In the past thirty years, the number of planets discovered beyond our Solar System has grown exponentially. Unfortunately, due to the limitations of our technology, the vast majority of these exoplanets have been discovered by indirect means, often by detecting the transits of planets in front of their stars (the Transit Method) or by the gravitational influence they exert on their star (the Radial Velocity Method).
Very few have been imaged directly, where the planets have been observed in visible light or infrared wavelengths. One such planet is Beta Pictoris b, a young massive exoplanet that was first observed in 2008 by a team from the European Southern Observatory (ESO). Recently, the same team tracked this planet as it orbited its star, resulting in some stunning images and an equally impressive time-lapse video.
Just. Wow. The motion of an alien world, reduced to a looping .gif. We truly live in an amazing age. A joint press release out of the Gemini Observatory and the University of Toronto demonstrates a stunning first: a sequence of direct images showing an exoplanet… in motion.
The world imaged is Beta Pictoris b, about 19 parsecs (63 light years) distant in the southern hemisphere constellation Pictor the Painter’s Easel. The Gemini Planet Imager (GPI), working in concert with the Gemini South telescope based in Chile captured the sequence.
The images span an amazing period of a year and a half, starting in November 2013 and running through April of earlier this year. Beta Pictoris b has an estimated 22 year orbital period… hey, in the year 2035 or so, we’ll have a complete animation of its orbit!
Current estimates place Beta Pictoris b in the 7x Jupiter mass range, about plus or minus 4 Jupiter masses… and yes, the high end of that range is flirting with the lower boundary for a sub-stellar brown dwarf. Several exoplanet candidates blur this line, and we suspect that the ‘what is a planet debate?’ that has plagued low mass worlds will one day soon extend into the high end of the mass spectrum as well.
Beta Pictoris has long been a target for exoplanetary research, as it is known to host a large and dynamic debris disk spanning 4,000 astronomical units across. The host star Beta Pictoris is 1.8 times as massive as our Sun, and 9 times as luminous. Beta Pic is also a very young star, at an estimated age of only 8-20 million years old. Clearly, we’re seeing a very young solar system in the act of formation.
Orbiting its host star 9 astronomical units distant, Beta Pictoris b has an orbit similar to Saturn’s. Place Beta Pictoris b in our own solar system, and it would easily be the brightest planet in the sky.
“The images in the series represent the most accurate measurements of a planet’s position ever made,” says astronomer Maxwell Millar-Blanchaer of the Department of Astronomy and Astrophysics at the University of Toronto in a recent press release. ‘With the GPI, we’re able to see both the disk and the planet at the exact same time. With our combined knowledge of the disk and the planet we’re really able to get a sense of the planetary system’s architecture and how everything interacts.”
A recent paper released in the Astrophysical Journal described observations of Beta Pictoris b made with the Gemini Planet Imager. As with bodies in our own solar system, refinements in the orbit of Beta Pictoris b will enable astronomers to understand the dynamic relationship it has with its local environment. Already, the orbit of Beta Pictoris b appears inclined out of our line of sight in such a way that a transit of the stellar disk is unlikely to occur. This is the case with most exoplanets, which elude the detection hunters such as the Kepler space telescope. As a matter of fact, watching the animation, it looks like Beta Pictoris b will pass behind the occluding disk and out of view of the Gemini Planet Imager in the next few years.
“It’s remarkable that Gemini is not only able to directly image exoplanets but is also capable of effectively making movies of them orbiting their parent star,” Says National Science Foundation astronomy division program director Chris Davis in Monday’s press release. The NSF is one of five international partners that funds the Gemini telescope program. “Beta Pic is a special target. The disk of gas and dust from which planets are currently forming was one of the first observed and is a famous laboratory for the study of young solar systems.”
The Gemini Planet Imager is part of the GPI Exoplanet Survey (GPIES), which discovered its first exoplanet 51 Eridani b just last month. The survey will target 600 stars over the next three years. The current tally of known exoplanets currently sits at 1,958 and counting, with thousands more in the queue courtesy of Kepler awaiting confirmation.
And as new spacecraft such as the Transiting Exoplanet Survey Satellite (TESS) take to orbit in 2018, we wouldn’t be surprised if the tally of exoplanets hits five digits by the end of this decade.
An amazing view of a brave new world in motion. It’s truly a golden age of exoplanetary science, with more exciting discoveries to come!
Between the time you got to work this morning and the time you leave today — assuming an eight-hour work cycle — an entire day will have passed on Beta Pictoris b, according to new measurements of the exoplanet.
This daily cycle, mapped for the first time on a planet outside of the solar system, may reveal a link between how big a planet is and how fast it rotates, astronomers stated. That said, caution is needed because there are only a handful of planets where the rotation is known: the eight planets of our Solar System and Beta Pictoris b.
