Astronomers Gear Up to Make the Most
As Comet Hale-Bopp becomes the brightest comet in European skies for many decades, Dr Alan Fitzsimmons of The Queen's University of Belfast will tell a meeting of the Royal Astronomical Society on Friday 14th March about the discoveries made so far about the comet, and what astronomers may see in the coming weeks. His talk, at 3.00 p.m., will wind up a discussion meeting on the topic 'Comet-Asteroid Interactions', running from 10.30 a.m. to 3.30 p.m. at the lecture theatre of the Geological Society, Burlington House, Piccadilly, London W1.
Since Comet Hale-Bopp was discovered in July 1995, both amateur and professional astronomers have been waiting for the present few weeks, when the comet is at its brightest. Although it will still be 123 million miles from Earth at its closest approach on the 22nd March, the comet has lived up to expectations, and it is now one of the brightest objects in the skies over Britain, best visible in the north-west in the evening or the north-east in the early hours of the morning.
To date, the most thorough study of a comet was of Halley's Comet in 1986. However, Halley's Comet never became very bright as seen from the Earth even though a fleet of spacecraft was sent to explore it. By contrast, radio telescope measurements indicate that Hale-Bopp is already ten times more active than Halley's Comet was at its peak, and is continuing to grow in activity and brightness. With the new detectors and instruments available to them, astronomers hope to take advantage of Comet Hale-Bopp's appearance to probe the secrets of comets as never before.
A comet is essentially a large solid mass of frozen ices and dust particles. When it gets near the sun and is warmed up, it loses its outermost layers. The gases and dust released then stream away from the central nucleus to form the extended atmosphere and tails so characteristic of comets.
Dr Fitzsimmons will discuss the multitude of chemical molecules so-far observed in Hale-Bopp. Many of these are first ever detections in a comet, including SO, HCO+ and the carbon- chain molecule HCCCN. Importantly, various different isotopes of carbon, nitrogen and sulphur have been detected. The relative amounts of these isotopes imply that the comet formed from the same material as the Earth. This discovery opens a window on cosmic history, allowing astronomers to look back 4.5 billion years to the time that the Earth and the rest of the solar system formed. The nucleus of Hale-Bopp has remained deep frozen since then, so by observing the comet, astronomers can study the gases and ices that went into building our solar system.
To understanding the behaviour of the comet fully, astronomers want to know the size and spin rate of the central icy nucleus. Although several attempts have been made so far to determine how quickly the comet rotates, they have come up with different answers, ranging between about 12 hours and 10 days; some estimates are even longer! Jets and hoods of material expelled from the nucleus are visible even to amateur astronomers with back-yard telescopes, and it is hoped that these can be deciphered in the near future to reveal the true behaviour of the nucleus.
The best estimate of the size of the nucleus is 40 km, as obtained from images obtained with the Hubble Space Telescope. However, the comet is now too close to the Sun in the sky for the Hubble to observe it safely.
A huge amount of data is being gathered using the British telescopes on the island of La Palma. Part of this will be done by British astronomers alone. However, the telescopes are also forming the linchpin of a pan-European study of the comet. A team of 19 European scientists will use the telescopes to carry out an in-depth investigation into Hale-Bopp during March and April, in which Dr Fitzsimmons will be playing a leading role.
Using up to seven telescopes simultaneously on a single night, they will be attempting to perform a multitude of investigations. These include tying down the rotation rate of the nucleus, and searching for yet more new molecules released from the comet. Another purpose-built camera will be used to observe the interaction of the solar wind with the gas tail of Hale-Bopp. As the comet will be lying above the North Pole of the Sun, it will allow astronomers to study the high-latitude solar wind in a region impossible to observe from Earth.
On Friday 14th March, for contact call the Royal Astronomical Society at Burlington House: 0171-734-4582 or 0171-734-3307.
Further information and images available via the WWW site: http://star.pst.qub.ac.uk/~af/hb.html
Issued by: Dr Jacqueline Mitton