Tag Archives: Kepler

The first transiting exo-comets?

Transits of extra-solar planets are pretty routine these days, but planets are not the only bodies expected to be orbiting nearby stars. How about exo-comets? Unlike planets, comets are fuzzy and changeable, so exocomet transits would vary in shape and depth. A team led by Saul Rappaport have now searched the entire archive of Kepler lightcurves looking for dips that could be exocomet transits. Here’s one in the data for the star KIC 11084727:

The authors reproduce such dips (red line) with a model of a comet about the size of Halley’s comet and having a tail made of dust, hence giving an asymmetric dip. Another Kepler, KIC 3542116, shows six possible comet transits. Here are three:

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Four planets around WASP-47!

As NASA’s Kepler mission covers fields in the ecliptic previously surveyed by WASP, it is obtaining photometry of unprecedented quality on some WASP planets. The big news this week is the discovery of two more transiting planets in the WASP-47 system.

WASP-47 had seemed to be a relatively routine hot-Jupiter system with the discovery of a Jupiter-sized planet in a 4-day orbit, reported in a batch of transiting planets from WASP-South by Hellier et al 2012.

But WASP-47 is anything but routine. Now Becker et al have announced that the Kepler K2 lightcurves show two more transiting planets: a super-Earth planet in an orbit of only 0.79 days, and a Neptune-sized planet in an orbit of 9.0 days. Being much smaller, these planets cause transits that are too shallow to have been seen in the original WASP data.

WASP-47 transits with Kepler K2

The super-Earth, labelled WASP-47c, has a radius of 1.8 Earths while the Neptune, labelled WASP-47d, has a radius of 3.6 Earths. The triple-planet system is dynamically stable, but the gravitational interaction causes perturbations in the orbits, leading to variations in the times of the transits.

Such “transit-timing variations” or TTVs lead to estimates of the planetary masses. Becker et al find that the hot Jupiter has a mass of 340 Earths (consistent with the mass of 360 Earths originally reported by Hellier et al from radial-velocity measurements), while the Neptune has a mass of 9 Earths. The super-Earth must be less massive than that, but current timing measurements are not sensitive enough to say more.

WASP-47 TTVs Transit timing variations

As if three planets were not enough, there is a probable fourth planet orbiting WASP-47. The Geneva Observatory group routinely monitor known WASP systems, taking radial-velocity measurements over years, to look for longer-period planets. Marion Neveu-VanMalle and colleagues have recently reported the detection of another Jupiter-mass planet orbiting WASP-47, this time in a much wider orbit of 571 days.

The WASP-47 system has now become hugely interesting for understanding exoplanets, and will trigger many additional observations of the system. For example, being bright enough to allow good radial-velocity data, it will provide a much-needed check that the mass estimates from TTVs match those from the more traditional radial-velocity technique.

The system will also be of strong interest to theorists, who will want to understand the formation and origin of a planetary system with this architecture. One immediate consequence is that it shows that a hot Jupiter can arise by inward migration through the proto-planetary disk, without destroying all other planets in its path.

NASA’s Kepler looks at a WASP planet

NASA’s Kepler planet-hunting mission is entering the “K2” phase of its life. The loss of reaction wheels and thus pointing stability mean that it couldn’t continue looking at the original Kepler field, but Kepler engineers have worked out that it can point to fields in the ecliptic by using the pressure of the Sun’s light to stablise the spacecraft.

Kepler's transit of WASP-28b

Kepler’s transit of WASP-28b

In engineering observations to test his concept Kepler pointed at WASP-28b, a hot-Jupiter planet previously found by WASP-South. The lightcurve from a short test in Jan 2014 shows that Kepler is working well and can still detect planets.

Several more WASP planets, incuding WASP-47b, WASP-67b, WASP-75b and WASP-85b are in planned Kepler-2 fields, promising high-quality Kepler lightcurves to really nail down the masses and radii of these planets.