Earth-Based Observatories

Mauna Kea Observatory

Background Information: Deep Impact will be the first mission to make a spectacular, football-stadium-sized crater, seven to 15 stories deep, into the speeding comet. Dramatic images from both the flyby spacecraft and the impactor will be sent back to distant Earth as data in near-realtime. These first-ever views deep beneath a comet's surface, and additional scientific measurements will provide clues to the formation of the solar system.

Earth-based observatories will also be used for observations of the impact of Comet 9P/Tempel 1 from Earth. The best case scenario would mean that the impact would take place when the comet is visible though the telescopes of more than one major observatory.

Questions:

1. What are some good reasons to use Earth-based observatories for observing the impact?

2. What are some reasons that the Deep Impact mission would not want to depend on Earth-based observatories?

Procedure: The following observatories are being considered for use by the Deep Impact team for Earth-based observations. Use an atlas/globe or the Web to find information about these observatories in order to fill in the chart.

United States

Haleakala (Maui)
www.ifa.hawaii.edu/haleakala/

Mauna Kea Observatory, Hawaii (the big island)
www.ifa.hawaii.edu/88inch/88inch.html

Palomar Observatory (Southern California)
www.astro.caltech.edu/palomarpublic/

Chile

Cerro Tololo Inter-American Observatory (Chile)
www.ctio.noao.edu

La Silla Observatory (Chile)
www.ls.eso.org/

Paranal Observatory (Chile)
www.eso.org/paranal/

Spain

La Palma Observatory (Canary Islands)
www.ing.iac.es/

Australia

Siding Spring Observatory (New South Wales)
www.mso.anu.edu.au/home.php

Answers!

1. What are some good reasons to use Earth-based observatories for observing the impact?

• Getting the Big Picture
  Looking at the comet from a distance gives us a different perspective than when we are 500 km away and using the flyby cameras and spectrometers. It is important to see it from the perspective of the entire comet.

• Looking through different "filters"
  Every ground-based telescope on Earth has a suite of scientific instruments that can be used with a particular telescope. Some telescopes are optimized for observing in the visible region of the spectrum (where our eyes are sensitive to light) while others are designed to optimize observations in the infrared spectral region that can sense the heat emitted from objects in space. Still others detect very long wavelength radiation of radio waves, these are in fact, radio telescopes. From the flyby spacecraft we can make two types of observations, visible imaging and infrared spectroscopy. From the ground we can observe from the visible, infrared, far infrared, millimeter and radio wavelengths, thus expanding the scientific return from our experiment.

• Mission Constraints
  It would be impossible to place a full suite of instruments such as can be found at observatories around the World, on the spacecraft for numerous reasons related to mission constraints. These include matters of mass: we can't lift an infinite amount of mass from the Earth into space; engineering complexity: integrating instruments into a spacecraft takes power and computer control. With more instruments, the spacecraft would be more complicated and be exposed to more possibilities for malfunction. More instruments would also mean more cost, and Discovery missions are cost-capped missions.

2. What are some reasons that the Deep Impact mission would not want to depend on Earth-based observatories?

• The Earth turns
  We can only see the comet for a limited time from different places on Earth. The flyby spacecraft is dedicated to observing the impact at close range and continuously just before, during and after impact.

• Weather
  We can't rely on the weather. If it is cloudy or raining, we would miss observing the impact.

• The Distant view is limited
  We can not observe the impact up close from the Earth. At the time of impact we will be approximately 90 million miles from the comet and we won't be able to see the details of the impact such as the ejecta blanket or the surface of the comet's nucleus. We need the instruments on the fly-by to observe the experiment up-close.

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