[meteorite-list] The Kuiper Belt at 20: Paradigm Changes in Our Knowledge of the Solar System

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Sun, 26 Aug 2012 15:10:24 -0700 (PDT)
Message-ID: <201208262210.q7QMAOfG020021_at_zagami.jpl.nasa.gov>

http://pluto.jhuapl.edu/overview/piPerspective.php?page=piPerspective_08_24_2012

The PI's Perspective

The Kuiper Belt at 20: Paradigm Changes in Our Knowledge of the Solar System
Alan Stern
August 24, 2012

New Horizons remains healthy and on course, now more than 24 times as
far from the Sun as the Earth is. This summer's spacecraft and payload
checkout went extremely well, as did both major flight-software updates
we loaded aboard New Horizons. And, the spacecraft's rehearsal of the
closest-approach day of the Pluto encounter went just about perfectly.

After finishing all of this at the beginning of July, we put New
Horizons back into hibernation, and we've been cruising that way for
almost eight weeks. As those who follow New Horizons on Twitter
(_at_NewHorizons2015) know, every Monday New Horizons checks in with a
beacon that tells us if all is well, or not. And almost every week we've
been able to report a "green beacon Monday" to our 22,000-plus Twitter
followers, indicating the spacecraft is in good health.

New Horizons will cruise quietly in hibernation until Jan. 6, 2013, when
we wake it up for a month of complex activities, including some advance
work on next summer's checkout, and the third of the four major software
upgrades needed before next summer's on-spacecraft rehearsal of the nine
days surrounding Pluto closest approach.

Since activity on New Horizons is pretty quiet right now, I'll take this
opportunity to mention that planetary science is celebrating the 20th
anniversary of the discovery of the Kuiper Belt. That came in 1992, when
the first Kuiper Belt Object (KBO) was discovered.

Actually, of course, the first object in the Kuiper Belt was discovered
in 1930 - Pluto itself; and the second such object, Pluto's giant moon
Charon, was discovered in 1978. The Kuiper Belt was first postulated -
most famously by Gerard Kuiper - by planetary scientists back in the
1930s, '40s and '50s. But it took until 1992 for technology to mature
sufficiently enough to find another object (outside the Pluto system)
orbiting the Sun beyond Neptune.

Since 1992, more than 1,000 KBOs have been discovered. But only a tiny
fraction of the sky has been surveyed for KBOs. It is estimated that
more than 100,000 KBOs exist with diameters of 100 kilometers or larger,
along with billions of smaller objects down to the size of cometary
nuclei, just a kilometer or two across. (By comparison, Pluto is huge -
its diameter is almost 2,400 kilometers, making a drive around its
equator as far as from Manhattan to Moscow!)

Most of the known KBOs are just 100 to 300 kilometers across, about
one-tenth of Pluto's diameter. But some are smaller than 100 kilometers
across, and some are larger than 300 kilometers across. In fact, there
is great diversity among KBOs:

    * Some are red and some are gray;
    * The surfaces of some are covered in water ice, but others (like
      Pluto) have exotic volatile ices like methane and nitrogen;
    * Many have moons, though none with more known moons than Pluto;
    * Some are highly reflective (like Pluto), others have much darker
      surfaces;
    * Some have much lower densities than Pluto, meaning they are
      primarily made of ice. Pluto's density is so high that we know its
      interior is about 70% rock in its interior; a few known KBOs are
      more dense than Pluto, and even rockier!

But I don't consider this surprising assortment of KBOs to be the most
important contribution to our knowledge of the solar system that has
come from telescope exploration of the Kuiper Belt. In my opinion, the
three greatest solar system lessons we've learned from the Kuiper Belt are:

    * That our planetary system is much larger than we used to
      think. In fact, we were largely unaware of the Kuiper Belt - the
      largest structure in our solar system - until it was discovered 20
      years ago. It's akin to not having maps of the Earth that included
      the Pacific Ocean as recently as 1992!

    * That the locations and orbital eccentricities and inclinations
      of the planets in our solar system (and other solar systems as
      well) can change with time. This even creates whole flocks of
      migration of planets in some cases. We have firm evidence that
      many KBOs (including some large ones like Pluto), were born much
      closer to the Sun, in the region where the giant planets now orbit.

    * And, perhaps most surprisingly, that our solar system, and very
      likely very many others, was very good at making small planets,
      which dominate the planetary population! Today we know of more
      than a dozen dwarf planets in the solar system, and those dwarfs
      already outnumber the number of gas giants and terrestrial planets
      combined. But it is estimated that the ultimate number of dwarf
      planets we will discover in the Kuiper Belt and beyond may well
      exceed 10,000. Who knew? (And which class of planet is the misfit
      now?)

What an amazing set of paradigm shifts in our knowledge the Kuiper Belt
has brought so far. Our quaint 1990s and earlier view of the solar
system missed its largest structure! It didn't know about the existence
of dwarf planets, the most populous class of planet in our solar system
- and very likely the galaxy. It didn't even contemplate that dwarf
planets would have such a wide range of colors, reflectivities, orbits
and surface compositions. And it didn't realize that the locations of
most planets in our solar system today - even including some of the very
largest planets - are different from where they were born.

Just imagine what our close flybys of the Pluto system and smaller KBOs,
combined with new giant telescopes coming on line to probe the sky, will
teach us about the Kuiper Belt in the next 20 years. It's an exciting
time, and its sometimes hard for me to believe after working on this
since 1989, that our 2015 exploration of Pluto and its many moons is
almost upon us - but it is!

Well, that's my update for now. Thanks again for following our journey
across the deep ocean of space, to a new planet and a truly new frontier.

Until I write again, I hope you'll keep on exploring - just as we do!
Received on Sun 26 Aug 2012 06:10:24 PM PDT