Astronomers Discover Exoplanet With Triple Sunrises and Sunsets

This graphic shows the orbit of the planet in the HD 131399 system (red line) and the orbits of the stars (blue lines). The planet orbits the brightest star in the system, HD 131399A. Credit: ESO
This graphic shows the orbit of the planet in the HD 131399 system (red oval) and the orbits of the stars (blue arcs). The planet orbits the brightest star in the triple system, HD 131399A with a period of about 550 years. Credit: ESO

In the famous scene from the Star Wars movie “A New Hope” we recall young Luke Skywalker contemplating his future in the light of a binary sunset on the planet Tatooine. Not so many years later in 2011, astronomers using the Kepler Space Telescope discovered Kepler-16b, the first Tatooine-like planet known to orbit two suns in a binary system. Now astronomers have found a planet in a triple star system where an observer would either experience constant daylight or enjoy triple sunrises and sunsets each day, depending on the seasons, which last longer than human lifetimes.

They used the SPHERE instrument on the European Southern Observatory’s Very Large Telescope to directly image the planet, the first ever found inside a triple-star system. The three stars are named HD 131399A, HD 131399B and HD 131399C in order of decreasing brightness; the planet orbits the brightest and goes by the chunky moniker HD 131399Ab.

This annotated composite image shows the newly discovered exoplanet HD 131399Ab in the triple-star system HD 131399. The image of the planet was obtained with the SPHERE imager on the ESO Very Large Telescope in Chile. This is the first exoplanet to be discovered by SPHERE and one of very few directly-imaged planets. With a temperature of around 580 degrees Celsius and an estimated mass of four Jupiter masses, it is also one of the coldest and least massive directly-imaged exoplanets. This picture was created from two separate SPHERE observations: one to image the three stars and one to detect the faint planet. The planet appears vastly brighter in this image than in would in reality in comparison to the stars. Credit: ESO/K. Wagner et al.
This composite image shows the newly discovered exoplanet HD 131399Ab in the triple-star system HD 131399. The image of the planet was obtained with the SPHERE imager.  This is the first exoplanet to be discovered by SPHERE and one of very few directly-imaged planets. This picture was created from two separate SPHERE observations: one of the three stars and one to detect the faint planet. The planet appears vastly brighter in this image than in would in reality in comparison to the stars. Credit: ESO/K. Wagner et al.

Located about 320 light-years from Earth in the constellation of Centaurus the Centaur HD 131399Ab is about 16 million years old, making it also one of the youngest exoplanets discovered to date, and one for which we have a direct image. With a temperature of around 1,075° F (580° C) and the mass about four times that of Jupiter, it’s also one of the coldest and least massive directly-imaged exoplanets.

This infrared image of Saturn’s largest moon, Titan, was one of the first produced by the SPHERE instrument soon after it was installed on ESO’s Very Large Telescope in May 2014. This picture shows how effective the adaptive optics system is at revealing fine detail on this tiny disc (just 0.8 arc seconds across). Credit: ESO/J.-L. Beuzit et al./SPHERE Consortium
This infrared image of Saturn’s largest moon, Titan, was one of the first produced by the SPHERE instrument soon after it was installed on ESO’s Very Large Telescope in May 2014. This picture shows how effective the adaptive optics system is at revealing fine detail on this tiny disc (just 0.8 arc seconds across). Credit: ESO/J.-L. Beuzit et al./SPHERE Consortium

To pry it loose from the glare of its host suns, a team of astronomers led by the University of Arizona used a state of the art adaptive optics system to give razor-sharp images coupled with SPHERE, an instrument that blocks the light from the central star(s) similar to the way a coronagraph blocks the brilliant solar disk and allows study of the Sun’s corona. Finally, the region around the star is photographed in infrared polarized light to make any putative planets stand out more clearly against the remaining glare.

The planet, HD 131399Ab, is unlike any other known world — its orbit around the brightest of the three stars is by far the widest known within a multi-star system. It was once thought that planets orbiting a multi-star system would be unstable because of the changing gravitational tugs on the planet from the other two stars. Yet this planet remains in orbit instead of getting booted out of the system, leading astronomers to think that planets orbiting multiple stars might be more common that previously thought.

This artist's impression shows a view of the triple star system HD 131399 from close to the giant planet orbiting in the system. The planet is known as HD 131399Ab and appears at the lower-left of the picture. Credit: ESO / L. Calcada
This artist’s impression shows a view of the triple star system HD 131399 from close to the giant planet orbiting in the system. The planet is known appears at the lower-left of the picture. Credit: ESO / L. Calcada

HD 131399Ab orbits HD 131399A, estimated to be 80% more massive than the Sun. Its double-star companions orbit about 300 times the Earth-Sun distance away. For much of the planet’s 550 year orbit, all three stars would appear close together in the sky and set one after the other in unique triple sunsets and sunrises each day. But when the planet reached the other side of its orbit around its host sun, that star and the pair would lie in opposite parts of the sky. As the pair set, the host would rise, bathing HD 131399Ab in near-constant daytime for about one-quarter of its orbit, or roughly 140 Earth-years.


