OJ 287


Discovery of the first quasi-satellite of Venus

An international team of astronomers, led by Seppo Mikkola of Tuorla Observatory, have discovered that a newly found asteroid is in a very special orbit, the first of its kind.

The asteroid, called 2002 VE68, was discovered in 2002 at Lowell Observatory. Like all asteroids, its orbit takes it around the Sun, with asteroids closer to the sun circling more rapidly and completing a "year" in a shorter time. The "year" for VE68 is shorter than the Earth year, clocking in at a little under 225 days.

This is almost exactly the same as the "year" of the planet Venus --- and it turns out that like synchronised divers in the olympic games, both VE68 and Venus are travelling around the Sun nearly in lock-step.

This means that VE68 has a very special property as seen from Venus: it appears to travel around the Venusian sky about once every Venus year. If you didn't know that VE68 is really travelling around the Sun, you might declare that Venus has a moon (or satellite) of its own.

Because its orbit is centered on the Sun, VE68 is not a real satellite of Venus in the sense that the moon is a satellite of the Earth. However, since it appears to travel around Venus, it is called a quasi-satellite. Very few quasi-satellites are known in the Solar Sytem. VE68 is the first quasi-satellite of Venus; two cases of asteroids in such orbits are known for the Earth and one for Mars (this is a special case where the asteroid is going to become a quasi-satellite in the near future). Tuorla astronomer Seppo Mikkola has been associated with the discovery of all of them.

The orbit of VE68 takes it quite far afield from Venus --- it dives in towards the Sun, passing within the orbit of Mercury, and travelling outwards just beyond the orbit of the Earth at its furthest from the Sun. Calculations performed by Mikkola's team indicate that there is no danger of impact with either the Earth, Venus or Mercury for the foreseeable future.

The paper on the discovery of the first Venus quasi-satellite is by Seppo Mikkola (Tuorla Observatory), Ramon Brasser (Tuorla Observatory and York University), Paul Wiegert (The University of Western Ontario) and Kimmo Innanen (York University) and has been published in the Monthly Notices of the Astronomical Society.

Updated August 17th 2004.

The figure shows the inner solar system, with the Sun and Venus marked by yellow circles. The orbits of Mercury, Venus and the Earth are shown in red, green and blue respectively. In this figure, the position of Venus has been fixed to always lie in the horizontal plane, allowing the movement of objects around it to be seen more clearly. The orbit of VE68 is shown in light blue. Although more properly in an orbit around the sun, from the point of view of Venus VE68 follows a regular path which gives it the appearance of being a Venusian satellite.