Uranus a riddle no more

January 25, 1986

Just hours ago, a significant cosmic moment

FOR ALL OF HISTORY, the world is unknown, and for years people speculated about its nature. Suddenly it is visited by a spacecraft, and it becomes a familiar object. Never again will it conjure up fantastic visions of endless possibilities.

Uranus is a giant planet that even in the smallest telescopes glows as a green disk in the constellation of Ophiuchus. A few hours ago, Voyager 2 flashed by the planet and through the system of nine moons that make up the Uranian system. In the history of astronomy, this will be remembered as a significant moment of discovery. Uranus will never seem the same.

It is suspected that the history of Uranus may be different and more violent than the other planets. Usually the axis of a planet is more or less perpendicular to the plane of the orbit. That means that the sun shines above the equatorial regions, as on earth. Uranus has its axis almost parallel to its orbit. This makes for strange seasons. During summer in the northern hemisphere, the North Pole points almost directly toward the sun, and the South Pole is in darkness for 42 years. Then the situation reverses. It is suspected that Uranus was once like the other planets, and some then great event, such as a collision, knocked the polls into the current alignment.

Now it is winter up north, and the South Pole is pointing toward the sun. From the point of view of the spacecraft, it approached from directly above the South Pole. The encounter period is from Nov. 4 to Feb. 25, with the closest point yesterday at noon. At last, we will have spectacular pictures of Uranus, it’s mysterious dark rings, and its nine moons.

Once everyone thought that rings around planets were very unusual, and we may see several solar systems before we find another planet with rings like Saturn. Then it was revealed the Jupiter has a faint ring system, and so does Uranus.

Because of its great distance from us and our telescopes, it is not even known how quickly Uranus rotates. Measurements seem to indicate either 16 or 24 hours. Because of the strange seasons, due to the tilt of its axis, weather on Uranus may be very different from other planets. (Orangeish clouds now have been spotted on the planet.) The other gas giant planets — Jupiter, Saturn and Neptune — all have an internal heat source. They radiate more heat than they receive from the sun. Uranus, and convections in the atmosphere of Uranus, could be very different from those observed on Jupiter and Saturn.

Five of the moons — Miranda, Ariel, Umbriel, Titania, and Oberon — are all small, compared with our moon. When this week started neither their sizes norther masses were accurately known. They are also dark, and this is led to speculation that both the moons, and the dark material of the rings, is coated with the same substance; perhaps a carbon material. But, the newly discovered moons are much darker than the first-known moons.

As a result of all of the discoveries that are about to be revealed, it will seem as if we have all whole new solar system to explore.

Voyager 2 has more adventures ahead. With a gravitational assist from Uranus, it has been accelerated in the direction of the next planet in the solar system, Neptune. Since it will not have any future targets, it will recklessly dived to within 1,300 kilometres of the cloud tops of that planet. The encounter is scheduled for Aug. 25, 1989. As you read this, the first new Uranus pictures are being processed and those of us at the planetarium cannot wait to find out what is happening.

Winnipeg Free Press, Saturday, January 25, 1986

In 1986 Robert Ballantyne was director of the Manitoba Planetarium. His weekly column in the Winnipeg Free Press, called Sky Watch, focused on the return of Comet Halley and astronomy.

© 1986 Robert Ballantyne and The Winnipeg Free Press

Added to this blog on 2014 October 10

Sky Watch - Robert Ballantyne | Winnipeg Free Press


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