Today’s post will hopefully begin a new feature on the TransientSky which will focus on newly discovered interesting asteroids and comets. On most nights the professional asteroid surveys as well as some dedicated amateur astronomers find hundreds, if not thousands, of new asteroids. A handful of these come close enough to Earth to be classified as near-Earth asteroids (NEAs).
Yesterday 10 NEAs were officially announced by the Minor Planet Center (MPC), the body authorized to keep track of all asteroids and comets. The official discovery announcements are called Minor Planet Electronic Circulars (MPEC) and links to each are provided in the table below. If the name of the author at the bottom of some MPECs looks familar it’s because my weekend job is to help out at the MPC.
Most NEAs are routine objects that are either very small or will never come close enough to Earth to be a worry. Some of the more interesting ones announced yesterday include 3 small asteroids that passed within 2 lunar distances. Unlike the pair of asteroids that made the news last week, these objects approached Earth from the sunward side and were not seen till after they passed the Earth. Small objects coming close to Earth are common and most happen “sight unseen”. As alarming as this sounds, there is a lot of space out there. For example a 15 meter asteroid will strike Earth once every 50 years on average (objects of this size are still too small to do any damage and will fragment into much smaller pieces long before they reach the ground) but nearly 600 will pass within 1 lunar distance every year. This means for every impactor, an average of (50 * 600) = 30,000 will pass within a lunar distance. The reason is simple, the volume of space within a lunar distance is ~30,000 times larger than the collisional cross-section of the Earth. So reports of small asteroids passing close to Earth really aren’t as scary as they seem.
2010 RM80 – Late on Sept. 5 UT, this tiny 5-20 meter object passed about 1.7 lunar distances from Earth. Based on its current orbit, the asteroid could have passed within half its miss distance. That is still not close enough for an impact though.
2010 RS80 – Another small object (10-35 meters across) passed just over 2 lunar distances from Earth on Sept. 9 UT. Its current orbit does not allow closer approaches.
2010 RM82 – This 15-40 meter in diameter rock traveled within 2.1 lunar distances of Earth on Sept 10 UT. This is about as close to Earth as its current orbit allows.
Asteroid Type MOID a e i H Mag Discoverer MPEC 2010 RN82 Amor 0.360 2.66 0.54 28.6 18.8 18 Siding Spring 2010-R105 2010 RM82 Apollo 0.005 1.18 0.42 4.9 25.7 17 LINEAR 2010-R104 2010 RT80 Amor 0.126 2.05 0.45 7.6 22.4 19 Siding Spring 2010-R103 2010 RS80 Apollo 0.006 1.46 0.37 8.9 26.4 18 Catalina 2010-R101 2010 RR80 Amor 0.229 1.39 0.16 13.4 22.3 20 Mount Lemmon 2010-R100 2010 RQ80 Amor 0.210 2.47 0.51 6.4 22.7 21 Mount Lemmon 2010-R98 2010 RP80 Amor 0.174 3.06 0.62 7.2 20.7 19 LINEAR 2010-R97 2010 RO80 Apollo 0.052 1.18 0.20 23.4 24.6 19 Catalina 2010-R96 2010 RN80 Amor 0.090 2.17 0.52 8.6 20.3 18 L. Elenin 2010-R95 2010 RM80 Apollo 0.002 1.16 0.19 2.2 27.8 20 Catalina 2010-R94 Comet Type MOID q a e i Mag Discoverer MPEC None Type Aten - Earth crossing with semi-major axis (avg distance from Sun) < 1 AU Apollo - Earth crossing with semi-major axis (avg distance from Sun) > 1 AU Amor - non-Earth crossing with perihelion distance < 1.3 AU JFC - Jupiter family comet HFC - Halley family comet LPC - Long-period comet MBC - Main belt comet MOID - Minimum Orbit Intercept Distance, minimum distance between asteroid and Earth's orbit a - semi-major axis, average distance from Sun in AU (1 AU = 93 million miles) e - eccentricity i - inclination H - absolute magnitude Mag - magnitude at discovery Discoverer - survey or person who discovered the object MPEC - Minor Planet Electronic Circular, the discovery announcement
The Transient Sky - Comets, Asteroids, Meteors 
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