Asteroid Lutetia May Have A Molten Core


Way out in space, 282 million miles from home, the intrepid ESA Rosetta spacecraft is still busy, but had time to send us an unprecedented view of ancient asteroid Lutetia. On July 10, 2010, Rosetta flew past Lutetia and the results of the imaging revealed surface features which point to an astonishing history. This particular asteroid might not have a “heart of gold”, but it may very well have – or had – a molten interior.

Buzzing by at a speed of 54 000 km/hr and a closest distance of 3170 km, Rosetta took a series of high resolution images and returned them to an international team of researchers from France, Germany, the Netherlands and the United States. By closely examining the craters, cracks and surface, the team was able to determine that Lutetia survived a multitude of impacts – yet retained much of its original structure.

Lutetia fly-by from Science News on Vimeo.

Benjamin Weiss, an associate professor of planetary sciences in MIT’s Department of Earth, Atmospheric and Planetary Sciences, reports Lutetia may have a molten core and this finding shows a “hidden diversity” for known structures within the greater asteroid belt.

“There might be many bodies that have cores and interesting interiors that we never noticed, because they’re covered by unmelted surfaces,” says Weiss, who is a co-author on both Science papers and lead author for the paper in PSS. “The asteroid belt may be more interesting than it seems on the surface.”

Although the encounter was brief, images from the OSIRIS camera revealed some surface features which are believed to be up to 3.6 billion years old – while others appear to be 50-80 million. These ages can be estimated through impact events and the amount and distribution of ejecta. Some of the areas on Lutetia are heavily cratered, implying greater age, while others appear to be landslide events perhaps caused by nearby fractures. While most asteroids are small, light, and have smooth surfaces – Lutetia is different. It appears to be dense, yet relatively porous… a finding that points toward a “dense metallic core, with a once melted interior underneath its fractured crust.”

“We don’t think Lutetia was born looking like this,” says Holger Sierks, of the Max-Planck-Institut für Sonnensystemforschung, Lindau, Germany. “It was probably round when it formed.”

You’ve got to hand it to Rosetta. By being able to study these images, the many teams of scientists now have evidence for a theory developed last year by Weiss, Elkins-Tanton and MIT’s Maria Zuber. By studying chondrite meteorites, they’ve speculated these strongly magnetized samples most likely occurred in an asteroid with a melted, metallic core. If this theory proves to be correct, the Lutetia simply managed to dodge the proverbial bullets and developed with a molten interior.

“The planets … don’t retain a record of these early differentiation processes,” Weiss says. “So this asteroid may be a relic of the first events of melting in a body.”

According to MIT news, Erik Asphaug, a professor of planetary science at the University of California at Santa Cruz, studies “hit-and-run” collisions between early planetary bodies. He says the work by Weiss and his colleagues is a solid step toward resolving how certain asteroids like Lutetia may have evolved.

“We’ve had decades of cartoon speculation, and here’s speculation that’s anchored in physical understanding of how the interiors of these bodies would evolve,” says Asphaug, who was not involved in the research. “It’s like getting through the first 100 pages of a novel, and you don’t know where it’s leading, but it feels like the beginnings of a coherent picture.”

Another Rosetta stone?

Original Story Sources: ESA News Release and MIT News Release.

7 Replies to “Asteroid Lutetia May Have A Molten Core”

  1. “…it may very well have – or had – a molten interior. ..” It would be VERY interesting if Lutetia still had a molten core! That would mean that it has a VERY radioactive interior? But wouldn’t that show up in an infra red survey?

    1. Was quoting the end of the first paragraph… Still, ”have” is the trigger here. Now why would researchers say that if they didn’t HAVE suspicious evidence? “Molten” may actually not be used in the traditional sense, where a rocky planet contains enough ‘residual’ heat to produce ‘lava’ or molten rock. Since icy material(s) melts at much lower temperatures, then I must rethink my earlier statement? Molten icy stuff? at what temperatures? Am thinking of Enceladus now… or how Titan’s ‘rocks’ are probably made of salt laden water ices which might then become fluidic or ‘lava like’ at _much_ lower temperatures than terrestrial magma.

      1. Yeah, I was commenting on the article (not a reply to your previous comment). The author of THIS article, Tammy Plotner, erred by using the present tense in the title “Asteroid Lutetia May Have A Molten Core” especially and again in the article (but with the caveat “or had” added). The original researchers certainly did not imply a presently molten core. They describe a differentiated object with a metal core which would have been molten for a few hundred thousand to a couple of million years after Lutetia formed billions of years ago. It is now ice cold. You suggested as a way out that perhaps “molten” implied something like melted ices (like Enceladus). But that is specifically ruled out by the data since the whole point –indeed the MAIN discovery here– is that Lutetia has a relatively high density (3.4 g/cm^3 which is higher than the mean density of the Moon). Given that the surface is composed of rocky materials and appears somewhat porous, the authors of the original paper concluded that Lutetia has a largely metallic core. This, they believe, implies that Lutetia went through a meltdown phase immediately after it formed. It has been ice-cold for billions of years.

        Incidentally, it’s possible that this article was influenced by a very poor article published on which mistakenly claimed that the core IS molten. That article was also picked up by So it’s spreading…

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