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The Transit Timing Variation (TTV) Planet-finding Technique Begins to Flower
08.23.2012

See also: NASA Feature Story.

The Transit Timing Variation (TTV) method of planet-finding, first used to discover Kepler-9d (Science online 26 August 2010), is really flowering with submission of two independent papers, currently under scientific peer-review, confirming a total of 41 new transiting planets in 20 multiple planet systems in the Kepler field of view. This speaks volumes about the proliferation of innovative and new ideas for confirming and validating populations of planets using the superbly precise photometry (star brightness) data being collected by the NASA Kepler Space Telescope. The TTV analyses and other novel techniques are allowing us to confirm planets, and even determine masses of planets, around much fainter stars than we previously thought possible.

Photo of Jason Steffen
Jason Steffen, prime author of Transit Timing Observations from Kepler: VII

In closely packed planet systems, the gravitational pull of the planets, as they periodically pass near each other in their orbits, causes the acceleration or deceleration of each planet along its orbit. These gravitational "tugs" cause the orbital period of each planet to change from one orbit to the next. This changes the timing of the transits (planet-crossings in front of the star), hence the term transit timing variation (TTV).

One paper by Jason Steffen et al, Transit Timing Observations from Kepler: VII (http://arxiv.org/pdf/1208.3499.pdf) confirms 27 transiting planets in 13 systems; and the other paper by Ji-Wei Xei, Transit Timing Variation of Near-Resonant KOI Pairs (http://arxiv.org/abs/1208.3312) confirms 24 transiting planets in 12 systems. Five of the systems are common to both of the independent studies: Kepler-38, Kepler-49, Kepler-53, Kepler-57, and Kepler-58.

The picture below shows the newly confirmed planets (in green) along with unconfirmed planet candidates in the same systems (grey).

Diagram of 41 new planets
41 New Planets in 20 Star Systems
right-click image to download higher resolution version
This diagram shows the 41 new planets in 20 Kepler star systems from two papers submitted to the Astrophysical Journal:
(1) J Steffen et al confirming 27 transiting planets in 13 systems
(2) Ji-Wei Xei confirming 24 transiting planets in 12 systems.
The systems are ordered horizontally by increasing KOI designation from the Kepler planet candidate list and vertically by orbital period. Newly submitted confirmed planets are in green along with the unconfirmed planet candidates in the same system in violet. The planets range from Earth-size to more than seven times the radius of Earth, but generally orbit so close to their parent stars that they are hot, inhospitable worlds.
Don't expect to see details about these planets in the Kepler Discoveries Table until the papers are accepted by the Astrophysical Journal, but details are publicly available in the papers themselves, linked in this news item.
Credit: Jason Steffen, Fermilab Center for Particle Astrophysics

The papers, once accepted after scientific peer-review, may increase the number of Kepler’s confirmed planets by more than 50 percent: to 116 planets hosted in 67 systems, over half of which contain more than one planet.

Lead researcher Jason Steffen, the Brinson postdoctoral fellow at Fermilab Center for Particle Astrophysics in Batavia, IL, commented, “These systems, with their large gravitational interactions, give us important clues about how planetary systems form and evolve. This information helps us understand how our own solar system fits into the population of all planetary systems.”

Natalie Batalha, Kepler mission scientist at NASA's Ames Research Center, Moffett Field, CA said, “The sheer volume of planet candidates being identified by Kepler is inspiring teams to look at the planet confirmation and characterization process differently. This TTV confirmation technique can be applied to large numbers of systems relatively quickly and with little or no follow-up observations from the ground. Perhaps the bottleneck between identifying planet candidates and confirming them just got a little wider.”

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