There is a cold, dimly lit, and mysterious region far beyond the
beautiful blue ice-giant Neptune--the most distant of the eight major
planets from our Sun. In this faraway domain called the Kuiper belt--that
astronomers are only now beginning to explore--a myriad of strange, icy
worldlets dance around our Star. Pluto, one of the largest worlds
inhabiting the Kuiper belt, was originally classified as the
ninth major planet from the Sun after its discovery in 1930, but the
realization that this icy little oddball is only one of several large
frozen bodies dwelling in the Kuiper belt prompted the International Astronomical Union (IAU)
to formally define "planet" in 2006--and poor Pluto was unceremoniously
booted out of the pantheon of major planets. Pluto, now newly
reclassified as a mere dwarf planet is nonetheless an object of
considerable interest, debate, and affection. Soon scientists will know
much more about this beloved little ice ball far, far away because,
after a journey of almost nine years and three billion miles--the
farthest any space mission has ever traveled to reach its main
target--NASA's New Horizons spacecraft came out of hibernation on December 6, 2014 in preparation for its long-awaited 2015 close encounter with Pluto.
Mission scientists at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Maryland, confirmed on December 6, 2014 that New Horizons,
operating on pre-programmed computer commands, had successfully
switched from its hibernation mode to its "active" mode. Zipping along
at the breathtaking speed of light, the radio signal dispatched from New Horizons--which,
as of this writing, has journeyed over 2.9 billion miles from Earth,
and just over 162 million miles from Pluto--required four hours and 26
minutes to reach NASA's Deep Space Network Station located in Canberra, Australia.
"This is a watershed event that signals the end of New Horizons
crossing of a vast ocean of space to the very frontier of our Solar
System, and the beginning of the mission's primary objective: the
exploration of Pluto and its many moons in 2015," explained Dr. Alan
Stern in a December 6, 2014 APL Press Release. Dr. Stern, who is from the Southwest Research Institute in Boulder, Colorado, is New Horizons Principal Investigator.
Since its launch on January 19, 2006, New Horizons
has spent 1,873 days--or about two-thirds of its flight time--in
hibernation mode. Its 18 separate hibernation periods, from mid-2007 to
late 2014, ranged from 36 days to 202 days in duration. The science team
used hibernation mode to save wear and tear on the long-journeying
spacecraft components and lessen the risk of system failures.
"Technically,
this was routine, since the wake-up was a procedure that we'd done many
times before. Symbolically, however, this is a big deal. It means the
start of our pre-encounter operations," explained Dr. Glen Fountain in
the December 6, 2014 APL Press Release. Dr. Fountain is New Horizons Project Manager at APL.
Alas, Poor Pluto!
Pluto is a relatively large inhabitant of the frigid, dark Kuiper belt,
where it circles around our Sun in the enchanting company of a vast
multitude of mysterious, bewitching icy objects of its own kind. From
this very distant domain, our Sun appears as only an especially large
star suspended in the dark sky!
Like other Kuiper Belt Objects (KBOs),
Pluto is thought to be primarily made up of rock and ice. It is a
relatively small world, only about 1/6 the mass of Earth's Moon and 1/3
its volume. Pluto also sports an eccentric and highly inclined orbit
that takes it from 30 to 49 Astronomical Units (AU) from our Star. One AU
is equivalent to the average Earth-Sun separation, which is 93,000,000
miles. Therefore, Pluto periodically approaches our Sun at a distance
closer than Neptune! However, an orbital resonance with Neptune very
fortunately prevents the two worlds from blasting into each other.
The Kuiper belt, sometimes called the Edgeworth-Kuiper Belt,
is a distant region of our Solar System beyond the realm of the
planets. It extends from the orbit of Neptune to approximately 50 AU.
Neptune's average distance from our Star is 30.1 AU--it's perihelion (closest to our Sun) is 29.8 AU, while its aphelion (most distant from our Sun) is 30.4 AU.
