Earth’s Fickle Companions

A small number of asteroids are currently in a temporary 1:1 orbital resonance with the Earth in their orbit around the Sun.  Unlike the Moon, which is in a stable orbit around the Earth, these much tinier “co-orbital” objects are “just passin’ through.”

3753 Cruithne (1986 TO)
Came relatively close to the Earth each November from 1994 to 2015.  This will next happen around 2292.
Wiki  JPL  Orrery

85770 (1998 UP1)
Passes close to Venus, too.  This next happens in 2115.
Wiki  JPL  Orrery

54509 YORP (2000 PH5)
This tiny asteroid, perhaps 492 × 420 × 305 feet across, is a rapid rotator, turning around once every 12m10s. It is named after the YORP effect, as it provided the first observational evidence of that effect speeding up its spin rate.  It’s day will be half as long in only 600,000 years, and it may eventually speed up to one rotation every 20 seconds!
Wiki  JPL  Orrery

2002 AA29
This near-Earth object has an orbit that is very similar to the Earth’s, and even more circular, though it is inclined a full 10.7° to the ecliptic.  This asteroid is a good candidate for an automated sample-return mission and then human exploration because it is relatively close to the Earth and the amount of energy needed to visit 2002 AA29 and return to Earth is relatively small.
Wiki  JPL  Orrery

164207 (2004 GU9)
Currently, this asteroid never strays far from Earth, sometime leading it and sometimes following it.
Wiki  JPL  Orrery

277810 (2006 FV35)
This asteroid is another good candidate for human exploration.
Wiki  JPL  Orrery

2006 RH120
This extremely tiny object (just 7 to 10 feet across) spins more rapidly than any other object on our list: once every 2m45s!  It may even be an old rocket booster from the Apollo era, but recent evidence indicates it is a bona fide space rock.  It is currently leading the Earth in a very similar orbit.
Wiki  JPL  Orrery

2009 BD
We’ve been able to observe orbital changes in this tiny object due to the Sun’s radiation pressure.  It is currently trailing the Earth.
Wiki  JPL  Orrery

419624 (2010 SO16)
This asteroid was discovered using an infrared space telescope (WISE) and is in an unusually stable orbit that will change little during the next several hundred thousand years.  It is currently trailing the Earth.
Wiki  JPL  Orrery

2010 TK7
Also discovered using WISE, about 1,000 ft. across.  The only known Earth trojan asteroid.  It currently orbits the Sun about the L4 Lagrange point (leading the Earth by 60°).
Wiki  JPL  Orrery

2013 LX28
This asteroid has the highest orbital inclination (50°) of all the objects on our list.
Wiki  JPL  Orrery

2014 OL339
Serendipitously discovered while observing asteroid 2013 VQ4.
Wiki  JPL  Orrery

2015 SO2
Discovered from Slovenia.  Currently leading the Earth.
Wiki  JPL  Orrery

469219 (2016 HO3)
Currently, a quasi-satellite of the Earth.  Always remains within 38 to 100 lunar distances from the Earth as it orbits the Sun.  Leads, then follows, then leads again.  Quite a do-si-do!
Wiki  JPL  Orrery

Acknowledgements
The orrery videos for each asteroid were generated using the Jet Propulsion Laboratory’s incredible Orbit Diagram Java applet on their Small Body Database Browser web site (http://ssd.jpl.nasa.gov/sbdb.cgi), and captured using the equally incredible ScreenFlow software from Telestream (http://www.telestream.net/screenflow).  Kudos to both organizations!

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