Tag Archives: GJ 687

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.

New Toys

New toys

New Toys (source)

A major limitation to the discovery rate of extrasolar planets is the hardware available with which to detect them. Instruments like HST, Spitzer and Keck have revolutionized astronomy, and have provided a major source of extrasolar planet science — both in atmospheric characterisation and planet detection. These instruments are not dedicated to extrasolar planets, though, and time on the instruments must be shared with astronomers investigating cosmology, interstellar dust, galactic structure, and dark matter, to name a few. There is considerable interest in dedicated exoplanet science instruments – instruments that were designed to do extrasolar planet science, as opposed to instruments and spacecraft designed years ago that we have been fortunate enough to be able to torture exoplanet data out of.

One such dedicated observatory is the Automated Planet Finder, a robotic 2.4 metre telescope whose task is to search for extrasolar planets around nearby stars with a Doppler precision of ~1 m s-1. It observes ten starts a night, and will observe about a thousand stars in the solar neighbourhood. By now, the APF has been in service for a few months, but its data has already been crucial in confirming a new four-planet system of gas giants at HD 141399, and a Neptune-mass planet at GJ 687 (.pdf link) which is only 4.5 pc away.

Automated Planet Finder

Automated Planet Finder

The age of the dominance of Doppler spectroscopy in the discovery of new planets is clearly over. Doppler spectroscopy has fallen to second place behind transit detection, largely as a result of Kepler‘s superb performance and its discovery of over 3,000 planet candidates, as well as a change in strategy by ground-based Doppler surveys. The discovery of planets are no longer interesting for the most part, so important assets are being targeted away from large surveys of bright, metal-rich stars in the hopes of detecting intermediate- to long-period Jovian planets, and toward focoused observations of nearby stars in the hopes of detecting low-mass planets that more closely resemble our solar system. The interest now is in attaining higher precision spectrometers to observe nearby stars to try to detect very low mass planets. This takes a lot of time, and explains both why the nature of discoveries from Doppler spectroscopy has changed in recent years, as well as why the discovery cadence has trailed off. As we move away slightly from discovery for the sake of understanding the underlying planet population distribution, and toward looking for nearby targets for future follow-up, the motto is quality over quantity.

However, the outer regions of planetary systems have been largely unprobed, as Doppler surveys and transit surveys are both biased toward short-period planets. Microlensing results have shed some light on the planet population distribution at higher separation, comparable to the outer Solar System, and it seems that the abundance of gas giant planets picks up quite a bit, but this will need to be confirmed. Fortunately, new instruments are coming online that will help address these issues.

The Gemini Planet Imager on the Gemini Observatory is another new toy that has come to light. It will be used to conduct a 890 hour survey of ~600 stars from 2014 to 2016, and this January they posted first-light images, including one of β Pictoris b.

Beta Pictoris b

Beta Pictoris b

Another imaging instrument that is about to contribute to extrasolar planet science is SPHERE for ESO’s Very Large Telescope, capable of detecting giant planets with orbital radii >5 AU. It will observe nearby young star associations with ages of 10 – 100 Myr within 30 – 100 parsecs, as the planets of these stars will be both bright in infrared due to their age, and well separated from their star due to their proximity. All stars within 20 parsecs will also be observed, as well as stars with known long-period planets. First light is expected to be soon in 2014, perhaps as early as within the month.

A more long-term instrument of interest is ESO’s ESPRESSO spectrograph, also on the VLT. ESPRESSO will surpass the highly successful HARPS spectrograph. With a required accuracy of 10 cm s-1 (and a goal of a few cm s-1), It is expected to be sensitive to terrestrial and Earth-like planets around sun-like stars as faint as V ~ 9. First light is expected to occur in 2016.

With new planet transit search missions such as TESS and PLATO to identify transiting planets around bright stars, and improved spectrographs for mass and density determination of those planets, in addition to new direct imaging instruments and astrometry with the GAIA mission to probe the population statistics of the middle to outer regions of planetary systems, the post-Kepler era is promising to be quite an exciting, with a diverse array of complementary instruments working together to further illuminate the nature of planetary systems in the Galaxy.