[meteorite-list] Sedna Reveals Pristine Surface in Gemini Near-infrared Spectra

From: Sterling K. Webb <kelly_at_meteoritecentral.com>
Date: Thu Apr 14 01:44:05 2005
Message-ID: <425E0302.FB0938F4_at_bhil.com>

Hi, Sedna Fans Everywhere!

    This is a special post for those for whom IMCA squabbles, an eBay sale of more
desert chondrites, or the latest episode of Dealer Vs. Dealer, are losing their
charm. Let's talk about Sedna, practically the hardest to see object in the solar
system.
    The failure to detect water ice or methane ice only enriches the mystery. It
should be pointed out that this is actually a failure to spot anything at all on
the surface of Sedna. It's got a surface -- there must be something on it!
    Yes, we can hypothesize that Sedna is covered with billions of years of
radiation-induced asphalt, but the failure to detect it or anything else hardly
qualifies as proof that Sedna is a planet-sized parking lot.
    That accumulation is only possible if Sedna suffers no impacts or at least so
few as to not interfere with the remarkably slow process of converting water and
methane to tar with no other source of energy than the very, very weak solar
radiation available dozens of billions miles from the Sun. The authors say,
"interactions or collisions between bodies are probably very rare."
    We don't know how many bodies, and of what sizes, and of what kinds, inhabit
the Outer System, now, do we? The Oort Cloud, further out than even Sedna, is
supposed to have literally trillions of objects in it. In fact, until we
discovered Sedna and the dozens of other KBO's, the general consensus was that
there was nobody home in the Kuiper Belt. We worried about it, or just assumed
everybody had moved away.
    If there are so few objects available for encounters out there in Exsolia that
you'd have to wait until the Sun exploded to get a date, why are there so many
binary objects? You can't pick up a moon without an "encounter" more intimate
than a one night stand, you know. No one batted an eye when the "detection" of a
Sednan "moon" was announced, even though the "moon" turned out not to be there.
One less binary object. There are plenty of others.
    "Very rare." Maybe, maybe. It could happen. However, in our solar system,
every body regardless of size that isn't geologically active is covered completely
or partially with craters on top of craters on top of craters on top of
craters... And when we find a body or region not saturated with craters, we say,
"Aha! Geologically active!"
    Just because Sedna is way out in the solar suburbs doesn't mean it can't be
geologically active. We've just seen that Titan is apparently as geologically
active as the Earth! Triton was popping with volcanoes the one random time we
went cruising by. So, why don't we say, "Aha! Geologically active!" instead?
    I guess I was just annoyed with the headline: "Sedna Reveals Pristine
Surface." Sedna hasn't revealed anything. We're shooting infra-red blanks here,
folks. I don't for a minute believe the Outer System is empty of bodies and
potential impactors. The explanation here is that there's some kind of
significant change in the whole character of the solar system at Pluto's orbit.
Nonsense.
    The Principal Investigator says, "Like a sandblaster operating for several
billion years, most of the objects out as far as Pluto are constantly being
resurfaced by impacts and collisions," then he hypothesizes that beyond Pluto
everything in solar life is completely different. Any rationale for that, beyond
convenience?
    Not to be a complete jerk, I realize that Sedna is a most "difficult" object
to observe, very far away, and very, very dark. We know it's red -- that's about
it. But let's find something before we announce we found something, OK?
    To be dark means that very little of the sunlight that falls on Sedna is
reflected back out into space. That doesn't mean only that Sedna must be painted
(or tarred) black. I can think of dozens of ways of doing that. Maybe Sedna is
covered from pole to pole with very efficient solar panels? Or something that
absorbs solar radiation -- Dyson's "comet trees" with dark red leaves? Or maybe
it is geologically active.
    Something is going on. With no atmosphere and supposedly a body composed of
ices, Sedna should be as bright as the reflective tape on a jogger's butt.
    When Sedna was discovered, the very first thing I thought of was Robert
Forward's novel "Camelot at 30K." It is as remarkable a piece of fortuitive
prediction as Percival Lowell imagining that Pluto was there. Written before
Sedna was discovered, Forward (a great physicist) worked out all the details for
an intelligent life form that could thrive on a big cold dark place like Sedna.
It's a piece of dazzling plausibility that covers every base.
    Of course, after having previously worked out all the details for an
intelligent life form that could thrive on the surface of a neutron star, it was
probably easy for him.
    Read "Camelot at 30K." Believe me, you'll never look at Sedna the same way
again.


