New Horizons Update - September 2005

http://pluto.jhuapl.edu/overview/piPerspective_current.html

New Horizons
The PI's Perspective - Alan Stern
September Comes, Complete With Sister Worlds
September 2005

August was a very good month for New Horizons. We completed the 6-week
long space-environment (thermal vacuum) testing of mankind's first
spaceship to Pluto. Thermal vacuum testing included thermal balance,
followed by multiple transitions of the spacecraft to hot and cold
temperatures while in vacuum, several mission simulations, numerous
payload instrument performance tests, and tests with NASA's Deep Space
Network (DSN). The thermal vacuum testing was the last step in our
pre-flight environmental test program (earlier tests included
vibration,
spin balance, and launch acoustic loads).

The successful environmental testing campaign we just completed is a
credit to a dedicated and talented Applied Physics Laboratory/NASA
Goddard Space Flight Center/Southwest Research Institute/contractor
team
of engineers, technicians, and scientists. This team was led by our
integration and test (I&T) manager, Mike Colby. Mike and his team are
my
heroes - for keeping us to schedule and making what is very hard look
very easy.

Another very important milestone accomplished in August was the
completion of the multi-month acceptance testing of our spacecraft
flight software. APL's Debbie Clancy and her team get the kudos for
this
big milestone.

As we enter September, New Horizons continues with mission simulations
and software testing. Additionally, we expect to complete the repair of
our finicky solid state data recorder, install fresh, flight detectors
in the Solar Wind Around Pluto (SWAP) plasma instrument, and resolve an
intermittent problem in an electrical connector that affected the
control of one of our attitude control system latch valves.

I'll be back in touch a month from now in this space. By then, New
Horizons should be in Florida!

Before I go, I have to remark on something that is, truly, remarkable.
While New Horizons was completing its vacuum chamber testing, news
emerged of the discovery of two Kuiper Belt Objects (KBOs) almost as
large as Pluto. Even more exciting was the discovery of an object
larger
than Pluto - and three times as distant - way far into the classical
Kuiper Belt. The object is provisionally called 2003 UB313; someday
soon
it'll receive a more poetic name.

But no matter what we call it, UB313 is an exciting find for planetary
science. On the next page you'll find a commentary that I wrote on the
meaning of this discovery to planetary science; this also ran in the
August 29 issue of Space News.


And Copernicus Smiled

A real revolution is afoot in planetary science. The first shot was
fired in 1930, with the discovery of Pluto, but almost no one realized
its import. The second and third shots came in the late 1970s, with the
discovery of distant objects called Chiron and Charon, but again, few
recognized what they would portend. Rapid-fire volleys began in the
1990s, as myriad discoveries of icy bodies hundreds to well over 1,000
kilometers across occurred in the Kuiper Belt, just beyond Neptune,
became an observational reality. But it was only this year, with the
recently announced discovery of 2003 UB313 - a world larger than Pluto
-
that we have heard the equivalent of the American Revolution's "shot
heard round the world."

When I was a boy in the 1960s, in college in the late 1970s, and in
graduate school in the 1980s, we were taught that our solar system
contains four rocky planets on the inside, four giant planets on the
outside, and one spit of a planetary misfit called Pluto, moving in a
markedly elliptical, and oddly inclined orbit beyond Neptune. Like many
people, I recall thinking: What an odd bird that lone Pluto is.

Today, however, we see a very different picture of our home solar
system
is emerging, one which reveals Pluto in context - as a nearby example
representing what is almost certainly the most populous class of planet
in our solar system - the "ice dwarfs."

Consider: less than 2% of the Kuiper Belt has been thoroughly
catalogued, yet over a thousand-plus rogue worlds and "worldlets" have
already been spotted there. And among just those bodies catalogued to
date, we know that half a dozen (like Sedna and Quaoar) already rival -
and in the case of the just-discovered 2003 UB313 - exceed, Pluto's
size. Moreover, most of these new worlds follow orbits that are as
cockeyed as Pluto's - some even more so.

