# Detecting dangerous asteroids

1. Jan 8, 2014

### GTOM

After a rock hit a Russian town unexpected, i think we still can develop in that field.

I would like to have two questions.

First, certain sources tell, that even with the help of passively detecting infrared radiation, objects can be detected from very far away in space, and a complete sky browse can be completed in hours.

If it is true, then how that meteor wasnt discovered from millions of km-s away?

http://en.wikipedia.org/wiki/Chelyabinsk_meteor

I gladly post my calculations here or the homework topic, i assumed it was warmed by sunlight to an average lunar temperature, 250K, and a radiating area about 227 m2.

I also read, that they underestimated the size of another, low albedo meteor, and they corrected it with the help of a radio-telescope. Can that mean that radars are still superior for observing, detecting things in the solar system?

2. Jan 8, 2014

### D H

Staff Emeritus
What "certain sources"? Those certain sources are very wrong. Yes, objects can be detected from very far away in space if they are bright enough. Small asteroids such as the one that detonated over Chelyabinsk, aren't very bright at all. A "complete sky browse can be completed in hours"? Nonsense.

I strongly recommend that you look at reputable sources rather than "certain sources". The following is from a reputable source, http://www.astro.uwo.ca/~wiegert/chelyabinsk (emphasis mine on the last paragraph):

Why wasn't the Chelyabinsk meteor detected beforehand?

As can be seen in some of the animations listed below, in the hours and days before contact, the Chelyabinsk meteoroid approached the Earth from the direction of the Sun. Even under ideal conditions, an approaching object the size of the Chelyabinsk meteor is visible for only a few hours before its arrival even in the very largest of telescopes. However, when approaching from the Sun's direction, objects become near-impossible to detect. The side of the meteoroid facing the Earth is buried in the object's own shadow and the glare from the Sun. Regardless, we did a check of nearly 6,000,000 images in the image catalogues of the major sky surveys on the off-chance that it had been imaged but not noticed for some reason. We checked for both the final approach of the meteoroid, and any possible near approaches in prior orbits. No images were found in which the object would be seen.

In fact, only about 500 of the estimated 20 million near-Earth asteroids the size of the Chelyabinsk impactor have been discovered to date. It is not easy, even with modern telescopes, to detect such small and faint objects.

The very recently launched Gaia satellite might be of assistance. However, discovering asteroids is not Gaia's primary or even secondary goal.

3. Jan 8, 2014

### GTOM

Thanks. I started to browse the link you gave me.

Well until i finish that, could you give me any equations, how could one calculate a more realistic detection range?
(If you dont know already a trajectory and cant focus to a certain location for hours, and the thing isnt coming from the direction of the Sun.)