The
demoted icy oddball that is Pluto was discovered by the American
astronomer Clyde Tombaugh in 1930, and this small world, shrouded in
perpetual darkness where it dwells in the deep freeze of our Solar
System's outer limits, was appropriately named in honor of the Roman god
of the underworld. Pluto's largest moon, Charon, was discovered in 1978
by astronomer James Christy, also an American. Charon is thought to be a
chunk torn off from Pluto itself during a catastrophic collision
between Pluto and some other object that was also tumbling around close
to it in the Kuiper belt.
For most of the 20th century,
it was wrongly believed that Pluto is a solitary little world where it
dwells in the frigid darkness, far from the comforting light and warmth
of our Star. However, in 1992, the very first KBO was discovered, and astronomers soon realized that Pluto is not far from the madding crowd of a multitude of other KBOs.
Indeed, since then, many other small icy worldlets akin to Pluto--also
sporting eccentric orbits--have been spotted. The most notable of these
is the scattered disc object dubbed Eris, that was discovered in 2005. Eris
is approximately 27% more massive than Pluto. The understanding that
Pluto is merely one of many resulted in its demotion and
reclassification. However, there are astronomers who oppose this
demotion, arguing that Pluto should have retained its classification as a
major planet, and that the other kindred dwarf planets that have been discovered should be added to the list of major planets along with Pluto.
Pluto
itself has five known moons: Charon, Nix, Hydra, Kerberos, and Styx.
Charon is by far the largest of Pluto's moons, and it boasts a diameter
of approximately 50% that of Pluto. Some astronomers consider Pluto and
Charon to be a binary system because the barycenter of their orbits does
not lie within either world. However, as of this writing, the IAU has yet to provide a definition for binary dwarf planets. Because of this, Charon is still officially classified as a moon of the dwarf planet Pluto.
Pluto
has a very thin atmosphere composed of nitrogen, methane, and extremely
toxic carbon monoxide, which is probably derived from the ice on
Pluto's frozen surface. As Pluto makes its way ever closer to our Star
in its orbit it grows warmer and warmer. The ice on its surface
evaporates as a result, and the gasses slowly float away into
interplanetary space. This continues until Pluto starts to make its long
journey away from the Sun again, becoming colder and colder as it does
so. Pluto's atmosphere again freezes, and then falls down to its surface
as snow--but it will evaporate again when Pluto begins its long journey
towards our Sun. Pluto's last approach to our Star was back in 1989. It
takes 248 years for the frozen little world to finish only a single
orbit around our Sun.
A Close Encounter With Poor Pluto!
The "active" mode awakening New Horizons from its hibernation was programmed into the spacecraft's onboard computer in August 2014, and it started to work aboard New Horizons on December 6, 2014. About one hour and a half after starting, New Horizons began transmitting signals to Earth reporting on its condition--including the news that it was back in "active" mode.
The New Horizons
team plans to spend several weeks monitoring the spacecraft, making
certain that its systems and science instruments are performing as they
should. The scientists will also continue to build and test the
computer-command sequences that will take New Horizons through its journey to, and close encounter with, the Pluto system.
Carrying
a seven-instrument science payload, including sophisticated imaging
infrared and ultraviolet spectrometers, two powerful particle
spectrometers, a space-dust detector, and a compact multicolor camera, New Horizons is scheduled to begin its mission of observing the mysterious Pluto system on January 15, 2015.
New Horizons
closest approach to its quarry will occur on July 14, 2015, but a
treasure trove of new discoveries are expected to be made before
then--including, by mid-May 2015, views of the Pluto system that are far
superior to what even the venerable Hubble Space Telescope is able to provide of this bewitching little ice-world and its many frozen moons.
"New Horizons
is on a journey to a new class of planets we've never seen, in a place
we've never been before. For decades we thought Pluto was this odd
little body on the planetary outskirts; now we know it's really a
gateway to an entire region of new worlds in the Kuiper belt, and New Horizons is going to provide the first close-up look at them," New Horizons Project Scientist Dr. Hal Weaver, of APL, told the press on December 6, 2014.
Judith E. Braffman-Miller is a writer and astronomer whose
articles have been published since 1981 in various newspapers, journals,
and magazines. Although she has written on a variety of topics, she
particularly loves writing about astronomy because it gives her the
opportunity to communicate to others the many wonders of her field. Her
first book, "Wisps, Ashes, and Smoke," will be published soon.
No comments:
Post a Comment