Distant planet’s strange orbit points to a violent and chaotic past

(ORDO NEWS) — If you close your eyes and imagine a system of planets revolving around a distant star, what do you see?

For most people, systems that mirror the solar system create such thoughts: planets orbiting their host star in near-circular orbits, rocky planets up close, and giants like Jupiter in the icy depths.

However, the more we study the cosmos, the more we begin to realize that planetary systems like ours may be the exception rather than the rule.

Imagine a system with a single gaseous planet, slightly larger than Saturn, that streaks across the surface of a host star in an extremely fast orbit. It is hot as hell and glows with a dull red light, incinerated by stellar radiation.

Then imagine another giant planet much farther away, larger than Jupiter, in a distant and highly elongated orbit that makes it look more like a comet than a traditional planet.

It doesn’t really feel like home, does it? But that’s exactly what we found.

Introducing the HD83443 Planetary System

The history of the HD83443 system begins in the late 20th century, when astronomers began obsessively observing Sun-like stars. They were looking for evidence that these stars oscillate back and forth under the influence of invisible planetary satellites.

Using the 3.9-meter Anglo-Australian Telescope at the Siding Spring Observatory near Coonabarabran, researchers have discovered a planet orbiting the star HD83443. This planet, HD83443b, was as massive as the gas giants Saturn and Jupiter.

But that’s where the similarities end. HD83443b is a “hot Jupiter”: a giant gas planet streaks across the surface of its host star (which is slightly smaller and colder than the Sun), completing each circuit in less than three Earth days!

For two decades after its discovery, we continued to observe the movement of HD83443. In recent years, we have been doing this work at the Mount Kent Observatory of the University of South Queensland.

By combining our observations with others, we have discovered a strange new planet in the system, which we described in a paper published last month.

This world, HD83443c, has been orbiting its host star for over 22 years and is about 200 times further away than its hellish counterpart. Because HD83443c’s “year” is so long, it took us over two decades of observations to confirm its existence by tracing one circle around its host star.

But what is really unusual is the eccentricity of its orbit. While the planets of the solar system move in near-circular orbits, HD83443c moves in a much more elongated trajectory, reminiscent of comets in our solar system.

Consequences of planetary tango

Planets like “hot Jupiter” HD83443b are of particular interest to astronomers because they don’t look like anything close. Gas giants like Jupiter start life away from their host star, where ice is abundant.

These ices allow them to grow rapidly, gaining enough mass to envelop themselves in vast atmospheres.

Unlike the giant planets of the solar system, HD83443b migrated into the interior of the planet as it grew and matured to be close to its star. What caused this migration?

Over the years, astronomers have discovered many hot Jupiters. In attempts to understand these strange planets, several mechanisms have been proposed to explain their migration, but in most cases any evidence for the cause of the migration is lost in the distant past.

However, in the specific case of HD83443b, it looks like our new discovery could provide evidence for a “smoking gun”. The newly discovered world of HD83443c may be the reason its sibling ended up in its current hellish orbit.

Imagine that HD83443c and HD83443b first formed in the icy depths of the HD83443 system. They would be buried in the massive disk of gas and dust surrounding the star, called the “protoplanetary disk”.

As they moved across the disk, the planets fed from it, becoming more massive, and slowly drifted inward, interacting with the disk that surrounded them.

Eventually they got too close to each other. They didn’t exactly collide, but as they streaked past each other, their huge gravitational pull acted like a slingshot, catapulting them both into new orbits.

HD83443b, a hot Jupiter, was ejected inward into an orbit that passes over the star’s surface on its closest approach, then veered back toward the site of the initial impact. Another planet, HD83443c, was ejected outward on its current elongated trajectory.

Something amazing has happened over the millennia. Each time HD83443b came close to its host star, its presence caused the tides to ebb and flow on the star, and the host star, in turn, caused the tides to ebb and flow on it. This, in fact, “slowed down” the movement of HD83443b.

This means that HD83443b lost a tiny bit of speed each time it swept past its host star. When she flew out again, she failed to fly as far as before, and her orbit slowly rounded. She was pulled inward until she reached her current tiny circular orbit, where she would spend the rest of her life.

HD83443c, however, did not suffer such a fate. Being thrown out during the first encounter with HD83443b, it remained at such a distance from the central star that its orbit was not affected.

Its very slow and elongated orbit indicates that the initial meeting of the planets occurred during the early days of the system.

Is there a better place than home?

This story is very exciting, but the main goal of our constant search for alien worlds is to find places that are much more like home.

We’re using the same tools that led us to HD83443c to find planetary systems like our own, with giant planets in orbits far from their host stars. We may have to look at the distant stars for decades, watching their graceful celestial waltz.

Undoubtedly, we will find many more amazing systems like HD83443 that will reveal to us the true diversity of planetary systems.


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