[meteorite-list] What If Voyager Had Explored Pluto?

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue, 24 Jun 2014 10:45:04 -0700 (PDT)
Message-ID: <201406241745.s5OHj4ou009887_at_zagami.jpl.nasa.gov>

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

The PI's Perspective
What If Voyager Had Explored Pluto?
Alan Stern
June 23, 2014

As I mentioned in my previous PI Perspective
<http://pluto.jhuapl.edu/overview/piPerspective.php?page=piPerspective_06_11_2014>,
New Horizons crosses the orbit of Neptune, the outermost planet explored
by the Voyager mission, late this August. Voyager's flyby of Neptune was
in August 1989, 25 years ago!

Across flights launched in 1977 and spanning the entirety of the 1980s,
Voyagers 1 and 2 performed the historic, first detailed reconnaissance of our
solar system's four giant planets (Jupiter, Saturn, Neptune, Uranus). The
essentially identical Voyagers were launched with a core mission to explore
the Jupiter and Saturn systems, and each spacecraft carried a powerful and
diverse scientific instrument suite. After Saturn, Voyager 2 was tasked with
reconnoitering Uranus and Neptune during an extended mission.

Although Pluto's orbital position relative to Neptune made it impossible
for Voyager 2 to travel to it from Neptune, Voyager 1 actually could
have reached Pluto after its Saturn flyby, had it been targeted to do
so. In fact, NASA and the Voyager project actually considered this
option, but eliminated it in 1980 - going instead with the very
exiting but lower-risk opportunity to investigate Saturn's large,
scientifically enticing, cloud-enshrouded and liquid-bearing moon Titan.

But if Voyager 1 had been sent to Pluto, it would have arrived in the
spring of 1986, just after Voyager 2's exploration of Uranus that
January. As New Horizons approaches Pluto in 2015, it's fun to think
what we might have found almost 30 years ago had Voyager 1 - rather than
New Horizons - been first to Pluto.

A Blind Venture

One big difference then was how much less we knew about Pluto and its
context in our solar system. After all, it was 1986: Pluto's atmosphere
wasn't discovered until 1988, and Pluto's surface wasn't imaged until
1994, when the Hubble Space Telescope (itself launched in 1990) revealed
its patchy surface and polar caps.

Even more importantly, Pluto's context in the solar system wasn't
appreciated back in 1986, six years before the discovery of the Kuiper
Belt. In fact, in 1986, we didn't even know that dwarf planets were a
class of planet and that Pluto was simply the largest of this cohort of
rocky, ice-covered worlds orbiting beyond Neptune. At the time we were
still three years away from Voyager's flight past Triton - Neptune's
largest moon and Pluto's best analog in the solar system - so we would
not have known much about what to expect.

And although Pluto's size, and the size of its Texas-sized satellite
Charon, were both approximately known in 1986, the two main constituents
of Pluto's surface ices-nitrogen and carbon monoxide and atmosphere-had
not yet been discovered. Nor was there a hint of Pluto's system of at
least four small moons, later discovered from 2005 to 2012. All in all,
a 1986 Voyager flyby of the Pluto system would have been a blind venture
to an unknown world.

Technological Advances

Voyager 1 carried a broad battery of cameras, spectrometers, plasma
experiments, and even a sensitive magnetometer that it could have
brought to bear on the exploration of Pluto. Because Pluto was almost
exactly the same distance from the Sun in 1986 as Neptune was for the
Voyager 2 flyby in 1989, it's clear that the instruments aboard Voyager
1 would have worked well at Pluto. And because Voyager 1 is /still/
working today, we know the spacecraft would likely have made the journey
to Pluto successfully.

Although Voyager 1 would have been able to map Pluto and Charon well
with its cameras, and detect Pluto's atmosphere and study the
atmosphere's basic properties, the Voyager science team would not have
known to plan observations of the small moons they would have discovered
on close approach, nor would they have been able to explore Pluto nearly
as thoroughly as the payload aboard New Horizons will.

That's because the onward march of technology between the design of
Voyager's payload of sensors in the early 1970s, and our payload's
design in the early 2000s, produced a revolution in capabilities every
bit as fundamental as the difference between computers of the 1970s and
computers of the 2000s.

For example, the New Horizons payload will map surface composition at
high resolution across essentially all of the close-approach hemispheres
of Pluto and Charon. Voyager 1 carried no such capability. Similarly,
whereas Voyager's ultraviolet spectrometer contained only two pixels,
the Alice ultraviolet spectrometer on New Horizons contains more than
32,000 pixels, making it a much more efficient device to survey the
Pluto system.

Voyager 1 would have brought a magnetometer and a more diverse array of
space plasma instruments to bear on Pluto than we will. But it's more
important that New Horizons has much more advanced mapping cameras and a
far more capable radio science experiment to determine atmospheric
pressure and temperature. We also carry a dust impact detector - Voyager
did not have such a device to study Pluto's environment.

One key technical advantage stemming from Voyager's larger antenna and
higher power budget was the ability to send data back at much faster
rates-about 10 times faster than New Horizons. Voyager also had a scan
platform that allowed its remote sensing instruments to be trained on
their targets even while the spacecraft was transmitting data to Earth-
a high-cost technology that the New Horizons team chose to forego. And
although Voyager would have been able to map Pluto's entire surface in
1986, since that surface was then oriented equator-on to the Sun (unlike
the high-latitude illumination to be seen in 2015, leaving much of the
winter hemisphere in darkness), Voyager's memory storage was much, much
smaller, so the resulting dataset would have been correspondingly less.

Spectacular Discoveries, Incredible Missions

One could debate this kind of detailed comparison at length, but my
overall conclusion is this: Had Voyager 1 been sent to Pluto in 1986,
rather than New Horizons arriving in 2015, it would have made many
spectacular discoveries, but with less data depth and diversity than New
Horizons is likely to achieve. And, not knowing of the Kuiper Belt in
1986, Voyager would then have unknowingly gone on (as it actually did),
sailing across the belt without even attempting flybys of primordial
Kuiper Belt Objects, as New Horizons will.

That said, consider how amazing it would have been in 1986 to rapidly
discover, in the few weeks prior to a Voyager closest approach, that
Pluto has an atmosphere; that Pluto has its own retinue of small moons,
much like a giant planet; and that the much more volatile snows of
nitrogen and carbon monoxide dominate its surface composition-rather
than the methane snow as was then known.

But make no mistake: Both spacecraft are extraordinary. And both have
their own places in the history of humankind's first exploration of the
planets. Both projects are staffed by outstanding teams of engineers and
scientists; and both projects are testaments to the leadership of the
United States in exploring our solar system for all humankind.

Hail Voyager! Hail New Horizons! Both missions are incredible. But most
incredible of all, I think, will be Pluto and its diverse system of
satellites themselves. They are the real stars in this story, regardless
of /when/ it is told. Pluto and its moons are billions of years old, but
completely new in our consciousness as real places, with real
personalities and histories of their own.

The decision long ago by NASA and the Voyager project to forgo Pluto
opened up a possibility for us now to once again experience the thrill
and adrenaline rush of first-time planetary exploration, and to offer it
to a new generation of young people not born or very much aware of
things in 1986. We on the New Horizons team look forward to bringing the
excitement, the adventure, and the pride of frontier reconnaissance to
this new generation.

With that, I'll close by saying thanks for following our journey across
the deep ocean of space, to explore a new planet, its moons, and a truly
new frontier.

Until I write again, I hope you'll keep exploring-just as we do!
Received on Tue 24 Jun 2014 01:45:04 PM PDT