We have exactly one world, in the entire Universe, that we know is actually hospitable to life: ours.
So when we search for habitable planets in other planetary systems, beyond our own corner of the galaxy, we often use Earth as the perfect model.
But a new study has revealed that Earth is not as habitable as it could be. In fact, it could be even more livable if Jupiter’s orbit shifted slightly.
This is an important study because tThere are many moving parts and ingredients in the solar system, and determining which ones contribute to Earth’s habitability is extremely difficult.
It could also help us better understand what makes a livable world habitable.
“If Jupiter’s position remained the same, but the shape of its orbit changed, it could actually increase the habitability of this planet,” says planetary scientist Pam Vervoort of the University of California, Riverside.
“Many are convinced that Earth is the epitome of a habitable planet and that any change in the orbit of Jupiter, being the massive planet that it is, could only be bad for Earth. We show that both assumptions are wrong.”
The findings also have implications for the search for habitable worlds outside the solar system, providing a new set of parameters with which to assess potential habitability.
Although we currently have no tools to conclusively assess the habitability of an exoplanet – planets that orbit stars outside our solar system – scientists have collected a population of worlds on which we should take a closer look, based on several features.
The first is where the exoplanet is in relation to its host star – it must be at a distance not so close that any surface liquid water would evaporate, nor so far that the water would freeze.
The second is the size and mass of the exoplanet – is it likely to be rocky, like Earth, Venus or Mars? Or gaseous, like Jupiter, Saturn or Uranus?
Increasingly, it looks like a Jupiter-like gas giant in the same system could be a good indicator of habitability. But there seem to be some caveats.
In 2019, the international team of researchers published a study in which they showed, based on simulations, that a change in Jupiter’s orbit could very quickly make the entire solar system unstable.
Now, more simulations have shown the reverse may be true, which will help narrow the range of gas giant orbits that help or hinder habitability.
The study was based on the eccentricity of Jupiter’s orbit – the degree to which that orbit is elongated and elliptical.
Currently, Jupiter has only a very slightly elliptical orbit; it’s almost circular.
However, if this orbit is stretched, it has a very noticeable effect on the rest of the solar system. This is because Jupiter is massive, 2.5 times the mass of all the other planets in the solar system combined.
So adjust Jupiter’s eccentricity, and the gravitational effect it will have on the other planets is real.
For Earth, this also means an increase in eccentricity. This means, according to the researchers, that parts of the planet would move closer to the Sun, warming into a temperate and habitable range.
But if you move Jupiter closer to the Sun, Earth’s habitability suffers. In effect, this will cause our home planet to tilt more pronounced on its axis of rotation than it currently does, a feature that gives us seasonal variations.
A steeper tilt, however, would cause large parts of our planet to freeze over, with more extreme seasons. The winter pack ice would extend over an area four times larger than it is today.
These findings can be applied to any multiplanetary systems we find, to assess their potential habitability, the researchers said.
But they also highlight how many factors may have influenced our presence here on our pale blue dot – how we may never have existed. And what could happen to the solar system if it ever destabilizes?
“To have water on its surface [is] a very simple first metric, and it doesn’t take into account the shape of a planet’s orbit, or the seasonal variations a planet might experience,” says astrophysicist Stephen Kane of the University of California, Riverside .
“It’s important to understand the impact Jupiter has had on Earth’s climate over time, how its effect on our orbit has changed us in the past, and how it might change us again in the future.”
The research has been published in The Astronomical Journal.
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