Below are the objectives for the 2000 apparition of Tempel 1. Please be sure to look at the current objectives and procedures for the 2005 apparition.

The objective of this program is to provide observations of Tempel 1 that will complement the professional observations. In particular, this science programs focuses on observations of:

• Brightness changes, and
• The coma, tail, and imbedded features.

Observations made by the participants in this program will allow the Deep Impact science team to determine, more accurately, the properties of the comet as a function of distance from the sun. In particular, observations of the features and the brightness changes of the coma and the tail will be used by the science team to develop a dust model of the Tempel 1. Observations of the coma can also provide information about the rotation period and state of the nucleus as well as information about the gas and dust production rates of the nucleus. The dust model will give information about the onset of dust activity, dust ejection velocities, and the dust size. This information will be used by mission planners to constrain the design of the spacecraft and its instruments. For example, instrument and spacecraft designers need this information to:

• Build instruments that can adapt to a rotating nucleus (for example, compensate for the smearing of images caused by rotation),
• Calculate when to launch and where to target the impactor so that impact occurs on the sun-lit side of the nucleus, and
• Determine shielding requirements for the spacecraft and its instruments.

Observing Possibilities: What cometary properties can small telescopes observations help refine?

Cometary gas and dust activity manifests itself as coma and tail formations, jets, fans, line emissions, thermal continuum emissions, and scattering of light from dust in the coma and tail. This science program focuses on brightness changes and dust in the coma and tail.

The coma, the tail, and any imbedded features often extend over thousands of kilometers. Coma/tail features and brightness will be observable by participants in this program since small telescopes equipped with CCD cameras can often achieve a pixel scale of 1 arcsecond per pixel, allowing coma/tail features larger than 1000km to be recorded (Tempel 1 is 1.7AU to 2.3AU from the Earth for most of the year 2000). The diameter of the nucleus is estimated to 10-20 km, yielding a maximum angular size of 0.006 arcseconds, so it cannot be resolved by our small telescopes.

To record brightness and dust features, the science program requires observations of the comet to be made with photometric "V" and "R" filters as well as without filters. The visual "V" filter captures the total flux of molecular emissions, in particular C2, within the wavelength range of 490-650 nanometers. The red "R" filter captures flux of sunlight scattered by dust within the wavelength range of 550-850 nanometers (dust preferentially scatters red light). Images made without filters provide general information about the brightness and structure of the coma and tail, including temporal changes of these properties.

As background information, please note that the following cometary properties will only be observable from large telescopes:

• Albedo and size of the nucleus. Albedo constrains the composition of the nucleus's crust. The nucleus size and composition allows us to determine the mass and density of the nucleus which constrain the parameters of the crater. Unfortunately, the nucleus of Tempel 1 spans only 0.0006 arcseconds of the sky during 2000 while one of our small telescope pixel spans 1 arcsecond or more. Small telescopes will not be able to resolve the nucleus, making it difficult to determine the albedo. However, small telescope observations will help constrain these cometary properties.

• Detailed gas production rates. To calculate accurate gas production rates, spectroscopic studies of the coma are required. Specific, narrow band filters are needed to capture the emissions from gas molecules such as CN, C2, and OH. The photometric "V" filter is a broad band filter; it captures the overall flux of the C2 molecule. Small telescope observations using the "V" filter may help constrain the C2 gas production rate.

The following cometary features and properties will be observable from small telescopes:

• Coma and its structure. Small telescopes can resolve the coma and imbedded features since these properties are often thousands of kilometers in size. Using photometric "V" and "R" filters to record the coma as a function of distance from the sun allow the science team to study:

  • Brightness (magnitude) changes of the coma,
  • Coma features such gas and dust jets and fans, and
  • Outbursts from the nucleus.

  Observations of the brightness changes in the "V" band will allow a more exact the rotation period for the nucleus to be calculated (ref 1). The rotation period can also be determined from observations of dust jets in the "R" band since dust jets and fans often live for several days (ref 2). Additionally, "R" band observations will allow the spin axes of the nucleus and the orientation of these axes to be calculated (ref 2).

  Observations of the coma using photometric "V" and "R" filters help constrain the gas production rate of the nucleus and determine the dust-to-gas ratio, dust emissivity, dust size, and dust production rate. Detailed observations the dust jets help determine the number and distribution of active zones on the surface of nucleus.

  Unfiltered observations of the coma will be analyzed for brightness changes that may indicate the spatial and temporal on-set and variations of gas production (ref 3).

• Tail(s) and structures. As with the coma, small telescopes will be able to resolve gas and dust structures in the comet's tail(s). Observations using photometric "V" and "R" filters will provide information about the spatial and temporal changes of the tail(s).

• Albedo and nucleus size. While small telescopes will not be able to resolve the nucleus, if Tempel 1 is not very active during 2000, small telescope observations may be able to constrain the albedo and size of the nucleus.

Text References:

1. Mueller, B.E.A., et al, 1997-1999, "Imaging the Structure and Evolution of the Coma Morphology of Comet Hale-Bopp (C/1995 01)" in Earth, Moon, and Planets, 77, No. 3, Kluwer Academic Publishers
2. Meech,K., et al, 1997, "Rotation of comet 46P/Wirtanen", Astronomy and Astrophysics, 326, 1268-1276
3. Kidger, M.R., et al, 1997, "The Visual Light Curve of C/1995 01 (Hale-Bopp) from Discovery to Late 1997" in Earth, Moon, and Planets, 78, Nos. 1-3, Kluwer Academic Publishers

Other References:

• Introduction to Comet Studies by NASA's Planetary Data Systems
• CCD Photometry of Faint Comets by Crni Vrh Observatory
• Observer's Tools by JPL's Solar System Dynamics, includes a Universal Time converter and What's Visible Tonight
• Ephemeris Generator by JPL's Horizons System

STSP Coordinator: Stef McLaughlin
Webmaster: Elizabeth Warner
Last Updated: Wednesday August 29, 2007