February 11, 2006

It is cold, distant and it may soon freeze and lose its atmosphere. Scientists are still debating whether Pluto deserves its status as a planet or it should be considered just a Kuiper Belt Object (KBO). It is also the least known planet in our solar system.

On Jan 19, Nasa launched a mission — the New Horizons — to Pluto. Scientists are banking on this venture to bring to light a lot of information regarding the planet and its moon, Charon. The mission to the farthest region of the solar system is the first such endeavour which will reveal many secrets of the zone, including the vast area called the Kuiper Belt.

This particular region is supposed to be a remnant of the formation of solar system, possessing a wealth of scientific information. The spacecraft, travelling through a huge distance of 5 billion kilometres, is expected to take just nine-and-a-half years and will make use of the “Jupiter gravity assist window”, which will provide it with the speed which it will need to reach Pluto.

Gravity assist involves a trajectory that passes close to a planetary body in order to gain energy from its gravitational field. In the case of the New Horizons, when the spacecraft will approach Jupiter, the planet’s gravity will pull it, speeding it up. If it hadn’t been for this, the spacecraft would have needed an additional three years to reach its destination.

The time-saving gravity assist that the spacecraft will utilize will open from mid-January to Feb 14. The New Horizons spacecraft, which is about the size of a grand piano, will encounter Jupiter after a year of its launch. It will take pictures as it goes along and take measurements as it speeds up and zooms off further on an eight-year-long journey.

“The New Horizons mission to Pluto completes our initial survey of the nine planets we believed comprised the solar system when we began the space age. In this sense, this mission truly marks the end of the beginning, and all of us look forward to receiving those first pictures of Pluto and Charon,” said Michael Griffin, the Nasa administrator. The pictures are expected to arrive in 2015.

“Everything we know about Pluto could basically fit on a postcard. We are truly going to a new frontier,” said the deputy associate minister for science, Colleen Hartman. Built by The Johns Hopkins University’s Applied Physics Laboratory, the spacecraft took ten years of research and development and an estimated $675 million in cost.

The wait

It has been a long and anxious wait for scientists for a mission to Pluto. The mysterious planet and the Kuiper Belt hold many answers to the puzzling question regarding the Solar System itself. Many missions were planned in the past, but failed mainly due to financial constraints.

Planetary scientist Alan Stern, the principal investigator for the New Horizons mission from the Southwest Research Institute in Colorado, is also keeping his fingers crossed. Stern believes that Pluto needs to be explored not just because it needs to be visited, but also because it happens to be the ninth discovered planet.

“I don’t know anybody who thinks that checking it off the list of planets is a good reason for going. We are going to Pluto to study the origins of the outer Solar System, to better understand the formation of binary planets, including the Earth-moon system, and to explore for the first time this different kind of planet — not a terrestrial planet and not a gas giant, but an ice dwarf,” said Stern. He added that these kinds of ice dwarves were more common in our solar system than gas giants and terrestrial planets.

Though it was previously thought that Pluto was a misfit in our solar system, given that its status as a planet was in doubt, it is now thought that it is our home planet that is the misfit, and not Pluto.

“It used to be said that Pluto is a misfit. But now we know that Earth is the misfit. This is the most populous class of planet in our solar system and we have never sent a mission to it,” remarked Alan Stern.

As Pluto completes its 248-year orbit around the Sun, researchers are of the opinion that it will not be long before its atmosphere freezes and collapses. The planet has been moving away from the Sun since 1989, when it came closest to the star. Scientists are also of the opinion that once its atmosphere freezes, it might not re-emerge for another 200 years. However, exactly when this ultimate freeze will happen is not known.

“Some people think it’s 20 years from now, and some think it’s five years from now. No one really knows when Pluto’s atmosphere will snow out and collapse,” said Stern. When the planet continues moving away from the Sun, its already frigid atmosphere will get even colder and the surface will be covered in thick layers of nitrogen-based snow. This, in turn, will hasten the process of the collapse of its atmosphere.

Scientists also believe that once the freezing process begins, it will accelerate extremely fast, so there is no saying how much time we actually have for studying the planet. According to Stern, his team is not sure if there even will be an atmosphere to study when the spacecraft reaches Pluto. He pointed out that “some models say that the collapse can be very sudden. It can happen in a matter of months”.

Picture perfect

The New Horizons spacecraft weighs almost 465 kilogrammes when it is fully fuelled and carries a host of scientific equipment, including a high resolution optical telescope, an ultraviolet spectrometer that will measure gas composition, a radio experiment for measuring atmospheric composition and temperature, a plasma sensing instrument that will measure the solar wind, and an instrument to measure the amount of dust that will hit the spacecraft on its journey. The combination spectrometer and colour camera will map the surface of the planet.

According to Richard Benzel, a professor at the Massachusetts Institute of Technology and a member of the New Horizons team, the cameras on the spacecraft will provide the best images of Pluto ever. The images will reveal surface erosion and craters, which are telltale signs of the planets past.

“We think the polar ice caps come and go seasonally. But is it just a few millimetres or is it tens of metres of ice that comes and goes? We can determine this by observing how much erosion there is on the surface. Is it heavily cratered, indicating that the surface is very old or does the seasonal process of ice movement erase the craters?” asked Benzal.

The only images that scientists have of Pluto at the present are the ones taken by the Hubble Space Telescope in the 1990s. Even after these images were significantly enhanced, they just showed dark patches at the equator and brighter regions, which are thought to be snow and ice on the poles.

The spacecraft will start the work of taking observations approximately four months after its initial encounter with Pluto. It will have its busiest day when it passes within 10,000 kilometres of the planet and 27,000 kilometres of its moon, Charon.

Eager scientists will have to wait nine months after this for the images and data to reach Earth through the Deep Space Network. It has been further planned that the tiny probe will go ahead to take a closer look at two selected Kuiper Belt Objects, provided it is in good health. This onward journey will take another three to five years.

Recently, quite precise data have come to light which relate to Pluto’s largest known moon, Charon. It has been suggested that there is no atmosphere on Charon. It is half the size of Pluto, with a diameter of 750-753 miles, which is 1,207 to 1, 212 kilometres.

The icy moon is estimated to comprise 50 per cent rock, and strangely, it is better known than its host planet. It is also presumed by scientists that the creation of Charon occurred when an impact took place on Pluto.

According to research published on Jan 5 in the journal Nature, the main theory regarding the formation of Pluto and Charon, and two more moons discovered recently, is that the bodies collided with each other and the system evolved out of their remains.

“Our observations show that there is no substantial atmosphere on Charon, which is consistent with an impact formation scenario,” says Amanda Gibbs, a researcher at MIT. Gibbs authors one of the papers in the journal.

As scientists and astronomers wait for answers regarding this cold, distant and evasive member of our solar system, let us hope that Pluto discloses its secrets when the spacecraft reaches its destination. Also, the uniquely strange Kuiper Belt might have many interesting objects in its folds. Mankind is expected to move a step forward in its understanding of the universe.

The writer fatimas@cyber.net.pk is a freelance contributor