Small asteroid 2011 MD is zipping by earth
Less than 24 hours before its closest encounter on June 27, 17:01 I had the chance to make some astrometric measurements on this small solar system body. 2011 MD was discovered by LINEAR four days earlier on June 22 and confirmed by J95 Great Shefford, Sandlot Observatory. Hidetaka Sato via RAS Obs. Mayhill , and Sabino Canyon Observatory on the same night. Just in time the cloudes cleared the view after three weeks of unstable weather. After acquiring 4 sets of 10 second exposures, spaced by 20 minutes, I decided to add a sequence of 180 images to get good animation where the asteroid would cross almost the entire field of view of my C14 and the attached ST-8 ccd camera. The image to the left is a combination of 30 two-second-exposures showing the asteroid leaving behind a streak because the single images where aligned and stacked on the stars. At this time 2011 MD was almost 200,000 km away from earth but already entered the earth-moon-system, travelling through the constellation Hercules. When reaching the smallest distance there will be only 12,280 km between the space rock and the earth's surface.
With only 5 - 20 m in size this near earth asteroid apposes no danger to us, even if it would hit the earth (what it does not) it would burn up in the atmosphere making only a spectacular fireball maybe with a few small meteroids reaching the ground.
The encounter is so close, that the gravitational field of the earth will change the path and orbit of 2011 MD significantly. Almost like a swing-by maneuver by a space probe. But it will be very hard to observe afterwards, because it's departing into the direction of the sun. The next visit will be in 2022.
I believed to notice a small drop in brightness in the middle of the animation. Other observers also reported brightness varations probably caused by the rotation of the asteroid. However I did not get photometry data and wasn't able to detect a periodicity.
Anyway - it was fun taking part in the worldwide tracking of this object - the fourth closest observed encounter of a near earth object.
(90403) 2003 YE45
2003 YE45 passed the earth on July 13 in a distance of 0.0424 AU (or 16.5 lunar distances). It was a radar target of Arecibo on July 6 and 7 and the observations revealed that it is a extremely slow rotator with a period of 1-2 weeks. Its size is about 1-2 km. 2003 YE45 reaches 15th magnitude in July and will be a good target for photometry. Goldstone observations were scheduled for July 16-19.
Our own astrometry observations on July 15 and 19 were sent to the Minor Planet Center and published in MPEC 2008-O11 and MPEC 2008-O02. 2003 YE45 is classified as Potential Hazardous Asteroid
Rotation rates of asteroids are important for understanding their formation and structure. Lately the influence of the Yarkovsky effect in increasing rotation periods is investigated extensively [nature]. A variant of the Yarkovsky effect is the so-called YORP-effect, describing absorption and reemission of sunlight leading also to deceleration of asteroids rotation rates. So also very slow rotators - like 2003 YE45 - could be explained by the YORP effect.
(90403) 2003 YE45, PHA, 15.1 mag , P.A. 104.6°, 10.6"/min
Sequence of 10 x 10 sec. exposures on July 19.96893 - 19.98155,
14 inch Schmidt-Cassegrain, ST8-XME 2x2 binned, image scale 1.75"/pixel
Close flyby of asteroid 1998 FW on September 29, 2009
This not so little sucker (approx. 400-600 meters) will encounter the earth at a distance of 8.63 LD (lunar distances) on September 29, 18:43 UT. It will be a radar target a Goldstone and Arecibo. Due to its highly eccentric orbit it is possibly an extinct comet belonging to the Jupiter-family.
We contributed astrometry on Aug. 23 and Sept. 9 to the MPC (MPEC 2009-R32). In the 30 minutes exposed image the asteroid shows up as a bright streak. During this time the object was clearly visible on a single 30 second exposure at mag. 17. It will brighten up to magnitude 14 and be an easy target for amateur telescopes. From September 19 - 30 1998FW4 is moving through the constellations Aquarius, Aquila and Ophiuchus accelerating rapidly. After September 30 it will be unobservable.
Comet 217P/Linear ...
... was recovered on March 17, 2009 by italian astronomers with a remote controlled telescope in New Mexico, USA at magnitude 18. The comet was last seen in 2002. On August 22 spanish comet observer David Cardenosa reported an outburst in activity and the appearance of a new jet. Further image filtering revealed a clockwise spiraling jet to the northwest.
We obtained follow-up observations on August 23, 30 and 31. On the picture of Aug 23 this feature and a second tail are clearly visible. Image processing with a Larson-Sekanin-Filter (3.0 pixel, 7.5 degree) reveal the details. The spiraled arc northwest of the central condensation interfere with a startrail but is still well-defined. Such arclets are indicators of possible fragmentation events or even nucleous splitting - sometimes also called "coma wings" (click on image to enlarge).