Space & Innovation

Forget Tatooine, This Exoplanet Has THREE Suns

An exoplanet has been discovered in a very strange star system more bizarre than most science fiction storylines.

As Luke Skywalker gazed longingly across the plains surrounding his aunt and uncle's desert dwelling as the binary stars of Tatoo set over the horizon, imagine how much better that classic "Star Wars" scene would have looked if there were three suns!

Whether or not a stellar addition would have impacted this iconic space opera scene is debatable, but astronomers have just announced the discovery of just that: an exoplanet in a stable orbit around a star that occupies a triple star system.

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But don't go having fantasies of standing on that planet's surface admiring some complex stellar dynamics at dusk, this particular world doesn't have a solid surface. And it would be a really bad place to hang out if you didn't want to be burned to a crisp.

Introducing KELT-4Ab: a gas giant world that orbits its parent star once every 3 days, but occupies a very rare multi-star system nearly 700 light-years from Earth.

The exoplanet was discovered by the wonderfully-named Kilodegree Extremely Little Telescope (KELT), a system of two small telescopes located in Arizona (KELT-North) and South Africa (KELT-South). Although the KELT-4 system has been known of for some time, it's only recently that their triple-star nature has been realized. The system consists of a main bright star called KELT-4A and a binary pair of stars - called KELT-4B and KELT-4C, collectively known as KELT-4BC. KELT 4BC orbit one another every 30 years at a distance of only 10 AU (the approximate distance Saturn orbits the sun).

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This binary pair then orbits KELT-4A once every 4,000 years or so at a distance of approximately 330 AU (over 8 times the distance Pluto orbits the sun). It is around KELT-4A that a transiting exoplanet, designated KELT-4Ab, a world around 50 percent bigger than Jupiter, has been discovered.

As if this triple star system wasn't bizarre enough, KELT-4Ab speeds around its host star in only 3 days, making this a "hot-Jupiter". Its close proximity to KELT-4A has caused the exoplanet's atmosphere to dramatically inflate. According to the planet's discoverers in a study published in The Astrophysical Journal, its host star is the brightest host of any inflated hot-Jupiter discovered to date, so it could prove to be an invaluable astronomical target for further studies into the nature of these extreme worlds.

KELT-4Ab is only the fourth such exoplanet to be found in a stable orbit within a multi-star system, so this will be a great scientific opportunity to understand how exoplanets can form in multiple star systems when logic suggests they shouldn't be gravitationally stable. But what would the sky of a planet in a 3-star system look like? Well, young Skywalker would be in for a shock.

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If you were able to float in the upper layers of KELT-4Ab's bloated atmosphere, you'd see the blindingly-bright main star, KELT-4A, take up a huge portion of the sky, 40 times wider than our sun appears to us on a clear day. The more distant KELT-4BC binary would appear much, much smaller as they are orbiting much further away, appearing no brighter than a full moon. They would, however, appear to be constantly hugging one another in their eternal orbital dance.

Source: The Astrophysical Journal via Physorg.com

An artist's impression of a triple-star system, including a "hot-Jupiter" in a stable orbit around one of the stars.

Astronomers using the Hubble Space Telescope recently completed the largest and most sensitive survey of dust surrounding young star systems. The survey zoomed-in on stars that are between 10 million to 1 billion years old and the source of the dust is thought to be the left-over debris from planet, asteroid and comet collisions after systems of planets have formed.

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The research is akin to looking far back into the history of our solar system, seeing the inevitable dusty mess left over after the Earth and other planets evolved. "It's like looking back in time to see the kinds of destructive events that once routinely happened in our solar system after the planets formed," said Glenn Schneider, of the University of Arizona's Steward Observatory and lead scientist on the survey team.

Read on to see some of the beautiful variety of circumstellar disks observed by Hubble.

One of the major findings to come from this survey is the stunning diversity of dust surrounding these young stars. Traditionally, circumstellar dust is thought to settle into an orderly disk-like shape -- but it turns out that the opposite is true.

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"We find that the systems are not simply flat with uniform surfaces," said Schneider. "These are actually pretty complicated three-dimensional debris systems, often with embedded smaller structures. Some of the substructures could be signposts of unseen planets."

One stunning observation of the star HD 181327 exhibits a bright ring of dust containing irregularities, potential evidence of a massive collision that has scattered debris far and wide. "This spray of material is fairly distant from its host star — roughly twice the distance that Pluto is from the Sun," said Christopher Stark of NASA's Goddard Space Flight Center, Greenbelt, Md., and co-investigator in the survey team. "Catastrophically destroying an object that massive at such a large distance is difficult to explain, and it should be very rare. If we are in fact seeing the recent aftermath of a massive collision, the unseen planetary system may be quite chaotic."

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Another interpretation for the irregularities could be some kind of interaction with unseen interstellar material. "Our team is currently analyzing follow-up observations that will help reveal the true cause of the irregularity," added Schneider.

Like the diversity of exoplanetary systems astronomers have discovered, it appears the accompanying dust disks also share this characteristic, possibly indicative of gravitational interactions with planets orbiting the stars surveyed by Hubble.

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"How are the planets affecting the disks, and how are the disks affecting the planets? There is some sort of interdependence between a planet and the accompanying debris that might affect the evolution of these exoplanetary debris systems," said Schneider.

Since 1995, thousands of exoplanets have been discovered orbiting stars in our galaxy. Over the same period, however, only a couple of dozen circumstellar disks have been imaged directly. This is down to the fact that the scattered light off these disks is extremely faint (around 100,000 times fainter than the parent star's light). The technology and techniques are only recently becoming available for scientists to not only block the star's blinding light, but to also boost the sensitivity of observations to pick out this scattered light that would otherwise be obscured from view. Fortunately, Hubble's high-contrast imaging has been key in making this survey a success.

By studying these disks of dust and their surprising variety of morphologies may help astronomers better understand how the Earth-moon and Pluto-Charon systems formed. Through planetary collisions, the debris from the early solar system may have coalesced to create many of the natural satellites we see today, 4.6 billion years later. The results of this survey have been published in The Astrophysical Journal.

For more information about this Hubble survey and high-resolution images, browse the HubbleSite.org news release.