"To look at this," he admitted, "you'd think the sun was going out. Of course it can't be," he added hastily. "Not possibly. But there is an extraordinary number of sunspots. Maybe they'll clear. But meanwhile the amount of heat reaching us is dropping. As far as I know there's no parallel for it. Night temperatures are thirty degrees lower than they should be. Not only here, either, but at all the robot weather-stations that have been spotted around the planet. They average forty below zero minimum, instead of ten. And—there is that terrific lot of sunspots...."
Bordman frowned. Sunspots are things about which nothing can be done. Yet the habitability of a border-line planet, anyhow, could very well depend on them. An infinitesimal change in sun-heat can make a serious change in any planet's temperature. In the books, the ancient mother planet Earth was said to have entered glacial periods through a drop of only three degrees in the planet-wide temperature, and to have been tropic almost to its poles from a rise of only six. It had been guessed that those changes on the planet where humanity began had been caused by a coincidence of sunspot maxima.
Lani III was already glacial to its equator. Sunspots could account for worsening conditions here, perhaps. That message from the inner planet could be bad, thought Bordman, if the solar constant drops and stays down awhile. But aloud he said:
"There couldn't be a really significant permanent change. Not quickly, anyhow. Lani's a sol-type star, and they aren't variables, though of course any dynamic system like a sun will have cyclic modifications of one sort or another. But they usually cancel out."
He sounded encouraging, even to himself.
There was a stirring behind him; Riki Herndon had come silently into her brother's office. She looked pale. She put some papers down on the desk.
"That's true," she said. "But while cycles sometimes cancel, sometimes they enhance each other. They heterodyne. That's what's happening."
Bordman scrambled to his feet, flushing. Herndon said sharply:
"What? Where'd you get that stuff, Riki?"
She nodded at the sheaf of papers she'd just laid down.