[meteorite-list] New Horizons: Is the Pluto System Dangerous?

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon, 7 Nov 2011 15:05:45 -0800 (PST)
Message-ID: <201111072305.pA7N5j7Y023607_at_zagami.jpl.nasa.gov>

http://pluto.jhuapl.edu/overview/piPerspective.php

The PI's Perspective

Is the Pluto System Dangerous?
Alan Stern
November 7, 2011

New Horizons remains healthy and on course, now almost two times as far
from the Sun as the Earth is, and approaching six years into its
9.5-year journey to the Pluto system.

We've taken the spacecraft out of hibernation to perform maintenance
activities, and to re-point our radio antenna to compensate for Earth's
movement around its orbit. This "hibernation wakeup' started November 5
and will last until November 15. Then New Horizons will hibernate again
until early January, when we'll perform a more extensive, almost
month-long wakeup.

I'll provide an update soon about how the November hibernation wakeup
went and what's in store for the January wake up and our cruise to
Active Checkout 6, which begins next May. But in this PI's log, I want
to concentrate on a question that has recently come to the fore on the
mission: "Is the Pluto system dangerous to New Horizons?"

If you're wondering what I mean, I'm referring to the fact that the more
moons that pop up in the system, the more we have to worry that there
are still more undiscovered moons that are too small and faint to
detect. When we discovered P4 this summer, along with possible evidence
of a couple of still-fainter moons (something we need more study to
confirm or reject), we began to worry about just how many tiny moons
Pluto might have and whether we might have to dodge them.

Even more worrisome than the possibility of many small moons themselves
is the concern that these moons will generate debris rings, or even 3-D
debris clouds around Pluto that could pose an impact hazard to New
Horizons as it flies through the system at high speed. After all, at our
14-kilometer-per-second flyby speed, even particles less than a
milligram can penetrate our micrometeoroid blankets and do a lot of
damage to electronics, fuel lines and sensors.

So to assess that hazard, we brought together about 20 of the world's
experts in ring systems, orbital dynamics and state-of-the-art
astronomical observing techniques to search for small satellites and
rings at distant Pluto. This group convened November 3-4 at the
Southwest Research Institute's offices in Boulder, Colo., where the New
Horizons science team is centered. During this two-day workshop, a
series of technical talks and discussions sections examined every aspect
of the hazards that debris and small moons orbiting in the Pluto system
might pose.

We found a plausible chance that New Horizons might face real danger of
a killer impact; and that to mitigate that hazard, we need to undertake
two broad classes of work.

First, we need to look harder at the Pluto system for still undiscovered
satellites and rings. The best tools for this are going to be the Hubble
Space Telescope, some very large ground-based telescopes, telescopes
that can make stellar occultation observations of the space between
Pluto and Charon where New Horizons is currently targeted, and thermal
observations of the system by the ALMA radio telescope array just now
being commissioned.

Then, we need to plan for an alternate, safer route through the Pluto
system in case those observations reveal strong evidence that our
current trajectory is too hazardous. Studies presented at the Encounter
Hazards Workshop indicate that a good "safe haven bailout trajectory"
(or SHBOT) could be designed to target a closest-approach aim point
about 10,000 kilometers farther than our nominal mission trajectory.
More specifically, a good candidate SHBOT aim point would be near
Charon's orbit, but about 180 degrees away from Charon on
closest-approach day. Why this location? Because Charon's gravity clears
out the region close to it of debris, creating a safe zone.

Making this situation still more complex is the fact that debris created
in the Pluto system may not lie in a plane, as in other ring systems,
but might instead be contained in a fat torus (donut-shaped) or even a
nearly-spherical 3-D cloud if the debris coming off small satellites has
high velocity (such debris is created by impactors from the Kuiper Belt,
which hit at pretty high speeds of 1-2 kilometers per second.)

The question of whether the Pluto system could be hazardous to New
Horizons remains open "but one we'll be studying hard over the next
year, with everything from computer models to big ground-based
telescopes to the Hubble.

I'll report on results as we obtain them, but it is not lost on us that
there is a certain irony that the very object of our long-held
scientific interest and affection may, after so many years of work to
reach her, turn out to be less hospitable than other planets have been.
We'll see.

In closing, I want to add a timely note and wish Patsy Tombaugh, the
widow of Pluto discoverer Clyde Tombaugh, a very happy 99th birthday
today (November 7). As Patsy begins her 100th year, we on New Horizons
marvel at her longevity, her energy, and her wonderful sense of humor.
Happy birthday Patsy!

Well, that's my update for now. Thanks again for following our journey
across the deep ocean of space to a truly new frontier. And I hope
you'll keep on exploring - just as we do!
Received on Mon 07 Nov 2011 06:05:45 PM PST