Snapshots of Secrets in the Sky
By “Awake!” correspondent in Germany
ON A bitterly cold European night last November, I dragged the telescope onto the balcony and scanned the sky in search of the Seven Sisters, or Pleiades. Then, peering at one pinpoint in the sky after another, I really wondered which one might be Halley’s comet and whether I would ever manage to see it.a Did you see it? Well, even if you and I didn’t spot the right dot, something did happen during this visit of Halley’s comet that has never occurred before. Do you know what that was?
Since our planet Earth was not in a good position this time for us to get a spectacular view of the visitor in the sky, professional astronomers planned some time ago to send spacecraft to meet the comet and take photographs of it. And that is why this tour of Halley’s comet proved to be different from all previous ones. Just like a bride prepared for the occasion with veil and bridesmaids, Halley’s comet came, attracting a train of curious onlookers.
Several nations sent research capsules into space to get nearer to the comet. The United States, Japan, and the Soviet Union all succeeded in adding to our knowledge of the makeup of the orbiter. But the most daring of all was an enterprise called Giotto.
“Giotto,” said Sir Bernard Lovell, “is one of the few visionary and exciting space projects of this decade.” What is Giotto?
For some years ESA (European Space Agency) had been working on plans to launch a space capsule especially to investigate Halley at close quarters. Named Giotto after the Italian painter who included a comet in one of his well-known works of art, the vehicle was shaped like an oil drum with a dish and tripod on top, standing nearly 3 meters (10 ft) high and with a diameter of 1.8 meters (6 ft). Giotto was rocketed into space from its launchpad at Kourou in French Guiana in July 1985 to begin a seven hundred million kilometer (430,000,000 mi) marathon to its rendezvous with Halley in March 1986. That’s like flying to the moon and back over nine hundred times!
As the months went by, Giotto rushed on its way toward the encounter, which was planned for March 13/14, 1986. Just how fast was the spacecraft traveling? At approximately 69 kilometers per second (43 mi/sec). What does that really mean? Well, suppose you wanted to fly across the Atlantic, say, from Paris to Washington, D.C. That is a distance of some 6,170 kilometers (3,830 mi). Normal flying time is between seven and eight hours. Concorde (the supersonic airliner) takes less than four hours. But flying with Giotto would get you there in about 90 seconds!
The aim was to send the craft through the coma (that is, the veil around the comet’s head) in front of the nucleus. But how would all the information get back to earth? Giotto was designed to transmit everything to the Space Operations Centre in Darmstadt, Federal Republic of Germany, by way of radio-telescope and communications installations in Australia and an orbiting satellite. Just imagine, each signal from Giotto would take more than eight minutes to cover the 150 million kilometers (93,000,000 mi) to earth! The big question on everyone’s mind was: Will we find out anything new about Halley?
With help from the Soviet Union and the United States, Darmstadt was able to fine-tune the capsule’s course in the days leading up to the climax. Full of anticipation, hundreds of scientists and astronomers gathered at the center on that night. Millions of other people in 36 countries were able to see the encounter as it happened, thanks to live TV coverage. As Giotto raced into the gigantic cloud of gas and dust that was speeding along with Halley, it succeeded in signaling pictures to earth for about 16 minutes. Then, at a distance of less than a thousand kilometers (620 mi) from the actual nucleus, particles of dust emitted from the comet at tremendous speed interfered with some of the instruments on board. Giotto surged onward but with its “eyes” closed.
Thus came to an end man’s first reconnoiter of a comet. Scientists now have to pause and reflect on information gleaned, then revise some current theories. This process will take months or even years. Nevertheless, ESA announced that the analysis of data received from Giotto had already revealed “remarkable scientific results.” For instance, the nucleus, previously thought by most to be roughly spherical, is actually elongated and shaped like a peanut. And although the presence of ice is no surprise, the fact that it appears to be enclosed in an outer crust of a black, carbonlike substance is new. The dust and gases radiating out of the nucleus seem to flow out of several holes in this crust and not, as was formerly believed, uniformly from the surface of the nucleus.
This “bride” didn’t stand still, even to be photographed. Now Halley’s comet is already out of our neighborhood, having revealed to us more of its secrets on this trip than ever before. Will we learn still more next time around, about 2060-61 C.E.? Let’s hope that at least there will be a better view of the procession in the sky, and perhaps someone will be able to take a few snapshots.
a For further details, see Awake! of November 8, 1985, page 12.
[Picture on page 13]
The spacecraft Giotto encounters Halley’s comet
European Space Agency photo