Public Lectures for the Session 2004-2005 held in Room F14 of the Renold Building, UMIST.
Delivered to the Manchester Astronomical Society

23 September 2004

''Observing Solar System Objects with the Hubble Space Telescope''

Dr. Ian Griffin
(Director of the Manchester Science and Industry Museum. And formerly: The Head of the Office of Public Outreach for NASA’s Hubble Space Telescope)

Dr Ian Griffin expressed his thanks in being invited to address the Society. This was Dr Griffin's first talk for ten years on astronomy in returning to Britain. His talk focused on the angle of the media side of the Hubble Space Telescope press releases and what goes into the background behind making observations with the HST.

As the former head of the Space Telescope Science Institute's Office of Public Outreach, Dr Griffin began a brief description of his career and what led him to become a research astronomer. He started as an astronomer at the UCL in London, where it was here that he decided to become a public outreach officer. During 1990 to 95 he directed the Armagh Planetarium. During his time there he visited numerous observatories in both the northern and southern hemispheres. In 2000 Ian took the position of head of Public Outreach for the HST. This gave him the opportunity to devote 20% of his time on research.

He became interested in Solar System objects by following up on newly discovered asteroids. From the John Hopkins University campus in Baltimore he made observations of NGC 2207 in Canis Major. Ian showed the Society detailed images that he made of the galaxy via instruments that were available to him at the time. He then gave a brief description of his experience using various telescopes and equipment at numerous locations. During this period Dr. Griffin and his colleagues discovered 5% of the asteroids currently known.

At Mount John Observatory in New Zealand, Ian used a Drift Scanning technique to hunt for asteroids. The drift scanning technique is achieved by scanning a region of sky by a non-driven telescope several times, then the obtained images are superimposed. The images are then "blinked" to match any objects which change position relative to fixed background stars. Ian discovered two Trans-Neptunian Objects named 1999 TD 10 and 1999 TC 36.

After doing this work Ian moved to the Space Telescope group who studied the Solar System. Ian gave a breakdown of how the Hubble Telescope works. The space telescope is not indifferent to telescopes here on Earth. As a telescope it is a very good instrument. It has a 2.4 metre reflecting mirror and its secondary mirror has to be aligned 1 to 2 microns with the primary mirror to obtain an image. The HST experienced a slight fault with the primary mirror being slightly out. Luckily this slight aberration has been corrected with specially adapted camera optics which corrected the images. Instruments onboard the HST include the NICMOS, COSTAR, STIS and the Wide Field Planetary camera. The high resolution Advanced Camera for Surveys was later added in a servicing mission. The ACS camera has a series of detectors which are selected for wavelength sensitivity. Fine guiders select a small field then pass the light from a guide star to point the telescope in the right direction.

The key to the success of the telescope is good communications. Data needs to get down to the ground. The data pipeline goes to a ground station in White Sands, New Mexico which is then sent for processing to the Space telescope Science Institute.

The HST 's High Gain Antenna tracks satellites to focus on sending information. Solid State recorders are used to buffer data from the HST instruments. A full recorder takes 195 minutes to dump data to the ground. High speed chips are not needed as the older chips are more robust and can stand a bombardment from space of Cosmic Rays. If there is a computer glitch the HST contains continuous memory chips to counteract any loss in the system if hit.

The computer software has a logical memory where the programme has a safety stop in case something goes wrong and the telescope has to be put into a safe state. Responses can change from ignoring a requested activity to stopping the observation program and setting the HST into a state of hibernation.

After a detailed description of Hubble's instrumentation Dr. Griffin gave a detailed analysis of the telescope's observing capabilities and what is involved in making preparations for an observation. Observing deep sky objects is relatively easy compared with certain solar system aspects. To track the Moon is virtually impossible. Dr. Griffin did a calculation to try and observe the Apollo landing sites to see if Hubble was capable of resolving an image. The Moon would be so bright it would blow up all the fine guiding systems so the application for this project was turned down. Venus is also a difficult object to observe due to its closeness to the Sun. Telescope proposals for observing time are graded by a committee of astronomers, and on several occasions Steve Beckwith cancelled the Venus programs as they were deemed too dangerous. Observations were eventually made on the 29th January 1996. The goal was to observe the spectrum of Venus. Enormous planning goes into planning observations and eventually an image was taken in Ultraviolet light using the Wide Field Planetary Camera 2.

The Closest Approach of Mars was not of enormous scientific importance but Ian asked if two images could be taken eleven hours apart and release the images as soon as possible. The image was taken and arrived at the astronomer's desks two hours after the original image was taken. The Hubble website received twenty million hits on the day that the Mars approach image was released.

Although the HST is famous for producing cosmological stories, Solar System issues also get a high impact from the public. At the other end of the Solar System from Venus is an object known as Quaoar. In 2002 Mike Brown and Chad Trujill from Caltech discovered a bright Trans-Neptunian Object. They put in an application or observing time. Due to the potential impact of the story media wise observation time was granted. A star needed to be caught in the image to find whether the object was bigger than Pluto. Unfortunately it was smaller. When the final paper was published Ian was given a vote of thanks by the astronomers for prodding Steve Beckwith into allowing the observations.

Finally, Dr. Griffin gave a break down of various Kuiper Belt objects which he discovered using the Hubble Space Telescope. The recovery images of an object now designated WW 31 proved to be a binary system. As a binary object was unusual this discovery was vital in allowing astronomers to calculate their combined mass. No mass had ever been calculated for a Kuiper Belt object so this would be a first. The object would be visible in 2055 as an eclipsing binary system. Ian showed the Society an animated fly-by of the binary system orbiting each other. Their mass was measured to be a hundredth of the mass of Pluto. Since that time other binary objects have been discovered enabling the mass of objects to be calculated giving astronomers a rough idea as to how much mass is contained in the Kuiper Belt region.

Dr. Griffin closed his lecture with a glimpse of hope for amateur astronomers thinking of becoming involved in the search for asteroids. A small telescope equipped with a CCD is capable of observing occultations of these objects. Using the new drift scanning technique amateurs can make new discoveries and become involved in the hunt for Trans-Neptunian objects.

Synopsis by Sotira Trifourki (Secretary)

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