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Near Earth Asteroids Vary Widely in Composition, Origin

The asteroid Eros, as seen by the NEAR mission. Credit: NASA

From the Spitzer website:

New research from NASA’s Spitzer Space Telescope reveals that asteroids somewhat near Earth, termed near-Earth objects, are a mixed bunch, with a surprisingly wide array of compositions. Like a piñata filled with everything from chocolates to fruity candies, these asteroids come in assorted colors and compositions. Some are dark and dull; others are shiny and bright. The Spitzer observations of 100 known near-Earth asteroids demonstrate that the objects’ diversity is greater than previously thought.

The findings are helping astronomers better understand near-Earth objects as a whole — a population whose physical properties are not well known.

“These rocks are teaching us about the places they come from,” said David Trilling of Northern Arizona University, Flagstaff, lead author of a new paper on the research appearing in the September issue of Astronomical Journal. “It’s like studying pebbles in a streambed to learn about the mountains they tumbled down.”

After nearly six years of operation, in May 2009, Spitzer used up the liquid coolant needed to chill its infrared detectors. It is now operating in a so-called “warm” mode (the actual temperature is still quite cold at 30 Kelvin, or minus 406 degrees Fahrenheit). Two of Spitzer’s infrared channels, the shortest-wavelength detectors on the observatory, are working perfectly.

One of the mission’s new “warm” programs is to survey about 700 near-Earth objects, cataloging their individual traits. By observing in infrared, Spitzer is helping to gather more accurate estimates of asteroids’ compositions and sizes than what is possible with visible light alone. Visible-light observations of an asteroid won’t differentiate between an asteroid that is big and dark, or small and light. Both rocks would reflect the same amount of visible sunlight. Infrared data provide a read on the object’s temperature, which then tells an astronomer more about the actual size and composition. A big, dark rock has a higher temperature than a small, light one because it absorbs more sunlight.

Trilling and his team have analyzed preliminary data on 100 near-Earth asteroids so far. They plan to observe 600 more over the next year. There are roughly 7,000 known near-Earth objects out of a population expected to number in the tens to hundreds of thousands.

“Very little is known about the physical characteristics of the near-Earth population,” said Trilling. “Our data will tell us more about the population, and how it changes from one object to the next. This information could be used to help plan possible future space missions to study a near-Earth object.”

The data show that some of the smaller objects have surprisingly high albedos (an albedo is a measurement of how much sunlight an object reflects). Since asteroid surfaces become darker with time due to exposure to solar radiation, the presence of lighter, brighter surfaces for some asteroids may indicate that they are relatively young. This is evidence for the continuing evolution of the near-Earth object population.

In addition, the fact that the asteroids observed so far have a greater degree of diversity than expected indicates that they might have different origins. Some might come from the main belt between Mars and Jupiter, and others could come from farther out in the solar system. This diversity also suggests that the materials that went into making the asteroids — the same materials that make up our planets — were probably mixed together like a big solar-system soup very early in its history.

The research complements that of NASA’s Wide-field Infrared Survey Explorer, or WISE, an all-sky infrared survey mission also up in space now. WISE has already observed more than 430 near-Earth objects — of these, more than 110 are newly discovered.

In the future, both Spitzer and WISE will tell us even more about the “flavors” of near-Earth objects. This could reveal new clues about how the cosmic objects might have dotted our young planet with water and organics — ingredients needed to kick-start life.

About 

Nancy Atkinson is Universe Today's Senior Editor. She also works with Astronomy Cast, and is a NASA/JPL Solar System Ambassador.

Comments on this entry are closed.

  • Lawrence B. Crowell September 2, 2010, 5:11 PM

    For those who have ideas about colonizing space, it would seem to me these objects should be the focus of attention. By using their materials some habitable region inside might be constructed.

    LC

  • Torbjorn Larsson OM September 2, 2010, 7:59 PM

    Meteorite grains in general can have a complex chemical history between protoplanetary disk formation and meteorite aggregation. (Up to “maximum entropy” and overwritten memory along some organic pathways.)

    colonizing space … these objects

    Don’t forget to set your alarm.

  • IVAN3MAN_AT_LARGE September 2, 2010, 8:39 PM

    @ LAWRENCE B. CROWELL:

    By using their materials some habitable region inside might be constructed.

    As in “For the World Is Hollow and I Have Touched the Sky“?

  • Aqua September 3, 2010, 7:13 AM

    I think that ‘key wording’ here is the statement: “…the presence of lighter, brighter surfaces for some asteroids may indicate that they are relatively young. This is evidence for the continuing evolution of the near-Earth object population.”

    “Continuing evolution” or ongoing nucleosynthesis in our solar system?

  • Torbjorn Larsson OM September 3, 2010, 7:57 AM

    Now you are just trolling. right? Fresh surfaces are brighter, that is what the post claims!

    Ongoing nucleosynthesis like solar fusion or cosmic ray spallation isn’t part of that. If anything, radiation helps make surfaces darker (by providing topography and photolysis products).

  • John Mendenhall September 3, 2010, 8:38 AM

    Hm. On even a modest size asteroid there is plenty of room to construct a centrifuge to use as living quarters to avoid the zero-g health problems.

  • Lawrence B. Crowell September 3, 2010, 3:58 PM

    There is clearly no nucleosynthesis going on with asteroids. I know nothing about the evolution of asteroids to be honest. I would suspect that if lighter coloring on the surface means “younger,” that this represents some sort of reprocessing. So if one asteroid bangs into another in a very low velocity collision they become broken up a bit and maybe re-coalesce into an asteroid where interior material less exposed to radiation ends up on the surface.

    It is my understanding that asteroids are not solid rocks, but loose amalgamations of rocky material and dust held together by weak gravity. So this model sort of makes sense.

    Colonizing asteroids might be an interesting possibility. A rotating drum might be anchored inside one of these, where the rotation of the drum might provide gravity. of course there is a vast level of complexity involved here, but at least there is not the problem of getting on and off the gravity field of a planet.

    LC

  • UniqueElectron September 4, 2010, 5:24 PM

    @John: Why would you create a centrifuge? Just rotate the entire asteroid!

  • Lawrence B. Crowell September 5, 2010, 4:39 AM

    The asteroid might not hold together. Asteroids are rather fragile structures. They are loosely held fragments of meteoroids and dust. If you try to spin them up they can fragment, as a previous UT post indicates. Solar radiation can spin these up, and sometimes they can fragment. To make use of an asteroid it would require a comprehensive survey of its interior mass distribution and a colony construction would have to be designed uniquely.

    LC

  • Aqua September 5, 2010, 7:45 AM

    The “continuing evolution” referred to in this article is most often related to impacts with other objects creating fresh white surfaces rather than any kind of ongoing nucleosynthesis… or is it?

    Ultraviolet light from Sol might ‘sputter up’ some interesting mixes of hydrogen, helium, carbon, oxygen or nitrogen, creating for example, the basic covalent bonds as HO or DO, H2O or H3O? (Which would be seen as brightening) Or with more carbon present as that found in CHON aggregations, the seeding of longer molecular chains. (Seen as darkening)

    In the creation of water the oxygen atom has a higher electronegativity than the hydrogen atoms. The oxygen atom(s) carries a slight negative charge, whereas the hydrogen atoms are slightly positive. As a result, water is a polar molecule with an electrical dipole moment. The energy required to split water into hydrogen and oxygen by electrolysis or any other means is greater than the energy released when the hydrogen and oxygen recombine.

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