The planet’s day is shorter than any other planet in our Solar System, which at first blush makes sense because the planet is also larger than any other planet in our Solar System. Beta Pictoris b is estimated at 16 times larger and 3,000 times more massive than Earth. (For comparison, Jupiter is about 11 times larger and 318 times more massive than Earth.)
“It is not known why some planets spin fast and others more slowly,” stated says co-author Remco de Kok, “but this first measurement of an exoplanet’s rotation shows that the trend seen in the Solar System, where the more massive planets spin faster, also holds true for exoplanets. This must be some universal consequence of the way planets form.”
Astronomers mapped the planet’s equatorial rotation using the CRIRES instrument on the Very Large Telescope. What helped was not only the planet’s large size, but also its proximity to Earth: it’s about 63 light-years away, which is relatively close to us.
As the planet ages (it’s only 20 million years old right now) it is expected to shrink and spin more quickly, assuming no other external forces. The Earth’s rotation is slowed by the moon, for example.
A Saturn-mass planet might be lurking in the debris surrounding Beta Pictoris, new measurements of a debris field around the star shown. If this could be proven, this would be the second planet found around that star.
The planet would be sheparding a giant swarm of comets (some in front and some trailing behind the planet) that are smacking into each other as often as every five minutes, new observations with the Atacama Large Millimeter/submillimeter Array (ALMA) show. This is the leading explanation for a cloud of carbon monoxide gas visible in the array.
“Although toxic to us, carbon monoxide is one of many gases found in comets and other icy bodies,” stated Aki Roberge, an astrophysicist at NASA’s Goddard Space Flight Center in Maryland who participated in the research. “In the rough-and-tumble environment around a young star, these objects frequently collide and generate fragments that release dust, icy grains and stored gases.”
ALMA captured millimeter-sized light from carbon monoxide and dust around Beta Pictoris, which is about 63 light-years from Earth (relatively close to our planet). The gas seems to be most prevalent in an area about 8 billion miles (13 kilometers) from the star — the equivalent distance of three times the length of Neptune’s location from the sun. The carbon monoxide cloud itself makes up about one-sixth the mass of Earth’s oceans.
Ultraviolet light from the star should be breaking up the carbon monoxide molecules within 100 years, so the fact there is so much gas indicates something must be replenishing it, the researchers noted. Their models showed that the comets would need to be destroyed every five minutes for this to happen (unless we are looking at the star at an unusual time).
While the researchers say they need more study to see how the gas is concentrated, their hypothesis is there is two clumps of gas and it is due to a big planet behaving similarly to what Jupiter does in our solar system. Thousands of asteroids follow behind and fly in front of Jupiter due to the planet’s massive gravity. In this more distant system, it’s possible that a gas giant planet would be doing the same thing with comets.
If the gas turns out to be in just one clump, however, another scenario would suggest two Mars-sized planets (icy ones) smashing into each other about half a million years ago. This “would account for the comet swarm, with frequent ongoing collisions among the fragments gradually releasing carbon monoxide gas,” NASA stated.
The world’s newest and most powerful exoplanet imaging instrument, the recently-installed Gemini Planet Imager (GPI) on the 8-meter Gemini South telescope, has captured its first-light infrared image of an exoplanet: Beta Pictoris b, which orbits the star Beta Pictoris, the second-brightest star in the southern constellation Pictor. The planet is pretty obvious in the image above as a bright clump of pixels just to the lower right of the star in the middle (which is physically covered by a small opaque disk to block glare.) But that cluster of pixels is really a distant planet 63 light-years away and several times more massive — as well as 60% larger — than Jupiter!
And this is only the beginning.
While many exoplanets have been discovered and confirmed over the past couple of decades using various techniques, very few have actually been directly imaged. It’s extremely difficult to resolve the faint glow of a planet’s reflected light from within the brilliant glare of its star — but GPI was designed to do just that.
“Most planets that we know about to date are only known because of indirect methods that tell us a planet is there, a bit about its orbit and mass, but not much else,” said Bruce Macintosh of the Lawrence Livermore National Laboratory, who led the team that built the instrument. “With GPI we directly image planets around stars – it’s a bit like being able to dissect the system and really dive into the planet’s atmospheric makeup and characteristics.”
And GPI doesn’t just image distant Jupiter-sized exoplanets; it images them quickly.
“Even these early first-light images are almost a factor of ten better than the previous generation of instruments,” said Macintosh. ” In one minute, we were seeing planets that used to take us an hour to detect.”
Despite its large size, Beta Pictoris b is a very young planet — estimated to be less than 10 million years old (the star itself is only about 12 million.) Its presence is a testament to the ability of large planets to form rapidly and soon around newly-formed stars.
“Seeing a planet close to a star after just one minute, was a thrill, and we saw this on only the first week after the instrument was put on the telescope!” added Fredrik Rantakyro a Gemini staff scientist working on the instrument. “Imagine what it will be able to do once we tweak and completely tune its performance.”
