Asteroid Vesta - Images from the Dawn Spacecraft
Asteroid Vesta - Images from the Dawn Spacecraft

With the New Horizons spacecraft hurtling toward its 2014 encounter with Pluto, and with the Dawn spacecraft now at its most up-close and personal encounter with Vesta, we are in the process of learning scads of information about two objects that are among the poorest understood and least explored bodies in the Solar System.

Before NASA’s Dawn settled into orbit around the asteroid Vesta—the second largest object in the Main Asteroid Belt, after the Dwarf Planet Ceres—we knew very little about it. That it is mega-mountain of rock 330 miles across that rotates rather quickly in space and is slightly egg-shaped, these things we knew—but not much more.

What Dawn has revealed to us, however, is a tiny world with unexpected complexities, inside and out.

Inside, Vesta’s anatomy may not be unlike Earth and the other Terrestrial planets, which all developed cores heavy with iron and mantles and crusts made of lighter silicate rocks when they were young and molten. This “differentiation” occurs for the same reason that gold particles sink to the bottom of a gold-pan as a prospector shakes the water-sand slurry back and forth: the gold is denser, the sand lighter, so the materials separate.

Outside, Vesta’s surface offers amazing landscape vista opportunities for a future robot lander or astronaut: complex topography of valleys, cliffs, troughs, ridges, and a huge mountain, with elevation differences deviating above and below the global average elevation by as much as 15 miles—that’s three Mount Everests, or two Marianas Trenches!

Parts of the surface resemble some of the basaltic formations of cooled lava in Hawaii, suggesting that, long ago, there may have been active volcanoes on Vesta, spewing out lava to shape the young surface.

What a sight it must have been—and it makes me smile when I think about the children’s book “The Little Prince.” My favorite part of that story was the description of how the Prince, on his little asteroid world (which was only twenty or thirty feet across, I’d guess), cooked his meals on a frying pan held over a miniature volcano, which he made sure to keep clean and functional with a periodic cleaning using a giant Q-tip….

All of these revelations—the core/mantle differentiation, complicated geography, possible tectonic features, and signs of past volcanism–have prompted some scientists to ask, should Vesta be reclassified as a Dwarf Planet, along with Ceres, Pluto, and the others thus dubbed?

I have on my desk at work a letter from a 3rd Grader. It starts, “I think Pluto should be a planet (not a Dwarf Planet)….” The letter continues in richer detail and quite a bit of passionate defense of Pluto, but I was struck by the fact that this 3rd Grader was, at the time Pluto was originally “demoted,” three years old. (And some thought the Pluto controversy would end with the previous generation of kids….)

But it did get me wondering. If Dawn has changed our view of Vesta from a mere large asteroid to something maybe worthy of promotion to Dwarf Planet, what might New Horizons do to our current view of Pluto? I’m not suggesting the International Astronomical Union will reinstate Pluto as a planet when we get our first up-close images of its surface—after all, no matter what Pluto’s surface may hold in store for us, this Dwarf Planet can’t meet one of the three conditions for planethood: being massive enough to clear the region of space in which it revolves. Alas, Pluto shares its orbital space with other objects.

But I fully expect that New Horizons will change our perspective on Pluto, as Dawn is doing for Vesta. The more we learn of the rich details of mysterious places like these, the more, I think, we regard them as “worlds”—regardless of their classification as asteroid, dwarf planet, or planet.

Operation Vesta: Pluto’s Devious Plan to Regain Status? 11 June,2013Ben Burress

  • Those three conditions set by four percent of the IAU are not gospel truth; they represent one point of view that is not supported by many planetary scientists and professional astronomers. New Horizons Principal Investigator Dr. Alan Stern first coined the term “dwarf planet” in 1991 to designate a third class of planets in addition to terrestrials and jovians–small planets large enough to be in hydrostatic equilibrium (squeezed into a round shape by their own gravity) but not large enough to gravitationally dominate their orbits. He never intended for dwarf planets to not be considered planets at all. That third condition set by the IAU is heavily biased in favor of a dynamical versus a geophysical planet definition. In other words, it focuses on where a body is rather than what the body is. If Earth were in Pluto’s orbit, it would not “clear that orbit” either; this was calcuated by dynamicist Dr. Hal Levison. A definition that takes the same object and classes it as a planet in one location and not a planet in another is seriously flawed. As an amateur astronomer, I have been actively advocating the planetary reinstatement of Pluto and all dwarf planet. This would be consistent with other uses of the term “dwarf” in astronomy, as dwarf stars are still stars, and dwarf galaxies are still galaxies. As for Vesta, it’s clearly more than an asteorid and should probably be considered a dwarf planet. The 2006 decision was premature, based on insufficient data, and enacted based on erroneous information that Eris is larger than Pluto, which it is not. Many astronomers believe that when the New Horizons flyby occurs, Pluto’s planet status will be reinstated, whether by the IAU or perhaps by a newly-formed planetary science organization. I invite you to visit my Pluto Blot at

  • guess we have to keep our fingers crossed till 2014

  • Remo

    Not too surprising that Vesta would be differentiated — assuming that it and the remainder of the planetary bodies is to a large extent composed of stardust from a supernova that blew up relatively close in time to the formation of the solar system. All that radioactive stuff, like Al26, that hadn’t decayed out would have provided the heat necessary (beyond just gravitational collapse) to cause it to differentiate.

    The theory about a nearby supernova seeding the solar system with radioactive particles and causing differentiation (and ultimately stuff like iron meteorites) has been kick around for the past couple of years. Nice to see the Vesta data collaborate the theory.


    @laurele, dwarf planets are planets. I don’t think anyone disputes that point. A better description would have been major and minor planets which is more descriptive; however, the term “minor planet” was already taken (and that definition describes just about everything!).

    And you are right that if the earth were placed in Pluto’s orbit, it would not yet have had enough time to clear out the orbit. This is because (1) Pluto’s orbit is 250 years, not 1 year, which slows the rate of clearing by a similar amount, and (2) the volume of space that would need to be cleared is so much greater. The Neptune-Pluto system is a prime example. Despite its mass of 17 earths and an overlapping orbit, Neptune has been unable to clear Pluto out of its orbit. All it has been able to do is clear out the non-resonate orbits of nearby Kuiper Belt objects.

  • Torbjörn Larsson

    Well, since some started to consider Mars as a planetesimal, I’m sure it will be happy if Vesta (and likely Ceres then) joins the club!

    @ laurele:

    The whole IAU set its decision due to the democratic process used.

    What you are telling us is that those who opposed couldn’t even scrounge up a 4 % interest. How is that better?

    And what Remo so correctly noted.


Ben Burress

Benjamin Burress has been a staff astronomer at Chabot Space & Science Center since July 1999. He graduated from Sonoma State University in 1985 with a bachelor’s degree in physics (and minor in astronomy), after which he signed on for a two-year stint in the Peace Corps, where he taught physics and mathematics in the African nation of Cameroon. From 1989-96 he served on the crew of NASA’s Kuiper Airborne Observatory at Ames Research Center in Mountain View, CA. From 1996-99, he was Head Observer at the Naval Prototype Optical Interferometer program at Lowell Observatory in Flagstaff, AZ.

Read his previous contributions to QUEST, a project dedicated to exploring the Science of Sustainability.

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