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Life, Unbounded

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Your Friendly Neighborhood Asteroid Swarm

The views expressed are those of the author and are not necessarily those of Scientific American.


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(NEAR Project, NLR, JHUAPL, Goddard SVS, NASA)

The solar system is full of bits and pieces, remnants of its heyday of activity 4.5 billion years ago. Planets are the most noticeable fossil leftovers, with giant Jupiter being two and a half times more massive that the sum total of the other major worlds. There’s also a vast assortment of far smaller bodies, from asteroids to cometary nuclei, all swirling around the Sun in a variety of orbits.

Perhaps the best known are the diminutive members of the Asteroid Belt, a great zone between the orbits of Mars and Jupiter where millions of objects reside. Altogether they amount to less than a few percent of the mass of the Moon, most are tiny, measured in meters, but a few are large enough to step into the near-planetary club, like the dwarf planet Ceres at nearly 1,000 kilometers across.

Despite their numbers, the members of the asteroid belt are still a remarkably dispersed crowd. Take your spacecraft from Mars to Jupiter and you’d be hard pressed to pass within even a million kilometers of an asteroid, so it can be tough to visualize the grander architecture of this population.

Unless, that is, you take the results of the Sloan Digital Sky Survey (SDSS) and render the locations and motions of 100,000 asteroids detected by its telescopic mapping. The movie here was generated by Alex Parker from SDSS data, and each of the objects is colored to reflect the actual variation in hue of the asteroids, a key to the nature of their composition. Darker (purplish) objects are ‘C-type’ or carbonaceous bodies, while lighter ones are generally ‘S-type’ or ‘V-type’, rocky bodies with lots of silicates.

Painted Stone: Asteroids in the Sloan Digital Sky Survey from Alex Parker on Vimeo.

You can also spot the (reddish) Trojan asteroids – objects lurking in Jupiter’s orbit, ahead and behind of it. This map is a wonderful, sweeping visualization of an important piece of our interplanetary neighborhood. The ‘belt’ of asteroids is thick, not confined to a thin band, orbits are strongly tilted, bodies belong to groups and families – the signs of earlier events, collisions, and gravitational hijinks. The precise composition of objects, and how that composition varies with position, is also a vital clue to the early history of the solar system, a record of earlier turbulence and rearrangement.

Caleb A. Scharf About the Author: Caleb Scharf is the director of Columbia University's multidisciplinary Astrobiology Center. He has worked in the fields of observational cosmology, X-ray astronomy, and more recently exoplanetary science. His latest book is 'Gravity's Engines: How Bubble-Blowing Black Holes Rule Galaxies, Stars, and Life in the Cosmos', and he is working on 'The Copernicus Complex' (both from Scientific American / Farrar, Straus and Giroux.) Follow on Twitter @caleb_scharf.

The views expressed are those of the author and are not necessarily those of Scientific American.





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  1. 1. tuned 10:22 am 02/24/2014

    Every one of them can ruin your day in a “spaceship” or spacesuit.

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  2. 2. Wayne Williamson 5:44 pm 02/24/2014

    WoW…That was really cool. Just wondering why there are two clumps at the orbit of Jupiter. I’m assuming that one of them is actually because of Jupiter, why does the other one exist…..

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  3. 3. JSBrooks 8:40 pm 02/24/2014

    As a research scientist I simply cannot buy the interpretation that the asteroid belt is “leftovers” from the “formation” (creation) of the solar system. With the concentration or asteroids in the asteroid belt, and the fact that carbonation condrites, as well as nickle iron asteroids, are there, suggests more strongly of a planet that was destroyed by a major impact.

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  4. 4. Caleb A. Scharf in reply to Caleb A. Scharf 2:48 pm 02/25/2014

    The general consensus is that the asteroid belt represents a mixture of leftovers (yes, that term is accurate, the Earth is also leftovers) – including material from differentiated bodies, i.e. planetesimals that melted internally 4.5 Gyr ago, hence the presence of nickel iron forms. And clearly Vesta or Ceres are on the border of dwarf-planet/planet in terms of size. However, the sweeping mean motion resonances with Jupiter (primarily) make this a very tricky region for a large planet to form, during the indicated orbital shifts that happened 3.8-4.5 Gyr ago.

    Link to this

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