for National Geographic News
Space scientists hitched a ride earlier this year aboard an F/A-18B fighter jet traveling through the stratosphere at 0.92 Mach. From the cockpit, the night sky was inky black and pierced with diamond-like planets, streaks of comet dust, and a zodiac of light.
Not out merely for a night ride, the scientists had their eyes trained on the western horizon, where twilight hung low in a range from deep blue to glowing red.
There, in the twilight space, is where a cluster of small asteroids known as vulcanoids are thought to exist, if they exist at all, said Daniel Durda, a senior research scientist at the Southwest Research Institute in Boulder, Colorado.
"Finding such objects and being able to study their physical properties would help astronomers better understand the conditions in the solar nebula from which the planets—our own Earth included—formed," he said.
Durda and his colleague Alan Stern, director of the institute's Space Studies Department, have enlisted the help of a high-tech camera and high-flying aircraft to better search the twilight sky for vulcanoids. That region of the sky is difficult to search from the ground because of atmospheric hazes, turbulence, and its proximity to the sun.
Vulcanoid Theory
When space scientists in the early 1900s were unable to account for all of the gravitational forces in the planet Mercury's orbit, they theorized that an undiscovered planet even closer to the Sun—called Vulcan—could cause the unaccounted-for gravitational pull.
In his general theory of relativity in 1915, Albert Einstein provided a more complete description of gravity and how it behaves close to a massive body such as the Sun. As a result, astronomers were able to account for all the tugs and pulls on Mercury's orbit, and astronomers abandoned their search for Vulcan.
"However, there remained some interest in looking for smaller debris—small asteroids—in the region, since such material might have remained from the disk of planet-forming material after the planets grew to their final size," said Durda.
Other astronomers theorize that Mercury suffered a major impact late in its formation that stripped the planet of its outer rocky layers. That debris might still be in the vicinity of the planet as a population of small asteroid-like bodies.
"Our motivation for looking for vulcanoids today is no longer linked in any real way with the original motivation for looking for Vulcan," said Durda. "Today, we're only treating the region as a more or less unexplored region in the solar system that could have undiscovered objects there."
Rationing Space
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