» Venus Astronomy

Astronomers have at last found definitive evidence that the universe's first dust - the celestial stuff that seeded future generations of stars and planets - was forged in the explosions of massive stars.

The findings, made with NASA's Spitzer Space Telescope, are the most significant clue yet in the longstanding mystery of where the dust in our very young universe came from. Scientists had suspected that exploding stars, or supernovae, were the primary source, but nobody had been able to demonstrate that they can create copious amounts of dust - until now. Spitzer's sensitive infrared detectors have found 10,000 Earth masses worth of dust in the blown-out remains of the well-known supernova remnant Cassiopeia A.

Space dust is everywhere in the cosmos, in our own neck of the universe and all the way back billions of light-years away in our infant universe. Developing stars need dust to cool down enough to collapse and ignite, while planets and living creatures consist of the powdery substance. In our nearby universe, dust is pumped out by dying stars like our sun. But back when the universe was young, sun-like stars hadn't been around long enough to die and leave dust.

That's where supernovae come in. These violent explosions occur when the most massive stars in the universe die. Because massive stars don't live very long, theorists reasoned that the very first exploding massive stars could be the suppliers of the unaccounted-for dust. These first stars, called Population III, are the only stars that formed without any dust.

Magellan Mission to Venus

Filed under: Venus — admin @ 12:05 am

Magellan Mission to Venus The Magellan spacecraft was the first planetary explorer to be launched by a space shuttle when it was carried aloft by the shuttle Atlantis from Kennedy Space Center in Florida on May 4, 1989. Atlantis took Magellan into low Earth orbit, where it was released from the shuttle’s cargo bay and fired by a solid-fuel motor called the Inertial Upper Stage (IUS) on its way to Venus. Magellan looped around the Sun one-and-a-half times before arriving at Venus on August 10, 1990. A solid-fuel motor on the spacecraft then fired, placing Magellan into a near-polar elliptical orbit around Venus.

The spacecraft carried a sophisticated imaging radar, which was used to make the most highly detailed map of Venus ever captured during its four years in orbit around Venus from 1990 to 1994. After concluding its radar mapping, Magellan also made global maps of Venus’s gravity field. Flight controllers then tested a new maneuvering technique called aerobraking, which uses a planet’s atmosphere to slow or steer a spacecraft. The spacecraft made a dramatic plunge into the thick, hot Venusian atmosphere on October 12, 1994, and was crushed by the pressure of Venus’s atmosphere. Magellan’s signal was lost at 10:02 Universal Time (3:02 a.m. Pacific Daylight Time) that day.

The Magellan mission was divided up into “cycles” with each cycle lasting 243 days (the time necessary for Venus to rotate once under the Magellan orbit). The mission proceeded as follows:

Date Mission Event

04 May 1989 - Launch
10 Aug. 1990 - Venus orbit insertion and spacecraft checkout
15 Sep. 1990 - Cycle 1: Radar mapping (left-looking)
15 May 1991 - Cycle 2: Radar mapping (right-looking)
15 Jan. 1992 - Cycle 3: Radar mapping (left-looking)
14 Sep. 1992 - Cycle 4: Gravity data acquisition
24 May 1993 - Aerobraking to circular orbit
03 Aug. 1993 - Cycle 5: Gravity data acquisition
30 Aug. 1994 - Windmill experiment
12 Oct. 1994 - Loss of radio signal
13 Oct. 1994 - Loss of spacecraft

In all, the highly successful imaging radar mapped more than 98 percent of the planet’s surface and collected high-resolution gravity data of Venus. The lessons learned from Magellan’s aerodynamic dive into the Venusian atmosphere will be applied to future planetary missions.

Views of Magellan

Magellan Assembly

Magellan Assembly On May 4, 1989, the Magellan spacecraft was deployed from the shuttle. The spacecraft is topped by a 3.7-meter diameter dish-shaped antenna that was a spare part left over from the Voyager program. The long, white, horn-shaped antenna, attached just to the left of the dish antenna, is the altimeter antenna that gathers data concerning the surface height of features on Venus. Most of the spacecraft is wrapped in reflective white thermal blankets that protect its sensitive instruments from solar radiation.

Deployment

The Magellan spacecraft’s deployment from the shuttle Atlantis’ cargo bay was captured by an astronaut with a hand-held camera pointed through the shuttle’s aft flight deck windows. Deployment occurred in the early evening of May 4, 1989, after Atlantis had carried Magellan and its Inertial Upper Stage (IUS) booster rocket, into low Earth orbit. Once the shuttle was safely away from the spacecraft, the IUS ignited and placed Magellan on course for its 15-month journey to Venus.

Magellan Orbiting Venus

Magellan Orbiting Venus On August 10, 1990, Magellan entered into orbit about Venus, as depicted in this artist’s view. During its 243-day primary mission, referred to as Cycle 1, the spacecraft mapped well over 80 percent of the planet with its high-resolution Synthetic Aperture Radar (SAR). The spacecraft returned more digital data in the first cycle than all previous U.S. planetary missions combined.

Magellan Mapping Venus

Magellan Mapping Venus The sequence of events that comprise a Magellan mapping orbit are shown in this artist’s conception. For the first 37.2 minutes of each orbit, the Synthetic Aperture Radar measures and records a 20-kilometer wide swath of the planet’s surface. When Magellan reaches the high point of its orbit, the spacecraft turns its antenna toward Earth and transmits the data. After 113.8 minutes of transmitting, the antenna is repositioned for another orbit about Venus.

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