Astronomers' Holiday Special -- a July 4 Comet Bash

Lori Stiles
June 21, 2005

Have a wish for the USA's birthday this year?

If you're a ground-based astronomer in Arizona and states west through Hawaii, you'll wish for clear, dark skies in early July.

It's your chance to watch what happens when NASA's Deep Impact spacecraft slams its 820-pound copper probe into comet Tempel 1 at 23,000 mph.

The impact is expected at 10:52 p.m. MST Sunday, July 3. The mothership will fly next to the comet to document the fireworks, and several major NASA space telescopes -- Hubble, Spitzer, Chandra -- will witness the result. Big telescopes in Hawaii and major observatories in California and Arizona will be watching from 83 million miles away, too.

Southern Arizona astronomers will be watching the comet impact. Some, like those with Arizona Radio Observatory, which supports the NASA Deep Impact Ground-based Radio Science campaign, and at Kitt Peak National Observatory have already logged many nights studying the comet.

The Deep Impact mission goal is to blast a crater for a first-ever look inside a comet, which is made of the same stuff that made up our solar system billions of years ago, before the planets formed. Scientists hope to learn a lot from the small comet, which is only about 8.7 miles long and 2.5 miles wide.

No one knows what will happen on impact.

"We expect to be surprised," said University of Arizona Regents Professor H. Jay Melosh, a member of the Deep Impact science team. "We don't know what the comet's surface is like. We could hit something as hard as concrete or as soft as cornflakes."

Melosh will be at the NASA Jet Propulsion Lab in Pasadena, Calif., during the probe-comet collision. The Jet Propulsion Lab is managing Deep Impact, which is a NASA Discovery class mission conducted by the University of Maryland, College Park, Md.

Melosh will talk on "First Results from the Deep Impact Mission" in Tucson on Saturday, July 9. His talk will be at 6:15 p.m. in the Kuiper Space Sciences Building, 1629 E. University Blvd.,Tucson. The lecture, which is part of a program sponsored by UA's Lunar and Planetary Laboratory Public Outreach Program, is free and open to the public. Seating is first come, first served, so event organizers recommend showing up when LPL opens its doors at 5 p.m.

Mike Belton, president of Belton Space Exploration Initiatives, Tucson, and deputy-principal investigator on the mission, came up with the mission name "Deep Impact" before a drama-sci-fi-thriller with the same title was released in 1998. (The movie, starring Robert Duvall and Tea Leoni, is about humans preparing to survive a catastrophic comet impact.)

Melosh noted that Deep Impact's copper probe could no more send comet Tempel 1 careening toward Earth than a kamikaze gnat could change the flight path of a fully loaded Boeing 747.

Here's the rundown of what southern Arizona observatories are doing the week of Deep Impact:

  • The Arizona Radio Observatory (ARO) 12-meter Kitt Peak telescope and ARO's 10-meter Heinrich Hertz Submillimeter Telescope on Mount Graham, Ariz. The 12-m ARO Web site:
    Science contacts: UA Professor Lucy Ziurys, ARO director. 520-621-6525,
    St. Cloud State University Professor Maria Womack, principal investigator 320-308-4171,

    The ARO 12-meter telescope has been observing comet Tempel 1 for baseline information on the kinds and quantities of molecules that are present around the comet before impact. ARO's Heinrich Hertz Submillimeter Telescope on Mount Graham, Ariz., begins making baseline observations June 23. The project is led by St. Cloud State University astronomer Maria Womack, a collaborator of the NASA Deep Impact Ground-based Radio Science team.

    The observers will study molecules ejected in debris after impact, molecules rarely detected in coma gas. "We're most interested in 'parent' molecules -- those which sublimate directly from the nucleus," Womack said. "By measuring their abundances we can determine the chemical composition of the comet nucleus and, therefore, get information about the conditions in which the comet formed." Womack added, "Remote observing procedures work so well that I don't need to be at the Arizona telescope, and that gives me the chance to collect much more data than I otherwise would have."

    "These molecules should be bright enough for our telescope to detect in a few minutes after impact," said ARO graduate student Stephanie Milam, who'll assist with the observations and is heavily involved in cometary studies.

