The Asteroid/Comet Connection's
daily news journal about
asteroids, comets, and meteors

Today's issue status: done

• News briefs – points & streaks + meteor news
• Risk monitoring

Cover: Two photos by Robert Verish (Index) show some of the beauty and magic, as well as the difficulty, of searching for meteorites in remote desert areas. The small find is shown where found on 4 November 2003, and the images are used with permission from the 30 April 2004 page on his Nevada Meteorite Picture site.

Points & streaks:  About the Raptor news item yesterday, Tim Spahr of the Minor Planet Center commented to A/CC that “no survey looks for streaks as a matter of principle. They look for motion over a fairly long time frame. LINEAR, for example, generally gets 45-60 minutes between frames. With this time interval, the diurnal parallax of an object that will impact in a few days is readily apparent. Thus, the idea that we would not detect impactors without a stereo system is really not true.”

He continues: “Also, most folks keep their exposures short enough to prevent the object from trailing. Even 1 degree per day motion (fairly typical of an NEO) will not result in a trailed image on most amateur CCD cameras until the exposure times are on the order of one minute. A one minute exposure can reach almost 20th magnitude for lots of folks.”

There was also discussion on the Minor Planet Mailing List (MPML) about the Los Alamos National Lab (LANL) article and the assertion that “the asteroids of most concern are headed straight for Earth and thus leave no streaks.” A message forwarded to A/CC contained a comment by Gordon Garradd that those are the asteroids that “will miss, unless they are already really close,

[because] by the time the object gets here the Earth will have moved around its orbit a bit!” (The Earth travels through its own diameter in six minutes, and the article talked of an eight-hour warning time.)

Alan Harris noted that “the diurnal parallax of a nearby object means that even something coming right at you is not stationary in angular motion.” And he said, “fundamentally, the point of an optical [NEO] survey is not to detect ‘death plunge objects,’” something that doesn't provide “a really meaningful advance warning.”

Meteor news:  The June Inframatics newsletter has been posted in multiple PDF resolutions with information of interest mainly to those with a technical understanding of infrasound detection and analysis, but also includes a brief status report on the Comprehensive Test Band Treaty (CTBT) International Monitoring System. The March issue has an article of four-plus pages that should of wider interest. It reports a 17 January 2004 meteor event north of the Arctic Circle (67.06N, 19.23E) that was recorded by four Swedish infrasound stations and had a main explosion corresponding “to about 1.7 tons of TNT.” The experience shows how much can be learned about such events from infrasound, and also some of the constraints, such as needing wind and temperature profiles to help determine the altitude of a sound source.

Risk monitoring 31 July

The Saturday Daily Orbit Update MPEC has observation of 2004 OT11 from yesterday morning from Francisquito Observatory in southern California, and today NEODyS slightly lowered its risk ratings for this kilometer-size object and JPL very slightly lowered its assessment.

The Minor Planet Center Last Observation page is showing that Powell Observatory in Kansas has reported both 2004 NL8 and 2004 OT11 from this morning.