(meteorobs) Close Approaching Asteroid Discovery Rate

[Wayne Hally]

To repeat the point made by Carl Hergenrother in his post of January 18th.

 

"To further this point, 22 NEAs were observed to pass within

1 Lunar Distance (LD) of Earth in 2010. Sounds impressive until we realize
that 4-5 10-meter asteroids should pass within 1 LD of Earth every day. If
we drop down to 1-meter objects the rate could be as high as a few thousand
per day! 

 

So it doesn't really matter if there are 1, 3, 5 or 20 known NEAs passing
within 0.15 AU of Earth on any single day because the number of unknown
objects (even within a few LD) is much much greater"

 

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The flux of asteroids is no higher than it's ever been, all that has changed
is that Catalina and Pan-STARRS have vastly increased the number of
asteroids (particularly small ones) we can now detect. Some stats.

 

Prior to this year for February, there were 20 KNOWN asteroids approaching
within 0.2 AU of the earth (0.2 AU is actually quite far away); that's the
cutoff used on the JPL Sentry Close Approach page. That's 0.71 per day. 40
were discovered, making the total KNOWN 60 for the month (2.14 per day). The
new discoveries included all 14 that came within 10 LD (0.50/day), 4 of
which passed within 2 LD (0.14/day).

 

For March, there were 19 previously known within 0.2 AU (0.61/day), 40 were
found for a total of 59 (1.90/day) including all 14 that passed within 10 LD
(0.45/day), 7 of which passed within 2 LD (0.23/day).

 

For obvious reasons, the week or so around the time of the new moon is when
the most are discovered (like now). For February's New Moon, the peak was
2.7 close approaching asteroids discovered per day, for March 2.1/day. The
minimum in discoveries is around the time of the Full Moon (0.6/day Feb,
0.7/day Mar).

 

>From Jan 15th through July 31, there are  261 KNOWN CA asteroids (0.2 AU),
59 within 10 LD (53 of them newly discovered), and 19 within 2 LD (18 newly
discovered). This will of course increase, since many new tiny asteroids
that pass within 10 LD will be found during the New Moon periods of May,
June, and July.

 

The point is that the flux of nearby asteroids does not change; there is no
statistical support for an assertion that this time is any more favored than
any other based on the KNOWN close approach asteroid rate. The current rate
of CA asteroids, those passing within 10 LD, and within 2 LD is no higher
this month than it is any other month. The only thing that has changed is
how many we can detect.

 

Wayne