This radar image of asteroid 2005 YU55 was generated from data taken in April of 2010 by the Arecibo Radar Telescope in Puerto Rico. Image credit: NASA/Cornell/Arecibo
It’s not unusual to have small asteroids pass closer to the Earth than the moon’s distance of 240,000 miles. Matter of fact, the house-sized 2011 UX255 buzzed only 96,000 miles from our planet last Friday and little 2011 MD gave us a close shave at just 7,500 miles on June 27. Next up is 2005 YU55. This one’s bigger than most at 1,300 feet or 400 meters in diameter, and will jitterbug across the evening sky next Tuesday night November 8 at a distance of 205,000 miles or about 4/5 the way to the moon. The orbit of the asteroid makes it a regular in the neighborhood, but this is the closest it’s come in the past 200 years.
As with the earlier asteroids, 2005 YU55 poses no threat to Earth now and for at least the next 100 years. Astronomers have used radar to refine its orbit with great precision so there’s no cause for concern. Nor will the space rock’s gravitational pull have any detectable effects on Earth. But if our featured asteroid did strike the planet, it would make a good mess of things, since even a relatively small object has tremendous energy due to its cosmic velocity of many thousands of miles per hour. It’s estimated that 2005 YU55 would tear into the planet with the equivalent explosive power of 60 hydrogen bombs.
The asteroid 2005 YU55 moves closer to our planet each day. Today it's 5.1 million miles away. Beware! Objects appear closer than they really are. Credit: NASA
2005 YU55 is darker than a charcoal briquette, nearly spherical and makes one spin on its axis about every 18 hours. NASA scientists will be tracking it with its 230-foot Deep Space Network radio telescope at Goldstone, California beginning this Friday the 4th. Tracking will continue at Goldstone for at least four hours each day from Nov. 6 through Nov. 10. Radar observations from the Arecibo Planetary Radar Facility in Puerto Rico will begin on Nov. 8, the same day the asteroid will make its closest approach to Earth.
Scientists are hoping to use the flyby as an ideal opportunity to map the asteroid’s surface by pinging it with radio waves and then collecting the returned signals. Analysis of the data will help them build a map showing details as small as 7 feet across as well as provide information about the object’s shape, size and composition. The pictures are reminiscent of sonograms and employ a similar echo-sensing technology. The more we learn about near-Earth approaching asteroids like 2005 YU55, the better equipped we’ll be to understand and plan for any future asteroids that might pass too close for comfort.
The green box in this wide view of the sky the night of Nov. 8 shows the portion of sky the asteroid will zip through between the hours of 8 and 9 p.m. Central Standard Time. Center your telescope on 13 and 9 Pegasi, then use the detailed charts below to star-step to the asteroid. Maps created with Stellarium
To spot this speedy space rock next Tuesday evening, you’re going to need a telescope. At brightest, it will shine at magnitude 11.2 or five levels below what the naked eye can see. Seasoned observers can track it in a scope as small as 3-inches, but most will need a 6-inch or larger instrument simply because a bright gibbous moon will be in the same region of sky. Moonlight has this bad habit of hiding fainter stars. You’ll also need a good star map and stick-to-itiveness, because 2005 YU55 will be traveling up to 7 arc seconds per second. That translates to one full moon diameter (one-half degree) in just under five minutes. Zippy!
Detailed view showing the asteroid's path every 10 minutes from 8-8:30 p.m. CST through the stars of Pegasus beginning just south of 9 and 13 Pegasi (top). Stars are shown to 12th magnitude. North is up and east to the left. Many telescopes invert the view, so remember to flip the map upside down if you're using a reflector.
Once found, the asteroid will appear at medium and high magnifications to move continuously like a faint satellite. I’ve watched a few close asteroid approaches and it’s very exciting to see a cosmic object move so rapidly. As you gaze through into the eyepiece, it dawns on you that you’re looking at a flying rock the size of a battleship a “hair’s breadth” from the home planet. Suddenly those twinkly little lights in the solar system feel much more real.
The asteroid is best seen from the U.S., where it will fly through the constellations Delphinus and Pegasus high in the southern sky from the time of closest approach through the remainder of the night. European observers can catch it early on in the constellations Serpens and Aquila, but it will be farther away and fainter with a magnitude between 13 and 14. Closest approach to Earth occurs around 5:30 p.m. CST Tuesday Nov. 8. That’s 12:30 a.m. Nov. 9 across most of central Europe, where the asteroid will still be visible but located low in the western sky.
This second map shows the asteroid's flight between 8:30 and 9 p.m. CST. Remember to add one hour for EST, subtract one hour for MST and two hours for PST. The path in both maps is drawn for Kansas City and the central U.S.
The very best map I’ve seen for tracking the space rock is on page 53 of the November 2011 issue of Sky and Telescope magazine. Because 2005 YU55 will be so close, it takes a slightly different track across the sky depending on where you live, similar to holding your index finger at arm’s length and watching it shift back and forth as you open and close either eye. The Sky and Telescope map includes a little map of the U.S. placed on the asteroid’s path that helps compensate for this shifting effect called parallax. If you don’t have access to the magazine, you can use the maps I created, which are based on the same information. UPDATE: Online version of the Sky and Telescope chart is now up.
The position of the moon in relation to the Pleiades cluster is shown from four widely separated places on Earth. Objects close to the Earth shift position against the distant background stars depending on your location. Credit: Tom Ruen
Positions are shown at 10-minute intervals – I did say it was moving fast – for Kansas City and central regions of the country. If you live in the far southern U.S., the asteroid’s path will lie almost 1/4 degree above (north of) the line and 1/4 degree below (south of) the line if you live along the northern border. And if you’re on the West Coast, the asteroid will be about 3 minutes ahead of the times shown. East Coasters will see it 2 minutes behind those times. Let’s do an example.
Someone living near New York City planning to see 2005 YU55 at 9 p.m. local time should look for it 2 minutes shy of the 8:00 p.m. map position. An observer in San Francisco looking at 6 p.m. local time would point their scope 3 minutes past the 8:00 p.m. mark.
If you have sky charting software like MegaStar, SkyOrb, SkyMap, Redshift, Guide and others, you can plot your own site-specific maps of the asteroid’s path by opening up your asteroid menu and adding 2005 YU55 and its orbital elements. Here are the latest elements from the JPL Horizons website:
* Epoch: 2011 November 13
* Mean anomaly (M) = 50.3717704
* Semi-major axis (a) = 1.1574416520
* Eccentricity (e) = .430606239
* Argument of perihelion = 273.574761
* Longitude ascending node = 35.9342364
* Inclination (i) = .34122817
* Equinox 2000
* H = 21.92, G=0.15
The good thing is that 2005 YU55 is fairly bright and will remain near it maximum brightness for much of the night. Even if you don’t compensate for parallax, just center your scope on one of the times shown and wait and watch. If you examine the field of view carefully, you should notice that one of the “stars” is slowly moving to the east after a minute or two. Congratulations – you’ve just found the asteroid! Now stay on its tail and enjoy the ride.