Is pluto made of comets?
A new revelation about the dwarf planet has left astronomers once again questioning its identity
Recent research suggests that there's much more to the dwarf planet than meets the eye
The scientific community has always had a problem with Pluto’s status. the icy world's demotion to a dwarf planet in 2006 still burns strong for some, whilst others still refuse to even accept its new position. the identity crisis has now resurfaced with a new theory that claims that it could actually be roughly a billion comets all squished together. If this theory is proven true then this is just another nail in the coffin for Pluto and the argument to allow it to join the 'fully-fledged' planetary family once again.
there were several factors that knocked Pluto from its planetary pedestal, but the instigator was the uprising discoveries of other dwarf planets such as eris, and other Kuiper Belt objects (KBos). the Kuiper Belt is the region beyond the orbit of Neptune from about 30 Astronomical Units (AU) to 55 AU, with one AU being the distance between the Sun and earth. the objects in this region are thought to be the remnants from the formation of our Solar System around 4.6 billion years ago.
“This work helps us to understand the origin and evolution of Pluto, which is a supreme challenge at over 30 AU,” Dr Christopher Glein of the Southwest Research Institute’s Space Science and Engineering Division in San Antonio, Texas, United States tells
All About Space. “This is important for learning about the conditions of planetary formation in the early outer Solar System, and the processes that have modified the initial composition to produce the Pluto we all know and love today.”
The most widely accepted theory for the formation of the planets is the Nebular Hypothesis; they formed from a spinning cloud of dust and gas surrounding the young Sun. The spinning motion of the cloud caused it to get thinner and flatten (like spinning pizza dough) to form a protoplanetary disc – the birthplace of the planets. Here, microscopic grains of material began to collide and stick together, and they increased in size until they developed a significant enough gravitational force to attract even more and more surrounding material. These are the building blocks of our planets, and are known as planetesimals.
This began an era of collisions and continuous smashing which formed the Solar System we see today. It is this period of madness that astronomers wish they could jump into a time machine to go back and see, as it would answer so many bewildering questions about the Solar
System and, for the sake of this argument, Pluto. Alas, technology is not quite capable of that, so all astronomers have to go on is the data that is laid out in front of them.
Pluto is a highly intriguing figure in the Solar System, and has caused much controversy; it still remains an enigma. On the 14
July 2015, NASA’s
New Horizons spacecraft made the near ten-year journey, over five billion kilometres
(three billion miles) to Pluto. In a flyby that got as close as
12,500 kilometres (7,767 miles) to the surface of the icy dwarf planet, New Horizons’ incredible suite of instruments gathered as much data as possible before journeying further into the Kuiper Belt region.
During this period, New Horizons saw a plethora of exciting surface and atmospheric attributes that had scientists bouncing off the walls. “We [the New Horizons team] got there and we found flowing glaciers and young terrains on a vast scale, which were created yesterday. We found evidence of mass motion of atmospheric waves. We found volcanoes that were geologically young on the surface, known as cryovolcanoes. Any one of these things alone would have been a headline, but to see them all was just stunning, and really, I don’t think anyone understands how Pluto does this,” Dr Alan Stern, principal investigator of the New Horizons mission, tells All About Space. “But it’s taught us now to expect that other small planets in the Kuiper Belt are likely to also be geologically active after long periods and that’s a fundamental paradigm shift in the field of planetary science.”
It is these discoveries that have completely changed the outlook on Pluto and the Kuiper Belt region. It has made scientists such as Glein think outside the box, particularly about their formation. The Kuiper Belt is not only home to dwarf planets and other such Kuiper Belt Objects, it also accommodates many comets. These distant balls of ices and dust — hence their nickname ‘dirty snowballs’ — have been considered as the possible building blocks for planets for a while among members of the astronomical community.
In August 2014, the European Space Agency (ESA) was successful in having
“Without New Horizons, we would have no idea how much nitrogen is on Pluto. Without Rosetta, we wouldn’t know how much nitrogen is in comets”
Dr Christopher Glein
the first human-made spacecraft visit one of these dirty snowballs. The Rosetta orbiter rendezvoused with Comet 67P/Churyumov-Gerasimenko and, three months later, its Philae lander touched ground on comet terrain for the first time in history. The science gathered from this extraordinary mission again brought in a new era of understanding when it comes to these mysterious mini-worlds. Among the many discoveries about comets was one that bears great interest to Glein’s research, and that is the detection of molecular nitrogen (N2) in the comet’s water by Rosetta.
These two missions are what have paved the way to this new theory that Pluto was initially formed from the culmination of a billion comets. “This research would have been impossible without both of these missions. Without New Horizons, we would have no idea how much nitrogen is on Pluto. Without Rosetta, we wouldn’t know how much nitrogen is in any comets,” explains Glein.
