Exoplanet-Hunting Survey Discovers Three More Giant Alien Worlds!

The discovery of extra-solar planets has certainly heated up in the past few years. With the deployment of the Kepler mission in 2009, several thousands of exoplanet candidates have been discovered and over 2,500 have been confirmed. In many cases, these planets have been gas giants orbiting close to their respective stars (aka. “Hot Jupiters”), which has confounded some commonly-held notions of how and where planets form.

Beyond these massive planets, astronomers also discovered a wide range of planets that range from massive terrestrial planets (“Super-Earths) to Neptune-sized giants. In a recent study, an international team astronomers discovered three new exoplanets orbiting three different stars. These planets are an interesting batch of finds, consisting of two “Hot Saturns” and one Super-Neptune.

This study, titled “The discovery of WASP-151b, WASP-153b, WASP-156b: Insights on giant planet migration and the upper boundary of the Neptunian desert“, recently appeared in the scientific journal Astronomy and Astrophysics. Led by Olivier. D. S. Demangeon, a researcher from the Institute of Astrophysics and Space Science in Portugal, the team used data from the SuperWASP exoplanet-hunting survey to detect signs of three new gas giants.

Artist’s concdption of a Neptune-sized planet with a clear atmosphere, passing across the face of its star. Credit: NASA/JPL-Caltech

The Super Wide Angle Search for Planets (SuperWASP) is an international consortium that uses wide-angle Transit Photometry to monitor the night sky for transit events. The program relies on robotic observatories located on two continents – SuperWASP-North, located at the Roque de los Muchachos Observatory in Canary Island; and SuperWASP South, at the South African Astronomical Observatory, near Sutherland, South Africa.

From the SuperWASP survey data, Dr. Demangeon and her colleagues were able to detect three transit signals coming from three distant stars – WASP-151, WASP-153 and WASP-156. This was then followed by spectroscopic observations performed using the Haute-Provence Observatory in France and the La Silla Observatory in Chile, which allowed the team to confirm the nature of these planets.

From this, they determined that WASP-151b and WASP-153b are two “hot Saturns”, meaning they are low-density gas giants with close orbits. They orbit their respective suns, which are both early G-type stars (aka. yellow dwarfs, like our Sun), with an orbital period of 4.53 and 3.33 days. WASP-156b, meanwhile, is a Super-Neptune that orbits a K-type (orange dwarf) star. As they indicated in their study:

“WASP-151b and WASP-153b are relatively similar. Their masses of 0.31 and 0.39 M Jup and semi-major axes of 0.056 AU and 0.048 AU respectively indicate two Saturn-size objects around early G type stars of V magnitude ~ 12.8. WASP-156b’s radius of 0.51R Jup suggests a Super-Neptune and makes it the smallest planet ever detected by WASP. Its mass of 0.128 M Jup is also the 3rd lightest detected by WASP after WASP-139b and WASP-107b. Also interesting is the fact that WASP-156 is a bright (magV = 11.6) K type star.”

Number of exoplanets discovered by the Kepler mission as of May 10th, 2016, based on their classification. Credit: W. Stenzel/NASA Ames

Taken together, these planets represent some major opportunities for exoplanet research. As they indicate, “these three planets also lie close to (WASP-151b and WASP-153b) or below (WASP-156b) the upper boundary of the Neptunian desert.” This refers to the boundary astronomers have observed around stars where shot period Neptune-size planets are very unlikely to be found.

Basically, of all  the short period exoplanets (less than 10 days) to be discovered so far, the majority have tended to be in the “Super-Earth” or “Super-Jupiter” category. This deficit of Neptune-like planets has been attributed to different mechanisms when it comes to the formation and evolution for hot Jupiters and short-period super-Earths, as well as it being the result of gas envelop-depletion caused by a star’s ultraviolet radiation.

So far, only nine “Super-Neptunes” have been discovered; so this latest discovery (who’s characteristics are well know) should provide plenty of opportunities for research. Or as Dr. Demangeon and her colleagues explain in the study:

“WASP-156b, being one of the few well characterised Super-Neptunes, will help to constrain the formation of Neptune size planets and the transition between gas and ice giants. The estimates of the age of these three stars confirms the tendency for some stars to have gyrochronological ages significantly lower than their isochronal ages.”

Artist’s impression of two super-Earths in the same system as a Neptune-sized exoplanet in the Kepler-62 system. Credit: David A. Aguilar (CfA)

The team also offered some possible explanations for the existence of a “Neptunian desert” based on their findings. For starters, they proposed that a high-eccentricity migration could be responsible, where Neptune-sized ice giants form in the outer reaches of a star system and migrate inward over time. They also indicate that their discovery offers compelling evidence that ultra-violet radiation and gas envelope-depletion could be a key part of the puzzle.

But of course, Dr. Demangeon and her colleagues indicate that further research will be necessary to confirm their hypothesis, and that further studies are needed to properly constrain the boundaries of the so-called “Neptunian desert”. They also indicate that future missions like NASA’s Transiting Exoplanet Survey Satellite and the ESA’s PLAnetary Transits and Oscillations of stars (PLATO) mission  will be vital to these efforts.

“Obviously, a more thorough analysis is necessary to investigate all the possible implications behind this hypothesis,” they conclude. “Such an analysis is out of the scope of this paper but we think that this hypothesis is worth investigating. In this context, a search for long period companions that might have triggered the high eccentricity migration or an independent age estimate through asterosiesmology with TESS or Plato would be particularly interesting.”

