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Obituary of a planet
ON Aug 24, Pluto — the youngest major object in the solar system — was declared dead as a planet. The death was caused by a lethal resolution passed by a group of astronomers at a meeting of the International Astronomical Union in Prague, not too far from the observatory where two of history’s greatest astronomers, Tycho Brahe and Johannes Kepler, had worked more than 300 years ago.
Pluto was known for only 76 years as a planet by human beings — a large group of warring but self-styled “intelligent beings” who live on the third planet in a rather obscure solar system. This solar system was until 1995 referred to as the solar system, giving the humans an aura of fragile exclusivity over intelligence in a universe filled with trillions of stars.
Pluto’s inauspicious and somewhat sudden death as a planet was reminiscent of its accidental, if not serendipitous, discovery on Feb 18, 1930 by Clyde Tombaugh — a 24-year-old farm boy from Kansas who had immense interest in astronomy. By the age of 20, Tombaugh had built several telescopes.
At the age of 23, he was invited by Percival Lowell — a Harvard-educated mathematician who was a diplomat before he became interested in astronomy at the age of 40. Lowell had predicted in 1915 that the gravitational influence of a very large planet beyond Neptune could explain the irregularities in the motion of Uranus that could not be accounted for by Neptune.
Neptune had been discovered in the same way in 1846 after two astronomers had predicted the presence of a large planet beyond Uranus a year earlier in order to explain the perturbation in its motion as envisaged by Newton’s laws of gravitation. Lowell commissioned Tombaugh to take pictures for a new observatory he had built in Flagstaff, Arizona.
Tombaugh initially did not have much interest in discovering planets, but Percival Lowell sure did. He asked Tombaugh to photograph the entire sky with a special camera attached to the observatory’s 13-inch telescope that took two pictures of the same part of the sky at regular intervals to detect any moving object.
Tombaugh’s job was to photograph the entire sky, a small portion at a time — a job that, according to Lowell’s estimate, would take at least 20 years. Largely for this reason, no professional astronomer wanted to devote his life to something that might not yield fruit even after two decades of hard work.
Tombaugh (whose ashes are being carried by a space probe, New Horizon, to the ex-planet) found Pluto where Neptune should have been according to Bode-Titius Law, a mathematical sequence that somehow holds true for the distance from Sun of all the planets with adjustment for asteroid belt.
After the initial euphoria had subsided, Pluto struggled to find a place distinct from the two established planetary families in the solar system: Inner and Jovian. Despite being physically closer to the Jovian planets, it clearly did not belong in that family of large gaseous planets.
The newly discovered planet’s name was coined by an 11-year-old English girl named Venetia Burney, who had suggested the name to her grandfather who, in turn, suggested it to a friend who was one of the astronomers looking for an appropriate name for the newly discovered planet. Venetia had named the new planet after the Greek mythology’s god of the underworld who could render himself invisible, an appropriate name for the barely visible farthest planet.
However, the name was chosen by Lowell Observatory on May 1, 1930 in part for another reason. The first two letters in “Pluto” are the initials of Percival Lowell, the man who had first predicted its existence.
An inauspicious life
On the cosmic timeframe, Pluto’s existence as a planet was, at best, ephemeral. Its life as a planet was shrouded in controversy from the beginning. It had been hastily given planetary status even though there wasn’t much information available about it.
Even today very little is known about it. It was initially considered to be another giant planet. It was later found to be smaller than our moon and its surface area was found to be smaller than that of the US. Its orbit also turned out to be inclined 17 degrees to the plane of the orbit of other planets. In later years it was found to have a very odd orbital motion around the Sun. It took 248 earth-years to complete one revolution around the Sun and during this time it was actually closer to the Sun than Neptune for more than 20 years, in effect it temporarily displaced Neptune as the 8th planet. Obviously, no serious astronomer was amused with this rather odd orbit and trajectory.
To be fair, Pluto’s discovery proved to be popular among the public as well as among scientists. The radioactive element Plutonium (atomic weight 94) was named after Pluto when it was discovered by Nobel laureate Glenn Seaborg and his team in 1940.
It only seemed logical to him and his team to name their discovery after Pluto because earlier that year another team of physicists had found the first trans-uranium element and had named it Neptunium (atomic weight 93) after the planet Neptune since it followed Uranium (atomic weight 92 and the last element on the periodic table to occur naturally on Earth).
