NASA’s New Horizon spacecraft designed to flyby Pluto having
travelled five billion kilometres for
the past nine and half years is going to have its closely approach with the
dwarf planet by 7:50 am, Eastern Day Light Time on July 14th 2015.
Astronomers and science enthusiasts’ world over are passionately waiting for
this epic moment that will last for few minutes. The probe will whiz past the
planet’s surface at a velocity of 53,000 kmph during which it will capture
thousands of images, collect scientific data of Pluto’s atmosphere, its surface
and environment. Pluto has been the least explored planet in the solar system
and no dedicated mission was ever commissioned for its study. New Horizons
mission was instituted to study Pluto and explore the vast swarm of frosty
bodies lying beyond Neptune and the bodies faintly moving in the frigid Kuiper
belt region.
The probe has travelled so far that it will take 4.5 hrs for
the radio signal sent from earth to reach the space craft. Hence it will remain
radio silent for the entire period of its closet encounter with Pluto and
Charon as the limited computing ability of the probe will be utilised in
collecting the necessary data. Close-up image and scientific data will be sent
to earth over a period of next 26 months and first high resolution pictures of
Pluto are expected to be transmitted by July 15th. The chances of
this event becoming successfully are very high as the chances of collision of
debris with probe is 1 in 10,000. This mission is of great relevance as it
would shed light on less know details of the planet, its composition, moons and
atmosphere but also it would help us in understanding the evolution of solar
system including the Earth.
History of Pluto
The year 2015 marks the 85th anniversary of
discovery of the dwarf planet Pluto.
In 1930 a 24 year old farmer-turned-astronomer Clyde Tombaugh
discovered the planet Pluto. The existence of a planet X in close proximity to
Neptune was suspected by the founder of Lowell Observatory, Percival Lowell on
the basis of perturbations experienced by the orbit of Neptune. The discovery
of the planet was announced on March 13th that coincided with the
birthday of Percival Lowell and with the discovery of the planet Uranus a
century and half earlier. Soon
suggestions were invited for naming of the new planet. The planet was
christened as Pluto after the Roman God of underworld as per suggestions of 11
year old Venetia Burney of Oxford, UK.
As a mark of respect, the dust counter built by students aboard NASA’s
New Horizons Space craft is named as Venetia.
In 1978 James Christy and Robert Harrington of the US Naval
Observatory at Flagstaff discovered Charon, the largest moon of Pluto. Charon
in Roman Mythology refers to the ferryman who brings souls of dead men to the
lair of Pluto. The moon which was visible as a bulge regularly appeared and
disappeared in the images as Pluto. Pluto and Charon seemed to orbit their
mutual centre of gravity and also because of the bigger size of Charon, these
two bodies were referred to as Binary Planets.
In 1988 astronomers aboard the Kuiper Airborne Observatory
made crucial observations about the atmosphere of Pluto. They indicated that
Pluto’s surface is covered by ice made of Methane, Nitrogen and Carbon monoxide.
These ices sublimate to form the thin atmosphere of Pluto.
In 2005 Hal Weaver and his colleagues at John Hopkins
Institute revealed the presence of two moons of Pluto, Nix and Hydra. Other
moons Kereberos and Styx were discovered in 2010 and 2011. Styx is faintest of
all moons.
On January 19th 2006 the New Horizons space craft,
the first probe to Pluto lifted off from the Cape Canaveral Air Force Base,
Florida
In August 2006, International Astronomical Union (IAU)
demoted Pluto to the status of dwarf planet as it failed to qualify the new
definition of a planet. It dictates that a planet must orbit around the sun, it
should be large enough for its gravity to shape it into a sphere and its must
have cleared its orbit of other similar-sized bodies. Pluto was relatively
small compared to the objects in its surrounding. It was just another object in
Kuiper belt and hence now the solar system is reduced from the earlier number
of nine to eight planets.
Following the reclassification of Pluto a section of scientific
community terribly opposed the new definition of the planet. Later in 2008, all
the trans-Neptunian dwarf bodies were classified under the category of Plutoids.
Also a new system of classification came into existence under the category of
dwarf planets which includes five planets in solar system: Pluto, Ceres,
Haumea, Makemake and Eris (Pluto destroyer).
Solar System is demarcated into three categories of planets-
the inner rocky planets (Mercury, Venus, Earth and Mars) the outer gas giants
(Jupiter, Saturn, Uranus and Neptune) and the ice dwarfs located on outer
fringes of the Solar system or the Kuiper belt region. These include Pluto and
Charon.
US Missions to Planets
The US has sent a space probe to each and every planet so far
and with this New Horizon mission its aims to complete the initial
reconnaissance of the solar system. In 1960 NASA has envisioned a plan of
sending probes to all the five planets. Missions were designed to take the
advantage of the celestial phenomenon of rare alignment of Jupiter, Saturn,
Uranus and Neptune (occurs once in every 175 years) and assisted flybys.
