That impact completely redirected the course
of biological evolution on Earth. Most species, including the dinosaurs,
became extinct in a very short period of time. Radar astronomy plays a critical role in studies
of Near-Earth Asteroids and especially in the context of
the asteroid impact risk. The first important contribution of radar
is that it enables considerable improvements to asteroid trajectory
predictions. Radar measurements allow us to locate an asteroid
with superb precision, about 1000 times better than optical measurements.
With these measurements, we can dramatically increase
the interval of reliable trajectory predictions. For instance, without
radar measurements you might be able to accurately predict the path
of an asteroid over a period of 90 years, with about 50 of those
years in the future. With the addition of radar measurements, the interval
of reliable trajectory predictions increases to 400 years,
which is 4 times as long, and with about 200 of those years in
the future. This gives us a much longer warning time should we have
to mitigate against a potential impact. The second important role of radar astronomy
in the asteroid impact hazard has to do with the physical characteristics
of the potential impactor. Perhaps the most crucial thing we
would want to know is whether we are dealing with 1, 2, or even
3 objects? Radar instruments have a unique ability to diagnose
binary and triple asteroids, and this knowledge is essential
for impact hazard mitigation efforts or any kind of spacecraft
proximity operations. Then we would want to get the best possible
description of the potential impactor. We would want to know
as much as we can about the size, spin, shape, mass, density, and porosity
of the potential impactor. Radar observations provide the most
realistic ground-based prospects of securing estimates of all of
these quantities. This is not only useful in the impact hazard context,
but also for sending astronauts to asteroids, or even for mining
asteroids. With optical telescopes, asteroids appear
as unresolved points of light. Radar observations allow us to obtain
images of asteroids with very high resolution, 10 meters or better.
With a sequence of such images we can create 3-dimensional shape models.
Overall, radar astronomy provides an exquisite description
of near-Earth asteroids. We use two facilities to make these observations.
The Arecibo Observatory in Puerto Rico is the largest
telescope on Earth, it’s 300 meters across and it’s equipped with a megawatt
transmitter. We also use the Goldstone antenna in the Mojave desert
in California, and that antenna is 70 meters across and is equipped
a 450 kw transmitter. We have detected over 400 near-earth asteroids
with radar so far. Last year we detected over 60. To learn more about the power of radar astronomy
to characterize asteroids and their trajectories, go to radarastronomy.org.
You will find additional information on how radar can
help protect our planet and facilitate the future exploration of asteroids”.