“Slow” comets could be key to the emergence of life

In comets there is water and substances essential for life. We have known this for a long time, when the panspermia hypothesis was put forward, according to which, life could have come to us planet in one of those frozen bodies. Little by little we have gathered evidence and, without going any further, a year ago the discovery of amino acids and vitamin B3 on the surface of comet Ryugu was announced. However, one thing is that kites They carry traces of prebiotic chemistry, but it is quite another matter if they manage to deposit it intact on the surface of a planet.

We can compare it to a catapult, we can load eggs in it and they will fly long distances, but possibly burst as soon as they hit the ground. However, a new study from the University of Cambridge has shown computationally that, in certain scenarios, it is possible that compounds chemicals from comets arrive safely. It all depends on the type of planet, its neighbors, the star it orbits and, ultimately: the speed at which the collision occurs. If the comet exceeds 15 km per second at the moment of impact, its molecules organics will be too affected.

It is often difficult to imagine speed expressed in kilometers per second, so let’s convert it to kilometers per hour. Thus we could say that, if a comet travels faster than 54000 kilometers per hour, will not be able to deposit its prebiotic chemistry on a planet. Seen this way, it doesn’t seem like such a strict restriction. However, these bodies travel really fast through space, so it is common for the collision occurs at higher speeds. The key, therefore, is not so much how quickly it crosses space, but how much we can stop it before impact.

For example, in computer simulations, scientists were able to verify that solar systems with smaller stars (comets) collided with greater speed, because their suns did not exert as much gravity to slow them down. So, if comets turn out to be important for the emergence of life, it is more unlikely that we will find it on planets orbiting an M dwarf, for example. And, if we continue talking about sizes, smaller planets seem to receive less violent impacts, in this case, because they exert less gravity on the comet and accelerate it less as it falls to earth.

But the most curious thing is that it also depends on the planets that surround the one with which it collides. If the planet that the comet collides with is surrounded by others more or less nearby, it is more likely that the prebiotic substances will survive the collision. And, in this case, the reason is not that the gravity of the other planets slows down the comet or, at least, not in a direct way. In fact, this is one of the main discoveries of this research. When there are several planets together, it is likely that the comet will begin to carom between them, passing from the orbit of one to that of the other before colliding. In this coming and going, the planets can accelerate it, but also slow it down.

What’s more, this strategy is used in astronautics to change the speed of our probes and is called gravitational assistance. In the article they are called bouncing comets, or bouncing comets. So, when a group of planets orbit very close to each other, as if they were a pod of peas, the chances of a comet depositing organic chemistry in good condition on them is greater.

In any case, in the article they make it clear that they do not assume that a comet is necessary for life to develop on a planet. It is possible that these same compounds could form on an inert planet, as they have on a comet. However, it seems like a good help. We could buy it from the bakery. We don’t need a fresh yeast tablet to make bread, which will be the comet. We can combine whole wheat flour and water and simply wait for the microorganisms to proliferate and give us a wonderful sourdough. The yeast tablet helps and ensures that this dough of flour and water ferments (unless we are very clumsy), but it is not necessary, as the sourdough demonstrates.

So, although these data are a good way to narrow the search for life in the universe, they are not everything, and we will have to continue investigating, open to seemingly impossible possibilities, such as there being life on a huge planet, without neighbors and around of a dwarf star. Because this is not about certainties, but about probabilities.


  • Although the panspermia hypothesis is quite popular, it does not solve the problem of the origin of life, because the life on that comet will have come from somewhere else, perhaps from another planet. In any case, this study does not contemplate that comets transport life, but rather the chemical bricks that are necessary to build it.


  • RJ Anslow, A. Bonsor and PB Rimmer Can comets deliver prebiotic molecules to rocky exoplanets? Proceedings of the Royal Society A Mathematical Physical and Engineering Sciences 10.1098/rspa.2023.0434
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Peggy McColl

Mentor l NY Times Bestselling Author. Hi, I'm Peggy McColl, and I'm here to deliver a positive message to you!

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