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Amateur astronomers get chance to support Rosetta mission

Paul Sutherland, Feature writer
Apr 4, 2015, 21:44 UTC

Sen—We are getting used to seeing spectacular close-ups of Comet 67P/Churyumov-Gerasimenko from ESA’s Rosetta spaceprobe. But as the cosmic wanderer gradually approaches the Sun and brightens, amateur astronomers are being encouraged to observe it too.

Scientists want them to join a ground-based campaign that will give them a different perspective on the comet, with a wide-angle view to monitor its brightness and show how its ghostly coma and tail develop.

Professional astronomers have already been studying 67P during its present apparition, using some of the world’s most powerful telescopes, and the Hubble Space Telescope, to help the Rosetta team prepare for their encounter with it.

As the probe went into orbit around the comet last year, the European Southern Observatory’s 8-metre Very Large Telescope (VLT) was one instrument that imaged the comet. Though it was then more than 500 million km from the Sun and still very faint, it could be seen to be shedding gas and dust to begin forming a tail, with a coma stretching at least 19,000 km into space.

Last year the comet was in the southern part of the sky, which is why telescopes in Chile were prominent in the observing campaign. And for the past several months, it has been unobservable from the ground because it has been on the far side of the Sun, in a daylight sky.

By the end of May, 2015, the comet will have crossed the celestial equator on its 6.45-year orbit, and become easier for observatories in the northern hemisphere to study as it appears to move further away from the Sun. (This is all due to the angle of viewing because the comet actually reaches the closest point to the Sun in its orbit, called perihelion, on Aug. 13.)

NASA is supporting a ground-based campaign to observe 67P that will involve amateur as well as professional astronomers. There is a Facebook group too. Though the comet is unlikely to become brighter than 11th magnitude, that will bring it within range of moderate-sized amateur telescopes, particularly with sensitive CCD cameras.

Rosetta project scientist Matt Taylor told Sen: “The ground-based side is very important, from both the professional and amateur sides. With both these efforts, we get the valuable context of what we see on Earth. The ground-based support was important operationally, for example, when Rosetta was in hibernation to ensure the comet was still there!

“This campaign puts all other cometary observations into context, giving us a broader science aspect. Also, with Rosetta we are right there next to the comet. Ground-based gives us the macroscopic scale. It also engages a wider part of the science community with the mission.”


The instruments making up the Very Large Telescope can be seen perched at Paranal, Chile, in this photo of another comet, the brilliant Comet McNaught, in January 2007. Image credit: S. Deiries/ESO

Observations for the campaign are being coordinated by Colin Snodgrass, of the UK's Open University, on the professional side, and Padma Yanamandra-Fisher, of the Space Science Institute, USA, for amateurs.

Dr Snodgrass told Sen: “What makes Rosetta different from previous missions (apart from the lander) is that it follows the comet at relatively low speed, and that means it can get close to the nucleus (typically 5-100km). 

“That is great for getting detailed information on the nucleus and central coma, but it means that the mission doesn’t sample the majority of the spatial extent of the comet, which covers tens of thousands of km. Ground images and spectra fill in information on what is going on around the spacecraft in the large scale coma, e.g. what molecules are detected at large scales for comparison with the in situ measurements, to better understand the chemistry going on in the coma.”

He added: “The context information is also important as it lets us compare 67P with other comets that are only observed from the ground, and therefore tie Rosetta results to things we see in the wider population.”

Dr Snodgrass believes amateurs will make a major contribution too. He told us: “A lot of the kit that more advanced amateurs are using is essentially professional standard now. In fact those using robotic telescopes are using exactly the same ones that pros use. 

“The big advantage that the amateur community has is that it is dispersed over the globe, and means that there is a good chance that the comet is visible to someone at any given time, while even the best professional sites get cloudy occasionally. 

“Also, and this is especially important in the coming months, amateurs with their own telescopes can often point much closer to the Sun, observing at low elevation in twilight. Since 67P stays within about 40° of the Sun until after its perihelion passage in August, images from amateurs will be a really important part of the global campaign this year.”

Dr Yanamandra-Fisher agrees. She told Sen: “Currently the comet is in solar conjunction and as it re-appears, the recovery will most probably be made by the amateurs. Professional facilities have limits on how close they can observe to the Sun. The amateurs, with their smaller aperture telescopes, have the advantage of being able to point their telescopes closer to the Sun (as is safely possible). 

“Also, if there are morphological changes in the comet, its coma and or tail, the amateur can send alerts to both the amateur and professional communities for follow-on observations. Knowing what the in-situ Rosetta observations reveal of the activity of the nucleus, Earth-based observers (both professional and amateur) can provide the global context for these observations.”

So what can amateurs hope to achieve? Dr Yanamandra-Fisher told us: “The first event will be the re-appearance or recovery of the comet in late April - early May. The last amateur observations were taken on 14 November, 2014, a couple of days after the Philae landed on the comet. 

“The continued evolution of the comet as it heads towards perihelion on 13 August 2015 is another goal. The comet is known for its post-perihelion brightness from previous apparitions, which we now know to be due to a change of seasons on the oddly-shaped bi-lobed nucleus.

“This is one of the windows of time where we expect the amateurs to make a major contribution. We welcome observations by amateur observers of all skill levels and types of observations.”