Between the comets

Siding Spring (circled) passing Mars (the glowing object, bottom left) as seen via the SLOOH telescope at the Pontificia Universidad Católica De Chile (PUC) Chile (images via SLOOH live feed, October 19th, 2014)
Siding Spring (circled) passing Mars (the glowing object, bottom left) as seen via the SLOOH telescope at the Pontificia Universidad Católica De Chile (PUC) – image via SLOOH live feed, October 19th, 2014

It’s now a week since Siding Spring passed by Mars as it hurtled through the inner solar system for what might be the very first time. As I reported on the day of the comet’s flyby, C/2013 A1 – to give the comet its official designation – passed by Mars at a distance of around 136,000km (85,000 miles) and at a speed of some 56 kilometres (35 miles) per second. Since then, the comet reached perihelion – the point of its closest approach to the Sun (Saturday, October 25th, 2014), and it is now on its way back out of the solar system, travelling “up” and out of the plane of the ecliptic as it does so.

It will not be back this way for at least a million years.

Despite some getting their knickers in something of a knot over video footage apparently showing an “explosion”/ “electromagnetic pulse” in the Martian atmosphere around the time of the comet’s closest approach to Mars. In particular, the video footage – some 75 images captured by amateur astronomer Fritz Helmut Hemmerich M.D., captured between 21:00 and 22:00 UT on October 19th, from an altitude of some 1200 metres in Tenerife, have had proponents of the “electric universe” theory (aka Plasma Cosmology) in something of a tizzy.

Quite what caused the artefact in Dr. Hemmerich’s images is unclear – but lens flare cannot be entirely ruled-out. Given that within hours of the comment’s passage the various orbital vehicles around Mars started popping-up and reporting their status, it would appear highly unlikely that the artefact was anything to do with some kind of massive electrical discharge within the Martian atmosphere, simply because it is not unreasonable to suppose had this been the case, it would have adversely affected at least some of the craft.

Siding Spring passing Mars, October 19th, 2014 (image: Scott Ferguson, Florida, USA)
Siding Spring passing Mars, October 19th, 2014 (image: Scott Ferguson, Florida, USA)

As it is, all of NASA’s vehicles reported absolutely no ill effects from the comet’s passage or as a result of the period of “peak dust flux” when they were expected to be at the greatest risk from the passage of very high velocity dust particles (travelling at tens of kilometres per second), and all were back in full operation within hours of the comet’s passage past Mars, as were both India’s MOM and Europe’s Mars Express. NASA’s Mars Reconnaissance Orbiter (MRO) in particular remained in contact with Earth throughout the time the comet passed by Mars and reported nothing to suggest the Tenerife images were showing anything of major significance occurring around Mars at the time of the flyby.

Currently, all of NASA’s orbital assets are continuing to study the comet and how dust and debris ejected from it has affected the Martian atmosphere, although it is expected to be several more days before the data being returned has been analysed and assessed.

In the meantime, on Friday, October 24th, and in a timely move, the European Space Agency reminded the world of another cometary encounter that is taking place. This was via the public premier of Ambition, a short film by Tomek Bagiński, starring Aidan Gillen (“Petyr Baelish” in Game of Thrones) and Aisling Franciosi (“Katie” in The Fall).

The film takes a unique look at the decade-long Rosetta mission, which is only now commencing its primary mission to observe a comet at very close quarters, including landing a robot vehicle on the surface of the comet on November 12th, 2014.

Rosetta and Philae (image: European Space Agency)
Rosetta and Philae (image: European Space Agency)

Launched on March 2nd, 2004, ESA’s Rosetta vehicle rendezvous with its intended target, the comet Churyumov–Gerasimenko (officially catalogued as 67P/C-G) on August 6th, 2014, ready to commence the most detailed study – lasting 17 months – of a comet as it makes its inward approach to the Sun and then swings around it.

67P/C-G is a short-period comet originating in the Kuiper belt, and has an orbital period of 6.45 years. Even so, the mission to rendezvous with it was long and complicated, requiring two flybys of Earth in March 2005 and November 2007, with a very close flyby of Mars ( at just 250 kilometres / 160 miles above the planet) between them, in February 2007. These boosted the vehicle’s velocity and adjusted its course so that it could rendezvous with 67P/C-G while the latter was still far enough from the sun that it hadn’t formed a significant tail / coma due to outgassing.

Ambition serves as a means of emphasising the mission’s importance and on humankind’s quest to understand the cosmos around us, and how we came to be. At the same time, it is seen as adding a “human dimension” to both the mission and our drive to explore and understand the solar system.

Having rendezvoused with 67P/C-G at the start of August 2014, Rosetta spent a further month refining its orbit and mapping the surface of the comet, which had until that point been entirely unknown, in order to find a suitable landing point fo the smaller robot vehicle.

On November 12th, this vehicle, called Philae, will detach from Rosetta and use a small thrust from a single small motor to drift down to the surface of the comet over a period of some seven hours. Even then, “landing” is something of a misnomer; the gravity well of the comet is so negligible that the 100 kg probe could actually bounce right off it at first contact.

To prevent this, Philae will use a combination of “harpoons” and drills mounted in its landing legs to anchor itself on the comet at the time of its touchdown. If successful, this will allow the probe to engage in its own studies of the comet, and assists Rosetta in its work through shared experiments.

Rosetta and Philae will accompany 67P/C-G around the Sun throughout the rest of 2014 and 2015, studying it with a battery of some 19 instruments, allowing the comet to be comprehensively studied, including how it enters into its period of peak activity as it falls towards the Sun (reaching perihelion in August 2015) and is increasingly warmed by solar heat and the solar wind.

Of particular interest to scientists is the search for organic compounds, molecules that are rich in carbon, hydrogen, oxygen, and nitrogen. These are the elements which make up nucleic and amino acids, the building blocks of life. As Ambition indicates, it is theorised that comets may well have been responsible for delivering huge amounts of water to Earth in the millennia after the inner solar system was formed (and to Venus and Mars as well). They may also have been responsible for seeding the Earth with organic molecules; thus by gathering samples of the comet’s nucleus and coma cloud of gas and dust, Rosetta and Philae may help us understand the role comets may actually have played in the beginnings of life here on Earth (or indeed, perhaps on Mars).

Just as they may well have given rise to life on Earth, comets (and asteroids) have also potentially brought elements of it to an end, perhaps most notably 65-66 million years ago with the K-Pg event That event ended the reign of the dinosaurs and was thought to have been caused by at least one impact from an object some 10 km (6 miles) across, which may have been an asteroid or comet fragment. We’ve since seen impacts still occur – particularly in 1994 with the Shoemaker-Levy 9 event on Jupiter (and of course there has been the famous Tunguska event, which saw a 30 megaton “air burst” over Tunguska, Siberia in 1908 caused by a cometary or asteroid fragment).

Comet 67P/C-G images to scale with comet Siding Spring and the city of Los Angeles
Comet 67P/C-G images to scale with comet Siding Spring and the city of Los Angeles

Measuring some 4.1 by 4.5 km, 67P/C-G does not present any threat to the Earth. It is, however, a reminder that there are some very big pieces of rock within the solar system, any one of which could wreak havoc were it strike this planet. And while I am not a fatalist, and prefer to think of the more positive reasons for extending our reach into space, it is nevertheless as a good a reason as any for humankind to attempt to step beyond this world, and to colonise those that are within our reach – such as Mars.


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