The atmosphere presently was visible. No need for us to use the pressure-suits. I envisaged at first that upon such a little world gravity would be very slight. But now the heavy, metallic quality of its rock-surface was apparent. A world, doubtless much denser than igneous Earth.
It was my plan to land on the side away from the Sun.
We rounded Vulcan at some two million miles out. The clouds were fairly dense in many places; sluggish, slow-moving. There were fires on the Sun side—a temperature there which would make it certainly uninhabitable to any creatures resembling humans....
It was the ninth day after the sighting of Vulcan that quite by chance I discovered its allurite. We were now fairly close over the dark hemisphere, with the Sun occulted behind it. At a thousand miles of altitude, we were dropping slowly down upon the spreading dark disc which now occupied most of our lower firmament. I had been making a series of routine spectro-color-graphs to file with my reports.
Jan heard my muttered exclamation and came crowding to gaze over my shoulder at the dripping little color spectrograph.
"What is it, Bob? Something important?"
"That bond-line there—see it? That's a metal on Vulcan—shining of its own light—radioactive type-A."
That much, I could determine. Then Jan and I looked it up in the Hughson list of Identified Spectrae. It was allurite.
"That's valuable?" Torrence murmured. "Pure allurite—"
I laughed. "It certainly would be, if we could find any sizable deposits here. On Earth, it takes some seventeen tons of the very richest allurium to get maybe a grain of pure allurite. We'll take a look around, try and get a sample of the ore here. If it pans out rich enough, they can send a well-equipped mining expedition."