 2003.
The severe radiation environment near Io caused a "spacecraft anomaly" which resulted in the loss of some of the Io observations. However, JPL's flight controllers successfully regained control of the probe, and it has resumed observations. It is currently moving away from Jupiter on an elliptical orbit, and is far enough from the intense radiation belts that normal operations are expected. This planned ending serves dual purposes: more data about Jupiter, and certain guarantee that the spacecraft will not crash on Europa. That icy moon has been determined to have a deep ocean of liquid water beneath its frozen surface. Astrobiologists have speculated that life may have arisen there, and they are interested in keeping the moon pristine until they can determine whether or not it actually harbors extraterrestrial life.
Lunar Phases for February: Last Quarter on the 4th, 8:33 am; New Moon on the 12th (Chinese New Year!), 2:41 am; First Quarter on the 20th, 7:02 am; Full Moon on the 27th, 4:37 am.
Evening planet watchers will have their fill this month, with Venus, Mars, Jupiter, and Saturn all visible across 104 degrees of the sky at month's end, with Mars, Jupiter, and Saturn all within about 65 degrees. Jupiter begins the month high to the east at dusk; Saturn is even higher to the southeast. Mars emerges to the southwest, and Venus makes its appearance as "evening star." Venus will appear higher to the west as the month progresses, and the other three bright planets will appear to move towards the setting Sun.
Our overhead view at about 9:00 pm finds the Milky Way arching from north-northwest to south-southeast. Bright and almost at zenith are the Twins, Castor and Pollux in Gemini. They're just to the southeast of the overhead point. Castor is the higher of the two, and they appear to make a narrow triangle with Jupiter. High to the south we see Orion's distinctive "belt" of three stars. Betelgeuse is the bright red star to the upper left, marking the shoulder of the Hunter. Rigel is the bright blue star below and to the right, which supposedly marks the hem of his tunic. To the left of Orion is the brightest star visible from Earth (other than the Sun), Sirius in the constellation Canis Major. Above and to the right of Orion is the distinct V of Taurus. Aldebaran, usually interpreted as marking the eye of the Bull, has company as Saturn lingers in this constellation. Saturn will be a bit higher, and will not noticeably twinkle. To the east we see Leo rising, with the heart of the Lion marked by bright Regulus. Ursa Major is above the northeast horizon, with the bowl of the Dipper inverted. Andromeda is settling towards the northwest.
George F. Spagna, Jr.