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Collision Course

Comet McNaught

Comet McNaught photographed from Perth revealing why it was sometimes called a “fountain in the sky”.

By Stephen Luntz

Rob McNaught discovered the brightest comet of recent years and alerted observers to a meteor storm, but is now struggling for funds to detect asteroids on a collision course with Earth.

Twice in the past dozen years, amateur astronomers have had reason to thank Rob McNaught as he has provided warning of possibly the two most spectacular events of those times. However, discovering comets and predicting meteor storms are sidelines to his work – detecting asteroids that may one day pose a threat to the Earth, or at least a small portion of it.

Although McNaught enrolled in a physics degree at Scotland’s University of St Andrews, he dropped out. He blames his lack of success on procrastination, saying: “I discovered I couldn’t learn everything I needed to in a couple of days before the exams”. Eventually McNaught graduated in psychology. However, the hours he spent as an amateur astronomer proved more useful.

“I have early memories of sitting at a window looking out at the sky,” says McNaught, ruefully adding: “These days I look at the sky through a computer screen”. In a sign of things to come, McNaught says: “In my teenage years I spent a lot of time watching meteor showers. Then I discovered my first comet in 1970 and was totally sold.”

McNaught has now discovered 70 comets (12 in collaboration), more than double anyone else. He is most proud of the first, which involved detailed measurements and skilled observations as an amateur. However, he is more famous for what he considers one of his lesser achievements, Comet McNaught 2006P1.

McNaught recognised 2006P1 as a long period comet in August 2006, and its path was calculated to take it well inside the orbit of Mercury as the year was ending. Some astronomers predicted that it would not survive such a close approach to the Sun, its entire surface expected to melt away while it was too close to the Sun to be seen. “I was confident it would survive perihelion,” says McNaught, referring to the point where the comet’s orbit brought it closest to the Sun. “But I never thought it would be so bright afterwards.” Bright it was, the second most brilliant comet since 1935 and visible during the day to those who knew where to look.

Sadly, few got to view the phenomenon at its most spectacular. For one thing, Comet McNaught was best seen from the Southern Hemisphere. For another, the anticipated destruction, and the absence of reporters over the New Year period, meant few people heard what was happening until the best viewing had passed.

Nevertheless, thousands of holiday-makers on romantic walks had their breath taken away by the “fountain in the sky”, while others following the news escaped cities to catch a once-in-a-lifetime sight – making up for the string of disappointing comets that began with Halley’s most recent pass in 1986. McNaught is modest about his contribution, saying: “It would have been a great comet whether I found it or not”.

The same cannot be said when he alerted millions to 2001’s meteor storm. Roughly every 33 years the Leonid meteors have lit up the November skies, with the best events displaying tens of thousands of shooting stars from good locations. A repetition was anticipated for 1998 or 1999, but both proved deeply disappointing. McNaught concluded that research determining when dust particles blown off the comet Tempel-Tuttle would intersect the Earth “lacked rigour”. He invented a better way to estimate when storms occur, but lacked the mathematical skill to carry it out.

In collaboration with astronomer David Asher of Armagh Observatory, however, McNaught predicted major meteor activity in 2001. While the event was not quite as spectacular as 1966 or some 19th century storms, it awestruck those lucky enough to witness it under dark skies.

McNaught and Asher were not the only astronomers to predict a meteor storm that night, but their capacity to predict several peak intensities to an accuracy within 10 minutes created a new sub-field of science.

Sadly, the Earth will miss the main remnants of Tempel-Tuttle on the next pass, so while small showers will occur every November 17, the Leonids will not provide a major show in most readers’ lifetimes.

There is, however, growing excitement of the use of McNaught’s technique to predict a substantial event in 2022, involving a different comet, that may once again provide an unforgettable light-show for those able to witness it.

It’s larger chunks of space-rock that exercise McNaught’s mind these days. As part of the Spaceguard program, McNaught photographs the skies for asteroids and comets that might one day collide with the Earth. All other telescopes participating in the Spaceguard program are in the Northern Hemisphere, leaving the deep southern skies for McNaught alone. While this has contributed to his comet-spotting success and the discovery of 410 asteroids, it also creates unique responsibility.

Photographs taken 15 minutes apart are compared to seek objects that move relative to background stars. “Software techniques can be used to analyse the images, but the human eye is still the best discriminant,” McNaught says, “so they are presented to the observer to see if something is just noise”.

In June this year McNaught detected 2012LZ1 just 3 days before it made a close approach to the Earth. There was considerable excitement and many people watched live footage of the object over the internet as it sailed past.

McNaught admits to some puzzlement about the interest in 2012LZ1 compared with less-famous asteroids. He describes its distance – seven times the orbit of the Moon – as “not that close” and notes that its current orbit never intersects that of the Earth, remaining further from the Sun even at its closest approach. This may eventually change as a result of gravitational effects of the larger planets, but not for a very long time.

This is not the case, however, for many other asteroids. Spaceguard exists to warn us of objects that may one day encounter the Earth, causing catastrophic damage in the process. Unfortunately federal funding for McNaught’s work was withdrawn in 1996. The Science Minister at the time, Peter McGauran, described the search for asteroid threats as a “fruitless, unnecessary, self-indulgent exercise”.

One argument put for removing funding was that if an object was on course to hit the Earth there was nothing that could be done even if we knew about it. However, McNaught says that had 2012LZ1 been on a collision course even his 3-day warning might have allowed time to calculate a likely landing site and evacuate the area.

In more frequent cases, an asteroid poses no immediate threat, but detection allows its orbit to be calculated to see if a collision is possible on a future pass. Under the best conditions, which McNaught admits would not always occur, he says a landing site could be calculated to an accuracy of around 1 km, potentially saving millions of lives where evacuation is required.

Considerable thought is going into how we could deflect an asteroid on a collision course with Earth (AS, April 2009, p.41), but all the techniques so far under consideration require an asteroid’s discovery during a previous close approach.

Fortunately for McNaught, and possibly the planet, the University of Arizona provided funding from 2004–11 for him to use the 0.5-metre Uppsala Telescope at Siding Spring to search the deep southern skies for threatening objects. This produced almost immediate success (AS, June 2004, pp. 4–5) when five asteroids were discovered within 2 months.

Now, however, McNaught says: “They have decided to focus their funds on their own Northern Hemisphere telescope”. Since then McNaught has had temporary support from the Australian National University, which operates the Siding Spring Observatory. This support is due to expire soon, and it is unclear if it will be renewed. McNaught adds: “The dome in which the telescope is housed is in such poor condition the project will not be sustainable for long without refurbishment”.

McNaught has enabled millions to witness astronomical events that put any fireworks display to shame, yet his efforts may cease for the lack of a budget smaller than what large cities spend each New Year’s Eve on their local fireworks show.