Fred Hoyle: The Black Cloud

The Astronomer Royal spent several minutes looking over the several sheets.

“This is most impressive, Kingsley. That computer of yours is certainly a quite fantastic instrument. Well, are you satisfied now? Everything fits into line. Everything fits the hypothesis of an external body invading the solar system. By the way, do you have the details of its mass, position, and motion? They’re not given here.”

“Yes, I’ve got those too,” answered Kingsley, picking another sheet out of a large file.

“And that’s just where the trouble arises. The mass comes out at nearly two-thirds of that of Jupiter.”

The Astronomer Royal grinned.

“I thought you estimated at the B.A.A. meeting that it would be equal to Jupiter at least.”

Kingsley grunted.

“Considering the distractions, that wasn’t a bad estimate, A.R. But look at the heliocentric distance, 21.3 astronomical units, only 21.3 times the Earth’s distance from the Sun. It’s impossible.”

“I don’t see why.”

“At that distance it must be easily visible to the naked eye. Thousands of people would have seen it.”

The Astronomer Royal shook his head.

“It doesn’t follow that the thing must be a planet like Jupiter and Saturn. It may have a much higher density and a lower albedo. That might make it a very difficult naked-eye object.”

“Even so, A.R., some telescopic sky survey would have picked it up. You see it’s in the night sky, somewhere south of Orion. Here are the co-ordinates; Right Ascension 5 hours 46 minutes, Declination minus 30 degrees 12 minutes. I don’t know the details of the sky very well, but that is somewhere south of Orion, isn’t it?”

The Astronomer Royal grinned again.

“When did you last look through a telescope, Kingsley?”

“Oh, about fifteen years ago, I suppose.”

“What happened then?”

“I had to show a party of visitors over the Observatory.”

“Well, don’t you think we ought to go up to the Observatory now and see what we can see, instead of arguing about it? It seems to me that this intruder, as we keep calling it, may not be a solid body at all.”

“You mean it might be a cloud of gas? Well, in some ways that would be better. It wouldn’t be so easily seen as a condensed body. But the cloud would have to be pretty localized, with a diameter not much greater than that of the Earth’s orbit. A pretty dense sort of cloud it would have to be too, about 10–10 gm. per cm3. A minute star in the process of formation perhaps?”

The Astronomer Royal nodded.

“We know that the very big gas clouds like the Orion nebula have average densities of perhaps 10–21 gm. per cm3. On the other hand, stars like the Sun with densities of 1 gm. per cm3 are constantly forming within the big gas clouds. This surely means that there must be patches of gas at all densities varying from say 10–21 gm. per cm3 at one extreme up to stellar densities at the other extreme. Your 10–10 gm. per cm3 is bang in the middle of this range, and looks quite plausible to me.”

“There is a great deal of truth in that, A.R. Clouds with that sort of density must exist, I suppose. But I think you were quite right about going up to the Observatory. I’ll give Adams a ring while you finish your wine, and I’ll get a taxi.”

When the two men reached the University Observatory the sky was overcast, and although they waited through the cold damp hours there was no sight of the stars that night. And so it was the following night, and the night after that. Thus did Cambridge lose the honour of the first detection of the Black Cloud, as it had lost the honour of the first detection of the planet Neptune more than a century before.

On 17 January, the day after Herrick’s visit to Washington, Kingsley and the Astronomer Royal again dined together in Erasmus. Again they made their way to Kingsley’s rooms after dinner. Again they sat before the fire, drinking Pommard ’57.

“Thank goodness we don’t have to sit up all night again. I think Adams can be trusted to ring through if the sky clears.”

“I really ought to be getting back to Herstmonceux tomorrow,” said the Astronomer Royal. “After all, we’ve got telescopes there too.”

“Evidently this damn weather has got you down the same as me. Look here, A.R., I’m in favour of throwing our hand in. I’ve drafted a cable to send to Marlowe in Pasadena. Here it is. They won’t be troubled by cloudy skies over there.”

The Astronomer Royal glanced down at the sheet of paper in Kingsley’s hand.

PLEASE INFORM WHETHER UNUSUAL OBJECT EXISTS AT RIGHT ASCENSION FIVE HOURS FORTY-SIX MINUTES, DECLINATION MINUS THIRTY DEGREES TWELVE MINUTES. MASS OF OBJECT TWO-THIRDS JUPITER, VELOCITY SEVENTY KILOMETRES PER SECOND DIRECTLY TOWARDS EARTH. HELIOCENTRIC DISTANCE 21.3 ASTRONOMICAL UNITS.

“Shall I send it?’ asked Kingsley, anxiously.

“Send it. I’m sleepy,” said the Astronomer Royal, good-naturedly stifling a yawn.

Kingsley had a lecture at nine a.m. the following morning, so he bathed, dressed, and shaved before eight. His ‘gyp’ had laid the table for breakfast.

“A wire for you, sir,” he said.

A quick glance showed the ‘wire’ to be a cable. Incredible, thought Kingsley, that they should have a reply so quickly from Marlowe. He was even more astonished when he opened the cable.

IMPERATIVE YOU AND ASTRONOMER ROYAL COME IMMEDIATELY REPEAT IMMEDIATELY TO PASADENA. CATCH 15.00 PLANE TO NEW YORK. TICKETS AT PAN AMERICAN, VICTORIA AIR TERMINAL. VISA ARRANGEMENTS AT AMERICAN EMBASSY. CAR WAITING LOS ANGELES AIRPORT. HERRICK.

The aircraft climbed slowly, heading westwards. Kingsley and the Astronomer Royal relaxed in their seats. It was the first moment of ease since Kingsley had opened the cablegram that morning. First he had to postpone his lecture, then he had discussed the whole matter with the Secretary of the Faculties. It was not easy to leave the University at such short notice, but eventually it was arranged. By then it was eleven a.m. This left three hours to get to London, fix his visa, collect the tickets, and board the bus from Victoria to London airport. It had been something of a rush. Things were a little easier for the Astronomer Royal, who travelled abroad so much that he always had passports and visas ready for just such an emergency.

Both men pulled out books to read on the journey. Kingsley glanced at the Astronomer Royal’s book and saw a vivid cover featuring a gun fight among desperados.

“Heaven knows what he’ll be reading next,” thought Kingsley.

The Astronomer Royal looked at Kingsley’s book and saw it was Herodotus’ Histories.

“My God, he’ll be reading Thucydides next,” thought the Astronomer Royal.

It is necessary now to describe the consternation that Kingsley’s cablegram produced in Pasadena. A meeting was held in Herrick’s office the morning after his return from Washington. Marlowe, Weichart, and Barnett were there. Herrick explained the importance of arriving quickly at a balanced view of the effects that the arrival of the Black Cloud would have.

“The position we’ve arrived at is this: our observations show that the cloud will take about eighteen months to reach us, or at any rate this seems rather likely. Now, what can we say about the cloud itself? Will there be any significant absorption of the Sun’s radiation when it comes between us and the Sun?”

“That’s very difficult to say without more information,” said Marlowe, puffing smoke. “At the moment we don’t know whether the cloud is just a tiny fellow quite close to us or whether it’s a biggish cloud farther away. And we’ve got no idea at all of the density of the material inside it.”