Asteroid impact 101

 While reading about the very recent fly-by of 2015 RN35 [1] which has been dubbed as the "Christmas Asteroid" by the European Space Agency (ESA), I saw reassurances from astronomers about the asteroid not impacting the Earth. This led me down the rabbit hole of the Torino Scale and its more quantitative cousin, the Palermo Technical Impact Hazard Scale, and how they are used to describe the destruction and our possible demise. [2]

    

      

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Torino Scale

The Torino scale is a communication tool between Astronomers and the general public. It wraps up the probability of an object hitting the Earth and the estimated kinetic energy with which it can hit it into a single (integer) threat value ranging from 0 to 10.

The Torino scale can also be divided into five categories.

1. No Hazard (0)

2. Normal (1)

3. Requires Attention (from astronomers) (2-4)

4. Threatening (5-7)

5. Disaster level (8-10)

Most objects get assigned some n>0 value when discovered first but after some more observation and calculations. They can get reassigned back to 0.

Public officials need only worry about smaller Torino-scale objects if they are confirmed to be in the same decade.

Most small meteors that enter the Earth's atmosphere get burned up and hence are placed on scale 0. Scale 0 also includes objects that do not come close enough to Earth.

The Chicxulub impact, which most scientists believe to be the cause of the extinction of non-avian dinosaurs, has been rated on at scale of 10.

The Barringer Crater and Tunguska event has been rated at 8.

Scale 10 events are capable of destroying all flora and fauna and can sometimes have an approach kinetic energy in orders of 10^8 megatons. One megaton = 4.18 x 10^12 kJ, which is enough energy for an active teenager to survive 1.6 x 10^11 years, which is greater than the universe's current age (~1.38 x 10^10 years).

Fortunately, no incoming object has been rated above four on the Torino scale. So the chances of mass destruction or outright extinction due to asteroid impact in the upcoming century are negligible.

Palermo Technical Impact Hazard Scale

Unlike the Torino scale, which lies more on the qualitative side of scaling owing to the ranking it does, the Palermo scale is more quantitative. It, too, combines the probability of the impact and the estimated kinetic yield into a single number. Still, the number is left as it is and not grouped into any such category.

Because of its quantitative nature and convenience, the Palermo scale is logarithmic. A rating of 0 on this scale means that the danger is equivalent to a background hazard which essentially is defined as the average risk possessed by objects of the same size or larger over the years until the date of potential impact. By estimating the background hazard level of Earth's impacts, we define a value for the threat from the entire asteroid averaged over very long periods. Because there are vastly more small asteroids than large ones in space, the rate of background impact depends upon the size of the NEO.[3]

If the hazard is represented by n, then the threat is 10^n times more dangerous than the background hazard. Values of n lesser than -2 are considered events without any likely consequences.

As of December 2022, only two objects have Palermo values greater than -3, one with -1.59 and the other with -2.05 [4].

Much of the utility of the Palermo scale lies in that it can be used to assess values less threatening than the Torino scale of 0, which makes up almost all of the impacts we have detected to date.

Sentry and cneos

cneos is short for Center for Near Earth Object Studies, a component of Jet Propulsion Laboratory (JPL) NASA, which, as the name suggests, is one of the few places near-earth objects are monitored and studied.

Sentry is an automated collision monitoring system developed by cneos that continuously scans the most current asteroid catalogs for possible impacts over the next 100 years. It is analyzed whenever a potential crash is detected, and the results are published onto the list. Objects are also removed from the list whenever there are no more potential impact detections. [5]

Extras:

[1]: While we do not have the luxury to see the asteroid ourselves, check out ESA's neo-toolkit to visualize the orbit and the fly-by. https://neo.ssa.esa.int/neo-toolkit

[2]: The title is somewhat misleading as the methods described below work for all NEOs (Near Earth Objects), which is a misnomer as they do not always stay near Earth. The Wikipedia page explains a great deal about them. https://en.wikipedia.org/wiki/Near-Earth_object

[3] : https://www.sciencedirect.com/science/article/abs/pii/S0019103502969101

[4] : https://cneos.jpl.nasa.gov/sentry/

[5] : https://cneos.jpl.nasa.gov/sentry/removed.html

- Kshitish Kumar Ratha (MS22174)