Explanation:
Though the sizes are not to scale, the Sun and planets of the inner
solar system are shown
in this illustration, where each red dot
represents an asteroid.
New results from NEOWISE, the
infrared asteroid hunting
portion of the
WISE mission,
are shown on the left compared to
old population projections of mid-size or larger
near-Earth asteroids
from surveys at visible wavelengths.
And
the good news is, NEOWISE observations estimate there are 40 percent
fewer near-Earth asteroids that are larger than 100 meters (330 feet),
than indicated by visible light searches.
Based on infrared imaging, the NEOWISE results are more accurate
as well.
Heated by the Sun, asteroids of the same size radiate the same amount
of infrared light, but can reflect very different amounts of visible
sunlight depending on how shiny their surface is, or
their surface albedo.
That
effect can bias
surveys based on optical observations.
NEOWISE results reduce the estimated number
of mid-size near-Earth asteroids from about 35,000 to 19,500,
but the majority
still remain undiscovered.
