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

“Super Saturn” Has an Enormous Ring System and Maybe Even Exomoons

Astronomers watching the repeated and drawn-out dimming of a relatively nearby Sun-like star have interpreted their observations to indicate an eclipse by a gigantic exoplanet’s complex ring system, similar to Saturn’s except much, much bigger. What’s more, apparent gaps and varying densities of the rings imply the presence of at least one large exomoon, and perhaps even more in the process of formation!

J1407 is a main-sequence orange dwarf star about 434 light-years away*. Over the course of 57 days in spring of 2007 J1407 underwent a “complex series of deep eclipses,” which an international team of astronomers asserts is the result of a ring system around the massive orbiting exoplanet J1407b.

“This planet is much larger than Jupiter or Saturn, and its ring system is roughly 200 times larger than Saturn’s rings are today,” said Eric Mamajek, professor of physics and astronomy at the University of Rochester in New York. “You could think of it as kind of a super Saturn.”

The observations were made through the SuperWASP program, which uses ground-based telescopes to watch for the faint dimming of stars due to transiting exoplanets.

The first study of the eclipses and the likely presence of the ring system was published in 2012, led by Mamajek. Further analysis by the team estimates the number of main ring structures to be 37, with a large and clearly-defined gap located at about 0.4 AU (61 million km/37.9 million miles) out from the “super Saturn” that may harbor a satellite nearly as large as Earth, with an orbital period of two years.

Watch an animation of the team’s analysis of the J1407/J1407b eclipse below:

The entire expanse of J1407b’s surprisingly dense rings stretches for 180 million km (112 million miles), and could contain an Earth’s worth of mass.

“If we could replace Saturn’s rings with the rings around J1407b,” said Matthew Kenworthy from Leiden Observatory in the Netherlands and lead author of the new study, “they would be easily visible at night and be many times larger than the full Moon.”

Saturn's relatively thin main rings are about 250,000 km (156,000 miles) in diameter. (Image: NASA/JPL-Caltech/SSI/J. Major)
Saturn’s relatively thin main rings are about 250,000 km (156,000 miles) in diameter. (Image: NASA/JPL-Caltech/SSI/J. Major)

These observations could be akin to a look back in time to see what Saturn and Jupiter were like as their own system of moons were first forming.

“The planetary science community has theorized for decades that planets like Jupiter and Saturn would have had, at an early stage, disks around them that then led to the formation of satellites,” according to Mamajek. “However, until we discovered this object in 2012, no one had seen such a ring system. This is the first snapshot of satellite formation on million-kilometer scales around a substellar object.”

J1407b itself is estimated to contain 10-40 times the mass of Jupiter – technically, it might even be a brown dwarf.

Further observations will be required to observe another transit of J1407b and obtain more data on its rings and other physical characteristics as its orbit is about ten Earth-years long. (Luckily 2017 isn’t that far off!)

The team’s report has been accepted for publication in the Astrophysical Journal.

Source: University of Rochester. Image credit: Ron Miller.

Note: the originally published version of this article described J1407 at 116 light-years away. It’s actually 133 parsecs, which equates to about 434 light-years. Edited above. – JM