Image of the Month - May 2005

Eccentric Minor Planet

On April 30, 2005, the Lowell Observatory Near-Earth Object Search ( LONEOS) picked up a faint, fast-moving object in the constellation Virgo. Orbital calculations soon showed that this object, which is now known as 2005 HC₄, moves on a very unusual orbit: While the aphelion distance Q=3.668 lies within the asteroid belt between Mars and Jupiter, the orbit is highly eccentric (e=0.964), more like the orbit of a comet. The most remarkable fact, however, is the perihelion distance of q=0.0624 (9.3 Million kilometers), the smallest of any known minor planet. Thus, this unusual object crosses the Orbit of all four terrestrial planets on it's way around the sun, once every 2.85 yeras.

Credit & Copyright: Yuri Ivashchenko, Andrushivka Astronomical Observatory, Ukraine

After the discovery, Yuri Ivashchenko at the Andrushivka Astronomical Observatory was the first observer to confirm 2005 HC₄, then known by its temporary designation 74U001. His image, shown above, is a stack of 19 images, each a 120 second exposure, taken with a Electron-Optronik SiC CCD-camera at the 0.6m reflector. The camera is operated at the prime focus of the f/4.0 telescope, but a focal reducer is used to bring the foal ratio to f/2.0. "It was the night of the Orthordox Easter and I felt like something unusual may happen" writes Ivashchenko. "I was alone at the Zeiss-600 reflector, as all my colleagues went to their relatives on the holiday. For me 74U001 was an ordinary object in need of confirmation, I measured it with Astrometrica, reported the results to the MPC, and switched over to 5H34371 (2005 HB₄)." When MPEC 2005-J02 was published the next day, the "ordinary object" turned out to be in a very unusual orbit, as described above.

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