Recent Discoveries – Sept 12, 2010

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

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