Hunting for Halley's Comet
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Right: The ghost of Edmund Halley looks on as the meteor balloon ascends to the stratosphere.
The 8 foot helium-filled balloon will lift off from the Johnson 'Near Space' Center south of Manhattan, Kansas at 7 a.m. CDT on May 8th, just 36 hours after the peak of the eta Aquarids meteor shower. The payload includes a lightweight dust collector developed at the NASA/Marshall Space Flight Center that scientists hope will capture micron-sized eta Aquarid meteoroids 120,000 ft above Earth's surface. If the experiment succeeds then the balloonists will have captured bits of Halley's Comet, the parent of the eta Aquarid meteor stream.
December 3: Mars Polar Lander nears touchdown
December 2: What next, Leonids?
November 30: Polar Lander Mission Overview
November 30: Learning how to make a clean sweep in space
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"The Kansas balloon is going up two days after the peak of the eta Aquarids. The meteor shower will be dying down by then, but it may be the best time to catch comet dust," explained Dr. John Horack of NASA's Marshall Space Flight Center. "Eta Aquarids hit the atmosphere at 140,000 mph and conventional wisdom says they lose most of their kinetic energy right away, about 80 km above the stratosphere. Then they drift slowly to the ground, kind of like a feather thrown from the top of a skyscraper. High altitude winds and the bouyancy of the particle affect how quickly meteoroids descend. They might not pass through the stratosphere until days after the shower's peak."
The meteoroid catcher scheduled to fly this Saturday includes 300 square centimeters of polyacrylic films, plus 30 square centimeters of silica xerogel. The xerogel is lower density than the polyacrylic material and probably more sensitive to lower velocity particles drifting slowly downward from higher altitudes. The polyacrylic films are denser and better suited to the capture of compact, higher velocity particles.
"The chances of catching an eta Aquarid are slim," says Dr. David Noever, a NASA/Marshall scientist. "The meteor shower will be 20 to 50 times weaker than the '98 Leonids, and the debris stream hits the earth slightly south of the equator. But, if we do catch something it should be relatively easy to tell whether or not it came from Halley. In 1985 Giotto [a European Space Agency spacecraft] flew right by Halley's nucleus through a cloud of debris bubbling off the comet. It got data on particle sizes, density, chemical composition -- just about everything you need to ID a meteoroid from Halley."
"Chemically speaking, a Halley meteoroid caught in the stratosphere won't look exactly like one from deep space," continued Noever. "All meteoroids experience a thermal spike (5-15 s) during deceleration in the atmosphere. Simply put, the fragmentary dust gets hot and some volatile elements boil away. This changes the internal chemical ratios. How long the heating lasts depends unpredictably on the particle size, density of both particle and atmosphere, entry velocity and entry angle. Despite these complications we think we know enough about volatile evaporation to make reasonable chemical comparisons with pristine Halley particles."
This weekend's adventure won't be the first science experiment carried aloft by the Kansas Near Space Project (KNSP). Since its inception in 1996 the KNSP has flown payloads to study cosmic rays, to test the response of microorganisms to the environment of the stratosphere, and to gather high-altitude meteorology data, among others. All the experiments were designed and executed by students and hobbyists.
"Above 100,000 ft the air pressure is only 1% of that at ground level and air temperatures are approximately -60 degrees F," explains Lloyd Verhage, the KNSP project manager at Kansas State University. "These are conditions closer to the surface of Mars than to the surface of Earth. The air up there is too thin to refract or scatter sunlight, so the sky looks black rather than blue. What we see at these altitudes is close to what shuttle astronauts see from orbit."
"My favorite experiment so far was the Flight of the Roachanauts," continued Verhage. "We sent several roaches in a plastic habitat to 84,000 ft. We know roaches can survive the winter, so felt that temperatures wouldn't be a problem for a short 3 hour flight. Unfortunately the insects returned dead. We're planning to repeat the experiments with improved habitats and monitoring to better understand what happened. Who says there is no risk to expanding the frontiers of science?"
In February 1999 Verhage and collaborators set a new altitude record for amateur launched balloons -- 114,600 ft. The previous record of 111,000 ft, established by Sky Science Over Kansas, had stood since 1994. The KNSP benchmark didn't last as long. Three weeks later, in March 1999, a Colorado group set a new standard by sending a balloon to 121,000 ft.
"We would like to recapture the record this weekend," said Verhage. "I want to reach 122,000 ft at least, and I'd say we have a better than 50% chance of making it."
This weekend's flight will begin just after dawn when the meteoroid flux over the launch site is greatest (see the figure below). The balloon will take about 2.5 hours to reach 120,000 ft. At that altitude the balloon, which measures 8 ft across at sea level, will have grown in size to over 25 feet and it will pop. The descent by parachute takes about 1 hour. If all goes as planned the meteoroid collector will be recovered by Kansas Near Space Project personnel and returned to the Marshall Space Flight Center for analysis.
Above:The rate of meteor activity is greatest near dawn because the earth's orbital motion is in the direction of the dawn terminator. Earth scoops up meteoroids on the dawn side of the planet and outruns them on the dusk side.
NASA/Marshall scientists plan to launch two more weather balloons later this year to capture meteoroid samples. In August, xerogel will be used to take samples of the Perseid meteoroid shower. This November, the Leonid shower is predicted to be an even better show than the much-hyped 1998 Leonid shower, and scientists will again fly collectors to the stratosphere in an attempt to "catch a falling star."
The Kansas Near Space Project - home page
Leonids' Particle Analyses from Stratospheric Balloon Collection on Xerogel Surfaces - conference abstract
Leonids Live! -site of the live webcast of the 1998 Leonids
Meteors Down Under -- May 3, 1999. Information about the eta Aquarids meteor shower and Halley's comet.
Leonid Sample Return Update -- Apr. 1, 1999. Scientists will describe initial results from a program to catch meteoroids in flight at the NASA/Ames Leonids Workshop April 12-15, 1999.
The Ghost of Fireballs Past -- Dec. 22, 1998. RADAR echoes from Leonid and Geminid meteors.
Bunches & Bunches of Geminids -- Dec. 15, 1998. The Geminids continued to intensify in 1998
The 1998 Leonids: A bust or a blast? -- Nov. 27, 1998. New images of Leonid fireballs and their smokey remnants.
Leonids Sample Return payload recovered! -- Nov. 23, 1998. Scientists are scanning the "comet catcher" for signs of Leonid meteoroids.
Early birds catch the Leonids -- Nov. 19, 1998. The peak of the Leonid meteor shower happened more than 14 hours earlier than experts had predicted.
A high-altitude look at the Leonids -- Nov. 18, 1998. NASA science balloon catches video of 8 fireballs.
The Leonid Sample Return Mission -- Nov. 16, 1998. NASA scientists hope to capture a Leonid meteoroid and return it to Earth.
Great Expectations: the 1998 Leonid meteor shower -- Nov. 10, 1998. The basics of what the Leonids are and what might happen on November 17.
|For more information, please contact:
Dr. John M. Horack , Director of Science Communications
|Author: Dr. Tony Phillips
Curator: Linda Porter
NASA Official: John M. Horack