March 2000 Sky from Keeble Observatory
Here are some miscellaneous spacecraft updates:
Mars Polar Lander – having massaged the data from the Stanford University radio telescope, mission controllers tried one final time to contact the probe. They are now convinced that the "signals" were likely terrestrial rather than from the probe. The spacecraft is now officially "lost in space." The inquiry board reviewing the failure is considering several possibilities. One which has surfaced recently is the discovery of a "design flaw" in the thrusters, which were supposed to have slowed the spacecraft to a soft landing. It now appears that the thrusters could have shut down prematurely after the separation of the aeroshell which protected the probe during reentry. No thrusters would mean a very hard landing, which would destroy the craft. An alternative suggestion is that surface structure near the Martian pole was very porous, and that the thrusters essentially excavated a hole into which the spacecraft disappeared. This scenario would also possibly explain the loss of the separate penetrator probes. If correct, they would have buried themselves far deeper than designed, which would prevent them from making contact with JPL. These are just conjectures at the present time. The actual fate of the probe may have to wait for human explorers to uncover first-hand!
Galileo – orbiting Jupiter for four years, this probe is well beyond its primary mission, and controllers are considering a variety of high-risk endings before its fuel is exhausted. As this is written, the probe is nearing its closest flyby of Io, a mere 127 miles from the tortured surface of this volcanically active moon. The danger to the spacecraft is not from volcanism, however. Rather, Io lies deep in the "radiation belts" which surround our solar system’s largest planet. Trapped ions wreak havoc with Galileo’s computers, making control and communication extremely difficult. Yet, the scientific promise seems worth the risk, as this probe has surpassed its primary mission several times over – all this in spite of a crippled high gain antenna! A final scenario under consideration is a "suicide plunge" into the atmosphere of Jupiter itself some time in 2001 – reminds us of Kubrick’s classic film, 2001 – A Space Odyssey. Are you out there, Hal?
NEAR – a little over a year after it missed its first opportunity to orbit an asteroid, the Near Earth Asteroid Rendezvous was placed successfully in orbit around 433 Eros on Valentine’s Day. The asteroid is a large chunk of rock, probably a fragment of one of the larger asteroids which orbit between Mars and Jupiter. Eros is about 30 miles long, and roughly 8 miles thick – it looks like a giant, misshapen potato. Like most objects in our solar system which do not have atmospheres, this one is heavily cratered from collisions with other debris. Standing on Eros would be barely possible – gravity is so weak that a slowly pitched ball (say 25 miles per hour) would be moving fast enough to escape forever. By comparison, escape speed from Earth is about 25,000 miles per hour. NEAR will orbit for about a year, with its orbit periodically reduced. Eventual planning calls for a landing attempt once the primary science mission is completed, even though the spacecraft is not designed as a lander.
Compton Gamma Ray Observatory – this is a gamma ray telescope in Earth orbit, and the spacecraft is sick. The gyroscopes which maintain pointing accuracy are also needed for controlling the end of the probe. Several have failed, leaving only two operating properly. The threat is, that if another fails we will be unable to safely de-orbit the satellite. While it is unlikely to hit anything (75% of Earth’s surface is ocean) NASA does not want to take the risk. Controllers are considering ending the mission and bringing the spacecraft to an early, but controlled, fiery end during reentry.
Lunar phases for March 2000: New Moon on the 6th, at 12:17 am; First Quarter on the 13th, at 1:59 am; Full Moon on the 19th, 11:44 pm; and Last Quarter on the 27th, and 7:21 pm.
Jupiter, Saturn, and Mars are all visible in the early evening, drawing closer together in the southwest sky as the month advances, but also setting earlier and earlier. Starting the month spread out over 28 degrees, by the end of the month, they will be only 10 degrees apart! Venus and Mercury are visible in the pre-dawn twilight, though Venus is getting lower and lower at sunrise. Mercury reaches greatest elongation on the 28th, after passing Venus on the 15th.
Looking toward zenith at midmonth, about two hours after sunset we see the Twins – Castor and Pollux in the constellation Gemini. The faint glow of the Milky Way threads from the north to the southern horizon, veering just a bit west with these two bright stars marking its eastern edge. To the northwest from Gemini lies the constellation Auriga, with its two brightest stars – Capella and Elnath. Not one of the "important" constellations, yet Auriga straddles the Milky Way, lying in the middle of a rich field of stars. From Auriga we go further northwest to Perseus, still in the rich fields of our Galaxy, then to the sideways W shape of Cassiopeia. Below and to the left of Cassiopeia lies the faint constellation of Andromeda, most notable because we are now looking through the thin part of the Galaxy’s disk toward another giant spiral galaxy, some two million light years distant.
Back to Gemini, but this time sweeping our attention toward the southwest horizon, we see majestic Orion. This way lies the richest nearby star-forming region. Just below the "belt" lies the Orion Nebula, glowing with the reflected light of the hot, young Trapezium Cluster. To the west we see that the Hunter is endlessly chasing the Bull – the constellation Taurus. On the shoulder of the bull ride the Seven Sisters, the cluster known as the Pleiades. To the south, bright Sirius in Canis Major, as the Dog follows the Hunter. Orion will soon drop below our western horizon, giving the celestial sign that spring is coming.
The Keeble Observatory at Randolph-Macon College continues its Wednesday evening public viewing sessions, 7:30 – 10:00 pm as weather and viewing conditions permit.