Science goals

As our main goal, we define a “searchable star” as a G or K dwarf star for which the Terra Hunting Experiment can obtain enough data for a secure detection of a Doppler signal with a semi-amplitude K = 10 cm/s. Secondly, we would like these signals to be between 60 and 300 days. These criteria are chosen to represent planets that resemble the Earth and that have gone largely undetected in previous surveys.

First priority -- Ensure there are at least 20 searchable stars, and maximise their number.

We need to design the survey (duration, time sampling, etc.) and the total noise budget (including anticipated levels of post-mitigation intrinsic radial velocity variations) to maximize the chances of detection of the signals in question. We need to validate these choices with realistic simulations. We are allowed to drop stars, or alter cadences, based on experience and add stars that might be more suitable.

Second priority -- Within the constraints of the First Priority, perform the survey in a manner that facilitates the determination of the planet occurrence rate.

Although the resulting occurrence rate might be accurate, it is unlikely to be precise, given the realistic limitations on sample size; this is one of the reasons that the occurrence rate is the Second Priority. To facilitate statistical analysis, the Experiment should be conducted with simple and easily modeled selection criteria. Operational decisions about modifying the target list, cadence, etc., should be made algorithmically based on rules determined ahead of time insofar as is possible. If we envision major interventions based on experience with data, we may wish to split the Experiment’s 10-year observing period into two (or more) surveys.

Third priority -- Within the constraints of the First and Second Priorities, operate the Experiment such that it delivers valuable data, methods, and scientific results to the exoplanet community.

There will likely be intensive Doppler surveys following the Experiment, which will benefit from the hardware and software, target selection process, data, methodology, and final results of the Experiment. We also want to support scientists performing contemporaneous and complementary scientific investigations. Some examples of the latter are Doppler monitoring with other instruments; performing photometric or other types of observations of THE targets; and using the THE target stars as a subset of a larger survey with complementary goals. The Third Priority motivates us to perform public data releases, deliver high-level data products, and share our survey design, strategy, scheduling methodology, and other information, consistent with our agreement with the ING. The Third Priority is another motivation to perform statistical inferences about planet populations, since they will be relevant to the design of next-generation surveys.