Sterling K. Webb
-----------------------------------------
Ron Baalke wrote:

> http://www.gemini.edu/index.php?option=content&task=view&id=126
>
> Sedna Reveals Pristine Surface in Gemini Near-infrared Spectra
> Gemini Observatory
> 12 April 2005
>
> ------------------------------------------------------------
> Sedna Discovery
>
> Sedna was discovered on November 14, 2003 by a CalTech team, using the
> 48-inch Samuel Oschin Telescope at Palomar Observatory. The object lies
> more than 8 billion miles from the Earth, making it the most distant
> object ever observed in the solar system. Its official IAU provisional
> designation was minor planet 2003 VB12, but as of September 28, 2004 it
> officially became known as Sedna after the Inuit goddess of arctic sea life.
> -----------------------------------------------------------
>
> Recent spectroscopic studies of infrared light reflected from the
> surface of Sedna reveal that it is probably unlike Pluto and Charon
> since Sedna's surface does not display evidence for a large amount of
> either water or methane ice. Due to Sedna's extreme distance from the
> Sun, the frigid surface has probably been untouched for millions of
> years by anything except cosmic rays and solar ultraviolet radiation.
>
> Gemini Observatory astronomer Chad Trujillo led an effort by the same
> California Institute of Technology research team responsible for Sedna's
> original discovery to obtain spectra of this distant planetoid using the
> Near Infrared Imager (NIRI) on Gemini North. Their aim was to better
> understand the surface of this distant world and how it has evolved
> since its formation. "It is likely that Sedna has experienced an
> extremely isolated life in the outskirts of our solar system," said
> Trujillo. "Out there beyond what we used to think was the edge of the
> solar system, interactions or collisions between bodies are probably
> very rare. Our observations confirm what you would expect from a surface
> that has been so far out in our solar system for such a long time and
> exposed to space weathering."
>
> Figure 1
>
> The relative reflectance spectrum of (90377) Sedna (black circles) and
> the spectrum of the nearby sky (grey circles). Gray curves are the model
> 3 sigma upper limits to the surface fraction of water ice (smooth gray line)
> and methane ice (jagged gray line). Surface fractions that cause more
> absorption than the indicated lines are ruled out by our observations at
> the 3 sigma level. The model shown is for 100-micron diameter particles.
> Spectrum error bars are computed from the reproducibility of the
> spectral data in each spectral point.
>
> The Sedna data lack the strong spectral lines that would indicate the
> existence of substances like methane and water ice, but deeper studies
> are needed to confirm how low the levels of these ices might be on this
> planetoid. Sedna might be more like the minor planet Pholus (that lies
> just inside the orbit of Saturn), which is similar in its redness in
> visible light. This same "space weathering" may also affect Pluto and
> Charon, but there may be other processes that replenish their water- and
> methane-rich surfaces, such as atmospheric effects, geological processes
> and collisions.
>
> The data could reveal something of Sedna's evolutionary history in the
> outer solar system. Astronomers think that objects like Sedna start out
> with icy surfaces. Over time cosmic rays and solar ultraviolet radiation
> "bake and burn" the surfaces into black hydrocarbon-rich substances
> similar to asphalt, which do not reveal themselves well in infrared
> spectra. Such a history might explain why Sedna doesn't exhibit traces
> of methane and water ice, whereas Pluto and Charon do.
>
> "Like a sandblaster operating for several billion years, most of the
> objects out as far as Pluto are constantly being resurfaced by impacts
> and collisions which expose and supply fresh surface materials before
> the black stuff can get baked on," said Michael Brown of California
> Institute of Technology, who is the Principle Investigator of the team
> that originally discovered Sedna. "Pluto and its moon Charon provide an
> excellent example of this process, with Pluto displaying a strong
> methane ice signature in its spectrum and Charon dominated by water ice."
>
> The team does not rule out the possibility that longer-duration (deeper)
> observations might reveal evidence of methane or water ice on Sedna.
> However, the Gemini data indicate that if they do exist their extent is
> limited.
>
> The results of these observations will appear in The Astrophysical Journal.
>
> Gemini Observations of Sedna
>
> The Gemini observations of Sedna were possible due to the observatory's
> powerful ability to collect infrared radiation reflected from the
> planetoid (which lies over 12 light-hours from Earth). The research team
> used NIRI (Near Infrared Imager) on Gemini North to obtain the spectra
> over a period of about two hours on the night of December 27, 2003.
>
> The infrared light captured by Gemini is really "recycled" starlight
> from the Sun, which at Sedna's distance would appear more like a very
> bright nighttime star. Just as some of the sunlight striking this object
> is reflected back as optical light (which allowed its discovery), some
> of the infrared light is also reflected back. Materials on the surface
> imprint a characteristic fingerprint on the re-emitted light, which can
> reveal details about the composition of the planetoid's surface.
>
> ______________________________________________
> Meteorite-list mailing list
> Meteorite-list_at_meteoritecentral.com
> http://six.pairlist.net/mailman/listinfo/meteorite-list
Received on Thu 14 Apr 2005 01:43:30 AM PDT