Venus Has a Moon?


Astronomers have been busy trying to determine the spin period and composition of Venus’ moon. December 8, 2010, results were announced by JPL/Caltech scientists, led by Michael Hicks.

“Wait a minute; back up”, I hear you ask. “Venus has a Moon?”
Of course it does. Well, kind of…
Let me explain.

It has the rather unfortunate name of 2002 VE68. That is because it was discovered on November 11, 2002 by LONEOS, the Lowell Observatory Near Earth Object Search. 2002 VE68 is an earth orbit-crossing asteroid that has been designated a Potential Hazardous Asteroid by the Minor Planet Center. For obvious reasons, this makes it a very interesting subject of study for JPL scientists.

2002 VE68 used to be a run of the mill, potential impact threat, Near Earth Object. But approximately 7000 years ago it had a close encounter with Earth that kicked it into a new orbit. It now occupies a place in orbit around the Sun where at its closest it wanders inside the orbit of Mercury and at its furthest it reaches just outside the orbit of the Earth. It is now in a 1:1 orbital resonance with Venus.

An orbital resonance is when two orbiting bodies exert a regular, periodic gravitational influence on each other due to their orbital periods being related by a ratio of two small numbers. For example, Pluto and Neptune are in an orbital resonance of 2:3, which simply means for every two times Pluto goes around the Sun, Neptune makes three trips around.

In the case of Venus and 2002 VE68, they both take the same time to orbit the Sun once. They are in a 1:1 orbital resonance. So by definition, 2002 VE68 is considered a quasi-satellite of Venus. If you watch the Orbital Viewer applet at the JPL small body page you can watch this celestial dance as the two bodies orbit the Sun and each other as 2002 VE68 dodges Earth and Mercury in the process.

Often these resonances result in an unstable interaction, in which the bodies exchange momentum and shift orbits until the resonance no longer exists. In this case, scientists believe 2002 VE68 will only remain a Venusian quasi-satellite for another 500 years or so.

So getting back to the story, Hicks and his team used the recent close apparition of 2002 VE68 to do photometric measurements over the course of three nights in November using the JPL Table Mountain 0.6m telescope near Wrightwood, California. From the color data they obtained they determined that 2002 VE68 is an X type asteroid. This is a group of asteroids with very similar spectra that could potentially have a variety of compositions. They are further broken down into Tholen classification types as either E, M or P types. Unfortunately Hicks’ team was not able to resolve the sub-classification with their equipment.

They were able to determine the approximate size of the asteroid to be 200 meters in diameter, based on its absolute magnitude, and they determined a spin rate of 13.5 hours. The amplitude of the fluctuation on the light curve of 2002 VE68 could imply hat it is actually a contact binary, two clumps of asteroidal material orbiting a center of mass in contact with each other.

For more information on some of the strange and curious beasts in the asteroidal zoo, visit the NASA Near Earth Object Program website.

11 Replies to “Venus Has a Moon?”

  1. Ah! It reminds me very much about the astronomer Jean le Rond d’Alembert (1717–1783) who thought he found an aphrodisiac or Venusian moon. Johann Lambert (1728-1777) wanted to name this non-existent moon after d’Alembert (as Alembert). d’Alembert sensibly declined the offer because he was unable to calculate any true or realistic orbit, and he therefore assumed the object was not real!
    One of the questions I find interesting, is did d’Alembert make the discovery up just to get some much needed attention for his work? (Sounds like the arsenic biological bacterium in a recent story!)

    Comment stupéfier est lui que D’Alembert a dénoncé sa propre découverte.

  2. The orbit of this asteroid should make it a candidate to soft land instrumentation for studying Sol’s interaction with Mercury and Venus?

  3. They are in a 1:1 orbital resonance. So by definition, 2002 VE68 is considered a quasi-satellite of Venus.

    I’m not sure I understand… what is the strict definition of a quasi-satellite, and that of a satellite? I wasn’t aware that moons had anything to do with orbital resonances. Is our moon in resonance with Earth? (I don’t see how…)

    1. A Quasi-Satellite is one in which the two bodies are in orbital resonance; as stated above this is when the two orbits are integer multiples of another. A Satellite however is a gravitationally bound object in orbit around another. 2002 VE68 still technically orbits the sun so it’s classified as quasi due to its 1:1 resonance with Venus.


    2. Oh, and to answer your other question, No i don’t believe that our Moon is in a resonance with Earth. However, it’s orbital period is in a 1:1 resonance with it’s orbit, which is why we always see the same face. Soon enough (millions of years from now) the tides enforced on the Earth by the Moon will slow Earth’s orbit enough so that we too will show the same face to the moon always, and then only some hemispheres will ever get to see it!

      1. CORRECTION: “…it’s orbital period is in a 1:1 resonance with it’s ROTATION period…”
        “…will slow Earth’s ROTATION enough…”

      2. Thanks astrofizix. It still seems a bit of a stretch to call the object a moon of venus though. I would consider a moon to be gravitationally bound to the planet of which it’s supposed to be a moon. I guess it’s just semantics though.

  4. This Venus / 2002 VE68 is an Astro 101 instructor’s dream come true! Two bodies with the same period but very different orbital eccentricities? The contrasting cases are amazing! Kepler’s Laws are screaming from the JPL sim: fastest speed at perihelion, slowest at aphelion; sweeping equal areas in equal times. Oh, and equal periods means equal semi-major axes which is not the “radius” of the orbit! Ahhh, beautiful!


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