Across North America, Europe and Japan, skywatchers will be out in force this weekend with high hopes of catching a never-before-seen meteor shower. Predicted to peak this Saturday, May 24, the shower is centred within the little-known northern constellation of Camelopardalis (the giraffe).
Unfortunately this section of sky is not visible from Australia. In fact, it lies very close to the northern hemisphere’s pole star, Polaris, and the famed Big Dipper, all of which are inaccessible from our location in the southern hemisphere.
But while Australians may not be able to see the shower first hand, if it occurs as predicted it will be a fantastic illustration of the dynamic and ever changing nature of our solar system, and a stark reminder that Earth continues to be bombarded by debris left over from the formation of the planets, more than 4.5 billion years ago.
Meteors throughout history
There are records of meteor showers dating back thousands of years. The most detailed and precise observations come from China, as astronomers were ordered to watch the night sky to glean any omens related to their Emperor’s reign.
Closer to home, meteors feature prominently in the oral traditions of Indigenous Australians, including the Boorong from north-west Victoria who observed the annual Lyrids meteor shower as the Mallee fowl Neilloan building her nesting mound.
But our modern understanding of meteor showers took form relatively recently. During the early hours of November 13, 1833 hundreds of thousands of meteors were seen coming from the constellation of Leo (the lion). This captivating event, a Leonid meteor storm, marked the birth of modern meteor astronomy.
But being able to predict a potential future meteor shower, such as the Camelopardalids, shows how knowledge of solar system dynamics along with computational modelling has rapidly increased over the past few decades.
And much of this new work owes a large debt to the Leonids, with researchers first successfully predicting storm activity in 1999, 2001 and 2002.
Comets – the parents of meteor showers
Among the vast array of debris left behind from the solar system’s formation, the comets are perhaps the most famed and often the most spectacular.
Though both comets and meteors have been seen since man first gazed skywards, the link between meteors and comets was not conclusively demonstrated until 1866. In that year, the great Italian astronomer Giovanni Schiaparelli showed that the orbits of Perseid meteors were almost identical to that of a bright comet that was visible in late 1861 and early 1862.
The revelation that the comet, now known as 109P/Swift-Tuttle, is the parent of the Perseid meteor shower led a renaissance in meteor astronomy, and soon many of the major showers had been firmly linked with their parent comets.
At the heart of every comet is a small object known as the nucleus. Typically tens of metres to tens of kilometres across, the nucleus consists of volatile material (or ices) and dust – in other words, a dirty snowball.
These snowballs move around the sun on highly elliptical orbits and spend most of their lives in cold storage, in the frigid depths of the solar system. But as they swing towards perihelion (their closest approach to the sun), the icy material on their surface heats up and sublimes, turning to gas and jetting off into space. As gas vents from the comet’s surface, dust is carried along with it to be ejected from the comet.
The dust slowly spreads out along the comet’s orbit, both ahead and behind it in space, but continues to follow essentially the same path. Orbit upon orbit, perihelion passage after perihelion passage, the comet lays down new dust trails, which gradually diffuse around its orbit to form a closed “tube” of material.
When Earth passes through one of these tubes of dust, the grains ejected by the comet crash into our atmosphere and a meteor shower is born.
The parent comet of the potential Camelopardalids meteor shower is 209P/LINEAR – a very faint and unremarkable object, as comets go.
When it was discovered by the Lincoln Near-Earth Asteroid Research project back in 2004, it was initially thought to be an asteroid. Soon afterward, though, famed Australian comet hunter Rob McNaught observed it to have a coma (a nebulous envelope around the comet’s nucleus) and it was added to the ever-growing catalogue of short-period comets.
Comet 209P/LINEAR currently orbits the sun every 5.1 years, on an orbit that crosses that of the Earth, which can bring it very close to our planet.
Tomorrow, Earth is expected to pass through several streams of debris ejected from the comet during its perihelion passages between 1798 and 1979.
The first predictions of a possible Camelopardalids outburst were made by Peter Jenniskens, a world expert for discovering new meteor showers and predicting otherwise unexpected outbursts.
Jenniskens has a storied history of meteor shower prediction, and has catalogued the prospects for future showers in his fantastic textbook Meteor Showers and their Parent Comets.
The most recent Camelopardalids study, a suite of numerical simulations published in the journal Monthly Notices of the Royal Astronomical Society, estimates that the meteor shower will peak during the early hours of May 24 for North America and that the shower could remain active for a few hours. It’s also likely that intense activity might occur on much shorter timescales, should the Earth chance to encounter a particularly dense trail of material.
What’s more, in their modelling, the researchers found that the dust left behind by the comet is dominated by large grains and could therefore result in bright meteors.
Fortunately for Australians, many groups will be covering the event live – such as Slooh and the Virtual Telescope Project. Even better, the broadcasts will begin at the reasonable hour of 1pm and 3:30pm AEST respectively, on Saturday afternoon.
Sites such as spaceweather.com also have information on major meteor showers and cometary apparitions and the International Meteor Organisation publishes an annual meteor calender so you can find out whether any showers are visible on any given night of the year.
A word of caution
Throughout history, meteor showers have been hard to predict. After the fizzle of the 1899 Leonid meteor shower, American astronomer Charles Olivier famously wrote that it was the “worst blow ever suffered by astronomy in the eyes of the public”.
Calculations have certainly improved since then, but for the Camelopardalids the main unknown is how active the comet might have been all those years ago. It’s barely active now – and perhaps has always been that way – so there might simply be no debris for the Earth to encounter.
On the other hand, the comet might be spent now because it was more active in the past (which is certainly feasible), so a spectacular meteor outburst, with hundreds of meteors per hour, may radiate from the northern sky.
Come Saturday, one thing is certain. Whatever the true activity of the Camelopardalids, astronomers will definitely learn something new and exciting about the recent history of comet 209P/LINEAR.