Concept of artist of habitable zones – zones in which liquid water can exist – in our solar system as opposed to the Trappist-1 system, about 40 light-years away. The Trappist-1 system has 3 planets in its habitable zone (the green area). Our solar system has just 1, our Earth. Image via NASA / JPL / Caltech.
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A new computer model developed by astrobiologists at the University of California, Riverside suggests that – in the absence of a gas giant planet like Jupiter – some stars in our Milky Way galaxy may have as many as seven terrestrial planets. This is in contrast to our solar system, which has a Jupiter and has only one planet in its habitable zone, our own Earth.
The peer-reviewed Astronomical Journal published this study on July 27, 2020.
So far, Earth is the only planet in the universe where we know that certain life exists. However, it is only logical that life exists elsewhere. As astrobiologists talk about other worlds that power host life, they tend to concentrate on those in the habitable zone, the zone around a star where liquid water can exist. Astrobiologist Stephen Kane studied the nearby planetary system Trappist-1, which caused a sensation when it was discovered that this system has at least seven planets, including three Earth-like planets in its habitable zone. Kane said in a statement:
This made me wonder about the maximum number of habitable planets that it is possible for a star to have, and why our star has only one. It did not seem honest!
Kane’s team created a computer model that formed planets of various sizes around their stars. An algorithm created responsibility for gravity and helped test how the planets interacted with each other over millions of years. The researchers found that for some stars it is possible to support seven planets in the habitable zone. Kane commented:
More than seven, and the planets get too close to each other and destabilize each other’s orbits.
This is Jupiter as seen by the Juno spacecraft in April 2018. Does this gigantic world occur when our solar system has more than one inhabited planet? Image via NASA / JPL-Caltech / SwRI / MSSS / Gerald Eichstad / Sean Doran.
What determines this abundance of planets in the habitable zone of a star? The answer does not lie within the star itself. These scientists said that a star like our sun could potentially support six planets with liquid water. But it does not have to. But why?
One factor is the shape of the orbits of the planets. It helps, these scientists explained, that the motions of the planets in the orbit around their star are more circular than, for example, the orbit of the earth. The orbit of our planet is very almost circular, but still somewhat elliptical, like a circle on which one sat. The Earth’s elliptical orbit explains why our planet is closest to the sun in early January (winter of the northern hemisphere) and farthest from the sun in early July (summer of the northern hemisphere). A more circular orbit – instead of a more eccentric or irregular orbit – minimizes close contacts between planets in the system and helps maintain stable orbits, these scientists explained. And it makes sense that a stable orbit – a constant distance from a star – would be beneficial to life as it evolves. It would not do to have ice ages and go on time scales of hundreds of years, for example – instead of thousands like on our own planet – as you would have on a planet with a very elliptical 100+ -year orbit.
There is also another major factor in our solar system that has kept more planets in the habitable zone of our sun. And that’s the largest planet in our solar system, giant Jupiter. Jupiter has a mass 2 1/2 times that of all other planets in the solar system combined. Kane explained:
It has a huge effect on the viability of our solar system because it is massive and disrupts other orbits.
These scientists are the first to indicate that the Trappist-1 system is a rarity for terrestrial astronomers to date; only it is known that a handful of stars have multiple planets in their habitable zones. Move forward planet Kane to search for more stars like Trappist-1, completely surrounded by smaller planets without large gas giants like Jupiter. He said these stars would be main targets for direct imaging with NASA telescopes such as those at Jet Propulsion Laboratory’s Jet Habits Exoplanet Observatory.
Kane’s study identified one such star – Beta Canum Venaticorum, aka Beta CVn – which is relatively close at 27 light-years. Because it has no Jupiter-like planet, it will be recorded as one of the stars controlled on multiple habitable solar planets, these scientists said.
Bottom line: A new study suggests that some stars may have up to 7 planets in their habitable zones.
Source: Dynamic packaging in the common zone: The case of Beta CVs
Via University of California, Riverside
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