View Full Version : Gamma Ray Bursts rule out Panspermia?

2014-Apr-02, 10:45 PM

This paper discusses the possibility that a Gamma Ray Burst triggered the rapid increase in diversity of life that occurred in the Cambrian era. I am very sceptical of such claims, since a similar claim is made by creationist for their own mechanism. In fact, in resisting such claims, the Cambrian explosion is now referred to as the Cambrian 'slow-fuse' since there is plenty of evidence of the more primitive examples of the clades that are already developed by the Cambrian in much earlier rocks, such as the 'small shelly fossils'. That is, the time over which the 'explosion' of diversity took place is many millions of years. However, this paper also makes an interesting side point that while GRB radiation may stimulate DNA mutation rates on a terrestrial planet;

"Unprotected primitive microscopic organisms carried by interstellar rocks may turn sterile after been exposed to GRB at certain distance. However, such seeds of panspermia would
evade GRB destruction if its migration and colonization rate is faster than the GRB event rate within a volume of destruction."

Concerning the GRB event rate the estimates vary, according to the same paper,

"One estimate gives one event per 0.1-1 My in Milky Way galaxy [7]. Coward et al. on the other hand estimated, based on the Swift satellite telescope data, a rate density
of 8-1100 Gpc��3y��1 [8]. Assuming 1 Mpc for the average distance between galaxies, this translates into a rate of one event per 1-5 My per galaxy."

Given likely transit times on the order of billions of years for transport of rocks from star to another passing star in the neighbourhood, does this effectively rule out interstellar panspermia?

2014-Apr-03, 07:29 AM
The thing about Gamma Ray Bursts is that they are likely to be directional, that is they only sterilise narrow sections of a galaxy at any one time. If this is true, the GRBs which are most directional will have a more concentrated beam, and any interstellar seeds will be sterilised in a relatively narrow region; other GRBs that are less focused will only affect a limited region near the star. Either way the effects of each GRB will only cover a small fraction of the galaxy at any one time; most interstellar seeds in the galaxy will be unaffected.

There are many reasons to doubt that panspermia has occurred on a large scale in the Galaxy; GRB sterilisation is only one of them, and probably not the most significant.

2014-Apr-05, 09:17 PM
How often do we detect objects, such as an asteroid, that came in from another solar-system?

It is possible that Panspermia does exist and life thrives in asteroids, that have been booted out of their system and the fact the only place we know of where life does exist is Earth, could mean it is rare.

2014-Apr-06, 02:50 PM
How often do we detect objects, such as an asteroid, that came in from another solar-system?...
So far, none have been observed. Estimates as to how many there should be suggest that if we had detected one, it would have been a very lucky event. Such things are probably out there. Do they have life thriving in them? Are they thick enough to protect such life from the radiation of a nearby GRB? That's part of this discussion and a note in the paper linked in the OP. Give it a read. It is fairly accessible as astronomy papers go.