Tag Archives: comets

A quest for sources of meteor showers

Hi there! Today I will present you a study entitled Dynamical modeling validation of parent bodies associated with newly discovered CMN meteor showers, by D. Šegon, J. Vaubaillon, P. Gural, D. Vida, Ž. Andreić, K. Korlević & I. Skokić, which has recently been accepted for publication in Astronomy and Astrophysics. It addresses the following question: when you see meteors, where do they come from?

The meteor showers

Imagine you have a comet, i.e. a small body, which wanders in the Solar System with a large eccentricity. This means that it orbits around the Sun, but with large variations of its distance with the Sun. The consequence is that it experiences large variations of temperature during its journey. In particular, when it reaches the perihelion, i.e. when its distance to the Sun is the smallest, the temperature is so hot that it outgasses. The result is the ejection of a cloud of small particles, which itself wanders in the Solar System, on its own orbit.

When the Earth meets it, then these particles are burnt in our atmosphere. This results in meteor showers. Such showers can be sporadic, or happen every year if the cloud is pretty static with respect to the orbit of the Earth. The body from which the particles originate is called the parent body. The study I present you today aims at identifying the parent body of some of these meteor showers.

How to observe them

Understanding the meteor showers is an issue for the safety of the Earth environment, particularly our artificial satellites. Some meteors can even impact the surface of the Earth. This is why numerous observation programs exist, and for that amateurs are very helpful!

The first way to observe meteor showers is visually. When you know that meteor showers are likely to happen, you look at the sky and take note of the meteors you see: when you saw it, from where, where it came from, its magnitude (~its brightness), etc. The point from where the meteor seems to come is called the radiant. It is written as a set of two angles α and δ, i.e. right ascension and declination, which localize it on the celestial sphere.

For unpredicted showers, we can use cameras, which continually observe and record the sky. Then, algorithms of image processing can detect the meteor. Meteors can also be detected in the radio wavelengths.

Dynamical modeling

If you want to simulate the orbit of a particle, you have to consider:

  • the location of the parent body when the particle was ejected (initial position),
  • the ejection velocity,
  • the ejection time, likely when the parent body was close to its perihelion. The question how close? cannot be accurately answered,
  • the gravitational action of the Sun and the planets of the Solar System,
  • the non-gravitational forces, which might have a strong effect on such small bodies.

These non-gravitational forces, here the Poynting-Robertson drag, are due to the Solar radiation, which causes a loss of angular momentum of the particle during its orbital journey around the Sun. It is significant for particles smaller than the centimeter, which is often the case for such ejecta.

You cannot simulate the orbit of a specific particle that you would have identified before, just because they are too small to be observed as individuals. However, you can simulate a cloud, composed of a synthetic population of fictitious particles, with various sizes, ejection times, initial velocities… in such a way that your resulting cloud will have global properties which are close to the real cloud of ejecta. Then you can simulate the evolution of the cloud with time, and in particular determine the time, duration, direction, and intensity of a meteor shower.

Simulating such a cloud reveals interesting dynamical features. It presents an initial size, because of the variations in the ejection times of the particles. But it also widens with time, since the particles present different ejection velocities. This usually (but not always!) results in a kind of a tire which enshrouds the whole orbit of the parent body. Unfortunately, it can be observed only when the Earth crosses it. So, simulating the behavior of the cloud will tell you when the Earth crosses it, how long the crossing lasts, and the density of the cloud during the crossing.
It should be kept in mind that a cloud is composed of a hyue number of particles. For this reason, dedicated computation means are required.

This study

This study aims at identifying the parent body of meteor showers, which were detected by the Croatian Meteor Network (CMN in the title). For that, the first step is to make sure that a shower is a shower.
The detected meteors should resemble enough, which can be measured with the D-criteria, that are a measurement of a distance, in a given space, between the orbits of two objects. Once a meteor shower is identified, the same D-criteria can be used to try to identify the parent body, from its orbit. The parent bodies are comets or asteroids, they are usually known enough for candidates to be determined. And once candidates are identified, then their outgassing is simulated, to predict the meteor showers associated. If a calculated meteor shower is close enough to an observed one, then it is considered that the parent body has been successfully identified. This last close enough is related to the time and duration of the showers, and the location of the radiants.

The authors analyzed 13 meteor showers, and successfully identified the parent body for 7 of them. Here is their list, the showers are identified under their IAU denominations:

  • #549FAN – 49 Andromedids comes from the comet 2001 W2 Batters,
  • #533 JXA – July ξ Arietids comes from the comet 1964 N1 Ikeya,
  • #539 ACP – α Cepheids comes from the comet 255P Levy,
  • #541 SSD – 66 Draconids comes from the asteroid 2001 XQ,
  • #751 KCE – κ Cepheids comes from the asteroid 2009 SG18,
  • #753 NED – November Draconids comes from the asteroid 2009 WN25,
  • #754 POD – ψ Draconids comes from the asteroid 2008 GV.

For this last stream, the authors acknowledge that another candidate parent body has not been investigated: the asteroid 2015 FA118.

For the 6 other cases, either the identification of a parent body is speculated but not assessed enough, or just no candidate has been hinted, possibly because it is an asteroid or a comet which has not discovered yet, and / or because data are missing on the meteor shower.

Some links

That’s it for today! As usual, I accept any comment, feel free to post!