I am involved in the fight between palaeontologists and aerodynamicists on the theoretical flight capabilities of the largest pterosaurs (who reached their climax in the Cretaceous and then disappeared at the K/T extinction event).

Is it possible that the earth's atmosphere was reduced at this time by a passing rogue planet or other sufficiently large body?

If so, the atmosphere would have been thicker.

Using the principle of Occam's razor, this one single hypothesis solves the problem of flight in the Mesozoic; the problem of how the dinosaurs could carry such weight; why they all had tails that would be much more use in a thick medium such as water...

The K/T extinction has attracted too many theories about what was 'added' to life on earth such as the comet/asteroid/Deccan Traps theories etc. No-one has looked at what might have been taken away from earth to cause the same effect!

If the earth's atmosphere had been much thicker (far higher pressure/density at the surface) the dinosaurs would have had a much easier time. Losing a huge amount of their atmosphere would kill them off because their 'effective weight' would have been doubled almost overnight.

  • $\begingroup$ Though this is definitely an interesting question, I have to say that it seems to be more of an Earth sciences question than an Astronomy question. (which would make it off-topic) $\endgroup$ Jan 12, 2014 at 6:53
  • $\begingroup$ Though the question as phrased in the body seems too Earth-centric, the question as phrased in the title does seem on-topic: it significantly involves another astronomical body besides Earth. I would suggest rephrasing the body to focus on the rogue planet atmosphere stripping aspect. $\endgroup$
    – called2voyage
    Jan 13, 2014 at 16:09
  • $\begingroup$ Since the OP hasn't come back in a while, I took the liberty of reframing the question around the part relevant to the Astronomy site. $\endgroup$
    – called2voyage
    Jan 15, 2014 at 15:52
  • $\begingroup$ I haven't carefully run the math but for a passing object to steal atmosphere from Earth, you run into enormous Roche Limit problems and orbital gravity assist problems. A gas giant planet like Jupiter or Saturn, then, maybe a fast moving, smaller rocky world could pass near a gas giant and steal some atmosphere without moving Jupiter from it's orbit significantly or damaging the planet in any significant way, whipping around the planet in the process, but on earth I don't see any way of making it work. $\endgroup$
    – userLTK
    Dec 2, 2015 at 11:27

1 Answer 1


Very interesting question. I'm okay with this question being here since you specifically ask for the effect of rogue planets on Earth's atmosphere. Thinking "astronomically" could be useful in coming to conclusions about whether or not your idea is even a possibility.

When I saw this I instantly thought of ice cores, since trapped gas bubbles could tell you about the composition of the atmosphere. Unfortunately ice cores go nowhere near that far back to be able to tell you about the composition of the atmosphere during the Mesozoic.

Now for the answer:

I can't really speak to the title of your question effectively, since I am unaware of any research involving rogue planets and atmospheric stripping, however, from an astronomy point of view, here is one other thing I would like to point out that may work to reduce the thickness of the atmosphere with time.

  • A small fraction of the gasses of the atmosphere exceed the escape velocity of Earth at any given time. Over time, many of these gasses get bombarded by high energy photons (as well as other particles) and fly out of Earth's gravitational potential well. If there are no other sources of these lighter gasses then there is a net loss.


Temperature does play a key role here (as the above plot suggests), but regardless, this process works to reduce the amount of atoms and molecules in the atmosphere (and it affects smaller mass atoms/molecules more so than heavier ones - this is why the Martian atmosphere is primarily carbon dioxide. Essentially it wasn't massive enough to be able to hold on to its lighter gasses, and over time the vast majority of them escaped).

If you had temperature information going back as far as the Mesozoic era, you could in theory run the clock backwards by running a simulation of the evolution of the atmosphere. I don't know how helpful this would really be (or how accurate), since there are potentially other things like volcanic outgassing and the bi-products of living things to complicate the situation. Quite honestly, I know little about these topics and so I couldn't tell you whether there is a net loss or gain of atmospheric gasses.

  • As far as rogue planets are concerned, I would find it rather unlikely that such a massive object would still be lurking around the solar system between about 252 to 66 million years ago. The early solar system was certainly more chaotic than it is now (for example, Giant impact hypothesis: $\sim 4.5$ Gya; the collision which caused Uranus' tilt: a few billion years ago), however it is not out of the realm of possibility.
  • $\begingroup$ Why would the rogue planet be 'lurking around the solar system'? Surely it would be hammering past, rip off Earth's atmosphere and disappear into deep space again. Remember that these planets are likely to be gas giants much larger than Jupiter and if they were travelling fast enough, they would not stay long within the clutches of the Sun's gravitational pull. $\endgroup$
    – user782
    Jan 28, 2014 at 17:51
  • $\begingroup$ And @user782, a large gas giant barreling through the solar system wouldn't affect anything else? $\endgroup$
    – HDE 226868
    Aug 13, 2014 at 19:08
  • $\begingroup$ @HDE226868: How sure are we about the orbits of everything else in the solar system? That said, if the planet was near enough to rip of parts of the athmosphere, wouldnt it be near enough to have disturbed earths orbit too... $\endgroup$
    – PlasmaHH
    Aug 30, 2016 at 14:20
  • $\begingroup$ @user782 A planet coming from deep space would have quite a high relative velocity. That means the interaction would be very short. I get the feeling that if the atmospheric transfer was fast enough to take significant amounts of air, it would also be enough to kill almost all life on Earth (air movement, heating, distruption of weather patterns...). We're talking about huge events here - most people tend to severely underestimate the scale we're considering here. Velikovski's Worlds Collide is a great example of completely ignoring the massive side-effects :) $\endgroup$
    – Luaan
    Oct 5, 2016 at 11:33
  • $\begingroup$ I don't understand why Earth losing part of it's atmosphere would double the weight of the dinosaurs ? Weight depends on gravity does it not, instead of atmosphere ? $\endgroup$
    – Peter U
    May 19, 2018 at 14:27

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