The ExoClock project is an inclusive, integrated, and interactive platform that was developed to monitor the ephemerides of the Ariel targets to increase the mission efficiency. The project makes the best use of all available resources, i.e., observations from ground telescopes, midtime values from the literature, and finally, observations from space instruments. Currently, the ExoClock network includes 280 participants with telescopes capable of observing 85% of the currently known Ariel candidate targets. This work includes the results of ∼1600 observations obtained up to 2020 December 31 from the ExoClock network. These data in combination with ∼2350 midtime values collected from the literature are used to update the ephemerides of 180 planets. The analysis shows that 40% of the updated ephemerides will have an impact on future scheduling as either they have a significantly improved precision or they have revealed biases in the old ephemerides. With the new observations, the observing coverage and rate for half of the planets in the sample has been doubled or more. Finally, from a population perspective, we identify that the differences in the 2028 predictions between the old and the new ephemerides have an STD that is double what is expected from Gaussian uncertainties. These findings have implications for planning future observations, where we will need to account for drifts potentially greater than the prediction uncertainties. The updated ephemerides are open and accessible to the wider exoplanet community both from our Open Science Framework repository and our website.

In the present paper we report the discovery of a new hot Jupiter, EPIC211089792 b, first detected by the Super-WASP observatory and then by the K2 space mission during its campaign 4. The planet has a period of 3.25d, a mass of 0.73±0.04 M , and a radius of 1.19±0.02R . The host star is a relatively bright (V=12.5) G7 dwarf with a nearby K5V companion. Based on stellar rotation and the abundance of Lithium, we find that the system might be as young as about 450 Myr. The observation of the Rossiter-McLaughlin effect shows the planet is aligned with respect to the stellar spin. Given the deep transit (20mmag), the magnitude of the star and the presence of a nearby stellar companion, the planet is a good target for both space-and ground-based transmission spectroscopy, in particular in the near-infrared where the both stars are relatively bright.

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The ExoClock project has been created to increase the efficiency of the Ariel mission. It will achieve this by continuously monitoring and updating the ephemerides of Ariel candidates, in order to produce a consistent catalog of reliable and precise ephemerides. This work presents a homogenous catalog of updated ephemerides for 450 planets, generated by the integration of ∼18,000 data points from multiple sources. These sources include observations from ground-based telescopes (the ExoClock network and the Exoplanet Transit Database), midtime values from the literature, and light curves from space telescopes (Kepler, K2, and TESS). With all the above, we manage to collect observations for half of the postdiscovery years (median), with data that have a median uncertainty less than 1 minute. In comparison with the literature, the ephemerides generated by the project are more precise and less biased. More than 40% of the initial literature ephemerides had to be updated to reach the goals of the project, as they were either of low precision or drifting. Moreover, the integrated approach of the project enables both the monitoring of the majority of the Ariel candidates (95%), and also the identification of missing data. These results highlight the need for continuous monitoring to increase the observing coverage of the candidate planets. Finally, the extended observing coverage of planets allows us to detect trends (transit-timing variations) for a sample of 19 planets. All the products, data, and codes used in this work are open and accessible to the wider scientific community.