MadSci Network: Astronomy
Query:

Re: What exactly do the astronomers that watch for asteroids and comets do?

Date: Thu Apr 19 18:51:01 2001
Posted By: Nicolle Zellner, Grad student, Studies of the Origin of Life/Astrobiology, Rensselaer Polytechnic Institute
Area of science: Astronomy
ID: 987196741.As
Message:

In the days before electronic and computer-controlled telescopes, astronomers would sit outside with their telescopes and search for objects that moved. They would just scan the heavens, back and forth, looking for some object that wasn't there the night before. In fact, some amateur astronomers (those who don't study Astronomy as a profession) still do this.

In 1781, the French astronomer Charles Messier scanned the sky and compiled a list of objects that weren't comets because he didn't want to get confused by other "fuzzy objects" while he was looking for comets. The list is now called the Messier Catalog and its members have names like M1 (the Crab Nebula in the constellation Taurus), M31 (the Andromeda Galaxy), and M57 (the Ring Nebula). There are 110 members total, though there are a few duplicates (1) and the designations are still used today.

With the age of photographic film and photographic plates, astronomers were able to take pictures of sections of the sky. To look for comets and asteroids, two pictures of the same section of the sky on two different nights were placed side by side. Using an instrument called a blink comparator, the pictures were alternatingly "blinked" on and off. Steady objects like stars and galaxies would stay in the same spot in both photographs; objects like comets and asteroids would move.

Today, sophisticated instruments like the Hubble Space Telescope (HST) (2), the Sloan Digital Sky Survey(SDSS)(3), and NEAT (Near-Earth Asteroid Tracking)(4) are discovering comets and asteroids and are tracking those whose orbits come close to Earth's orbit. The high-speed imaging allows hundreds of scans of the sky in a very short time period, and complex computer programming is able to distinguish which objects are comets and asteroids and which are not.

Instruments on spacecraft like NEAR, the Near-Earth Asteroid Rendezvous (5) and Stardust (6) allow scientists to determine what asteroids and comets are made of. By analyzing spectra, we know what kinds of elements and molecules exist on these bodies. So far, we know that water, methane, ammonia, and even cyanide are common (7). Stardust's mission is to return some comet particles to Earth (6) where we can actually study them in a laboratory. Knowing what comets and asteroids are made of has implications for a lot of other sciences, particularly biology. Organic molecules and water exist on these bodies and these bodies collided (and continue to collide) with Earth. It's very likely that asteroids and comets delivered Earth's first biological ingredients, and if it happened on Earth, it's very likely that it happened (or is happening) on other planetary bodies, both in our Solar Sytem and outside of it.

(1) "Introductory Astronomy and Astrophysics", Zeilik, Gregory, and Smith, 3rd Edition, 1992.
(2) http://www.stsci.edu
(3) http://www.sdss.org/
(4) http://neat.jpl.nasa.gov/
(5) http://near.jhuapl.edu/Education/intro/NEARintro.html
(6) http://stardust.jpl.nasa.gov/
(7) "Moons and Planets", Hartmann, 4th Edition, 1999.


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