The sheer number of exoplanets discoveries made in recent decades has allowed astronomers to test and revise commonly-held theories about how planetary systems form and evolve. These same discoveries have also helped advance our understanding of how our own Solar System came to be. In the end, being able to study a diverse array of planetary systems, which are different stages in their history, is allowing us to create a sort of timeline for cosmic evolution.

Further Reading: Astronomy and Astrophysics

Astronomers Spot a Intriguing ‘5-Star’ Multiple System

An interesting multiple star discovery turned up in the ongoing hunt for exoplanetary systems.

The discovery was announced by Marcus Lohr of Open University early this month at the National Astronomy Meeting that was held at Venue Cymru in Llandudno, Wales.

The discovery involves as many as five stars in a single stellar system, orbiting in a complex configuration.

The name of the system, 1SWASP J093010.78+533859.5, is a phone number-style designation related to the SuperWASP exoplanet hunting transit survey involved with the discovery. The lengthy numerical designation denotes the system’s position in the sky in right ascension and declination in the constellation Ursa Major.

Image credit:
The SuperWASP-North array of cameras at La Palma in the Canary Islands. Image credit: The SuperWASP consortium

And what a bizarre system it is. The physical parameters of the group are simply amazing, though not as unique as some media outlets have led readers to believe. What is amazing is the fact that both pairs of binaries in the quadruple group are also eclipsing along our line of sight. Only five other quadruple eclipsing binary systems of this nature are known, to include BV/BW Draconis and V994 Herculis.

The very fact that the orbits of both pairs of stars are in similar inclinations will provide key insights for researchers as to just how this system formed.

The first pair in the system are contact binaries of 0.9 and 0.3 solar masses respectively in a tight embrace revolving about each other in just under six hours. Contact binaries consist of distorted stars whose photospheres are actually touching. A famous example is the eclipsing contact binary Beta Lyrae.

 

 

 

 

 

 

 

An animation of the orbits of the contact binary pair Beta Lyrae captured using the CHARA interferometer. Image credit: Ming Zhao et al. ApJ 684, L95 

A closer analysis of the discovery revealed another pair of detached stars of 0.8 and 0.7 solar masses orbiting each other about 21 billion kilometres (140 AUs distant) from the first pair. You could plop the orbit of Pluto down between the two binary pairs, with room to spare.

But wait, there’s more. Astronomers use a technique known as spectroscopy to tease out the individual light spectra signatures of close binaries too distant to resolve individually. This method revealed the presence of a fifth star in orbit 2 billion kilometers (13.4 AUs, about 65% the average distance from Uranus to the Sun) around the detached pair.

“This is a truly exotic star system,” Lohr said in a Royal Society press release. “In principle, there’s no reason it couldn’t have planets in orbit around each of the pairs of stars.”

Indeed, ‘night’ would be a rare concept on any planet in a tight orbit around either binary pair. In order for darkness to occur, all five stellar components would have to appear near mutual conjunction, something that would only happen once every orbit for the hypothetical world.

Such a planet is a staple of science fiction, including Tatooine of Star Wars fame (which orbits a relatively boring binary pair), and the multiple star system of the Firefly series. Perhaps the best contender for a fictional quadruple star system is the 12 colonies of the re-imagined Battlestar Galactica series, which exist in a similar double-pair configuration.

How rare is this discovery, really? Multiple systems are more common than solitary stars such as our Sun by a ratio of about 2:1. In fact, it’s been suggested by rare Earth proponents that life arose here on Earth in part because we have a stable orbit around a relatively placid lone star. The solar system’s nearest stellar neighbor Alpha Centauri is a triple star system. The bright star Castor in the constellation of Gemini the Twins is a famous multiple heavyweight with six components in a similar configuration as this month’s discovery. Another familiar quadruple system to backyard observers is the ‘double-double’ Epsilon Lyrae, in which all four components can be split. Mizar and Alcor in the handle of the Big Dipper asterism is another triple-pair, six-star system. Another multiple, Gamma Velorum, may also possess as many as six stars. Nu Scorpii and AR Cassiopeiae are suspected septuple systems, each perhaps containing up to seven stars.

Fun fact: Gamma Velorum is also informally known as ‘Regor,’ a backwards anagram play on Apollo 1 astronaut ‘Roger’ Chaffee’s name. The crew secretly inserted their names into the Apollo star maps during training!

What is the record number of stars in one system? Hierarchy 3 systems such as Castor are contenders. A.A. Tokivinin’s Multiple Star Catalogue lists five components in a hierarchy 4 system in Ophiuchus named Gliese 644AB, with the potential for more.

How many stars are possible in one star system? Certainly, a hierarchy 4 type system could support up the eight stars, though to our knowledge, no example of such a multiple star system has yet been confirmed. Still, it’s a big universe out there, and the cosmos has lots of stars to play with.

A wide-field view of the constellation Ursa Major, with Theta Ursae Majoris selected (inset). image credit; Stellarium
A wide-field view of the constellation Ursa Major, with Theta Ursae Majoris selected (inset). Image credit; Stellarium

And you can see 1SWASP J093010.78+533859.5 for yourself. At 250 light years distant, the +9th magnitude binary is about 1.5 degrees north-northwest of the star Theta Ursa Majoris, and is an tough but not impossible split with a separation of 1.88” between the two primary pairs.

Image credit: Stellarium
Finder chart for 1SWAP J093010.78+533859.5 with a five degree Telrad foV. Image credit: Stellarium

Congrats to the team on this amazing discovery… to paraphrase Haldane, the Universe is proving to be stranger than we can imagine!