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

Today's issue status: done, updated

• 2004 FH as meteor event
  by Marco Langbroek
• News briefs – comet, meteor & 2004 FH news Panel 2 – comet, 2003 VB12 & Hubble news
• Risk monitoring

Cover: Three views of little 2004 FH. At upper left, confirmation images from Felix Hormuth at Starkenburg Observatory Wednesday night. Next to it, from later that night, a four-minute exposure by Bill Yeung at Desert Eagle Observatory, who notes, "if you look closely you can see three peaks" in brightness, "definitely a fast rotator." Pasquale Tricarico's ORSA animation shows a schematic view from 2004 FH, looking toward Earth while flying through the Earth-Moon system (without the rapid spin!). See also a 368Kb version at 5° FOV and an overhead view.

2004 FH as meteor event
  By Marco Langbroek – updated March 20th, see change log

There was a small discussion on the MeteorObs mailing list about what would have happened if 2004 FH hadn't flown past Earth (e.g., atmospheric radiant and speed). For some indication, I turned to the model work of Hills and Goda[1]. Assuming a diameter of about 20 meters, such an object would give a magnitude -25 fireball, and would violently and almost completely disintegrate in the atmosphere if it is a stony asteroid. Only very small fragments would survive, if any. If it is an iron object, however, multi-ton fragments could survive, and could retain part of their cosmic speed to ground level, creating craters some tens of meters wide and blast damage within several thousand meters{c1}.

An object 20 meters wide is close to the realm of larger meteoroids that cause meteor fireballs. Out of curiosity, I calculated the theoretical radiant of 2004 FH

1. Hills, J.G. & Goda, M.P., The fragmentation of small asteroids in the atmosphere, Astron. J., v105 n3, 1114-1144, ADS.

2. Neslusan, L. et al., A computer program..., Astron, & Astroph., v331 (1998), 411-413, ADS.

The orbits of Earth, 2004 FH, and three 1950s meteors.

and particles in similar orbits using the software of Neslusan et al.[2]. Based on the pre-encounter orbit given in MPEC 2004-F26, the result is a theoretical radiant of very slow meteors, with atmospheric speed 13.2 km/s and geocentric

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speed 6.9 km/s. For comparison, the slow Peekskill fireball had 14.7-km/s atmospheric and 10.1-km/s geocentric speeds. The radiant would be in northern Libra near RA 226°, Dec. -4° for March 19.0.

Searching the IAU photographic meteor database for such meteors using Drummond's D' criterion (threshold D' < 0.105), I found three — all from the Harvard Super Schmidt project, photographed on 13 March 1953, 16 April 1953, and 13 December 1956. While this is perhaps not enough to confidently talk about a "stream," it does show that Earth has encountered cosmic debris in similar orbits before. The spread in dates is largely because Earth encounters these particles near aphelion, and small variations in aphelion distance result in different times of orbit intersection.

The spread in perihelion direction of these three meteors is a bit large, too, and that has more bearing on whether these meteoroids and 2004 FH are part of a coherent stream. The spread might be a bit too large,

but we should realize here that meteoroids in this type of orbit can have frequent encounters with the inner planets, causing them to spread fast. For example, the encounter with Earth changed the perihelion direction of 2004 FH by almost 10 degrees. Last but not least, we should also bear in mind that the pre-encounter orbit for 2004 FH is based on a limited arc of observations, so the perihelion direction of the asteroid itself will have an intrinsic uncertainty as well.

See also information about the Super Schmidt cameras.
Marco Langbroek is a professional archaeologist and an amateur meteor astronomer active with the Dutch Meteor Society. He is published on topics as diverse as Neanderthals and comet dust trails, and has helped inform A/CC readers about recent European meteor events (Index).

To cite this article, please use:
Langbroek, M., 2004 FH as meteor event, A/CC 19 March 2004, http://www.hohmanntransfer.com/mn/0403/19.htm#04fh.

Comet news:  Space.com has a guide today for observing comets C/2001 Q4 (NEAT) and C/2002 T7 (LINEAR), both of which could become visible to the unaided eye in late April and early May.

Space.com also has an item today about Stardust 81P/Wild 2 flyby images, as does Sky & Telescope from yesterday. They report less dust was detected at the comet than expected, and the detector may have been shadowed somehow. S&T notes, "Scientists were unable to determine the mass and thus the density of the comet's nucleus." See yesterday's report for more links about this latest Stardust news.

Meteor news:  BBC reported yesterday, "UFO streaks through Martian sky," telling that MER Spirit caught maybe "the first meteor seen from the surface of another world," or maybe the old Viking 2 orbiter.

The Paragould Daily Press has an article today, "Local resident recalls uncovering piece of 'Paragould Meteorite'," about the February 1930 Arkansas event

and finding a smaller piece. The paper told Tuesday about an effort to bring back the biggest piece.

2004 FH news coverage:  Astrobiology Magazine has a report today, "Spaceguard Redux, Put to Test," summarizing 2004 FH news, and there are perfunctory AP and Reuters wire stories on most news sites about the flyby, but the Albuquerque, New Mexico Tribune has a fresh take today, telling discoverer LINEAR's point of view. Reports were all over the place about how dangerous an object of 2004 FH's estimated size (20 to 30 meters/yards wide) would be if it hit Earth:

"The smallest impactor that can penetrate the atmosphere deep enough to cause any damage on the ground is not much smaller than . . . 50 to 70 meters." – Alan Harris, Space Science Inst., Astrobiology Magazine

"If it hit . . . it would cause significant local damage." – Grant Stokes, LINEAR, Albuquerque Tribune

"If it had struck [it] could have wiped out a city." – Addi Bischoff, Univ. of Muenster Inst. for Planetology, Expatica

See above for a different explanation.

more news briefs >>

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New comet:  MPEC 2004-F39 announces newly discovered comet P/2004 F1 (NEAT), with the first NEAT observation yesterday morning with its Mt. Palomar telescope, and also showing Catalina Sky Survey (CSS) observations at about the same time as well as LINEAR observations from February 16th and March 14th. Five other observatories confirmed the discovery overnight. The first early calculation has perihelion out beyond Mars at 2.45 AU last October 20th.

More about 2003 VB12:  Science News, from its edition dated tomorrow, has an article, "Planetoid on the Fringe: Solar system record breaker."

The Flagstaff, Arizona Daily Sun has an article today, "Redefining our solar system," about planetary science semantics.

Hubble news:  An Associated Press wire story appearing on many news sites, such as at CNN today ("Astronauts who fixed Hubble fight to save it"), reports that "many of the astronauts who worked on Hubble hundreds of miles above Earth are dismayed, bewildered or both by NASA's decision to pull the plug on the mighty observatory."

The Philadelphia Inquirer has an article today, "Rescuing Hubble – via robot," that reports "NASA Administrator Sean O'Keefe has authorized his engineers to seek a robotic alternative to a space shuttle flight to replace Hubble's failing gyroscopes and batteries."

Risk monitoring 19 March

The Friday Daily Orbit Update MPEC has a large photometric set of 2004 FH observations from Desert Eagle Observatory in Arizona yesterday along with positions reported from Auckland Observatory in New Zealand, and observations from this morning from Tenagra II Observatory in Arizona. Today NEODyS slightly lowered the rating for its one impact solution, but JPL added two solutions beyond the NEODyS 2080 time horizon and slightly raised its low overall risk assessment.

Late update:  JPL has issued a new 2004 FH risk assessment based on the previously available data, increasing its impact solution count by one and slightly lowering its overall risk ratings. Of 203 reported positions, the new assessment uses all, while previously one had been rejected (the current NEODyS assessment rejects ten).