MINOR PLANET 2003 XJ7 ZOOMS BY
This AstroAlert is being issued right about the time another asteroid has entered Earth-Moon space. The object will pass just 150,000 kilometers from Earth -- 40 percent of the distance to the Moon -- around 19:04 Universal Time December 6th (today). It will then be racing 0.4 degree per MINUTE across Canis Major, heading south.
The interloper was first picked up only yesterday by the LINEAR minor-planet survey in Socorro, New Mexico. Some 19 hours later, amateur astronomer Peter Birtwhistle of West Berkshire, England, reimaged it with his 12-inch Schmidt-Cassegrain telescope. He has posted an animated GIF on his Web site at
http://www.birtwhi.demon.co.uk…20031206_PBirtwhistle.gif
LINEAR's and Birtwhistle's measurements allowed Kyle E. Smalley of the Minor Planet Center in Cambridge, Massachusetts, to compute details of the flyby. In announcing the find on an electronic circular late last night, the center designated the object 2003 XJ7. The Minor Planet Center's Web site is at
http://cfa-www.harvard.edu/iau/mpc.html
Smalley calculates that 2003 XJ7 is heading toward the Sun in an orbit inclined 18 degrees to the ecliptic. Every 1.38 years it ranges from 1.82 astronomical units (just beyond Mars's orbit) inward to 0.66 a.u. (the orbit of Venus) and back out again.
Only a half dozen asteroids have ever been observed to pass this close to Earth. The closest of all, 2003 SQ222, came within 78,000 km of Earth's surface in late September. While 2003 XJ7 will miss by almost twice this distance, it is a much larger body -- perhaps 20 meters across.
Because 2003 XJ7 could be potentially hazardous to Earth at some future approach, refining knowledge of its orbit is urgent before it becomes lost in solar glare during the early hours of December 7th (UT). Experienced amateurs who can make astrometric measurements should submit them to the Minor Planet Center -- but you haven't got much time! Southern Europe and Africa may be the last places on Earth from which the object can be imaged as it recedes.
For the next few hours, the ephemeris below gives the asteroid's rough equinox-2000.0 right ascension and declination, distance from Earth, and visual magnitude. But because it is passing so close, it can appear shifted as much as 2 degrees by parallax. Would-be observers should use the Minor Planet Center's online Ephemeris Service to obtain its exact trajectory as seen from their own geographical location.
Roger W. Sinnott
Senior Editor
SKY & TELESCOPE
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2003 UT R.A. Decl. Delta Mag.
h h m o a.u.
Dec 6 15 06 14 +28.6 0.0019 13.9
Dec 6 16 06 24 +21.3 0.0016 13.5
Dec 6 17 06 36 +10.4 0.0013 13.3
Dec 6 18 06 54 -05.9 0.0011 13.3
Dec 6 19 07 19 -27.2 0.0010 13.6
Dec 6 20 07 58 -48.5 0.0011 14.5
Dec 6 21 08 59 -63.8 0.0013 15.5
Dec 6 22 10 32 -72.1 0.0016 16.6
Dec 6 23 12 18 -74.9 0.0019 17.5
Dec 7 00 13 42 -74.6 0.0022 18.2
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