Click to see a wonderful simulation showing how the planet orbits within the trinary system

Planets in multi-star systems are of special interest to astronomers and planetary scientists because they provide an example of how the mechanism of planetary formation functions in these more extreme scenarios. Since multi-star systems are just as common as single stars, so planets may be too.

How would our perspective of the cosmos change I wonder if Earth orbited triple suns instead of a single star? Would the sight deepen our desire for adventure like the fictional Skywalker? Or would we suffer the unlucky accident of being born at the start of a multi-decade long stretch of constant daylight? Wonderful musings for the next clear night under the stars.

Astrophoto: Sunset Echo

Sunset on Tatooine? Nah, just an unusual combination of a dazzling orange sunset, clouds and a sun pillar that creates an “echo” effect of the setting Sun. As seen by astrophotographer Dave Walker in the UK on May 31, 2014.

Want to get your astrophoto featured on Universe Today? Join our Flickr group or send us your images by email (this means you’re giving us permission to post them). Please explain what’s in the picture, when you took it, the equipment you used, etc.

Kepler’s Weirdest Exoplanets

Captain Kirk has nothing on the “strange new worlds” the Kepler space telescope has found.

NASA’s planet-probing orbiting observatory launched its quest to find more Earths four years ago this week. Since then, it’s found thousands of planets ranging from ginormous gas giants to tiny rocky worlds that are even smaller than our planet. NASA extended its mission to 2016 last year, putting the telescope into planet-hunting overtime and, we assume, scientists into overdrive.

Along the way, Kepler has revealed some bizarre star systems. Check out some of the weirdest exoplanets Kepler has found so far:

‘Tatooine’ (Kepler-16b)

Kepler 16b. Credit: NASA/JPL-Caltech
Kepler-16b. Credit: NASA/JPL-Caltech

“Circumbinary” is the scientific explanation for Kepler-16b’s 2 star-system. But “Tatooine” is the name that took the public by storm (or is that Stormtrooper?) when this world, orbiting two stars, was revealed in 2011. Although it’s named after Luke Skywalker’s home in Star Wars, proving Kepler-16b is habitable would be a bit of a stretch. The planet’s mass is about one-third that of Jupiter, and surface temperatures reach an estimated and frigid -100 degrees Celsius.

Deciphering a tune (Kepler-37b)

Kepler-37b, a moon-sized exoplanet. Credit: NASA/Ames/JPL-Caltech
Kepler-37b, a moon-sized exoplanet. Credit: NASA/Ames/JPL-Caltech

Scientists found Kepler 37-b through listening to its parent star sing. Seriously. The planet (just slightly larger than our moon) was revealed through measuring oscillations in brightness caused by star-quakes, then converting those to sound. “The bigger the star, the lower the frequency, or ‘pitch’ of its song,” said Steve Kawaler, a research team member from Iowa State University in a past Universe Today interview.

The 6-planet swarm (Kepler-11b, 11c, 11d, 11e, 11f, 11g)

Kepler's planets displayed by size comparison. The six new planets around Kepler 11 are on the bottom. Image credit: NASA/Wendy Stenzel
Kepler’s planets displayed by size comparison. The six new planets around Kepler 11 are on the bottom. Image credit: NASA/Wendy Stenzel

It’s sure crowded around the star Kepler-11. There are six planets orbiting in circles smaller than Venus’ orbit around the Sun. Not only that, but five of those planets are even closer to their parent star than Mercury is to our sun. Excited astronomers said the system will rewrite planetary formation theories. “We really were just amazed at his gift that nature has given us,” said Jack Lissauer, co-investigator of the Kepler mission, in 2011. “With six transiting planets, and five so close and getting the sizes and masses of five of these worlds, there is only one word that adequately describes the new finding: Supercalifragilisticexpialidocious.”