After the initial euphoria had subsided, Pluto struggled to find a place distinct from the two established planetary families in the solar system: Inner and Jovian. Despite being physically closer to the Jovian planets, it clearly did not belong in that family of large gaseous planets (Jupiter, Saturn, Uranus and Neptune). Pluto’s size was closer to the inner planets (Mercury, Venus, Earth and Mars) but was separated by distance.
And as long as it was alone, it did not qualify to be a member of a new family of planets. One member does not a family make. Some astronomer even debated the possibility that Pluto was a lost moon of Neptune due to the similarity in size with Triton, the only known moon of Neptune at the time.Thus, Pluto only briefly attained the status of a “true” planet. For one reason or the other the sword of Damocles always hung on its status. In 1950, a Dutch astronomer, Jan Oort, presented a hypothesis that the solar system was surrounded by a large number (probably 6 trillion) of small icy bodies (known as Oort’s cloud) that orbit the Sun at about 50,000 times the distance of Earth to the Sun.
Shortly thereafter, in 1951 a Dutch-American astronomer Gerrit Kuiper suggested that comets originated in another belt of object that resided just outside the orbit of Neptune about 30 to 50 times the distance of Earth to the Sun. These trans-neptunium objects came to be known as the Kuiper Belt Objects (or simply KBOs).
Many scientists wondered whether Pluto was a KBO instead of a planet. However, no KBO was discovered for 40 years and they existed only in theory. In 1992, scientists discovered a body slightly larger than Pluto that was so far from the Sun that it appeared to be a KBO.
In later years several hundred such bodies were detected in the same region, one of them larger than Pluto. Since Pluto seemed to share many characteristics with these newly discovered bodies, it now seemed to confirm doubts that Pluto was a KBO that had been captured in a smaller orbit around the Sun by Neptune’s gravity.
Pluto’s status as a planet was strengthened slightly after the discovery in 1978 of a rather large satellite, Charon, which orbited it. All the known planets except Mercury and Venus had satellites around them and Ceres did not. Ironically, however, Charon’s discovery also dealt fatal blows to Pluto’s status as a planet after scientists realised that Charon’s diameter was about half that of Pluto’s.
The centre of gravity of the Pluto-Charon system was found to be outside Pluto’s surface. Charon was rather too big to be Pluto’s satellite. Pluto and Charon were either double planets or not planets at all. Indeed, the discovery of two other bodies to be a part of the Pluto-Charon system only added to Pluto’s state of limbo.
Soon after Charon’s discovery, astronomers discovered many double asteroids and double KBOs. These discoveries, many scientists argued, proved that Pluto and Charon were really Kuiper Belt Objects that had been captured by Neptune’s gravity and had wandered away from their original orbit inside the Kuiper Belt.
The term “planet” was originally used by ancient Greeks to define stars that were wanderers since they moved in the sky instead of remaining motionless like other stars. Two thousand years later, scientists somewhat paradoxically argued that Pluto was not a planet as it had wandered away from the Kuiper Belt.
A predictable death
In the end, Pluto’s death as a planet was swift. To many, it came as a surprise. To others, it came in the true panoply of justice. Pluto’s demise as a planet had been anticipated within the professional circles for some time.
In an irony almost as large as its orbit around the Sun, Pluto was discovered by an amateur astronomer, named by an 11-year-old girl and its life as a planet was terminated by professional astronomers. If there is any solace in Pluto’s death as a planet, it is that it has been demoted to a newly created family of solar system objects called dwarf planets.
Pluto no longer stands alone — confused, with no sense of belonging to two previously known families of planets. Even in its death as a planet, Pluto stands defiant. Many astronomers wanted Pluto to be buried in the Kuiper Belt, along with thousands of other known KBOs far from Earth.In the end, however, Pluto’s death as a planet gave rise to a new class of planets. Pluto, like the mythical Phoenix, arose from its ashes — more sure of where it belongs. It has finally found the family it belongs to. And that family is young and growing.
Its members may not be as large as the members of the Jovian family of large outer planets. They may not be as diverse as the members of inner planets. But one thing is sure. The potential number of members of this family is huge.
Dwarf planets may be small individually, but collectively their family is a large one. Even if its new family resides in the cold darkness of the outer reaches of the solar system, Pluto, unlike its mythological namesake, cannot render itself invisible.
The author works as a credit specialist in New York
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