Cosmic Collisions Could Eject Habitable Planets

Article written: 19 Aug , 2011
Updated: 24 Dec , 2015


When it comes to solar systems, chances are good that we’re a lot more special than we thought. According to a German-British team led by Professor Pavel Kroupa of the University of Bonn, our orderly neighborhood of varied planet sizes quietly orbiting in a nearly circular path isn’t a standard affair. Their new models show that habitable planets might just get ejected in a violent scenario where forming solar systems mean highly inclined orbits where hot Jupiters rule.

Some 4600 million years ago, our local planetary system was surmised to have evolved from a blanket of dust surrounding a rather ordinary star. Its planets orbited the same direction as the solar spin and lined up neatly on a plane fairly close to the solar equator. We were good little children… But maybe other systems aren’t so hospitable. There could be systems where the planets cruise around in the opposite direction of their host star’s spin – and have highly inclined orbits. What could cause one protoplanetary disk to take on quiet properties while another is more radical? Try a cosmic crash.

This new study focuses on the theory of a protoplanetary disk colliding with another cloud of material… not unrealistic thinking since most stars form within a cluster. The results could mean the inclusion of up to thirty times the mass of Jupiter. This added “weight” of extra gas and dust could add a tilt to a forming system. Team member Dr Ingo Thies, also of the University of Bonn, has carried out computer simulations to test the new idea. What he has found is that adding extra material can not only incline a forming disk, but cause a reverse spin as well. It may even speed up the planetary formation, leaving the rogues in retrograde orbits. This inhospitable scenario means that smaller planets get ejected systematically, leaving only hot Jupiters to hug in close to the parent star. Thankfully our path was a bit less disturbing.

Says Dr Thies: “Like most stars, the Sun formed in a cluster, so probably did encounter another cloud of gas and dust soon after it formed. Fortunately for us, this was a gentle collision, so the effect on the disk that eventually became the planets was relatively benign. If things had been different, an unstable planetary system may have formed around the Sun, the Earth might have been ejected from the Solar System and none of us would be here to talk about it.”

Professor Kroupa sees the model as a big step forward. “We may be on the cusp of solving the mystery of why some planetary systems are tilted so much and lack places where life could thrive. The model helps to explain why our Solar System looks the way it does, with the Earth in a stable orbit and larger planets further out. Our work should help other scientists refine their search for life elsewhere in the Universe.”

Original News Source: Royal Astronomical Society News.

Tammy was a professional astronomy author, President Emeritus of Warren Rupp Observatory and retired Astronomical League Executive Secretary. She’s received a vast number of astronomy achievement and observing awards, including the Great Lakes Astronomy Achievement Award, RG Wright Service Award and the first woman astronomer to achieve Comet Hunter’s Gold Status.

(Tammy passed away in early 2015… she will be missed)

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10 Responses

  1. Member
  2. Interesting article but the scientific community seems a little divide in the question about how rare earth size planets are. Over the latest years articles and news on how common such planets are have been overwhelmingly more usual than articles claiming the opposite, but here we have one.

    I don´t complain about the scientific process it is good to consider any possibility. It is just that you get the impression that news sources like Universe today is a little ambivalent. 😛

    • Anonymous says

      earth size planets are maybe not rare,but a solar system like ours with inner rocky planets and outer gas giants are not as commen. The kepler data say that other solar system are very different. We also do not now if there is a planet in the habitable zone that it mean there is life

      • Isn´t the Kepler data telling us that systems like ours are very usual? It´s the old method using the wobble of stars that suggest that a high percentage of the systems has hot Jupiters close to the star. Of course the scientist has been aware of that is due to that the “wobble method” can only detect large planets and the closer to the star they are the easier they are to detect. The common press has not been as aware of this fact.

        About habitable zones: Life might not need to be configured in such way that it need to be in the kind of life zones that we acquire. Again Kepler data has shown of dozens of rocky planets within our type of life zone.

      • Anonymous says

        earth size planets are common, but i mean alien solar system are vey different look at this

        kepler discoverert 56 planets in the Habitable zone. That is great
        most planets that kepler discoverer in the Habitable zone were large planets. I mean larger than earth. 5 of them where earth size planets, but it is still very great. Of course they still need to be confirmed. We only need to find a way to go to those planets. On 23 September they will release new kepler data

      • Torbjörn Larsson says

        What Kepler shows is a) there are a lot of planets b) there is a lot of variation c) planetary systems like ours (plane) are common.

        Other sources (with worse statistics) have ejected planets as quite as common.

        So perhaps there are a lot of weird systems, but our type is not special AFAIU. Just don’t expect other many planet systems to be exactly like ours, see b).

      • Anonymous says

        Actually the data indicates that terrestrial worlds are relatively common. This is particularity the case if an extrapolation is made into the planetary range below Earth mass, a region that would naturally push Keplar’s reliability in detecting a signal.

    • Anonymous says

      Universe Today doesn’t really need to take a “position.” They simply report on things as discoveries are made. Some discoveries seem to contradict others but that strikes me as the nature of a mysterious universe.

  3. Adam Fausey says

    Thanks for the link Ivan. Yeah, the abstract seems to say that it’s more about explaining current “weird” systems with eccentric and epistellar giants than determining the frequency of ones like ours. Any anomalous system begs an explanation of how it got that way. I think the reason why words like “common” and “rare” get thrown around is because those words are really subjective!

  4. Peter says

    It looks like this isn’t a “new study”. This report from August 2008 looks very similar :-

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