# Transit timing variations in the WASP-4 planetary system

## TL;DR

This paper confirms transit timing variations in WASP-4, suggesting possible orbital decay, and rules out common causes, contributing to understanding hot Jupiter dynamics.

## Contribution

It provides the first high-confidence detection of TTVs in WASP-4 and discusses potential causes like orbital decay and precession.

## Key findings

- Transit times are 80s earlier than expected.
- Confirmed TTVs fit a quadratic ephemeris with period decay.
- Orbital decay and precession are plausible causes.

## Abstract

Transits in the planetary system WASP-4 were recently found to occur 80s earlier than expected in observations from the TESS satellite. We present 22 new times of mid-transit that confirm the existence of transit timing variations, and are well fitted by a quadratic ephemeris with period decay dP/dt = -9.2 +/- 1.1 ms/yr. We rule out instrumental issues, stellar activity and the Applegate mechanism as possible causes. The light-time effect is also not favoured due to the non-detection of changes in the systemic velocity. Orbital decay and apsidal precession are plausible but unproven. WASP-4b is only the third hot Jupiter known to show transit timing variations to high confidence. We discuss a variety of observations of this and other planetary systems that would be useful in improving our understanding of WASP-4 in particular and orbital decay in general.