  • National Optical Astronomy Observatory (NOAO) on Kitt Peak, Ariz. Web site:
    Media contact: Douglas Isbell, 520-318-8230,
    All major NOAO telescopes on Kitt Peak will be observing the comet for several nights before impact as well as the impact itself. These include the Mayall 4-meter telescope, the Kitt Peak 2.1-meter telescope, and the WIYN 3.5-meter telescope.

  • The UA/Smithsonian 6.5-meter MMT Observatory on Mount Hopkins, Ariz. Web site:
    Science contacts: MMTO Director Faith Vilas, 281-483-5056,
    Richard Cool, UA Steward Observatory,

    Cool will be observing stars and galaxies with a multi-object spectrograph on the MMTO on July 3-4, but also comet Tempel 1 according to a strategy being developed by Faith Vilas, the new MMTO director.

  • The Catalina Sky Survey, a consortium of three cooperating surveys: the original Catalina Sky Survey and the Mount Lemmon Sky Survey in the Santa Catalina Mountains north of Tucson, and the Siding Spring Survey near Coonabarabran, New South Wales, Australia. Web site:
    Science contact: Steve Larson, 520-621-4973,
    Rob McNaught,

    The cooperating surveys share a common goal - to help inventory more than 90 percent of Near Earth Objects (NEOs) that are one kilometer or larger. The three surveys have been monitoring the Tempel 1 comet and will observe during impact from both the northern and southern hemispheres.

  • UA's 61-inch Kuiper Telescope in the Santa Catalina Mountains north of Tucson. Web site:
    Science contact: Carl Hergenrother, 520-621-9690,

    The comet will be about 20 degrees above the horizon, and sets about two hours after impact. With a 61-inch telescope, Hergenrother plans to observe as many as 50 other comets as well as Tempel 1 from July 2 through July 5.

  • Spacewatch on Kitt Peak, Ariz. Web site:
    Science contacts: Spacewatch Director Robert McMillan, 520-621-6968,
    James Scotti, 520-621-2717,

    McMillan and Scotti have made no specific plans for watching comet Tempel 1 during Deep Impact because the comet is so low in the sky, although Scotti said he may try for some before-and-after impact images of Tempel 1. The 25-year-old Spacewatch project is the pioneering comet-and-asteroid survey, and another source of top comet and asteroid experts.

  • Campus Station 21-inch telescope, adjacent to the astronomy department buildings on the UA campus. Web site:
    Science contacts: Steward Observatory associate astronomer Thomas Fleming, 520-621-5049,
    UA astronomy major Joshua V. Nelson,

    Fleming and Nelson photographed the comet with Steward Observatory's 21-inch telescope at Campus Station on June 8, using a light-pollution reduction filter to cut out some of the street light pollution. They'll use the same setup to observe the comet on encounter night, starting at 10 p.m.

Tempel 1 is named after Ernst Wilhelm Leberecht Tempel, who discovered the comet on April 3, 1867, in Marseilles, France. The comet is now on a south-southeast course through constellation Virgo. It is about 40 times dimmer than is visible to the unaided eye, but could brighten enough after impact to be seen through binoculars, astronomers say. However, they add, it could take minutes to hours, even days before the comet fully brightens, and there's no guarantee that Earth-based telescopes will even see the immediate impact flash.

Flandrau Science Center will open its observatory special hours Sunday, June 3, through Saturday, June 9. Because comet Tempel 1 will be so faint and low in the Arizona sky during its collision with the probe at 11 p.m. Sunday night, the comet will be difficult to find in large amateur telescopes from light polluted city locations. For stargazers who want to try Sunday night, Flandrau will open its 16-inch telescope from 7:30 p.m. until midnight, for real time video imaging and for direct viewing if the comet is bright enough.

The best nights to view the comet from Flandrau's 16-inch telescope may be Monday, Tuesday and Wednesday nights after impact. The telescope will be open for the public from 7:30 p.m. to 10 p.m. Monday through Saturday, July 4 - 9. Flandrau's 16-inch telescope is the only free public telescope open on a regular basis in the state of Arizona. Normal telescope hours are 7 p.m. to 10 p.m. Monday through Wednesday, weather permitting. For more information, visit Flandrau's Web page at and call the Flandrau Astronomy News line at 520-621-4310.


Resources for the media

Lori Stiles, UA
Virginia Pasek, LPL
Mike Terenzoni, Flandrau
Doug Isbell, NOAO