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Six of the eight planets in our Solar System have moons
(all except Mercury and Venus) and minor planets like
Pluto have moons, or satellites, too.
And as the image of the Near Earth Asteroid 2005LW3 shows,
asteroids can have moons too!
2005LW3 was discovered at Siding Spring Observatory in June 2005.
The optical brightness suggested a diameter of about
150 meters but with large uncertainty.
The orbit of 2005LW3 brings it very close to the Earth's orbit,
leading to its classification as both a Near Earth Asteroid and
a Potentially Hazardous Asteroid.
Last November, 2005LW3 approached within 3 lunar distances of the
Earth, allowing bistatic radar observations to refine its orbit and better
characterise the asteroid itself. As it was approaching from the sun side
of the Earth's orbit, it was not possible to refine the orbit with
additional optical observations as it approached. Nevertheless,
observations using a CDSCC antenna to bounce radio waves off the
asteroid and detect them with the Australia Telescope Compact Array
enabled the orbit to be refined, and showed hints of a possible
companion.
Follow-up observations with Goldstone tracking station
antennas, and using coded waveform transmissions, enabled
delay-Doppler images to be obtained, clearly confirming that 2005LW3 is
another asteroid being orbited by a smaller moon.
(Image credit: Lance Benner)
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