However due to highly constrained budget of NASA, the grand mission has been
reduced to missions Voyager 1 and Voyager 2. These missions have successfully
completed the flybys of the four gas giants. By 1989, Pluto was the only
bonafide planet left unexplored. However when Pluto was derecognised as a
planet in 2006, it meant that all planets were explored.
New Horizons Mission
Several programs like the Pluto fast flyby, Pluto Kuiper
Express were designed to study and understand the key characteristics of
Pluto’s atmosphere. But these were abandoned due to budgetary constraints. By
2001 New Horizons Mission was selected by the NASA’s New Frontier Program. Over
the next five years South West Research Institute (SRI) and John Hopkins Applied
Physics Laboratory built the spacecraft. Unlike the spacecrafts designed for
the inner solar system, this space craft had limited electronic activity. Since
it is destined to travel to the outer boundaries of the space the interior
paint and exterior blanket were designed to maximise heat retention in the
outer space. As it moved into realms farther from the Sun, the probe wasn’t
equipped with solar arrays. Instead it had built in Radio Isotope
Thermoelectric Generator (RTG) to provide power that can last through the launch
and Pluto-Charon encounter. Spacecraft carried the Plutonium-238 Oxide pellets
as fuel enclosed in the Iridium and Graphite shell. Hence the US Department of
Energy carried out several pre-launch tests to make sure that the launch
wouldn’t cause accidental contamination of the Earth’s atmosphere. Altogether
there are seven scientific instruments on board
Launch and Flybys
The New Horizons was scheduled for a launch on January 11th
2006 to allow for the gravity of Jupiter to assist a flyby. It soon missed the target and was the launch
was postponed to January 17th but was stalled due to high winds.
Second attempt on the next day was halted due to low clouds. Finally the probe,
hoisted by the Atlas V 551 variant lifted off majestically from the Cape
Canaveral Air Force Station, Florida on January 19th. During its course of flight it had an
incidental encounter with the asteroid 132524 APL in June 2006 from a distance
of 63, 297 miles followed by a Jovian (Jupiter and its moons) encounter in 2007
and finally with Pluto in 2015.
Accomplishments
These encounters acted as trial runs for the scientists at
ground station to use some instruments on board for making crucial observations
and test space craft’s ability to perform automated manoeuvres during planetary
flyby operations. Spacecraft was fitted with state-of-art instruments that
delivered good quality of data about the atmospheric conditions, structures and
composition of Jupiter clouds. It discovered debris from recent collisions
within Jupiter rings and searched for new rings and moons of Jupiter as well.
The probe was so meticulously designed that the gravity
assisted sling shot manoeuvre during the Jupiter flyby has accelerated probe
velocity to 53,000kmph relative to Sun. This shortened the probe’s journey to
Pluto by three years. Following close encounter with Jupiter the mission
command has decided to send the probe into a phase of hibernation which lasted
from February 2007 to December 2014. The probe was intermittently awakened by
the flight control team to keep systems operational. It crossed the Orbital
Boundary of Saturn in March 2008 and Uranus in March 2011.
In July 2014 during its non-hibernation phase the probe successfully
imaged Pluto and Charon separated by a distance of 2.4 AU (average orbital
distance of Earth from Sun) as two distinct bodies. In December 2014, the probe
was finally awakened by the NASA team and official operations began in January
2015. By February 2015, it captured the first images of Hydra and Nix and by
end of April the probe could capture images of Kerberos and Styx. In mid May
the probe delivered high resolution images of entire Plutonian system and
started making observations of Kuiper belt objects too. The probe encountered a
minor technical glitch on July 4th following which it entered into
safe mode. Soon it was rectified and it officially entered flyby mode by July 8th. The close approach flyby mode is destined for
July 14th when the New Horizons will pass by Pluto from a distance
of 12,500 kilometers and 28,800
kilometers from Charon. Since probes close approach to Charon is more than
twice the distance of Pluto the images of Charon will be twice as coarser than
those of Pluto.
Post Pluto Flyby
After the completion of the Pluto’s flyby operation, the
probe instead of entering into the orbit of dwarf planet will enter into the
deeper recesses of space into the Kuiper belt objects. It was planned that the
probe will identify the Kuiper Belt Objects (KBO). In this process if the probe
travels beyond orbital boundary of 55AU, communication system will become weak,
power supply too will run out and chances of assisted flybys would become
bleak. Scientists have identified three KBO in range of 43 and 44 AU for
plausible flybys but the final decision will be taken in August 2015.
Post flybys of KBO the probe is expected to join Voyager
probes on the outer realms of Solar System. Based on the Plutonium decay, the
probe is expected to be active till 2026. If it is healthy and robust like the
Voyagers by the time it reached Heliosphere, it can meet Heliopause in 2047 and
join Voyagers 1 and 2 floating in the interstellar space.
The mission is a glorious tribute to the scientific temper and
inquisitiveness of the human mind. It reflects the deep seated urge of the
humankind to explore, understand and study the intricacies of the celestial
World and the invincible space.
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