Asteroid 2012 TC4 On Track For Close Earth Flyby

In this flyby simulation, Earth is the blue dot; the purple dot and orbit represent a geosynchronous satellite and its orbit, and the white dot and orbit is the moon. Watch how the orbit of 2012 TC4 gets deflected as it passes by Earth. Earth is blue. The green path of 2012 TC4 turns darker as it dips below the ecliptic plane. Credit: Tony873004, created with

Here comes another one! Early Thursday morning, Oct. 12, the house-sized asteroid 2012 TC4 will pass fewer than 9,000 miles from the geostationary belt of communications satellites that ring the Earth. At closest around 12:42 a.m., the flying boulder zips about 31,180 miles (50,180 km) above Earth’s surface, coming closest around 12:42 a.m. Central time. Observers in the Americas (especially South America) will get the best views as 2012 TC4 hurtles from Capricornus across Microscopium and into southern Sagittarius during early evening hours.

Later Thursday at 2:19 p.m., the asteroid will pass some 172,000 miles (277,000 km) from the moon. Because it will get so close, Earth’s gravity will alter the asteroid’s orbit. No worries through — this rock will pass by harmlessly.

This locator map, with stars to magnitude 8, shows the asteroid’s trajectory across the evening sky on the evening of Oct. 11. Positions are shown every hour starting at 8:30 p.m. CDT. 2012 TC4 will be much fainter, around magnitude 13. To see it, you’ll need to make your own tracking map using sky charting software and the instructions near the end of the blog. Created with Chris Marriott’s SkyMap

2012 TC4 has a fascinating history. It was discovered by the PanSTARRS-1 survey atop Mt. Haleakala on Maui on Oct. 4, 2012, but astronomers weren’t able to observe it long enough to get a exact fix on its orbit. That left astronomers in limbo on just how close the asteroid might come this time around. Estimates ranged as high as 170,000 miles (274,000 km) down to just 4,200 miles (6,760 km). To firm that distance up, new observations were made with one of the European Southern Observatory’s large 8.2-meter telescopes in late July, which allowed astronomers to refine 2012 TC4’s orbit and distance.

Still, of the many near-Earth asteroids discovered, 2012 TC4 has slightly larger than usual chance of striking the Earth because it sometimes passes very close to Earth’s orbit. Astronomers who calculate the odds of impact originally gave the asteroid a 1 in 630 chance of smacking the planet in the next 100 years, but the odds are now even smaller after the new observations. This happens often with asteroids. Once we get a precise orbit, chances of a strike almost always lessen.

Near Earth Asteroid 2012 TC4 appears as a dot at the center of this composite of 37 individual 50-second exposures obtained with the FORS2 instrument on ESO’s Very Large Telescope. The individual images have been shifted to compensate for the motion of the asteroid, so that the background stars and galaxies appear as bright trails. At magnitude 27, this is the faintest near-Earth asteroid so far measured.
Credit: ESO / ESA NEOCC / Olivier Hainaut (ESO), Marco Micheli (ESA) and Detlef Koschny (ESA)

NASA scientists plan to use this month’s close approach not only to get to know 2012 TC4 better but to test NASA’s network of observatories and scientists who work with planetary defense. They’re calling it the 2012 TC4 Observing CampaignThe most recent headline on the site reads: New orbit solution precludes an Earth impact in 2050. Well, THAT makes me feel better. Observatories around the world are coordinating observations nightly on this test run to become better prepared for a potential future threat from space.

“This effort will exercise the entire system, to include the initial and follow-up observations, precise orbit determination, and international communications,” said Professor Vishnu Reddy of the University of Arizona’s Lunar and Planetary Laboratory in Tucson, who led the campaign to track down the asteroid this summer.

Asteroid 2012 TC4 is a small, irregularly shaped asteroid with a fast rotation period. A day there lasts just 12 minutes and 14 seconds. The asteroid’s light varies by nearly a magnitude during a rotation, enough to see with your own eyes through a telescope. Credit: NASA

If you want to see it, you’ll need a darn good map and an 8-inch or larger telescope. At brightest, 2012 TC4 will shine near its peak magnitude of 12.8 for only about two hours as it races to the southwest across the evening sky. By 12:30 a.m., it will have already faded to magnitude 14 and at 1 a.m. to magnitude 15. See it while you can!

I’ve found the best way is to make your own maps suited for your location, especially when it comes to asteroids that pass this close. Here’s how to do it:

If you already have a program like Starry NightMegastar, etc. that can plot an asteroid path, just go to the Minor Planet and Comet Ephemeris Service, type 2012 TC4 in the open box, then key in your latitude and longitude. Scroll to the end of the page, select your software program. and click on the Generate ephemerides/HTML button. Save the file that pops up on your screen into your program, open the program, select the asteroid, and create a custom map with time intervals and a magnitude range to your liking.

If for whatever reason, you’re unable to track the asteroid yourself, astronomer Gianluca Masi in Italy will stream it live on his Virtual Telescope Project site at two different times: 2 p.m. CDT (19:00 UT) from Italy on Oct. 11 and at 9 p.m. CDT Oct. 11 (2:00 UT – Oct. 12) from Arizona.