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Earth orbits between the Sun and the massive planet Jupiter.

My question involves a similar set-up except that Jupiter is replaced by a small star.

Here's a size comparison between Sol, Jupiter, and OGLE-TR-122b https://bit.ly/2D0AGXQ

enter image description here

Question

Could we theoretically replace Jupiter with a small star without disrupting the solar system in such a way that would endanger life on Earth?

Note: I'm not asking about techniques to replace a planet. I'm asking about the results if it is done somehow.

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The least massive M class red dwarves (smallest objects correctly called stars) are some 20-30 times Jupiter's mass, even though they're barely larger in diameter. Such a massive object would make any orbits between that secondary star and the Sun unstable, due to the perturbations.

Even a Brown Dwarf (deuterium burner, say) must be at least a dozen or so times Jupiter's mass, so same problem.

If you've read 2010 by Arthur C. Clarke, you may recall that at the point Jupiter was stellified it was by adding a huge amount of synthetic mass in the form of billions (trillions?) of copies of the Monolith. These provided gravity to compress Jupiter to the point of fusion ignition -- but somehow didn't pull everything else nearby off its orbit. This why it's science fiction.

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  • $\begingroup$ Thanks. I didn't realise 2001 was a book. I thought it was just a movie! (EDIT Just noticed that 2010 is in fact a sequel to 2001 - I misread it) $\endgroup$
    – chasly - supports Monica
    Commented Jul 23, 2020 at 20:27
  • $\begingroup$ The book made a lot more sense to me than the movie. The movie was very pretty, though. $\endgroup$
    – NomadMaker
    Commented Dec 13, 2020 at 15:07
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To add to what Zeiss Ikon said: the barycenter of Jupiter and the Sun together is on average slightly above the surface of the Sun. If all the gas giants lined up, they could cause the barycenter of the solar system to be momentarily further. This means that planets would orbit a point outside the Sun, not the Sun itself. This arrangement has been working well for billions of years.

Jupiter has a mass of 0.0009543 M☉, and it's got more than twice all other giant planets mass combined. The smallest stars have a mass of about 0.08 M☉ (which is still smaller than OGLE-TR-122b, which has 0.1 M☉). That's two orders of magnitude more mass than Jupiter, which makes for that much a stronger pull.

Put that star anywhere within the orbit of Neptune, and the barycenter of the whole system will be WAY outside the Sun. This means that all planets would orbit a point in the empty space between the two stars. If your new star simply pops into existence the orbits would be readjusted in very dangerous ways. In the very least the stars would complete an orbit around the point in very short time (maybe some years, which is almost zero time in geological and astrophysical terms) and in the process they would change distances from each planet enough to destabilize their orbits. Each planet would go into either higher or lower orbits, possibly with most of them colliding against either star and some being thrown out of the system due to gravity assists.

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  • $\begingroup$ Suppose we hypothesise some collision that occurs way outside the orbit of Neptune. This results in a new asteroid belt that gradually turns into a star. Is there a size of star and a distance from the sun that would not disturb life on Earth catastrophically? $\endgroup$
    – chasly - supports Monica
    Commented Jul 23, 2020 at 20:01
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    $\begingroup$ The linked Wikipedia page shows that the Jupiter-Sun barycenter is, on average, outside the Sun, at 1.07 Sun radii, or roughly 50,000km from the surface. Due to Jupiter's orbital eccentricity, the barycenter is occasionally inside the Sun, but most of the time, it is not. $\endgroup$
    – Nuclear Hoagie
    Commented Jul 23, 2020 at 20:06
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    $\begingroup$ @chasly-reinstateMonica it is hypothesised that even from 1.5 light years away a brown dwarf could cause mass extinctions on Earth. These things are simply not safe. $\endgroup$
    – The Square-Cube Law
    Commented Jul 23, 2020 at 20:15
  • $\begingroup$ @Renan Actually my statement was somewhat wrong, but not for the reason you think. If you read the article again, you'll see that it fails to qualify as a system where the barycenter is sometimes inside and sometimes outside the more massive body. The barycenter is always outside - see sciencealert.com/…. $\endgroup$
    – Nuclear Hoagie
    Commented Jul 23, 2020 at 20:17
  • $\begingroup$ @NuclearWang yeah but you were way more to the point than I was. Thanks for the heads up, I've adjusted my answer accordingly. $\endgroup$
    – The Square-Cube Law
    Commented Jul 23, 2020 at 20:19

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