"No word yet," I reassured him. "I'll let you know. Meanwhile, what's
the trouble around here?"
"Trouble?" repeated Lancelot wonderingly.
The Old Man groaned and pawed at what little remains of his hair.
"Don't look now," he rasped, "but didn't Todd call me a couple of
minutes ago with some wild-and-woolly tale about Themis disappearing?"
"Oh--_that_!" smiled Biggs gently. "I thought for a second you
meant there was something wrong. Why, yes, Dad. Themis _has_
disappeared--temporarily. Oddest thing--"
"Talk sense!" I moaned. "Todd said something about there being a large
body in our path, too. Did it--" I took a look at the central vision
plate which reflected nothing between us and the far stars--"did it go
away?"
"Oh, no," drawled Biggs nonchalantly. "It's still there."
"Still there!" I looked again, more closely, at the vision plate. It
was as bare as a debutante's backbone at a ball. "What's still _where_,
Lanse? Have you gone off your gravs, or are my optics myopic?"
"The large body," said Biggs blandly. "It's Themis' moon. It's there.
Three points to starboard, and one degree to loft."
"Themis' _moon_!" croaked the Old Man. "What in Hades are you talkin'
about, Lancelot! Themis _is_ a moon!"
"I know," agreed Biggs. His larynx bobbled pleasantly. "That's the
curious part of it. This is the first time in the solar system that
any satellite has ever been found to have a satellite of its own!
But we've located it, charted its trajectory, and cross-checked our
calculations--haven't we, Dick?"
Todd looked up from the plot table.
"That's right," he said hollowly. "Themis _has_ got a moon of its own.
An--an invisible moon!"
"_Invisible moon!_" The skipper and I did a twin act.
"Yes," said Biggs. "You know, I believe that's why
Themis--er--'disappears' periodically. It is circled by a large, opaque
satellite with the peculiar property of being able to bend light waves
around itself. Consequently, every time the moon, revolving around its
primary, comes between Themis and observers, Themis is occulted--and
disappears!"
* * * * *
The Old Man looked at him like he had just grown a second head.
"B-but that's impossible, son!" he gasped.
"Oh, no," said Lanse quietly. "Unlikely, yes. But not impossible.
Because--well, because the situation _does_ exist, you see." He clucked
thoughtfully. "Strange, isn't it, that we should be the first to find
it out? After these many years. But that's the Laws of Chance for you.
Every other time a ship visited Themis, the invisible moon must have
been on the far side."
Hanson was fidgeting like he had wasps in his weskit. Now he broke in,
"That's all very interestin'! But how about the chances of our crackin'
up on this aforesaid moon-of-a-moon?"
"Oh," replied Biggs negligently, "that's all taken care of. We've
plotted a new trajectory around it. We should see Themis again in a
moment--Aaah!" He breathed a sigh of satisfaction. "There she is! Nice
looking little satellite, isn't it!"
And true enough, Themis was beginning to appear in the vision plate
before us. A weird looking sight it was. A thin sliver of terrain at
first ... then widening, growing into a full sized cosmic body as it
stopped being occulted by its phenomenal little companion.
Biggs punched the intercommunicating stud and spoke to the engine room.
"All right, Mac," he called. "You can cut the V-I. Prepare to land in
about fifty minutes." Then he turned to us again. "Remarkable thing,
what? Some day when we're not so busy we'll have to drop jets on that
invisible moon, eh? Should be an interesting visit to make."
The skipper groaned feebly.
"Interestin'! He finds an invisible moon, figures a trajectory around
it, then says it's--Oooh! Let me out of here! I'm feelin' heat-waves!"