The idea of a new planet, the so-called Planet 9, has captured the attention of scientists and the public alike. Likewise, the debate about Pluto’s planetary status inspires support of its new-found “dwarf planet” title in some, but the passionate voices of hearty displeasure in its demotion by others.
The essence of both these topics presents scientists with a unique opportunity – to understand a fundamental, scientific aspect of our Solar System while at the same engaging with a very willing public, eager to understand and contribute.
The possible existence of Planet 9 takes us to the far edges of the Solar System, way beyond the orbit of Neptune to a region known as the Kuiper belt. And citizen scientists can go there too, by joining the Planet 9 search and Stargazing Live.
Why we think Planet 9 exists
Pluto was kicked out of the planet club because it failed one of the definitions of a planet - it had not cleared its path around the Sun. In other words, Pluto is not its own boss.
However, Pluto is not the only dwarf planet - four other confirmed dwarf planets exist, along with multiple candidate and potential dwarf planets, including the notorious Eris, aka “Pluto Killer”. These all lurk in the outer edges of our Solar System, and have been discovered in recent times.
The location and movement of dwarf planets in the Kuiper belt cannot be explained by the objects we know in our Solar System - there must be something else we have not seen. This is where the idea of Planet 9 began, in 2014.
Most of the known Kuiper belt objects tend to lie on one side of the Solar System with orbit at an incline to the plane of our Solar System (where the planets lie). Scientists have theorised that a source of gravity exists, causing this inclined orbit phenomenon – Planet 9. Even new discoveries, objects discovered after the prediction of Planet 9 such as 2015 RR245, also seem to fit within the proposed existence of Planet 9.
The search for Planet 9
Still in 2017, we know very little about Planet 9.
In order for Planet 9 to affect the dynamics of the Kuiper Belt, it must exert enough gravitational influence over these objects. This implies either a small object close in the Solar System, or a more massive object further out. This range of possible existence means it can be anything from an object ten times the mass and four times the radius of Earth, to a “Super-Earth” – objects we regularly find around other star systems.
The chance to do something no human has done in more than 150 years – discover a new planet – has captured the enthusiasm of astronomers across the world. Since the clear prediction of Planet 9 was first made in 2016, a massive effort has been undertaken to find (or refine) where and what Planet 9 may be.
Astronomers are able to predict the sorts of physical measurements Planet 9 would have. For example, it is proposed to be far out, between 300 and 900AU (300-900 times the distance the Earth is from the Sun), and to appear to be 100-1,000 times fainter in an image than Pluto.
Modern astronomy has been revolutionised by all-sky surveys, such as the Sloan Digital Sky Survey (SDSS) and the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS). These surveys digitally cover the sky, cataloguing billions of objects that astronomers can use for their science.
These surveys means that the sky has been searched in great detail before the Planet 9 prediction. However, one fatal flaw exists – the lack of coverage in the Southern Hemisphere.
SkyMapper – The Southern Sky Survey
SkyMapper is a 1.35 metre telescope based at the Australian National University’s Siding Spring Observatory, and is being used to conduct the first digital survey of the entire southern sky - the same sky that has not been combed over for Planet 9.
SkyMapper was designed to fill this void, starting the Southern Sky Survey in 2013. However, it was built with a feature that makes it perfect for finding Planet 9 – repeatedly imaging the same patches of sky.
By imaging an area of sky multiple times, we can detect things that move or change – things like Planet 9. But it would mean looking through hundreds of thousands of images.
Citizen science to find Planet 9
Sifting through hundreds of thousands of images is a tedious task. A computer algorithm could be written to sift through the images, flagging potential objects for further investigation. However, with the huge parameter space of how and what Planet 9 is, it does not compare to the efficiency of humans.
Citizen science – the relative new field pioneered by groups like Zooniverse which has bridged the gap between scientific research and public engagement – is the answer. Citizen science recruits interested people to contribute to real science questions, like finding Planet 9.
By making the data accessible, members of the public with relatively no background and no special equipment (other than a computer) can participate in finding Planet 9.
With the launch of planet9search.org, members of the public have sifted through nearly 120,000 images in under three days – a task that would take one PhD student working continuously 4 years to do.
An example of an image in this project is provided below.
Engaging the public for help
In fact, the discovery of Neptune followed a very similar path as that underway with Planet 9. Urbain Le Verrier showed in 1845 that the irregularities in Uranus’ orbit could be explained by an object like Neptune – both in its location and mass. Upon hearing this news, a massive search was undertaken, with the discovery of Neptune coming just a year later.
Astronomy has clashed head on with the public in the past. Galileo, the founder of modern astronomy, not only revolutionised our idea of the Solar System and the Universe, but did so in the face of harsh backlash of society and the Catholic Church.
Now, the public has a hunger for astronomy that is unmatched in other areas of science. And it’s an opportunity we, as scientists, must embrace.
Involving the public means we can show the scientific process in action. We can show that sometimes not having a result means we are testing the hypothesis, informing it, and then refining it – the essence of science. We can share the triumphs and tribulations. We can share the knowledge.
In the end, maybe we will share the discovery of a new planet in our Solar System, Planet 9.