Now we can see just how naive our 20 th century perspectives were:
Pluto
is no misfit. Instead, once the advance of technology allowed us to
probe deeply enough, it is becoming clear that Pluto was the advance
harbinger of a populous new region of the solar system lying beyond the
giant planets.

Modern simulations of planetary formation, performed by different
research groups around the world, led to broad agreement that in the
process of forming the giant planets, some hundreds to thousands of
smaller worlds, ranging from a goodly fraction of Pluto's size to at
least Earth's size, were also formed. Most of these bodies were dwarf
planets, like Pluto, with steeply declining populations at larger and
larger sizes, so that only a few or few tens of bodies Earth's size
were
formed. These simulations also show that most of these bodies were
ejected from the giant planets region to more much more distant orbits
as Jupiter, Saturn, Uranus, and Neptune , neared their current sizes
and
gravitationally cleared out their formation zones, some 4-plus billion
years ago.

Importantly, these numerical models are supported by some solid
forensic
clues that are scattered about the outer solar system, and which lead
us
to similar conclusions: One such clue is the fact that Pluto's moon,
Charon (itself half of Pluto's size) seems to have been formed by a
giant impact with a body nearly as large as Pluto itself. What is most
important in this finding is that, in order to make such a collision
probable, there must have been hundreds or more 1,000-kilometer
diameter
bodies orbiting in the ancient outer solar system. A second clue comes
in the form of Triton, a 2,700-kilometer diameter moon, which circles
Neptune on a retrograde orbit that is the hallmark of gravitational
capture from a previous orbit around the Sun. Triton is compositionally
much like Pluto, but a tad larger. Apparently, it is one of the "many
Plutos" that once formed, and it seems to have escaped ejection by
becoming caught in a long-lasting orbit around Neptune. Yet another
clue
comes from the polar tilts or Uranus (98 degrees) and Neptune (30
degrees). The only viable mechanism known to be able to generate such
extreme tilting of these gargantuan (15 Earth mass-class) planets, are
off-center collisions with bodies of one to several Earth masses.
Crucially, calculations also reveal that in order for both Uranus and
Neptune to have had a high probability of suffering such collisions, as
many as a few dozen such Earth-mass objects may have once orbited in
their region of the solar system.

As a result of the modeling capability that modern computers give us,
combined with the forensic observational clues just discussed, and now
the discoveries of rivals and even successors to Pluto's throne, we are
slowly but surely coming to a simultaneously jarring and exciting new
conclusion: that our solar system formed not just the nine planets we
were taught to name in school, but many dozens, if not hundreds of
others as well!

A revolutionary aspect of this emerging, new paradigm is the dawning
realization that the long-known eight rocky and giant planets, Mercury
through Neptune , now seem to be the misfits.

Less than two centuries ago it was discovered that all the stars one
can
see by eye, and their innumerable brethren seen by telescope, are
distant Suns, with numbers too great to count. Similarly, it was just
under a century ago that our galaxy, the Milky Way, was realized to be
but one of literally billions of galaxies. Both of these realizations,
like the 16 th century realization that the Sun (not Earth!) is the
center of our solar system, jarred perceptions and changed textbooks in
revolutionary ways. Just as jarring to us now is the newly emerging
view
that our solar system made, and is still littered with, very many
distant planets, most of which are nothing like the familiar planets
that orbit close to the Sun, like Earth. In a real sense, we are seeing
a new chapter unfold in the revolution that Copernicus wrought when he
displaced the Earth from the center of everything.

Indeed, from today's 21 st century perspective, the solar system seems
likely to be dominated by a huge population of rock and ice planets
ranging from dwarf sizes like Pluto to perhaps super-Earths. Most of
these new worlds are expected to follow elliptical, highly inclined
orbits, like those of Pluto, Quaoar, Sedna, and UB313. Further still,
of
all the planets now expected to orbit within our sun Sol's grasp, most
orbit between ten and a thousand times farther than do any of the
planets we were taught about in school. It's not at all your father's
solar system.

.