The main area of investigation was the western lobe of Pluto’s famous ‘heart’, formally known as Tombaugh Regio. When New Horizons flew past this lobe, in the Sputnik Planitia region, it found that this bright and icy plain is relatively young at no more than 100 million years old, due to the lack of craters caused by meteorite impacts. This plain is covered in a freezing glacial sheet of nitrogenrich ices, with temperatures as low as -240 degrees Celsius (-400 degrees Fahrenheit) on the surface of Pluto. In an attempt to gain insight into the dwarf planet’s past, Glein and his collaborators estimated the formation of Pluto in its earlier years based on models using nitrogen-based data of its planetary and atmospheric chemical conditions.
Two main theories arose from this work: one called the ‘cometary model’ and other the ‘solar model’. These two models are largely based upon exploring the possibility of Pluto forming from building blocks with two different chemical compositions. The cometary model suggests that these building blocks had a nitrogen abundance similar to a comet, which is compared to the results from ESA’s Rosetta mission at Comet 67P. Playing the devil’s advocate is the solar model, which suggests Pluto formed from cold ices that would have had a chemical composition similar to the Sun.
“The chief difference between them is the formation temperature of the building blocks,” says Glein. “Because the solar model is richer in nitrogen, a lower formation temperature is required. [It’s] probably closer to 20 degrees Kelvin [-253 degrees Celsius] for the solar model, while closer to 30 degrees Kelvin for the cometary model.”
Generally, it is safe to assume that the closer to the Sun an object is, the warmer the environment is. This is why, based on Glein’s comments, it is inferred that the cometary model suggests
Pluto was most probably formed closer to the
Sun compared to the solar model. Although it’s impossible to predict exactly what happened in either scenario, the solar model predicts Pluto formed from a planetesimal in the outer region of the early Solar System. This planetesimal accreted enough surrounding material, including comets, to develop into the Pluto we see today.
The other theory that is being suggested, and the more likely theory according to in-depth analysis, is that roughly a billion comets bundled together closer to the Sun. Being closer to the Sun also means that some event had to throw it out into the Kuiper Belt where it resides now. This could have been from a planetary migration that scattered
Pluto, among other objects, into the Kuiper Belt, or there could have been a collision that sent the dwarf planet flying outward. “If my hypothesis is correct, then the widely suspected, but unconfirmed notion of comets as building blocks of the outer Solar System would be supported in an analogous fashion to the role of meteorites and asteroids in the inner Solar System,” explains Glein.
This theory has now instigated an expedition that hopes to find the first evidence for comets being actual building blocks to planets. If scientists could make a clear link between the two, with Pluto being the dwarf planet ‘bridge’ between them, then scientists would have more pieces to the puzzle that is our Solar System’s formation and evolution. However, this is just the tip of the iceberg. A lot more work has to be done before scientists can make clear definitive statements about Pluto’s – and other planets’ – beginnings.
When it comes to Pluto, Stern believes an orbiter like Rosetta would bring the valuable information about Pluto which astronomers’ hearts desire. “Unless we go back [to Pluto] with instrumentation that can penetrate the ice with radars, see how deep it is and determine the surface images better with having high-resolution cameras and spectrometers… unless we bring more instruments there and watch the time variability, we are never going to figure this place out. So we need an orbiter,” Stern explains.
Although Stern does have an eye set on going back to Pluto for further exploration, he has another eye set on New Horizons’ next target, KBO (486958) 2014 MU69, given the nickname ‘Ultima Thule’ by NASA. Due to arrive at Ultima Thule on New Year’s Day of 2019, New Horizons will fire up its instrumental suite again to observe a frozen block of rock leftover from the Solar System’s formation hidden in its darkest, deepest realm. When asked if Ultima Thule could make a possible impact on this research, Glein replies, “It could. I will be eager to see if New Horizons finds any nitrogen ice on that body. What’s intriguing is that Ultima is intermediate in size between comets and
Pluto, so perhaps it can serve as a missing link between them. This could help to clarify their compositional relationships.”
If the Solar System is the human body, then
Pluto is a human cell. KBOs such as Ultima Thule are a strand of DNA, and comets are the atoms that constitute everything. The body of the Solar System seems to be the same at first glance, but it seems to be ever-changing with whatever new data and analyses come our way. With new missions being commissioned and new targets acquired, Pluto’s past will become more clear. For now we still have to ask, is Pluto really a planet?
“Unless we bring more instruments there, we are never going to figure this place out. We need an orbiter”
Dr Alan Stern