Another of GPI’s first-light images captured light scattered by a ring of dust that surrounds the young star HR4796A , about 237 light-years away:
The left image shows shows normal light, including both the dust ring and the residual light from the central star scattered by turbulence in Earth’s atmosphere. The right image shows only polarized light. Leftover starlight is unpolarized and hence removed. The light from the back edge of the disk (to the right of the star) is strongly polarized as it reflects towards Earth, and thus it appears brighter than the forward-facing edge.
It’s thought that the reflective ring could be from a belt of asteroids or comets orbiting HR4796A, and possibly shaped (or “shepherded,” like the rings of Saturn) by as-yet unseen planets. GPI’s advanced capabilities allowed for the full circumference of the ring to be imaged.
GPI’s success in imaging previously-known systems like Beta Pictoris and HR4796A can only indicate many more exciting exoplanet discoveries to come.
“The entire exoplanet community is excited for GPI to usher in a whole new era of planet finding,” says physicist and exoplanet expert Sara Seager of the Massachusetts Institute of Technology. “Each exoplanet detection technique has its heyday. First it was the radial velocity technique (ground-based planet searches that started the whole field). Second it was the transit technique (namely Kepler). Now, it is the ‘direct imaging’ planet-finding technique’s turn to make waves.”
This year the GPI team will begin a large-scale survey, looking at 600 young stars to see what giant planets may be orbiting them.
“Some day, there will be an instrument that will look a lot like GPI, on a telescope in space. And the images and spectra that will come out of that instrument will show a little blue dot that is another Earth.”
– Bruce Macintosh, GPI team leader
The observations above were conducted last November during an “extremely trouble-free debut.” The Gemini South telescope is located near the summit of Cerro Pachon in central Chile, at an altitude of 2,722 meters.
For the first time, astronomers have been able to directly follow the motion of an exoplanet as it moves from one side of its host star to the other. The planet has the smallest orbit so far of all directly imaged exoplanets, lying almost as close to its parent star as Saturn is to the Sun. The star, beta Pictoris is only 12 million years old, and so this exoplanet confirms that gas giant planets can form very rapidly—in only a few million years—within such circumstellar disks, and experts say that this discovery validates the theory that these unique, gaseous disk structures can be used as a sort of “fingerprint” to characterize their embedded planets.
Beta Pictoris is 75% more massive than our Sun, and is located about 60 light-years away towards the constellation of Pictor (the Painter). This is one of the best-known examples of a star surrounded by a dusty debris disc. Earlier observations showed a warp of the disc, a secondary inclined disc and comets falling onto the star.
“Those were indirect, but tell-tale signs that strongly suggested the presence of a massive planet, and our new observations now definitively prove this,” said team leader Anne-Marie Lagrange. “Because the star is so young, our results prove that giant planets can form in discs in time-spans as short as a few million years.”
This exoplanet, dubbed Beta Pictoris b, was thought to have been spotted first in 2003, and then was first imaged back in 2008. But the astronomer couldn’t rule out definitively that the possible planet wasn’t just a foreground or background object. These new observations confirm that, indeed, the object is a gas giant planet orbiting the star.
Other recent observations have shown that discs around young stars disperse within a few million years, and that giant planet formation must occur faster than previously thought.
Only about ten exoplanets have been imaged, Beta Pictoris b, has the smallest orbit known so far. It is located at a distance between 8 and 15 times the Earth-Sun separation — or 8-15 Astronomical Units — which is about the distance of Saturn from the Sun.
“The short period of the planet will allow us to record the full orbit within maybe 15-20 years, and further studies of Beta Pictoris b will provide invaluable insights into the physics and chemistry of a young giant planet’s atmosphere,” said student researcher Mickael Bonnefoy.
The planet has a mass about nine times that of Jupiter, and the right mass and location to explain the observed warp in the inner parts of the disc. This discovery therefore bears some similarity to the prediction of the existence of Neptune by astronomers Adams and Le Verrier in the 19th century, based on observations of the orbit of Uranus.
The team used the NAOS-CONICA instrument mounted on one of the 8.2-metre Unit Telescopes of ESO’s Very Large Telescope (VLT).
These most recent observations, taken during autumn 2009, revealed the object on the other side of the disc from where it was seen in 2008, and after a period of hiding either behind or in front of the star (in which case it is hidden in the glare of the star). This confirmed that the source indeed was an exoplanet and that it was orbiting its host star. It also provided insights into the size of its orbit around the star.
“Together with the planets found around the young, massive stars Fomalhaut and HR8799, the existence of Beta Pictoris b suggests that super-Jupiters could be frequent byproducts of planet formation around more massive stars,” said team member Gael Chauvin.
“The recent direct images of exoplanets — many made by the VLT— illustrate the diversity of planetary systems,” said Lagrange. “Among those, Beta Pictoris b is the most promising case of a planet that could have formed in the same way as the giant planets in our Solar System.”