The warring siblings (Kepler-36b and 36c)

In this artist’s conception, a “hot Neptune” known as Kepler-36c looms in the sky of its neighbor, the rocky world Kepler-36b. The two planets have repeated close encounters, experiencing a conjunction every 97 days on average. At that time, they are separated by less than 5 Earth-Moon distances. Such close approaches stir up tremendous gravitational tides that squeeze and stretch both planets, which may promote active volcanism on Kepler-36b. Credit: David A. Aguilar (CfA)
In this artist’s conception, a “hot Neptune” known as Kepler-36c looms in the sky of its neighbor, the rocky world Kepler-36b. The two planets have repeated close encounters, experiencing a conjunction every 97 days on average. At that time, they are separated by less than 5 Earth-Moon distances. Such close approaches stir up tremendous gravitational tides that squeeze and stretch both planets, which may promote active volcanism on Kepler-36b.
Credit: David A. Aguilar (CfA)

Take a planet the size of Neptune and put it near Earth, and you’d have some scary results. Tides from the constant interaction would raise the water and the ground, causing fissures and no end of local zoning headaches for municipal authorities as the ground shifts, to say the least. Seriously, though, Kepler-36b (the rocky world) comes within less than 5 Earth-Moon distances of Kepler 36-c (a gaseous world about 8 times larger) every 97 days or so. They’ll never crash into each other, but just like young human siblings, they can cause quite a bit of chaos.

The mirror (Kepler-7b)

Kepler 7b, at right, was one of the first planets discovered by Kepler. Credit: NASA
Kepler 7b, at right, was one of the first planets discovered by Kepler. Credit: NASA

Well, Kepler-7b isn’t quite as reflective as a mirror, but it certainly catches more sunlight than scientists expected. This “hot Jupiter” was among the first planets that Kepler spotted. In 2011, however, it was revealed that its albedo, or reflectivity, flirted with the upper limit for these humongous planets. What’s causing this? Could be clouds, or could be the composition of its atmosphere. Shows we still have a lot to learn about these exoplanets.

Kepler Mission Discovers “Tatooine-like” Planet

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In a news conference today, Kepler mission scientists announced the first confirmed circumbinary planet ( a planet that orbits a binary star system). The planet in question, designated Kepler-16b has been compared to the planet Tatooine from the Star Wars saga.

Would it be possible for someone like Luke Skywalker to stand on the surface of Kepler-16b and see the famous “binary sunset” as depicted in Star Wars?

Despite the initial comparison between Kepler-16b and Tatooine, the planets really only have their orbit around a binary star system in common. Kepler-16b is estimated to weigh about a third the mass of Jupiter, with a radius of around three-quarters that of Jupiter.

Given the mass and radius estimates, this makes Kepler-16b closer to Saturn than the rocky, desert-like world of Tatooine. Kepler-16b’s orbit around its two parent stars takes about 229 days, which is similar to Venus’ 225-day orbit. At a distance of about 65 million miles from its parent stars, which are both cooler than our sun, temperatures on Kepler-16b are estimated in the range of around -100 C.

The team did mention that Kepler-16b is just outside of the habitable zone of the Kepler-16 system. Despite being just outside the habitable zone, the team did mention that it could be possible for Kepler-16b to have a habitable moon, if said moon had a thick, greenhouse gas atmosphere.

Binary Sunset as seen on Tatooine
Tatooine appears to have twin stars like our sun, versus the orange (type K) and red (type M) stars of Kepler-16
During the press conference John Knoll, visual effects supervisor at ILM, mentioned: “When I was a kid, I didn’t think it was going to be possible to make discoveries like this.” Knoll also added, “The science is stranger and cooler than fiction!”

The Kepler mission detects exoplanet candidates by using the transit method which detects the dimming of the light emitted from a star as a planet crosses in front of it. In the case of Kepler-16b, the detection was complicated by the two stars in the system eclipsing each other.

The system’s brightness showed variations even when the stars were not eclipsing each other, which hinted at a third body. What further complicated matters was that the variations in brightness appeared at irregular time intervals. The irregular time intervals hinted that the stars were in different positions in their orbit each time the third body passed. After studying the data, the team came to the conclusion that the third body was orbiting, not just one, but both stars.

“Much of what we know about the sizes of stars comes from such eclipsing binary systems, and most of what we know about the size of planets comes from transits,” added Kepler scientist Laurance Doyle of the SETI Institute. “Kepler-16 combines the best of both worlds, with stellar eclipses and planetary transits in one system.” Doyle’s findings will be published in the Sept. 15th issue of the journal Science.

The Kepler mission is NASA’s first mission capable of finding Earth-size planets in or near the habitable zone – the region around a star where liquid water can exist on the surface of an orbiting planet. A considerable number of planets and planet candidates have been detected by the mission so far. If you’d like to learn more about the Kepler mission, visit: http://kepler.nasa.gov/

You can also read more about the Kepler-16b discovery at: http://kepler.nasa.gov/Mission/discoveries/kepler16b/

Source: NASA news conference / NASA TV

Ray Sanders is a Sci-Fi geek, astronomer and space/science blogger. Visit his website Dear Astronomer and follow on Twitter (@DearAstronomer) or Google+ for more space musings.