Printer Friendly

Venus: on the nose at last.

Venus: On the nose at last

Numerous spacecraft have been studying Venus for nearly a quarter century, beginning with the first one ever sent to another planet, the United States' Mariner 2 in 1962. Yet only now has such a probe finally been able to answer a key question about the planet's interaction with the sun, an exotic relationship that may be unique amount all the planets of the solar system.

At the heart of the matter is a single measurement: the distance from Venus of the "nose' of the huge shock wave formed where the planet is struck at supersonic speeds by the sun-spawned outpouring of charged particles called the solar wind. The resulting shock wave resembles a vast, blunt cone whose sides trail out into the distance like the wake of a blunt boat facing into a rapid stream. Venus is atypical among the planets studied from spacecraft in that it has a substantial atmosphere but only a very weak magnetic field. At earth, Jupiter and Saturn, the field keeps the solar wind from ever reaching the atmosphere, but at Venus, it strikes the atmosphere directly. The question has been, how close does it get to the planet's surface?

The answer has come from the U.S. Pioneer Venus Orbiter spacecraft, which has been circling the planet since late 1978 but whose orbit has only recently risen enough to measure the shock wave where it directly faces the sun. According to Christopher T. Russell and his colleagues at the University of California at Los Angeles, writing in the October GEOPHYSICAL RESEARCH LETTERS, the altitude of the shock wave at that point is about 2,280 kilometers.

Several months ago, notes Russell, a Soviet researcher predicted that the measured altitude would be about 30 percent greater than that. This idea was based on the expectation that the sun's extreme ultraviolet (EUV) radiation would increase the ionization of neutral atoms from Venus's upper atmosphere and thus raise the height of the obstacle to the solar wind. The lower altitude measured by the spacecraft, Russell says, suggests that another factor must also be involved: the neutralization of some of the incoming ions by a process called "charge-exchange' with the atmospheric atoms. As a result, the solar wind can penetrate closer to the planet.

This same balance of forces--EUV ionization vs. charge-exchange--may also govern the solar wind's interaction with comets. Surprisingly, it may even be the case at Uranus, for which the approaching Voyager 2 spacecraft has so far failed to reveal signs that would indicate a magnetic field.
COPYRIGHT 1985 Science Service, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1985, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

Article Details
Printer friendly Cite/link Email Feedback
Title Annotation:measurements of solar winds on Venus
Author:Eberhart, Jonathan
Publication:Science News
Date:Nov 2, 1985
Previous Article:Probing deeper into quasicrystals.
Next Article:Estrogen use raises questions.

Related Articles
Was it a comet, or merely the solar wind?
The winds and rocks of Venus.
Venus's volcanism: present or past?
Magellan mapping Venus.
An unexpected solar effect on Venus.
Why three planets radio the sun.
Computer elevates Venus to new heights.
Magellan finds wind sculpture on Venus.
Halos on Venus: an explosive finding.
X-ray craft sees Venus in whole new light. (Science News of the week).

Terms of use | Copyright © 2016 Farlex, Inc. | Feedback | For webmasters