What if a hot Jupiter existed in our Solar System?

Imagine if the planet Jupiter orbited much closer to the Sun. What effect would a so-called hot Jupiter have on our Solar System?

An artist's conception of a hot Jupiter. These are exoplanets similar to Jupiter in our own Solar System, but orbiting much closer to their host star. Credit: NASA/Ames/JPL-Caltech
Published: February 7, 2022 at 2:01 pm
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Jupiter is the giant of our Solar System. It is a massive gas planet with twirling, swirling storms and a huge Great Red Spot.

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Its orbit lies 5.2 astronomical units (AU) from the Sun, where 1 AU is the average distance between Earth and the Sun. That's around 780 million km away.

But what if Jupiter were much closer to the Sun than it currently is today?

A view of Jupiter and its moon Europa captured on 25 August 2020 by the Hubble Space Telescope. Credit: NASA, ESA, A. Simon (Goddard Space Flight Center), and M. H. Wong (University of California, Berkeley) and the OPAL team.
A view of Jupiter and its moon Europa captured on 25 August 2020 by the Hubble Space Telescope. Credit:
NASA, ESA, A. Simon (Goddard Space Flight Center), and M. H. Wong (University of California, Berkeley) and the OPAL team.

As astronomers learn more about planets beyond our Solar System - known as exoplanets - the more they learn just how unlike our Solar System other planetary systems are.

Our Solar System is arranged with the smaller, rocky planets closer to the Sun, while the huge gas giants are further out.

Before the explosion of exoplanet study that has occurred over the past two decades or so, we had good reason to predict that this arrangement might be common around other stars.

But it's become clear that this is by no means the case. Many distant stars have gas giants orbiting much closer to them, and these are known as hot Jupiters.

Artist's impression of a hot Jupiter exoplanet. Credit: NASA/JPL-Caltech/R. Hurt
Artist's impression of a hot Jupiter exoplanet. Credit: NASA/JPL-Caltech/R. Hurt

Our Solar System doesn't have a hot Jupiter, but what if it did?

Venus was known to ancient astronomers as the morning or evening star. Its orbit is tighter than Earth’s and so Venus is never far from the Sun in the sky.

The planet’s highly reflective clouds cause it to shine like a beacon at dawn and dusk.

If our Solar System had a ‘hot Jupiter’ – a large gaseous, Jupiter-like planet found in orbit very close to its parent star – it would appear as the ultimate morning star. 

If Jupiter moved to an orbit 0.1AU (15 million km) from the Sun it would be seven times closer to the Sun in the sky than Venus and 15 times brighter.

It would be spectacular at dawn or dusk, and especially during a solar eclipse when the Sun’s glare is hidden.

Artist's impression of a hot Jupiter twinkling in Earth's sky.
Artist's impression of a hot Jupiter twinkling in Earth's sky.

But could Earth exist alongside a hot Jupiter?

Jovian planets can’t form in tight orbits around a star because they need large rocky and icy cores to drag in great swathes of gas to form.

This gas is found further away from the star when the planets are forming, so gas giants must be born in the outer planetary system and later migrate into tighter orbits.

With a giant marauding through the inner system a young, habitable planet like the Earth, would be in serious danger

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This article originally appeared in the September 2009 issue of BBC Sky at Night Magazine.

Authors

Astrobiologist Lewis Dartnell University of Westminster
Lewis DartnellAstrobiologist

Dr. Lewis Dartnell is an astrobiologist and science author based at the University of Westminster.

Iain Todd, BBC Sky at Night Magazine
Iain ToddScience journalist

Iain Todd is BBC Sky at Night Magazine's Staff Writer. He fell in love with the night sky when he caught his first glimpse of Orion, aged 10.

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