07/02/06

HELLO AGAIN, 1990DA! (WITH A POP QUIZ, AT NO EXTRA CHARGE)

From the Director:

Certainly the most exciting (and dare I say most glamorous?!) part of observing Near Earth Objects is participating in the discovery of a new asteroid or comet.  There is the initial posting of a possible new discovery on the Minor Planet Center's "Near Earth Object Confirmation (web) Page", a scramble to program observations for the object in that evening's imaging session, and then the oft times hair-pulling time spent scrutinizing CCD images with blurry eyes in the wee-hours of the morning, trying to pick out that distinctive set of moving smudges of light as they dodge between background stars.  And there is a palpable spirit of competition as well, with observatories all around the world trying to locate the same object and get their measurements reported to the MPC at the earliest possible moment, before the confirmation process is completed and a discovery announcement made.  Phew!  I get excited just thinking about it!

But, there is a down & dirty, roll-up-your-sleeves aspect of this work that is just as important, and often neglected.  An object's calculated orbit is no better than the sum of all the observations made to determine the unique set of numerical constants which define the orbit.  And although an orbit has been calculated at one point in time, it is possible that its orbit has been perturbed in an unforeseen way by another object or force which was not factored into the most recent set of orbit calculations.  Hence the need for continued follow-up observations.  This is particularly important for Near Earth Objects, which may pose a potential future impact threat to our own planet.

Follow-up observations made one or more years after the initial discovery are usually timed to coincide with an object's "opposition" - that is, when the Earth is situated in more or less a straight line between the Sun and the object of interest.  This ensures that the object is illuminated by the Sun to the maximum possible degree and is thus easier to observe.

On June 17th, 2004, it was noted on the MPC's listing of "Last Observations of Unusual Minor Planets" that there was a need for observations of an object designated 1990DA.  This asteroid was discovered by the Dynic Observatory near Kyoto, Japan in February 1990 and according to MPC records, was last observed in June 2003.  1990DA was programmed into Francisquito's observation list for the evening of June 17th and 5 clear images were obtained, thus enabling a precise reporting of its position back to the MPC.  As asteroids go, 1990DA is a big boy (or girl, to be completely fair) with an estimated diameter of 4.2km to 9.4km.  But, because it was imaged by Francisquito at a distance of over 331 million kilometers (see the orbit diagram at the bottom of this article) it was quite faint, at about magnitude 20.  This represents the most distant observation yet made of a minor planet by Francisquito.  And as expected, 1990DA dropped off the 'desirable for observations' list the day after Francisquito's measurements were sent in.  There was something uniquely satisfying about being the first human eyes to see an object after having completed our most recent trip around the Sun.

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And now, as promised, a Pop Quiz!  No, no - don't run away!  It'll be fun...you'll see.

This will be a chance for you to try out NASA/JPL's Orbit Diagram Tool, which is a cool way to visualize the paths of bits of rock and ice which roam the inner and outer Solar System.  First the quiz question:

When (closest month and year) will 1990DA next be at opposition?

And a bonus question for extra credit: How far away (in kilometers, miles, furlongs or whatever unit of your choosing) will 1990DA be at the opposition date that you identified?

Here is some help using the Orbit Diagram Tool:

Go to the web page: http://neo.jpl.nasa.gov/orbits/

* In the empty box under the heading "Object Number, Designation, or Name", type in 1990 DA and then press the Search button.

* Your Internet browser must be 'Java enabled' for this tool to work, so if nothing happens, you may need to update your browser and/or adjust its settings.  Immediately after pressing the Search button, some browsers will generate an error message which says "A Runtime Error has occurred.  Do you wish to Debug?"  Just select "No" and you should see an orbit diagram appear in a few moments.  The Sun is the red dot at the center of the orbits of the other planets and objects.

* Here is one of the coolest features of this tool: the slider bars immediately under, and to the right of the graphic image allow you to rotate the viewing perspective.  This enables you to see how the orbital planes of asteroids and comets are often wildly different from the orbital planes of the major planets.

* Using the playback control buttons, you can step forward or backward one day at a time, or move continuously forward or backward through time, to any date of your choosing, past or future.

*  To help you answer the quiz question, it is recommended that you rotate the viewing perspective so that you see more or less a "plan view" (from above) of the inner Solar System.

*  Remember what "opposition" is: when the Earth is in situated in a nearly straight line between the Sun and the object of interest.  As you step through 1990DA's orbital path, it may seem that the Earth is just about catch up with 1990DA, only to have it pull away again.  Be patient....we'll catch up, I promise.  This is an excellent way to see one of Keppler's laws in action: as an object approaches the massive body about which it is orbiting (the Sun in this case), its angular speed will increase.  It's all about conservation of energy: Potential Energy + Kinetic Energy = Constant.

Good luck with your Pop Quiz!  We'd love to hear from you with your answers.  You may E-mail your answers to: director@francisquito.org

Image generated with NASA/JPL's Orbit Diagram Tool (http://neo.jpl.nasa.gov/orbits/)