Monthly Archives: December 2014

2014 Review

Comets

Comets orbiting β Pic (Credit: ESO)

Results from Kepler data continued to stream in. We were graced with the discovery of a transiting Uranus-sized planet in a 704-day orbit. This is the first time a transiting planet has been discovered beyond its system’s ice line, and this may even be where the planet formed, instead of the typical case for transiting planets where we see them were they are today because of extensive inward migration in their past. Kepler’s 10th transiting circumbinary planet was reported, Kepler’s second multi-planet system orbiting a sdB star was announced and Kepler’s second disintegrating short-period planet was identified.
Kepler short-cadence data may have allowed for the detection of a non-spherical (oblate, like Saturn) exoplanet for the first time, by looking at photometry for Kepler-39 b. While the planet itself is unremarkable, a transiting sub-Neptune around HIP 116454 marks an exciting development: The first planet discovered by Kepler during it’s new “K2” mission.

The dramatic turn of events in the investigation of the planetary system at GJ 581 seems to have finally come to a conclusion. In 2007 a media frenzy accompanied the discovery of two new planets found to accompany the known 5-day Neptune. The innermost of the two new planets was a 5 Earth-mass planet in a 12-day orbit, and a 7 Earth-mass planet in a 80-day orbit. The 12-day planet was hailed as the first habitable planet candidate, despite getting more stellar insolation than Venus. In 2009, an Earth-mass planet at 3-days was found, and the new dataset brought the orbit of the 80-day planet closer to the star, down to ~60 days. Since most people had come to their senses regarding the habitability of the 12-day planet, the 60-day planet became the flag-bearer for habitability in the GJ 581 system. Everything changed in late 2010 when a 3 Earth-mass planet in the habitable zone was announced by the HARPS team. This was truly the most habitable exoplanet candidate known to date… if it were real. Multiple studies drawn out over the following several years debated back and forth how many planets exist around GJ 581. Three? Four? Five? Six? It depended on how you merged your datasets, how you handled noise in your data, and so on. This year, the issue seems to have been resolved by carefully examining the H-alpha lines of the star’s spectrum and finding variation in them that had affected the stellar radial velocity measurements. When corrected for, suddenly all of the habitable zone planets vanished. As of the end of 2014, there are no habitable planet candidates orbiting the star that only a few years ago was unanymously acknowledged to be the most promising extrasolar planetary system for habitability. Interestingly, a similar story may be unfolding at GJ 667, where some planet signals have turned up missing in other studies of the RV data. The morale of this story? Finding low-mass planets is hard.

HARPS continued to give us new planets, but the pace seemed somewhat slow. Some interesting results are the presence of planets in the cluster M67 (link). Planets were found orbiting the stellar companion to XO-2, as well, making the system an example of a binary system with planets orbiting both components. Interestingly, both host at least two planets, and one of each of them are a hot Jupiter. The hot Jupiter around the other star doesn’t transit, suggesting some misalignment between the two planetary systems. Other HARPS results included the identification of two families of comets around β Pictoris, with the identification of hundreds of individual comets through via transmission spectroscopy through their tails.

The news media nearly peed their pants with excitement over the discovery of a planet that, most optimistically, isn’t habitable now, nor has it ever been, in the habitable zone of the very nearby Kapteyn’s Star. Similar unwarranted attention was given to a mini-Neptune discovered in the habitable zone of GJ 832. While the excitement that planets like these get is unwarranted, it is at least gratifying to see the general public so interested in planets that vaguely resemble something habitable-ish. I just hope that when we do find more planets that are more like Earth, the interest hasn’t faded away already. HIRES also found a super-Earth orbiting the very nearby star GJ 15.

We saw first results from the Automated Planet Finder, a radial velocity based system to look for planets in the solar neighbourhood. The project gave us a nice four-planet system orbiting HD 141399 and aided in the discovery of a Neptune-mass planet at GJ 687. We also got to see first results from ESO’s SPHERE instrument.

A number of naked-eye stars were found to have planets, as well, such as planets around β Cnc, μ Leo, β UMi and one around σ Per.

On the direct imaging, we got a new planet imaged orbiting GU Psc with a mass ratio of ~30 and a separation of ~2000 AU… which seems more like a low-mass binary star than a true planetary system. Also, while not planets, ALMA observations of HL Tau have revealed increible detail showing planet formation carving out gaps in the circumstellar disk.

Microlensing gave us a hand-full of planets this year, among the most interesting is OGLE-2013-BLG-0341L Bb, a terrestrial-mass planet orbiting the secondary component of a binary system with a projected separation of 15 AU. For the microlensing event OGLE-2014-BLG-0124L, the event was observed both from the ground and from Spitzer, making the first joint ground+space detection of an exoplanet microlensing event. Observing the event from two different perspectives allowed for the distance to the lens to be accurately measured.

In early year-review posts, the hints of a planetary ring system around a planet orbiting 1SWASP J140747.93-394542.6 has been discussed. We now find that radial velocity observations of the star have place limits to the mass of the orbiting body, restricting it to a planet or brown dwarf. The rings do exist, and they extend far enough away from the planet to expect them to form moons.

2014 has been an interesting year. A thousand planets have been reported this year, mostly because of Kepler’s enormous contributions. It’s hard to know what 2015 will bring. RV surveys are continuing, and there are still thousands of Kepler candidates awaiting confirmation.