November 1999 Sky from the Keeble Observatory

Last month we mentioned the loss of the Mars Climate Observer. A perfectly good space probe burned or broke up in the atmosphere of the Red Planet because of an avoidable error in translating units. What do we do with an otherwise useful probe which is nearing the end of its useful lifetime? There have been two recent examples of innovative applications which hold promise of real science gains.

The Lunar Prospector was a small remote observing platform which had orbited the Moon, collecting data to support or refute the possible presence of water ice in deep, cold craters near the lunar poles. The tentative conclusion supports initial findings made by another probe, Clementine. As the Prospector’s on-board reserves of fuel dwindled, flight controllers entertained the novel idea of using the last available thrust to crash the spacecraft into one of those craters. The hope was that the explosive impact would dredge up some of the water ice, and that the "cloud" so released would be observable with telescopes from Earth. A variety of instruments were deployed, including the Hubble Space Telescope, radio telescopes, infrared telescopes - all to no avail.

None of these were able to detect any water from the impact. Does this mean that there is no water? Not necessarily. The probe might have missed its intended target. Or the intended target may have been a spot where there was no water, or the water was too deep for the small impact to release. Alternatively, the water may have been bound in the lunar rock in a form which made it difficult to release by a simple mechanical explosion.

Another late-mission diversion of a probe has taken place at Jupiter. The Galileo probe, which has now accomplished both its primary objectives and successfully completed its "extended mission" is also running low on fuel. When it arrived at Jupiter almost 3 years ago, Galileo had to omit a set of planned observations of Io (Jupiter’s innermost large moon) because of the need to preserve telemetry with the atmospheric probe which it had released to penetrate the giant planet’s cloud deck. Io orbits deep within the "radiation belts" (plasma from the solar wind, trapped by Jupiter’s magnetic field), where it would seriously damage the orbiter if it had to spend too much time there. Now that Galileo is nearing the end of its operations, it was determined to adjust its orbit for a final set of observations of Io – nothing ventured, nothing gained, but we sacrifice nothing to complete these observations.

The first flyby was last October 10^th. The encounter was apparently a success, and the data from Io will be returned over the next few weeks. This was the closest any probe has been to Io, and we expect some spectacular images of its active volcanic vents and tortured surface. More about Io next month.

Lunar phases for November: New Moon on the 7^th at 10:53 EST; First Quarter on the 16^th at 4:03 am; Full Moon on the 23^rd at 2:04 am; Last Quarter at 6:16 pm on the 29^th.

Jupiter and Saturn are visible nearly all night. Jupiter starts ESE sets north of due west before sunrise. It will still be visible in predawn at the beginning of the month, but sets about 3 ½ hours before sunrise by the end of the month. Saturn follows Jupiter across the sky about 15 degrees behind. Mercury will be visible to the west at sunset in the early part of the month, at sunrise to the east at the end of the month.

At mid-month the Andromeda galaxy is almost directly overhead at 8:30 pm. You’re looking out of the plane of our Galaxy, so this region of the sky is pretty empty. The Winter Triangle (Deneb, Vega, Altair) is now to the west. As Cygnus sets, we can more easily discern its shape as the "Northern Cross." The binary star Albireo is the foot of the cross, with Deneb marking its top. Albireo is a faint binary, but is easy to find because there are few brighter stars in that region of the sky. With a small telescope you can see that the two stars in this binary are very different in brightness and color. Meanwhile, the best show of the season is rising to the east, as Taurus and Orion ascend from the horizon. These constellations will dominate the southward sky through the winter and into early spring. Aldebaran marks the eye of the bull in Taurus, near the bright cluster of the Pleiades.